Psychotropic

Psychology 2e

SENIOR CONTRIBUTING AUTHORS
ROSE M. SPIELMAN, FORMERLY OF QUINNIPIAC UNIVERSITY
WILLIAM J. JENKINS, MERCER UNIVERSITY
MARILYN D. LOVETT, SPELMAN COLLEGE

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978-1-975076-45-0
978-1-975076-44-3
978-1-951693-23-7
2020

HARDCOVER BOOK ISBN-13
B&W PAPERBACK BOOK ISBN-13
DIGITAL VERSION ISBN-13
ORIGINAL PUBLICATION YEAR
2 3 4 5 6 7 8 9 10 JAY 22 20

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CONTENTS

Preface 1

CHAPTER 1

Introduction to Psychology 7
Introduction 7
1.1 What Is Psychology? 8
1.2 History of Psychology 9
1.3 Contemporary Psychology 18
1.4 Careers in Psychology 26
Key Terms 30
Summary 30
Review Questions 32
Critical Thinking Questions 34
Personal Application Questions 34

CHAPTER 2

Psychological Research 35
Introduction 35
2.1 Why Is Research Important? 36
2.2 Approaches to Research 41
2.3 Analyzing Findings 48
2.4 Ethics 59
Key Terms 63
Summary 64
Review Questions 66
Critical Thinking Questions 69
Personal Application Questions 70

CHAPTER 3

Biopsychology 71
Introduction 71
3.1 Human Genetics 72
3.2 Cells of the Nervous System 78
3.3 Parts of the Nervous System 84
3.4 The Brain and Spinal Cord 86
3.5 The Endocrine System 97
Key Terms 100
Summary 102
Review Questions 103
Critical Thinking Questions 106
Personal Application Questions 106

CHAPTER 4

States of Consciousness 109
Introduction 109
4.1 What Is Consciousness? 110

4.2 Sleep and Why We Sleep 114
4.3 Stages of Sleep 117
4.4 Sleep Problems and Disorders 121
4.5 Substance Use and Abuse 126
4.6 Other States of Consciousness 134
Key Terms 137
Summary 139
Review Questions 140
Critical Thinking Questions 143
Personal Application Questions 143

CHAPTER 5

Sensation and Perception 145
Introduction 145
5.1 Sensation versus Perception 146
5.2 Waves and Wavelengths 149
5.3 Vision 153
5.4 Hearing 161
5.5 The Other Senses 164
5.6 Gestalt Principles of Perception 168
Key Terms 172
Summary 174
Review Questions 175
Critical Thinking Questions 178
Personal Application Questions 179

CHAPTER 6

Learning 181
Introduction 181
6.1 What Is Learning? 182
6.2 Classical Conditioning 183
6.3 Operant Conditioning 192
6.4 Observational Learning (Modeling) 203
Key Terms 207
Summary 208
Review Questions 208
Critical Thinking Questions 210
Personal Application Questions 211

CHAPTER 7

Thinking and Intelligence 213
Introduction 213
7.1 What Is Cognition? 214
7.2 Language 218
7.3 Problem Solving 222
7.4 What Are Intelligence and Creativity? 228
7.5 Measures of Intelligence 231
7.6 The Source of Intelligence 237
Key Terms 241
Summary 242
Review Questions 243

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Critical Thinking Questions 246
Personal Application Questions 246

CHAPTER 8

Memory 247
Introduction 247
8.1 How Memory Functions 248
8.2 Parts of the Brain Involved with Memory 255
8.3 Problems with Memory 259
8.4 Ways to Enhance Memory 269
Key Terms 273
Summary 274
Review Questions 275
Critical Thinking Questions 276
Personal Application Questions 277

CHAPTER 9

Lifespan Development 279
Introduction 279
9.1 What Is Lifespan Development? 280
9.2 Lifespan Theories 284
9.3 Stages of Development 292
9.4 Death and Dying 313
Key Terms 315
Summary 316
Review Questions 317
Critical Thinking Questions 319
Personal Application Questions 320

CHAPTER 10

Emotion and Motivation 321
Introduction 321
10.1 Motivation 322
10.2 Hunger and Eating 328
10.3 Sexual Behavior 334
10.4 Emotion 342
Key Terms 353
Summary 354
Review Questions 355
Critical Thinking Questions 357
Personal Application Questions 357

CHAPTER 11

Personality 359
Introduction 359
11.1 What Is Personality? 360
11.2 Freud and the Psychodynamic Perspective 362
11.3 Neo-Freudians: Adler, Erikson, Jung, and Horney 368
11.4 Learning Approaches 373
11.5 Humanistic Approaches 377
11.6 Biological Approaches 378

11.7 Trait Theorists 379
11.8 Cultural Understandings of Personality 384
11.9 Personality Assessment 386
Key Terms 391
Summary 392
Review Questions 394
Critical Thinking Questions 397
Personal Application Questions 397

CHAPTER 12

Social Psychology 399
Introduction 399
12.1 What Is Social Psychology? 400
12.2 Self-presentation 406
12.3 Attitudes and Persuasion 409
12.4 Conformity, Compliance, and Obedience 415
12.5 Prejudice and Discrimination 422
12.6 Aggression 429
12.7 Prosocial Behavior 432
Key Terms 437
Summary 439
Review Questions 440
Critical Thinking Questions 444
Personal Application Questions 444

CHAPTER 13

Industrial-Organizational Psychology 447
Introduction 447
13.1 What Is Industrial and Organizational Psychology? 448
13.2 Industrial Psychology: Selecting and Evaluating Employees 456
13.3 Organizational Psychology: The Social Dimension of Work 467
13.4 Human Factors Psychology and Workplace Design 477
Key Terms 480
Summary 481
Review Questions 481
Critical Thinking Questions 483
Personal Application Questions 484

CHAPTER 14

Stress, Lifestyle, and Health 485
Introduction 485
14.1 What Is Stress? 486
14.2 Stressors 496
14.3 Stress and Illness 502
14.4 Regulation of Stress 514
14.5 The Pursuit of Happiness 521
Key Terms 529
Summary 530
Review Questions 531
Critical Thinking Questions 534
Personal Application Questions 535

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CHAPTER 15

Psychological Disorders 537
Introduction 537
15.1 What Are Psychological Disorders? 538
15.2 Diagnosing and Classifying Psychological Disorders 542
15.3 Perspectives on Psychological Disorders 545
15.4 Anxiety Disorders 548
15.5 Obsessive-Compulsive and Related Disorders 554
15.6 Posttraumatic Stress Disorder 558
15.7 Mood and Related Disorders 560
15.8 Schizophrenia 570
15.9 Dissociative Disorders 574
15.10 Disorders in Childhood 576
15.11 Personality Disorders 582
Key Terms 589
Summary 591
Review Questions 594
Critical Thinking Questions 597
Personal Application Questions 598

CHAPTER 16

Therapy and Treatment 599
Introduction 599
16.1 Mental Health Treatment: Past and Present 600
16.2 Types of Treatment 605
16.3 Treatment Modalities 617
16.4 Substance-Related and Addictive Disorders: A Special Case 621
16.5 The Sociocultural Model and Therapy Utilization 623
Key Terms 627
Summary 628
Review Questions 630
Critical Thinking Questions 632
Personal Application Questions 632

References 633
Index 733

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Preface
Welcome to Psychology 2e, an OpenStax resource. This textbook was written to increase student access to
high-quality learning materials, maintaining highest standards of academic rigor at little to no cost.

About OpenStax

OpenStax is a nonprofit based at Rice University, and it’s our mission to improve student access to education.
Our first openly licensed college textbook was published in 2012, and our library has since scaled to over 35
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About OpenStax Resources

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About Psychology 2e

Psychology 2e is designed to meet scope and sequence requirements for the single-semester introduction to
psychology course. The book offers a comprehensive treatment of core concepts, grounded in both classic

Preface 1

studies and current and emerging research. The text also includes coverage of the DSM-5 in examinations of
psychological disorders. Psychology 2e incorporates discussions that reflect the diversity within the discipline,
as well as the diversity of cultures and communities across the globe.

Coverage and scope

The first edition of Psychology has been used by thousands of faculty and hundreds of thousands of students
since its publication in 2015. OpenStax mined our adopters’ extensive and helpful feedback to identify the
most significant revision needs while maintaining the organization that many instructors had incorporated
into their courses. Specific surveys, pre-revision reviews, and customization analysis, as well as analytical data
from OpenStax partners and online learning environments, all aided in planning the revision.

The result is a book that thoroughly treats psychology’s foundational concepts while adding current and
meaningful coverage in specific areas. Psychology 2e retains its manageable scope and contains ample
features to draw learners into the discipline.

Structurally, the textbook remains similar to the first edition, with no chapter reorganization and very targeted
changes at the section level.

• Chapter 1: Introduction to Psychology
• Chapter 2: Psychological Research
• Chapter 3: Biopsychology
• Chapter 4: States of Consciousness
• Chapter 5: Sensation and Perception
• Chapter 6: Learning
• Chapter 7: Thinking and Intelligence
• Chapter 8: Memory
• Chapter 9: Lifespan Development
• Chapter 10: Motivation and Emotion
• Chapter 11: Personality
• Chapter 12: Social Psychology
• Chapter 13: Industrial-Organizational Psychology
• Chapter 14: Stress, Lifestyle, and Health
• Chapter 15: Psychological Disorders
• Chapter 16: Therapy and Treatment

Changes to the Second Edition

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Content revisions for clarity, accuracy, and currency

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coverage, research-informed data, and clearer language. In other chapters, the revisions focused mostly on
currency of examples and updates to statistics.

Over 210 new research references have been added or updated in order to improve the scholarly
underpinnings of the material and broaden the perspective for students. Dozens of examples and feature
boxes have been changed or added to better explain concepts and/or increase relevance for students.

Research replication and validity

To engage students in stronger critical analysis and inform them about research reproducibility, substantial
coverage has been added to the research chapter and strategically throughout the textbook whenever key

2 Preface

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studies are discussed. This material is presented in a balanced way and provides instructors with ample
opportunity to discuss the importance of replication in a manner that best suits their course.

Diversity, representation, and inclusion

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Art and illustrations

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Accessibility improvements

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To learn more about our commitment and progress, please view our accessibility statement
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second edition.

Pedagogical foundation

Psychology 2e engages students through inquiry, self-reflection, and investigation. Features in the second
edition have been carefully updated to remain topical and relevant while deepening students’ relationship to
the material. They include the following:

• Everyday Connection features tie psychological topics to everyday issues and behaviors that students
encounter in their lives and the world. Topics include the validity of scores on college entrance exams, the
opioid crisis, the impact of social status on stress and healthcare, and cognitive mapping.

• What Do You Think? features provide research-based information and ask students their views on
controversial issues. Topics include “Brain Dead and on Life Support,” “Violent Media and Aggression,”
and “Capital Punishment and Criminals with Intellectual Disabilities.”

• Dig Deeper features discuss one specific aspect of a topic in greater depth so students can dig more
deeply into the concept. Examples include discussions on the distinction between evolutionary
psychology and behavioral genetics, recent findings on neuroplasticity, the field of forensic psychology,
and a presentation of research on strategies for coping with prejudice and discrimination.

• Connect the Concepts features revisit a concept learned in another chapter, expanding upon it within a
different context. Features include “Emotional Expression and Emotional Regulation,” “Tweens, Teens,

Preface 3

and Social Norms,” and “Conditioning and OCD.”

Art, interactives, and assessments that engage

Our art program is designed to enhance students’ understanding of psychological concepts through simple,
effective graphs, diagrams, and photographs. Psychology 2e also incorporates links to relevant interactive
exercises and animations that help bring topics to life. Selected assessment items touch directly on students’
lives.

• Link to Learning features direct students to online interactive exercises and animations that add a fuller
context to core content and provide an opportunity for application.

• Personal Application Questions engage students in topics at a personal level to encourage reflection and
promote discussion.

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About the authors

Senior contributing authors

Rose M. Spielman (Content Lead)
Dr. Rose Spielman has been teaching psychology and working as a licensed clinical psychologist for 20 years.
Her academic career has included positions at Quinnipiac University, Housatonic Community College, and
Goodwin College. As a licensed clinical psychologist, educator, and volunteer director, Rose is able to connect
with people from diverse backgrounds and facilitate treatment, advocacy, and education. In her years of work
as a teacher, therapist, and administrator, she has helped thousands of students and clients and taught them to
advocate for themselves and move their lives forward to become more productive citizens and family
members.

William J. Jenkins, Mercer University
Marilyn D. Lovett, Spelman College

4 Preface

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Contributing Authors

Mara Aruguete, Lincoln University
Laura Bryant, Eastern Gateway Community College
Barbara Chappell, Walden University
Kathryn Dumper, Bainbridge State College
Arlene Lacombe, Saint Joseph’s University
Julie Lazzara, Paradise Valley Community College
Tammy McClain, West Liberty University
Barbara B. Oswald, Miami University
Marion Perlmutter, University of Michigan
Mark D. Thomas, Albany State University

Reviewers

Patricia G. Adams, Pitt Community College
Daniel Bellack, Trident Technical College
Christopher M. Bloom, Providence College
Jerimy Blowers, Cayuga Community College
Salena Brody, Collin College
David A. Caicedo, Borough of Manhattan Community College, CUNY
Bettina Casad, University of Missouri–St. Louis
Sharon Chacon, Northeast Wisconsin Technical College
James Corpening
Frank Eyetsemitan, Roger Williams University
Tamara Ferguson, Utah State University
Kathleen Flannery, Saint Anselm College
Johnathan Forbey, Ball State University
Laura Gaudet, Chadron State College
William Goggin, University of Southern Mississippi
Jeffery K. Gray, Charleston Southern University
Heather Griffiths, Fayetteville State University
Mark Holder, University of British Columbia
Rita Houge, Des Moines Area Community College
Colette Jacquot, Strayer University
John Johanson, Winona State University
Andrew Johnson, Park University
Shaila Khan, Tougaloo College
Cynthia Kreutzer, Georgia State University Perimeter College at Clarkston Campus
Carol Laman, Houston Community College
Dana C. Leighton, Texas A&M University—Texarkana
Thomas Malloy, Rhode Island College
Jan Mendoza, Golden West College
Christopher Miller, University of Minnesota
Lisa Moeller, Beckfield College
Amy T. Nusbaum, Heritage University
Jody Resko, Queensborough Community College (CUNY)
Hugh Riley, Baylor University
Juan Salinas, University of Texas at Austin
Brittney Schrick, Southern Arkansas University
Phoebe Scotland, College of the Rockies

Preface 5

Christine Selby, Husson University
Sally B. Seraphin, Centre College
Brian Sexton, Kean University
Nancy Simpson, Trident Technical College
Jason M. Smith, Federal Bureau of Prisons – FCC Hazelton
Robert Stennett, University of Georgia
Jennifer Stevenson, Ursinus College
Eric Weiser, Curry College
Jay L. Wenger, Harrisburg Area Community College
Alan Whitehead, Southern Virginia University
Valjean Whitlow, American Public University
Rachel Wu, University of California, Riverside
Alexandra Zelin, University of Tennessee at Chattanooga

6 Preface

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FIGURE 1.1 Psychology is the scientific study of mind and behavior. (credit “background”: modification of work by
Nattachai Noogure; credit “top left”: modification of work by Peter Shanks; credit “top middle”: modification of work
by “devinf”/Flickr; credit “top right”: modification of work by Alejandra Quintero Sinisterra; credit “bottom left”:
modification of work by Gabriel Rocha; credit “bottom middle-left”: modification of work by Caleb Roenigk; credit
“bottom middle-right”: modification of work by Staffan Scherz; credit “bottom right”: modification of work by Czech
Provincial Reconstruction Team)

INTRODUCTION

CHAPTER OUTLINE
1.1 What Is Psychology?
1.2 History of Psychology
1.3 Contemporary Psychology
1.4 Careers in Psychology

Clive Wearing is an accomplished musician who lost his ability to form new memories when
he became sick at the age of 46. While he can remember how to play the piano perfectly, he cannot remember
what he ate for breakfast just an hour ago (Sacks, 2007). James Wannerton experiences a taste sensation that is
associated with the sound of words. His former girlfriend’s name tastes like rhubarb (Mundasad, 2013). John
Nash is a brilliant mathematician and Nobel Prize winner. However, while he was a professor at MIT, he would
tell people that the New York Times contained coded messages from extraterrestrial beings that were intended
for him. He also began to hear voices and became suspicious of the people around him. Soon thereafter, Nash
was diagnosed with schizophrenia and admitted to a state-run mental institution (O’Connor & Robertson,

1Introduction to Psychology

2002). Nash was the subject of the 2001 movie A Beautiful Mind. Why did these people have these
experiences? How does the human brain work? And what is the connection between the brain’s internal
processes and people’s external behaviors? This textbook will introduce you to various ways that the field of
psychology has explored these questions.

1.1 What Is Psychology?
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Define psychology
• Understand the merits of an education in psychology

What is creativity? What are prejudice and discrimination? What is consciousness? The field of psychology
explores questions like these. Psychology refers to the scientific study of the mind and behavior. Psychologists
use the scientific method to acquire knowledge. To apply the scientific method, a researcher with a question
about how or why something happens will propose a tentative explanation, called a hypothesis, to explain the
phenomenon. A hypothesis should fit into the context of a scientific theory, which is a broad explanation or
group of explanations for some aspect of the natural world that is consistently supported by evidence over
time. A theory is the best understanding we have of that part of the natural world. The researcher then makes
observations or carries out an experiment to test the validity of the hypothesis. Those results are then
published or presented at research conferences so that others can replicate or build on the results.

Scientists test that which is perceivable and measurable. For example, the hypothesis that a bird sings because
it is happy is not a hypothesis that can be tested since we have no way to measure the happiness of a bird. We
must ask a different question, perhaps about the brain state of the bird, since this can be measured. However,
we can ask individuals about whether they sing because they are happy since they are able to tell us. Thus,
psychological science is empirical, based on measurable data.

In general, science deals only with matter and energy, that is, those things that can be measured, and it cannot
arrive at knowledge about values and morality. This is one reason why our scientific understanding of the
mind is so limited, since thoughts, at least as we experience them, are neither matter nor energy. The scientific
method is also a form of empiricism. An empirical method for acquiring knowledge is one based on
observation, including experimentation, rather than a method based only on forms of logical argument or
previous authorities.

It was not until the late 1800s that psychology became accepted as its own academic discipline. Before this
time, the workings of the mind were considered under the auspices of philosophy. Given that any behavior is,
at its roots, biological, some areas of psychology take on aspects of a natural science like biology. No biological
organism exists in isolation, and our behavior is influenced by our interactions with others. Therefore,
psychology is also a social science.

WHY STUDY PSYCHOLOGY?

Often, students take their first psychology course because they are interested in helping others and want to
learn more about themselves and why they act the way they do. Sometimes, students take a psychology course
because it either satisfies a general education requirement or is required for a program of study such as
nursing or pre-med. Many of these students develop such an interest in the area that they go on to declare
psychology as their major. As a result, psychology is one of the most popular majors on college campuses
across the United States (Johnson & Lubin, 2011). A number of well-known individuals were psychology
majors. Just a few famous names on this list are Facebook’s creator Mark Zuckerberg, television personality
and political satirist Jon Stewart, actress Natalie Portman, and filmmaker Wes Craven (Halonen, 2011). About
6 percent of all bachelor degrees granted in the United States are in the discipline of psychology (U.S.
Department of Education, 2016).

8 1 • Introduction to Psychology

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An education in psychology is valuable for a number of reasons. Psychology students hone critical thinking
skills and are trained in the use of the scientific method. Critical thinking is the active application of a set of
skills to information for the understanding and evaluation of that information. The evaluation of
information—assessing its reliability and usefulness— is an important skill in a world full of competing “facts,”
many of which are designed to be misleading. For example, critical thinking involves maintaining an attitude
of skepticism, recognizing internal biases, making use of logical thinking, asking appropriate questions, and
making observations. Psychology students also can develop better communication skills during the course of
their undergraduate coursework (American Psychological Association, 2011). Together, these factors increase
students’ scientific literacy and prepare students to critically evaluate the various sources of information they
encounter.

In addition to these broad-based skills, psychology students come to understand the complex factors that
shape one’s behavior. They appreciate the interaction of our biology, our environment, and our experiences in
determining who we are and how we will behave. They learn about basic principles that guide how we think
and behave, and they come to recognize the tremendous diversity that exists across individuals and across
cultural boundaries (American Psychological Association, 2011).

LINK TO LEARNING

Watch a brief video about some questions to consider before deciding to major in psychology
(http://openstax.org/l/psycmajor) to learn more.

1.2 History of Psychology
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Understand the importance of Wundt and James in the development of psychology
• Appreciate Freud’s influence on psychology
• Understand the basic tenets of Gestalt psychology
• Appreciate the important role that behaviorism played in psychology’s history
• Understand basic tenets of humanism
• Understand how the cognitive revolution shifted psychology’s focus back to the mind

Psychology is a relatively young science with its experimental roots in the 19th century, compared, for
example, to human physiology, which dates much earlier. As mentioned, anyone interested in exploring issues
related to the mind generally did so in a philosophical context prior to the 19th century. Two 19th century
scholars, Wilhelm Wundt and William James, are generally credited as being the founders of psychology as a
science and academic discipline that was distinct from philosophy. This section will provide an overview of the
shifts in paradigms that have influenced psychology from Wundt and James through today.

Wundt and Structuralism

Wilhelm Wundt (1832–1920) was a German scientist who was the first person to be referred to as a
psychologist. His famous book entitled Principles of Physiological Psychology was published in 1873. Wundt
viewed psychology as a scientific study of conscious experience, and he believed that the goal of psychology
was to identify components of consciousness and how those components combined to result in our conscious
experience. Wundt used introspection (he called it “internal perception”), a process by which someone
examines their own conscious experience as objectively as possible, making the human mind like any other
aspect of nature that a scientist observed. He believed in the notion of voluntarism—that people have free will
and should know the intentions of a psychological experiment if they were participating (Danziger, 1980).
Wundt considered his version experimental introspection; he used instruments such as those that measured
reaction time. He also wrote Volkerpsychologie in 1904 in which he suggested that psychology should include
the study of culture, as it involves the study of people. Edward Titchener, one of his students, went on to

1.2 • History of Psychology 9

develop structuralism. Its focus was on the contents of mental processes rather than their function (Pickren &
Rutherford, 2010). Wundt established his psychology laboratory at the University at Leipzig in 1879 (Figure
1.2). In this laboratory, Wundt and his students conducted experiments on, for example, reaction times. A
subject, sometimes in a room isolated from the scientist, would receive a stimulus such as a light, image, or
sound. The subject’s reaction to the stimulus would be to push a button, and an apparatus would record the
time to reaction. Wundt could measure reaction time to one-thousandth of a second (Nicolas & Ferrand, 1999).

FIGURE 1.2 (a) Wilhelm Wundt is credited as one of the founders of psychology. He created the first laboratory for
psychological research. (b) This photo shows him seated and surrounded by fellow researchers and equipment in
his laboratory in Germany.

However, despite his efforts to train individuals in the process of introspection, this process remained highly
subjective, and there was very little agreement between individuals.

Functionalism

William James, John Dewey, and Charles Sanders Peirce helped establish functional psychology (Figure 1.3).
They accepted Darwin’s theory of evolution by natural selection and viewed this theory as an explanation of an
organism’s characteristics. Key to that theory is the idea that natural selection leads to organisms that are
adapted to their environment, including their behavior. Adaptation means that a trait of an organism has a
function for the survival and reproduction of the individual, because it has been naturally selected. As James
saw it, psychology’s purpose was to study the function of behavior in the world, and as such, his perspective
was known as functionalism. Functionalism focused on how mental activities helped an organism fit into its
environment. Functionalism has a second, more subtle meaning in that functionalists were more interested in
the operation of the whole mind rather than of its individual parts, which were the focus of structuralism. Like
Wundt, James believed that introspection could serve as one means by which someone might study mental
activities, but James also relied on more objective measures, including the use of various recording devices,
and examinations of concrete products of mental activities and of anatomy and physiology (Gordon, 1995).

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FIGURE 1.3 William James, shown here in a self-portrait, was the first American psychologist.

Freud and Psychoanalytic Theory

Perhaps one of the most influential and well-known figures in psychology’s history was Sigmund Freud (Figure
1.4). Freud (1856–1939) was an Austrian neurologist who was fascinated by patients suffering from “hysteria”
and neurosis. Hysteria was an ancient diagnosis for disorders, primarily of women with a wide variety of
symptoms, including physical symptoms and emotional disturbances, none of which had an apparent physical
cause. Freud theorized that many of his patients’ problems arose from the unconscious mind. In Freud’s view,
the unconscious mind was a repository of feelings and urges of which we have no awareness. Gaining access to
the unconscious, then, was crucial to the successful resolution of the patient’s problems. According to Freud,
the unconscious mind could be accessed through dream analysis, by examinations of the first words that came
to people’s minds, and through seemingly innocent slips of the tongue. Psychoanalytic theory focuses on the
role of a person’s unconscious, as well as early childhood experiences, and this particular perspective
dominated clinical psychology for several decades (Thorne & Henley, 2005).

FIGURE 1.4 (a) Sigmund Freud was a highly influential figure in the history of psychology. (b) One of his many
books, A General Introduction to Psychoanalysis, shared his ideas about psychoanalytical therapy; it was published
in 1922.

Freud’s ideas were influential, and you will learn more about them when you study lifespan development,
personality, and therapy. For instance, many therapists believe strongly in the unconscious and the impact of

1.2 • History of Psychology 11

early childhood experiences on the rest of a person’s life. The method of psychoanalysis, which involves the
patient talking about their experiences and selves, while not invented by Freud, was certainly popularized by
him and is still used today. Many of Freud’s other ideas, however, are controversial. Drew Westen (1998) argues
that many of the criticisms of Freud’s ideas are misplaced, in that they attack his older ideas without taking
into account later writings. Westen also argues that critics fail to consider the success of the broad ideas that
Freud introduced or developed, such as the importance of childhood experiences in adult motivations, the role
of unconscious versus conscious motivations in driving our behavior, the fact that motivations can cause
conflicts that affect behavior, the effects of mental representations of ourselves and others in guiding our
interactions, and the development of personality over time. Westen identifies subsequent research support for
all of these ideas.

More modern iterations of Freud’s clinical approach have been empirically demonstrated to be effective (Knekt
et al., 2008; Shedler, 2010). Some current practices in psychotherapy involve examining unconscious aspects
of the self and relationships, often through the relationship between the therapist and the client. Freud’s
historical significance and contributions to clinical practice merit his inclusion in a discussion of the historical
movements within psychology.

Wertheimer, Koffka, Köhler, and Gestalt Psychology

Max Wertheimer (1880–1943), Kurt Koffka (1886–1941), and Wolfgang Köhler (1887–1967) were three
German psychologists who immigrated to the United States in the early 20th century to escape Nazi Germany.
These scholars are credited with introducing psychologists in the United States to various Gestalt principles.
The word Gestalt roughly translates to “whole;” a major emphasis of Gestalt psychology deals with the fact that
although a sensory experience can be broken down into individual parts, how those parts relate to each other
as a whole is often what the individual responds to in perception. For example, a song may be made up of
individual notes played by different instruments, but the real nature of the song is perceived in the
combinations of these notes as they form the melody, rhythm, and harmony. In many ways, this particular
perspective would have directly contradicted Wundt’s ideas of structuralism (Thorne & Henley, 2005).

Unfortunately, in moving to the United States, these scientists were forced to abandon much of their work and
were unable to continue to conduct research on a large scale. These factors along with the rise of behaviorism
(described next) in the United States prevented principles of Gestalt psychology from being as influential in
the United States as they had been in their native Germany (Thorne & Henley, 2005). Despite these issues,
several Gestalt principles are still very influential today. Considering the human individual as a whole rather
than as a sum of individually measured parts became an important foundation in humanistic theory late in the
century. The ideas of Gestalt have continued to influence research on sensation and perception.

Structuralism, Freud, and the Gestalt psychologists were all concerned in one way or another with describing
and understanding inner experience. But other researchers had concerns that inner experience could be a
legitimate subject of scientific inquiry and chose instead to exclusively study behavior, the objectively
observable outcome of mental processes.

Pavlov, Watson, Skinner, and Behaviorism

Early work in the field of behavior was conducted by the Russian physiologist Ivan Pavlov (1849–1936). Pavlov
studied a form of learning behavior called a conditioned reflex, in which an animal or human produced a
reflex (unconscious) response to a stimulus and, over time, was conditioned to produce the response to a
different stimulus that the experimenter associated with the original stimulus. The reflex Pavlov worked with
was salivation in response to the presence of food. The salivation reflex could be elicited using a second
stimulus, such as a specific sound, that was presented in association with the initial food stimulus several
times. Once the response to the second stimulus was “learned,” the food stimulus could be omitted. Pavlov’s
“classical conditioning” is only one form of learning behavior studied by behaviorists.

John B. Watson (1878–1958) was an influential American psychologist whose most famous work occurred

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during the early 20th century at Johns Hopkins University (Figure 1.5). While Wundt and James were
concerned with understanding conscious experience, Watson thought that the study of consciousness was
flawed. Because he believed that objective analysis of the mind was impossible, Watson preferred to focus
directly on observable behavior and try to bring that behavior under control. Watson was a major proponent of
shifting the focus of psychology from the mind to behavior, and this approach of observing and controlling
behavior came to be known as behaviorism. A major object of study by behaviorists was learned behavior and
its interaction with inborn qualities of the organism. Behaviorism commonly used animals in experiments
under the assumption that what was learned using animal models could, to some degree, be applied to human
behavior. Indeed, Tolman (1938) stated, “I believe that everything important in psychology (except … such
matters as involve society and words) can be investigated in essence through the continued experimental and
theoretical analysis of the determiners of rat behavior at a choice-point in a maze.”

FIGURE 1.5 John B. Watson is known as the father of behaviorism within psychology.

Behaviorism dominated experimental psychology for several decades, and its influence can still be felt today
(Thorne & Henley, 2005). Behaviorism is largely responsible for establishing psychology as a scientific
discipline through its objective methods and especially experimentation. In addition, it is used in behavioral
and cognitive-behavioral therapy. Behavior modification is commonly used in classroom settings. Behaviorism
has also led to research on environmental influences on human behavior.

B. F. Skinner (1904–1990) was an American psychologist (Figure 1.6). Like Watson, Skinner was a behaviorist,
and he concentrated on how behavior was affected by its consequences. Therefore, Skinner spoke of
reinforcement and punishment as major factors in driving behavior. As a part of his research, Skinner
developed a chamber that allowed the careful study of the principles of modifying behavior through
reinforcement and punishment. This device, known as an operant conditioning chamber (or more familiarly, a
Skinner box), has remained a crucial resource for researchers studying behavior (Thorne & Henley, 2005).

FIGURE 1.6 (a) B. F. Skinner is famous for his research on operant conditioning. (b) Modified versions of the operant
conditioning chamber, or Skinner box, are still widely used in research settings today. (credit a: modification of work
by “Silly rabbit”/Wikimedia Commons)

1.2 • History of Psychology 13

The Skinner box is a chamber that isolates the subject from the external environment and has a behavior
indicator such as a lever or a button. When the animal pushes the button or lever, the box is able to deliver a
positive reinforcement of the behavior (such as food) or a punishment (such as a noise).

Skinner’s focus on positive and negative reinforcement of learned behaviors had a lasting influence in
psychology that has waned somewhat since the growth of research in cognitive psychology. Despite this,
conditioned learning is still used in human behavioral modification (Greengrass, 2004).

Maslow, Rogers, and Humanism

During the early 20th century, American psychology was dominated by behaviorism and psychoanalysis.
However, some psychologists were uncomfortable with what they viewed as limited perspectives being so
influential to the field. They objected to the pessimism and determinism (all actions driven by the
unconscious) of Freud. They also disliked the reductionism, or simplifying nature, of behaviorism.
Behaviorism is also deterministic at its core, because it sees human behavior as entirely determined by a
combination of genetics and environment. Some psychologists began to form their own ideas that emphasized
personal control, intentionality, and a true predisposition for “good” as important for our self-concept and our
behavior. Thus, humanism emerged. Humanism is a perspective within psychology that emphasizes the
potential for good that is innate to all humans. Two of the most well-known proponents of humanistic
psychology are Abraham Maslow and Carl Rogers (O’Hara, n.d.).

Abraham Maslow (1908–1970) was an American psychologist who is best known for proposing a hierarchy of
human needs in motivating behavior (Figure 1.7). Although this concept will be discussed in more detail in a
later chapter, a brief overview will be provided here. Maslow asserted that so long as basic needs necessary for
survival were met (e.g., food, water, shelter), higher-level needs (e.g., social needs) would begin to motivate
behavior. According to Maslow, the highest-level needs relate to self-actualization, a process by which we
achieve our full potential. Obviously, the focus on the positive aspects of human nature that are characteristic
of the humanistic perspective is evident (Thorne & Henley, 2005). Humanistic psychologists rejected, on
principle, the research approach based on reductionist experimentation in the tradition of the physical and
biological sciences, because it missed the “whole” human being. Beginning with Maslow and Rogers, there was
an insistence on a humanistic research program. This program has been largely qualitative (not
measurement-based), but there exist a number of quantitative research strains within humanistic psychology,
including research on happiness, self-concept, meditation, and the outcomes of humanistic psychotherapy
(Friedman, 2008).

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FIGURE 1.7 Maslow’s hierarchy of needs is shown.

Carl Rogers (1902–1987) was also an American psychologist who, like Maslow, emphasized the potential for
good that exists within all people (Figure 1.8). Rogers used a therapeutic technique known as client-centered
therapy in helping his clients deal with problematic issues that resulted in their seeking psychotherapy. Unlike
a psychoanalytic approach in which the therapist plays an important role in interpreting what conscious
behavior reveals about the unconscious mind, client-centered therapy involves the patient taking a lead role in
the therapy session. Rogers believed that a therapist needed to display three features to maximize the
effectiveness of this particular approach: unconditional positive regard, genuineness, and empathy.
Unconditional positive regard refers to the fact that the therapist accepts their client for who they are, no
matter what they might say. Provided these factors, Rogers believed that people were more than capable of
dealing with and working through their own issues (Thorne & Henley, 2005).

FIGURE 1.8 Carl Rogers, shown in this portrait, developed a client-centered therapy method that has been
influential in clinical settings. (credit: “Didius”/Wikimedia Commons)

Humanism has been influential to psychology as a whole. Both Maslow and Rogers are well-known names
among students of psychology (you will read more about both later in this text), and their ideas have influenced
many scholars. Furthermore, Rogers’ client-centered approach to therapy is still commonly used in
psychotherapeutic settings today (O’hara, n.d.)

1.2 • History of Psychology 15

LINK TO LEARNING

View a brief video of Carl Rogers describing his therapeutic approach (http://openstax.org/l/crogers1) to learn
more.

The Cognitive Revolution

Behaviorism’s emphasis on objectivity and focus on external behavior had pulled psychologists’ attention away
from the mind for a prolonged period of time. The early work of the humanistic psychologists redirected
attention to the individual human as a whole, and as a conscious and self-aware being. By the 1950s, new
disciplinary perspectives in linguistics, neuroscience, and computer science were emerging, and these areas
revived interest in the mind as a focus of scientific inquiry. This particular perspective has come to be known
as the cognitive revolution (Miller, 2003). By 1967, Ulric Neisser published the first textbook entitled Cognitive
Psychology, which served as a core text in cognitive psychology courses around the country (Thorne & Henley,
2005).

Although no one person is entirely responsible for starting the cognitive revolution, Noam Chomsky was very
influential in the early days of this movement (Figure 1.9). Chomsky (1928–), an American linguist, was
dissatisfied with the influence that behaviorism had had on psychology. He believed that psychology’s focus on
behavior was short-sighted and that the field had to re-incorporate mental functioning into its purview if it
were to offer any meaningful contributions to understanding behavior (Miller, 2003).

FIGURE 1.9 Noam Chomsky was very influential in beginning the cognitive revolution. In 2010, this mural honoring
him was put up in Philadelphia, Pennsylvania. (credit: Robert Moran)

European psychology had never really been as influenced by behaviorism as had American psychology; and
thus, the cognitive revolution helped reestablish lines of communication between European psychologists and
their American counterparts. Furthermore, psychologists began to cooperate with scientists in other fields,
like anthropology, linguistics, computer science, and neuroscience, among others. This interdisciplinary
approach often was referred to as the cognitive sciences, and the influence and prominence of this particular
perspective resonates in modern-day psychology (Miller, 2003).

Feminist Psychology
The science of psychology has had an impact on human wellbeing, both positive and negative. The dominant
influence of Western, White, and male academics in the early history of psychology meant that psychology
developed with the biases inherent in those individuals, which often had negative consequences for members of
society who were not White or male. Women, members of ethnic minorities in both the United States and other
countries, and individuals with sexual orientations other than straight had difficulties entering the field of
psychology and therefore influencing its development. They also suffered from the attitudes of White male
psychologists who were not immune to the nonscientific attitudes prevalent in the society in which they

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developed and worked. Until the 1960s, the science of psychology was largely a “womanless” psychology
(Crawford & Marecek, 1989), meaning that few women were able to practice psychology, so they had little
influence on what was studied. In addition, the experimental subjects of psychology were mostly men, which
resulted from underlying assumptions that gender had no influence on psychology and that women were not of
sufficient interest to study.

An article by Naomi Weisstein, first published in 1968 (Weisstein, 1993), stimulated a feminist revolution in
psychology by presenting a critique of psychology as a science. She also specifically criticized male psychologists
for constructing the psychology of women entirely out of their own cultural biases and without careful
experimental tests to verify any of their characterizations of women. Weisstein used, as examples, statements by
prominent psychologists in the 1960s, such as this quote by Bruno Bettleheim: “We must start with the
realization that, as much as women want to be good scientists or engineers, they want first and foremost to be
womanly companions of men and to be mothers.” Weisstein’s critique formed the foundation for the subsequent
development of a feminist psychology that attempted to be free of the influence of male cultural biases on our
knowledge of the psychology of women.

Crawford & Marecek (1989) identify several feminist approaches to psychology that can be described as feminist
psychology. These include re-evaluating and discovering the contributions of women to the history of psychology,
studying psychological gender differences, and questioning the male bias present across the practice of the
scientific approach to knowledge.

Multicultural And Cross-Cultural Psychology

Culture impacts individuals, groups, and society. An ongoing issue researchers are trying to correct is that
certain populations have been over-studied and the results of these studies have been applied to other
populations. For example, Henrich, Heine, and Norenzayan discuss how WEIRD societies have been
overstudied and the results have been wrongly applied to non-WEIRD societies (2010). WEIRD stands for
western, educated, industrialized, rich, and democratic. Henrich, Heine, and Norenzayan found that there are
many differences between people in the WEIRD group and people in less industrialized, less urban, and non-
Western societies. These differences occur in a variety of areas, including perception, cooperation, and moral
reasoning. That is, people vary depending on their culture and environment. Multicultural psychologists
develop theories and conduct research with diverse populations, typically within one country. Cross-cultural
psychologists compare populations across countries, such as participants from the United States compared to
participants from China.

In 1920, Francis Cecil Sumner was the first African American to receive a PhD in psychology in the United
States. Sumner established a psychology degree program at Howard University, leading to the education of a
new generation of African American psychologists (Black, Spence, and Omari, 2004). Much of the work of early
psychologists from diverse backgrounds was dedicated to challenging intelligence testing and promoting
innovative educational methods for children. George I. Sanchez contested such testing with Mexican American
children. As a psychologist of Mexican heritage, he pointed out that the language and cultural barriers in
testing were keeping children from equal opportunities (Guthrie, 1998). By 1940, he was teaching with his
doctoral degree at University of Texas at Austin and challenging segregated educational practices (Romo,
1986).

Two famous African American researchers and psychologists are Mamie Phipps Clark and her husband,
Kenneth Clark. They are best known for their studies conducted on African American children and doll
preference, research that was instrumental in the Brown v. Board of Education Supreme Court desegregation
case. The Clarks applied their research to social services and opened the first child guidance center in Harlem
(American Psychological Association, 2019).

Listen to the podcast below describing the Clarks’ research and impact on the Supreme Court decision.

1.2 • History of Psychology 17

LINK TO LEARNING

Listen to a podcast about the influence of an African American’s psychology research on the historic Brown v.
Board of Education civil rights case (http://openstax.org/l/crogers2) to learn more.

The American Psychological Association has several ethnically based organizations for professional
psychologists that facilitate interactions among members. Since psychologists belonging to specific ethnic
groups or cultures have the most interest in studying the psychology of their communities, these organizations
provide an opportunity for the growth of research on the interplay between culture and psychology.

WOMEN IN PSYCHOLOGY

Although rarely given credit, women have been contributing to psychology since its inception as a field of
study. In 1894, Margaret Floy Washburn was the first woman awarded the doctoral degree in psychology. She
wrote The Animal Mind: A Textbook of Comparative Psychology, and it was the standard in the field for over 20
years. In the mid 1890s, Mary Whiton Calkins completed all requirements toward the PhD in psychology, but
Harvard University refused to award her that degree because she was a woman. She had been taught and
mentored by William James, who tried and failed to convince Harvard to award her the doctoral degree. Her
memory research studied primacy and recency (Madigan & O’Hara, 1992), and she also wrote about how
structuralism and functionalism both explained self-psychology (Calkins, 1906).

Another influential woman, Mary Cover Jones, conducted a study she considered to be a sequel to John B.
Watson’s study of Little Albert (you’ll learn about this study in the chapter on Learning). Jones unconditioned
fear in Little Peter, who had been afraid of rabbits (Jones, 1924).

Ethnic minority women contributing to the field of psychology include Martha Bernal and Inez Beverly Prosser;
their studies were related to education. Bernal, the first Latina to earn her doctoral degree in psychology
(1962) conducted much of her research with Mexican American children. Prosser was the first African
American woman awarded the PhD in 1933 at the University of Cincinnati (Benjamin, Henry, & McMahon,
2005).

1.3 Contemporary Psychology
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Appreciate the diversity of interests and foci within psychology
• Understand basic interests and applications in each of the described areas of psychology
• Demonstrate familiarity with some of the major concepts or important figures in each of the described areas of

psychology

Contemporary psychology is a diverse field that is influenced by all of the historical perspectives described in
the preceding section. Reflective of the discipline’s diversity is the diversity seen within the American
Psychological Association (APA). The APA is a professional organization representing psychologists in the
United States. The APA is the largest organization of psychologists in the world, and its mission is to advance
and disseminate psychological knowledge for the betterment of people. There are 54 divisions within the APA,
representing a wide variety of specialties that range from Societies for the Psychology of Religion and
Spirituality to Exercise and Sport Psychology to Behavioral Neuroscience and Comparative Psychology.
Reflecting the diversity of the field of psychology itself, members, affiliate members, and associate members
span the spectrum from students to doctoral-level psychologists, and come from a variety of places including
educational settings, criminal justice, hospitals, the armed forces, and industry (American Psychological
Association, 2014). G. Stanley Hall was the first president of the APA. Before he earned his doctoral degree, he
was an adjunct instructor at Wilberforce University, a historically Black college/university (HBCU), while
serving as faculty at Antioch College. Hall went on to work under William James, earning his PhD. Eventually,

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he became the first president of Clark University in Massachusetts when it was founded (Pickren & Rutherford,
2010).

The Association for Psychological Science (APS) was founded in 1988 and seeks to advance the scientific
orientation of psychology. Its founding resulted from disagreements between members of the scientific and
clinical branches of psychology within the APA. The APS publishes five research journals and engages in
education and advocacy with funding agencies. A significant proportion of its members are international,
although the majority is located in the United States. Other organizations provide networking and
collaboration opportunities for professionals of several ethnic or racial groups working in psychology, such as
the National Latina/o Psychological Association (NLPA), the Asian American Psychological Association (AAPA),
the Association of Black Psychologists (ABPsi), and the Society of Indian Psychologists (SIP). Most of these
groups are also dedicated to studying psychological and social issues within their specific communities.

This section will provide an overview of the major subdivisions within psychology today in the order in which
they are introduced throughout the remainder of this textbook. This is not meant to be an exhaustive listing,
but it will provide insight into the major areas of research and practice of modern-day psychologists.

LINK TO LEARNING

Please visit this website about the divisions within the APA (http://openstax.org/l/biopsychology) to learn more.

View these student resources (http://openstax.org/l/studentresource) also provided by the APA.

Biopsychology and Evolutionary Psychology

As the name suggests, biopsychology explores how our biology influences our behavior. While biological
psychology is a broad field, many biological psychologists want to understand how the structure and function
of the nervous system is related to behavior (Figure 1.10). As such, they often combine the research strategies
of both psychologists and physiologists to accomplish this goal (as discussed in Carlson, 2013).

FIGURE 1.10 Biological psychologists study how the structure and function of the nervous system generate
behavior.

The research interests of biological psychologists span a number of domains, including but not limited to,

1.3 • Contemporary Psychology 19

sensory and motor systems, sleep, drug use and abuse, ingestive behavior, reproductive behavior,
neurodevelopment, plasticity of the nervous system, and biological correlates of psychological disorders.
Given the broad areas of interest falling under the purview of biological psychology, it will probably come as no
surprise that individuals from all sorts of backgrounds are involved in this research, including biologists,
medical professionals, physiologists, and chemists. This interdisciplinary approach is often referred to as
neuroscience, of which biological psychology is a component (Carlson, 2013).

While biopsychology typically focuses on the immediate causes of behavior based in the physiology of a
human or other animal, evolutionary psychology seeks to study the ultimate biological causes of behavior. To
the extent that a behavior is impacted by genetics, a behavior, like any anatomical characteristic of a human or
animal, will demonstrate adaption to its surroundings. These surroundings include the physical environment
and, since interactions between organisms can be important to survival and reproduction, the social
environment. The study of behavior in the context of evolution has its origins with Charles Darwin, the co-
discoverer of the theory of evolution by natural selection. Darwin was well aware that behaviors should be
adaptive and wrote books titled, The Descent of Man (1871) and The Expression of the Emotions in Man and
Animals (1872), to explore this field.

Evolutionary psychology, and specifically, the evolutionary psychology of humans, has enjoyed a resurgence in
recent decades. To be subject to evolution by natural selection, a behavior must have a significant genetic
cause. In general, we expect all human cultures to express a behavior if it is caused genetically, since the
genetic differences among human groups are small. The approach taken by most evolutionary psychologists is
to predict the outcome of a behavior in a particular situation based on evolutionary theory and then to make
observations, or conduct experiments, to determine whether the results match the theory. It is important to
recognize that these types of studies are not strong evidence that a behavior is adaptive, since they lack
information that the behavior is in some part genetic and not entirely cultural (Endler, 1986). Demonstrating
that a trait, especially in humans, is naturally selected is extraordinarily difficult; perhaps for this reason,
some evolutionary psychologists are content to assume the behaviors they study have genetic determinants
(Confer et al., 2010).

One other drawback of evolutionary psychology is that the traits that we possess now evolved under
environmental and social conditions far back in human history, and we have a poor understanding of what
these conditions were. This makes predictions about what is adaptive for a behavior difficult. Behavioral traits
need not be adaptive under current conditions, only under the conditions of the past when they evolved, about
which we can only hypothesize.

There are many areas of human behavior for which evolution can make predictions. Examples include
memory, mate choice, relationships between kin, friendship and cooperation, parenting, social organization,
and status (Confer et al., 2010).

Evolutionary psychologists have had success in finding experimental correspondence between observations
and expectations. In one example, in a study of mate preference differences between men and women that
spanned 37 cultures, Buss (1989) found that women valued earning potential factors greater than men, and
men valued potential reproductive factors (youth and attractiveness) greater than women in their prospective
mates. In general, the predictions were in line with the predictions of evolution, although there were deviations
in some cultures.

Sensation and Perception

Scientists interested in both physiological aspects of sensory systems as well as in the psychological
experience of sensory information work within the area of sensation and perception (Figure 1.11). As such,
sensation and perception research is also quite interdisciplinary. Imagine walking between buildings as you
move from one class to another. You are inundated with sights, sounds, touch sensations, and smells. You also
experience the temperature of the air around you and maintain your balance as you make your way. These are

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all factors of interest to someone working in the domain of sensation and perception.

FIGURE 1.11 When you look at this image, you may see a duck or a rabbit. The sensory information remains the
same, but your perception can vary dramatically.

As described in a later chapter that focuses on the results of studies in sensation and perception, our
experience of our world is not as simple as the sum total of all of the sensory information (or sensations)
together. Rather, our experience (or perception) is complex and is influenced by where we focus our attention,
our previous experiences, and even our cultural backgrounds.

Cognitive Psychology

As mentioned in the previous section, the cognitive revolution created an impetus for psychologists to focus
their attention on better understanding the mind and mental processes that underlie behavior. Thus, cognitive
psychology is the area of psychology that focuses on studying cognitions, or thoughts, and their relationship to
our experiences and our actions. Like biological psychology, cognitive psychology is broad in its scope and
often involves collaborations among people from a diverse range of disciplinary backgrounds. This has led
some to coin the term cognitive science to describe the interdisciplinary nature of this area of research (Miller,
2003).

Cognitive psychologists have research interests that span a spectrum of topics, ranging from attention to
problem solving to language to memory. The approaches used in studying these topics are equally diverse.
Given such diversity, cognitive psychology is not captured in one chapter of this text per se; rather, various
concepts related to cognitive psychology will be covered in relevant portions of the chapters in this text on
sensation and perception, thinking and intelligence, memory, lifespan development, social psychology, and
therapy.

Developmental Psychology

Developmental psychology is the scientific study of development across a lifespan. Developmental
psychologists are interested in processes related to physical maturation. However, their focus is not limited to
the physical changes associated with aging, as they also focus on changes in cognitive skills, moral reasoning,
social behavior, and other psychological attributes.

Early developmental psychologists focused primarily on changes that occurred through reaching adulthood,
providing enormous insight into the differences in physical, cognitive, and social capacities that exist between
very young children and adults. For instance, research by Jean Piaget (Figure 1.12) demonstrated that very
young children do not demonstrate object permanence. Object permanence refers to the understanding that
physical things continue to exist, even if they are hidden from us. If you were to show an adult a toy, and then
hide it behind a curtain, the adult knows that the toy still exists. However, very young infants act as if a hidden
object no longer exists. The age at which object permanence is achieved is somewhat controversial (Munakata,
McClelland, Johnson, and Siegler, 1997).

1.3 • Contemporary Psychology 21

FIGURE 1.12 Jean Piaget is famous for his theories regarding changes in cognitive ability that occur as we move
from infancy to adulthood.

While Piaget was focused on cognitive changes during infancy and childhood as we move to adulthood, there is
an increasing interest in extending research into the changes that occur much later in life. This may be
reflective of changing population demographics of developed nations as a whole. As more and more people live
longer lives, the number of people of advanced age will continue to increase. Indeed, it is estimated that there
were just over 40 million people aged 65 or older living in the United States in 2010. However, by 2020, this
number is expected to increase to about 55 million. By the year 2050, it is estimated that nearly 90 million
people in this country will be 65 or older (Department of Health and Human Services, n.d.).

Personality Psychology

Personality psychology focuses on patterns of thoughts and behaviors that make each individual unique.
Several individuals (e.g., Freud and Maslow) that we have already discussed in our historical overview of
psychology, and the American psychologist Gordon Allport, contributed to early theories of personality. These
early theorists attempted to explain how an individual’s personality develops from their given perspective. For
example, Freud proposed that personality arose as conflicts between the conscious and unconscious parts of
the mind were carried out over the lifespan. Specifically, Freud theorized that an individual went through
various psychosexual stages of development. According to Freud, adult personality would result from the
resolution of various conflicts that centered on the migration of erogenous (or sexual pleasure-producing)
zones from the oral (mouth) to the anus to the phallus to the genitals. Like many of Freud’s theories, this
particular idea was controversial and did not lend itself to experimental tests (Person, 1980).

More recently, the study of personality has taken on a more quantitative approach. Rather than explaining how
personality arises, research is focused on identifying personality traits, measuring these traits, and
determining how these traits interact in a particular context to determine how a person will behave in any
given situation. Personality traits are relatively consistent patterns of thought and behavior, and many have
proposed that five trait dimensions are sufficient to capture the variations in personality seen across
individuals. These five dimensions are known as the “Big Five” or the Five Factor model, and include
dimensions of conscientiousness, agreeableness, neuroticism, openness, and extraversion (Figure 1.13). Each
of these traits has been demonstrated to be relatively stable over the lifespan (e.g., Rantanen, Metsäpelto, Feldt,
Pulkinnen, and Kokko, 2007; Soldz & Vaillant, 1999; McCrae & Costa, 2008) and is influenced by genetics (e.g.,
Jang, Livesly, and Vernon, 1996).

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FIGURE 1.13 Each of the dimensions of the Five Factor model is shown in this figure. The provided description
would describe someone who scored highly on that given dimension. Someone with a lower score on a given
dimension could be described in opposite terms.

Social Psychology

Social psychology focuses on how we interact with and relate to others. Social psychologists conduct research
on a wide variety of topics that include differences in how we explain our own behavior versus how we explain
the behaviors of others, prejudice, and attraction, and how we resolve interpersonal conflicts. Social
psychologists have also sought to determine how being among other people changes our own behavior and
patterns of thinking.

There are many interesting examples of social psychological research, and you will read about many of these
in a later chapter of this textbook. Until then, you will be introduced to one of the most controversial
psychological studies ever conducted. Stanley Milgram was an American social psychologist who is most
famous for research that he conducted on obedience. After the holocaust, in 1961, a Nazi war criminal, Adolf
Eichmann, who was accused of committing mass atrocities, was put on trial. Many people wondered how
German soldiers were capable of torturing prisoners in concentration camps, and they were unsatisfied with
the excuses given by soldiers that they were simply following orders. At the time, most psychologists agreed
that few people would be willing to inflict such extraordinary pain and suffering, simply because they were
obeying orders. Milgram decided to conduct research to determine whether or not this was true (Figure 1.14).
As you will read later in the text, Milgram found that nearly two-thirds of his participants were willing to
deliver what they believed to be lethal shocks to another person, simply because they were instructed to do so
by an authority figure (in this case, a man dressed in a lab coat). This was in spite of the fact that participants

1.3 • Contemporary Psychology 23

received payment for simply showing up for the research study and could have chosen not to inflict pain or
more serious consequences on another person by withdrawing from the study. No one was actually hurt or
harmed in any way, Milgram’s experiment was a clever ruse that took advantage of research confederates,
those who pretend to be participants in a research study who are actually working for the researcher and have
clear, specific directions on how to behave during the research study (Hock, 2009). Milgram’s and others’
studies that involved deception and potential emotional harm to study participants catalyzed the development
of ethical guidelines for conducting psychological research that discourage the use of deception of research
subjects, unless it can be argued not to cause harm and, in general, requiring informed consent of
participants.

FIGURE 1.14 Stanley Milgram’s research demonstrated just how far people will go in obeying orders from an
authority figure. This advertisement was used to recruit subjects for his research.

Industrial-Organizational Psychology

Industrial-Organizational psychology (I-O psychology) is a subfield of psychology that applies psychological
theories, principles, and research findings in industrial and organizational settings. I-O psychologists are often
involved in issues related to personnel management, organizational structure, and workplace environment.
Businesses often seek the aid of I-O psychologists to make the best hiring decisions as well as to create an
environment that results in high levels of employee productivity and efficiency. In addition to its applied
nature, I-O psychology also involves conducting scientific research on behavior within I-O settings (Riggio,
2013).

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Health Psychology

Health psychology focuses on how health is affected by the interaction of biological, psychological, and
sociocultural factors. This particular approach is known as the biopsychosocial model (Figure 1.15). Health
psychologists are interested in helping individuals achieve better health through public policy, education,
intervention, and research. Health psychologists might conduct research that explores the relationship
between one’s genetic makeup, patterns of behavior, relationships, psychological stress, and health. They may
research effective ways to motivate people to address patterns of behavior that contribute to poorer health
(MacDonald, 2013).

FIGURE 1.15 The biopsychosocial model suggests that health/illness is determined by an interaction of these three
factors.

Sport and Exercise Psychology

Researchers in sport and exercise psychology study the psychological aspects of sport performance,
including motivation and performance anxiety, and the effects of sport on mental and emotional wellbeing.
Research is also conducted on similar topics as they relate to physical exercise in general. The discipline also
includes topics that are broader than sport and exercise but that are related to interactions between mental
and physical performance under demanding conditions, such as fire fighting, military operations, artistic
performance, and surgery.

Clinical Psychology

Clinical psychology is the area of psychology that focuses on the diagnosis and treatment of psychological
disorders and other problematic patterns of behavior. As such, it is generally considered to be a more applied
area within psychology; however, some clinicians are also actively engaged in scientific research. Counseling
psychology is a similar discipline that focuses on emotional, social, vocational, and health-related outcomes in
individuals who are considered psychologically healthy.

As mentioned earlier, both Freud and Rogers provided perspectives that have been influential in shaping how
clinicians interact with people seeking psychotherapy. While aspects of the psychoanalytic theory are still
found among some of today’s therapists who are trained from a psychodynamic perspective, Roger’s ideas
about client-centered therapy have been especially influential in shaping how many clinicians operate.
Furthermore, both behaviorism and the cognitive revolution have shaped clinical practice in the forms of
behavioral therapy, cognitive therapy, and cognitive-behavioral therapy (Figure 1.16). Issues related to the
diagnosis and treatment of psychological disorders and problematic patterns of behavior will be discussed in

1.3 • Contemporary Psychology 25

detail in later chapters of this textbook.

FIGURE 1.16 Cognitive-behavioral therapists take cognitive processes and behaviors into account when providing
psychotherapy. This is one of several strategies that may be used by practicing clinical psychologists.

By far, this is the area of psychology that receives the most attention in popular media, and many people
mistakenly assume that all psychology is clinical psychology.

Forensic Psychology

Forensic psychology is a branch of psychology that deals questions of psychology as they arise in the context
of the justice system. For example, forensic psychologists (and forensic psychiatrists) will assess a person’s
competency to stand trial, assess the state of mind of a defendant, act as consultants on child custody cases,
consult on sentencing and treatment recommendations, and advise on issues such as eyewitness testimony
and children’s testimony (American Board of Forensic Psychology, 2014). In these capacities, they will typically
act as expert witnesses, called by either side in a court case to provide their research- or experience-based
opinions. As expert witnesses, forensic psychologists must have a good understanding of the law and provide
information in the context of the legal system rather than just within the realm of psychology. Forensic
psychologists are also used in the jury selection process and witness preparation. They may also be involved in
providing psychological treatment within the criminal justice system. Criminal profilers are a relatively small
proportion of psychologists that act as consultants to law enforcement.

1.4 Careers in Psychology
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Understand educational requirements for careers in academic settings
• Understand the demands of a career in an academic setting
• Understand career options outside of academic settings

Psychologists can work in many different places doing many different things. In general, anyone wishing to
continue a career in psychology at a 4-year institution of higher education will have to earn a doctoral degree
in psychology for some specialties and at least a master’s degree for others. In most areas of psychology, this
means earning a PhD in a relevant area of psychology. Literally, PhD refers to a doctor of philosophy degree,
but here, philosophy does not refer to the field of philosophy per se. Rather, philosophy in this context refers to
many different disciplinary perspectives that would be housed in a traditional college of liberal arts and
sciences.

The requirements to earn a PhD vary from country to country and even from school to school, but usually,
individuals earning this degree must complete a dissertation. A dissertation is essentially a long research
paper or bundled published articles describing research that was conducted as a part of the candidate’s
doctoral training. In the United States, a dissertation generally has to be defended before a committee of expert

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reviewers before the degree is conferred (Figure 1.17).

FIGURE 1.17 Doctoral degrees are generally conferred in formal ceremonies involving special attire and rites.
(credit: Public Affairs Office Fort Wainwright)

Once someone earns a PhD, they may seek a faculty appointment at a college or university. Being on the faculty
of a college or university often involves dividing time between teaching, research, and service to the institution
and profession. The amount of time spent on each of these primary responsibilities varies dramatically from
school to school, and it is not uncommon for faculty to move from place to place in search of the best personal
fit among various academic environments. The previous section detailed some of the major areas that are
commonly represented in psychology departments around the country; thus, depending on the training
received, an individual could be anything from a biological psychologist to a clinical psychologist in an
academic setting (Figure 1.18).

FIGURE 1.18 Individuals earning a PhD in psychology have a range of employment options.

LINK TO LEARNING

Use this interactive tool and explore different careers in psychology based on degree levels
(http://openstax.org/l/degreecareer) to learn more.

Other Careers in Academic Settings

Often times, schools offer more courses in psychology than their full-time faculty can teach. In these cases, it is
not uncommon to bring in an adjunct faculty member or instructor. Adjunct faculty members and instructors
usually have an advanced degree in psychology, but they often have primary careers outside of academia and
serve in this role as a secondary job. Alternatively, they may not hold the doctoral degree required by most

1.4 • Careers in Psychology 27

4-year institutions and use these opportunities to gain experience in teaching. Furthermore, many 2-year
colleges and schools need faculty to teach their courses in psychology. In general, many of the people who
pursue careers at these institutions have master’s degrees in psychology, although some PhDs make careers at
these institutions as well.

Some people earning PhDs may enjoy research in an academic setting. However, they may not be interested in
teaching. These individuals might take on faculty positions that are exclusively devoted to conducting
research. This type of position would be more likely an option at large, research-focused universities.

In some areas in psychology, it is common for individuals who have recently earned their PhD to seek out
positions in postdoctoral training programs that are available before going on to serve as faculty. In most
cases, young scientists will complete one or two postdoctoral programs before applying for a full-time faculty
position. Postdoctoral training programs allow young scientists to further develop their research programs
and broaden their research skills under the supervision of other professionals in the field.

Career Options Outside of Academic Settings

Individuals who wish to become practicing clinical psychologists have another option for earning a doctoral
degree, which is known as a PsyD. A PsyD is a doctor of psychology degree that is increasingly popular among
individuals interested in pursuing careers in clinical psychology. PsyD programs generally place less emphasis
on research-oriented skills and focus more on application of psychological principles in the clinical context
(Norcross & Castle, 2002).

Regardless of whether earning a PhD or PsyD, in most states, an individual wishing to practice as a licensed
clinical or counseling psychologist may complete postdoctoral work under the supervision of a licensed
psychologist. Within the last few years, however, several states have begun to remove this requirement, which
would allow people to get an earlier start in their careers (Munsey, 2009). After an individual has met the state
requirements, their credentials are evaluated to determine whether they can sit for the licensure exam. Only
individuals that pass this exam can call themselves licensed clinical or counseling psychologists (Norcross,
n.d.). Licensed clinical or counseling psychologists can then work in a number of settings, ranging from private
clinical practice to hospital settings. It should be noted that clinical psychologists and psychiatrists do different
things and receive different types of education. While both can conduct therapy and counseling, clinical
psychologists have a PhD or a PsyD, whereas psychiatrists have a doctor of medicine degree (MD). As such,
licensed clinical psychologists can administer and interpret psychological tests, while psychiatrists can
prescribe medications.

Individuals earning a PhD can work in a variety of settings, depending on their areas of specialization. For
example, someone trained as a biopsychologist might work in a pharmaceutical company to help test the
efficacy of a new drug. Someone with a clinical background might become a forensic psychologist and work
within the legal system to make recommendations during criminal trials and parole hearings, or serve as an
expert in a court case.

While earning a doctoral degree in psychology is a lengthy process, usually taking between 5–6 years of
graduate study (DeAngelis, 2010), there are a number of careers that can be attained with a master’s degree in
psychology. People who wish to provide psychotherapy can become licensed to serve as various types of
professional counselors (Hoffman, 2012). Relevant master’s degrees are also sufficient for individuals seeking
careers as school psychologists (National Association of School Psychologists, n.d.), in some capacities related
to sport psychology (American Psychological Association, 2014), or as consultants in various industrial
settings (Landers, 2011, June 14). Undergraduate coursework in psychology may be applicable to other careers
such as psychiatric social work or psychiatric nursing, where assessments and therapy may be a part of the
job.

As mentioned in the opening section of this chapter, an undergraduate education in psychology is associated
with a knowledge base and skill set that many employers find quite attractive. It should come as no surprise,

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then, that individuals earning bachelor’s degrees in psychology find themselves in a number of different
careers, as shown in Table 1.1. Examples of a few such careers can involve serving as case managers, working
in sales, working in human resource departments, and teaching in high schools. The rapidly growing realm of
healthcare professions is another field in which an education in psychology is helpful and sometimes required.
For example, the Medical College Admission Test (MCAT) exam that people must take to be admitted to medical
school now includes a section on the psychological foundations of behavior.

Top Occupations Employing Graduates with a BA in Psychology (Fogg, Harrington, Harrington, & Shatkin,
2012)

Ranking Occupation

1 Mid- and top-level management (executive, administrator)

2 Sales

3 Social work

4 Other management positions

5 Human resources (personnel, training)

6 Other administrative positions

7 Insurance, real estate, business

8 Marketing and sales

9 Healthcare (nurse, pharmacist, therapist)

10 Finance (accountant, auditor)

TABLE 1.1

LINK TO LEARNING

The APA provides career information (http://openstax.org/l/careers) about various areas of psychology.

1.4 • Careers in Psychology 29

Key Terms
American Psychological Association (APA) professional organization representing psychologists in the

United States
behaviorism focus on observing and controlling behavior
biopsychology study of how biology influences behavior
biopsychosocial model perspective that asserts that biology, psychology, and social factors interact to

determine an individual’s health
clinical psychology area of psychology that focuses on the diagnosis and treatment of psychological disorders

and other problematic patterns of behavior
cognitive psychology study of cognitions, or thoughts, and their relationship to experiences and actions
counseling psychology area of psychology that focuses on improving emotional, social, vocational, and other

aspects of the lives of psychologically healthy individuals
developmental psychology scientific study of development across a lifespan
dissertation long research paper about research that was conducted as a part of the candidate’s doctoral

training
empirical method method for acquiring knowledge based on observation, including experimentation, rather

than a method based only on forms of logical argument or previous authorities
forensic psychology area of psychology that applies the science and practice of psychology to issues within

and related to the justice system
functionalism focused on how mental activities helped an organism adapt to its environment
humanism perspective within psychology that emphasizes the potential for good that is innate to all humans
introspection process by which someone examines their own conscious experience in an attempt to break it

into its component parts
ology suffix that denotes “scientific study of”
personality psychology study of patterns of thoughts and behaviors that make each individual unique
personality trait consistent pattern of thought and behavior
PhD (doctor of philosophy) doctoral degree conferred in many disciplinary perspectives housed in a

traditional college of liberal arts and sciences
postdoctoral training program allows young scientists to further develop their research programs and

broaden their research skills under the supervision of other professionals in the field
psychoanalytic theory focus on the role of the unconscious in affecting conscious behavior
psychology scientific study of the mind and behavior
PsyD (doctor of psychology) doctoral degree that places less emphasis on research-oriented skills and focuses

more on application of psychological principles in the clinical context
sport and exercise psychology area of psychology that focuses on the interactions between mental and

emotional factors and physical performance in sports, exercise, and other activities
structuralism understanding the conscious experience through introspection

Summary
1.1 What Is Psychology?

Psychology is defined as the scientific study of mind and behavior. Students of psychology develop critical
thinking skills, become familiar with the scientific method, and recognize the complexity of behavior.

1.2 History of Psychology

Before the time of Wundt and James, questions about the mind were considered by philosophers. However,
both Wundt and James helped create psychology as a distinct scientific discipline. Wundt was a structuralist,
which meant he believed that our cognitive experience was best understood by breaking that experience into
its component parts. He thought this was best accomplished by introspection.

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William James was the first American psychologist, and he was a proponent of functionalism. This particular
perspective focused on how mental activities served as adaptive responses to an organism’s environment. Like
Wundt, James also relied on introspection; however, his research approach also incorporated more objective
measures as well.

Sigmund Freud believed that understanding the unconscious mind was absolutely critical to understand
conscious behavior. This was especially true for individuals that he saw who suffered from various hysterias
and neuroses. Freud relied on dream analysis, slips of the tongue, and free association as means to access the
unconscious. Psychoanalytic theory remained a dominant force in clinical psychology for several decades.

Gestalt psychology was very influential in Europe. Gestalt psychology takes a holistic view of an individual and
his experiences. As the Nazis came to power in Germany, Wertheimer, Koffka, and Köhler immigrated to the
United States. Although they left their laboratories and their research behind, they did introduce America to
Gestalt ideas. Some of the principles of Gestalt psychology are still very influential in the study of sensation
and perception.

One of the most influential schools of thought within psychology’s history was behaviorism. Behaviorism
focused on making psychology an objective science by studying overt behavior and deemphasizing the
importance of unobservable mental processes. John Watson is often considered the father of behaviorism, and
B. F. Skinner’s contributions to our understanding of principles of operant conditioning cannot be
underestimated.

As behaviorism and psychoanalytic theory took hold of so many aspects of psychology, some began to become
dissatisfied with psychology’s picture of human nature. Thus, a humanistic movement within psychology
began to take hold. Humanism focuses on the potential of all people for good. Both Maslow and Rogers were
influential in shaping humanistic psychology.

During the 1950s, the landscape of psychology began to change. A science of behavior began to shift back to its
roots of focus on mental processes. The emergence of neuroscience and computer science aided this
transition. Ultimately, the cognitive revolution took hold, and people came to realize that cognition was crucial
to a true appreciation and understanding of behavior.

1.3 Contemporary Psychology

Psychology is a diverse discipline that is made up of several major subdivisions with unique perspectives.
Biological psychology involves the study of the biological bases of behavior. Sensation and perception refer to
the area of psychology that is focused on how information from our sensory modalities is received, and how
this information is transformed into our perceptual experiences of the world around us. Cognitive psychology
is concerned with the relationship that exists between thought and behavior, and developmental psychologists
study the physical and cognitive changes that occur throughout one’s lifespan. Personality psychology focuses
on individuals’ unique patterns of behavior, thought, and emotion. Industrial and organizational psychology,
health psychology, sport and exercise psychology, forensic psychology, and clinical psychology are all
considered applied areas of psychology. Industrial and organizational psychologists apply psychological
concepts to I-O settings. Health psychologists look for ways to help people live healthier lives, and clinical
psychology involves the diagnosis and treatment of psychological disorders and other problematic behavioral
patterns. Sport and exercise psychologists study the interactions between thoughts, emotions, and physical
performance in sports, exercise, and other activities. Forensic psychologists carry out activities related to
psychology in association with the justice system.

1.4 Careers in Psychology

Generally, academic careers in psychology require doctoral degrees. However, there are a number of
nonacademic career options for people who have master’s degrees in psychology. While people with bachelor’s
degrees in psychology have more limited psychology-related career options, the skills acquired as a function of

1 • Summary 31

an undergraduate education in psychology are useful in a variety of work contexts.

Review Questions
1. Which of the following was mentioned as a skill to which psychology students would be exposed?

a. critical thinking
b. use of the scientific method
c. critical evaluation of sources of information
d. all of the above

2. Before psychology became a recognized academic discipline, matters of the mind were undertaken by
those in ________.
a. biology
b. chemistry
c. philosophy
d. physics

3. In the scientific method, a hypothesis is a(n) ________.
a. observation
b. measurement
c. test
d. proposed explanation

4. Based on your reading, which theorist would have been most likely to agree with this statement: Perceptual
phenomena are best understood as a combination of their components.
a. William James
b. Max Wertheimer
c. Carl Rogers
d. Noam Chomsky

5. ________ is most well-known for proposing his hierarchy of needs.
a. Noam Chomsky
b. Carl Rogers
c. Abraham Maslow
d. Sigmund Freud

6. Rogers believed that providing genuineness, empathy, and ________ in the therapeutic environment for his
clients was critical to their being able to deal with their problems.
a. structuralism
b. functionalism
c. Gestalt
d. unconditional positive regard

7. The operant conditioning chamber (aka ________ box) is a device used to study the principles of operant
conditioning.
a. Skinner
b. Watson
c. James
d. Koffka

32 1 • Review Questions

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8. A researcher interested in how changes in the cells of the hippocampus (a structure in the brain related to
learning and memory) are related to memory formation would be most likely to identify as a(n) ________
psychologist.
a. biological
b. health
c. clinical
d. social

9. An individual’s consistent pattern of thought and behavior is known as a(n) ________.
a. psychosexual stage
b. object permanence
c. personality
d. perception

10. In Milgram’s controversial study on obedience, nearly ________ of the participants were willing to
administer what appeared to be lethal electrical shocks to another person because they were told to do so
by an authority figure.
a. 1/3
b. 2/3
c. 3/4
d. 4/5

11. A researcher interested in what factors make an employee best suited for a given job would most likely
identify as a(n) ________ psychologist.
a. personality
b. clinical
c. social
d. I-O

12. If someone wanted to become a psychology professor at a 4-year college, they would probably need a
________ degree in psychology.
a. bachelor of science
b. bachelor of art
c. master’s
d. PhD

13. The ________ places less emphasis on research and more emphasis on application of therapeutic skills.
a. PhD
b. PsyD
c. postdoctoral training program
d. dissertation

14. Which of the following degrees would be the minimum required to teach psychology courses in high
school?
a. PhD
b. PsyD
c. master’s degree
d. bachelor’s degree

1 • Review Questions 33

15. One would need at least a(n) ________ degree to serve as a school psychologist.
a. associate’s
b. bachelor’s
c. master’s
d. doctoral

Critical Thinking Questions
16. Why do you think psychology courses like this one are often requirements of so many different programs

of study?

17. Why do you think many people might be skeptical about psychology being a science?

18. How did the object of study in psychology change over the history of the field since the 19th century?

19. In part, what aspect of psychology was the behaviorist approach to psychology a reaction to?

20. Given the incredible diversity among the various areas of psychology that were described in this section,
how do they all fit together?

21. What are the potential ethical concerns associated with Milgram’s research on obedience?

22. Why is an undergraduate education in psychology so helpful in a number of different lines of work?

23. Other than a potentially greater salary, what would be the reasons an individual would continue on to get a
graduate degree in psychology?

Personal Application Questions
24. Why are you taking this course? What do you hope to learn about during this course?

25. Freud is probably one of the most well-known historical figures in psychology. Where have you
encountered references to Freud or his ideas about the role that the unconscious mind plays in
determining conscious behavior?

26. Now that you’ve been briefly introduced to some of the major areas within psychology, which are you most
interested in learning more about? Why?

27. Which of the career options in the field of psychology is most appealing to you?

34 1 • Critical Thinking Questions

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FIGURE 2.1 How does television content impact children’s behavior? (credit: modification of work by
“antisocialtory”/Flickr)

INTRODUCTION

CHAPTER OUTLINE
2.1 Why Is Research Important?
2.2 Approaches to Research
2.3 Analyzing Findings
2.4 Ethics

Have you ever wondered whether the violence you see on television affects your behavior?
Are you more likely to behave aggressively in real life after watching people behave violently in dramatic
situations on the screen? Or, could seeing fictional violence actually get aggression out of your system, causing
you to be more peaceful? How are children influenced by the media they are exposed to? A psychologist
interested in the relationship between behavior and exposure to violent images might ask these very
questions.

Since ancient times, humans have been concerned about the effects of new technologies on our behaviors and
thinking processes. The Greek philosopher Socrates, for example, worried that writing—a new technology at
that time—would diminish people’s ability to remember because they could rely on written records rather than
committing information to memory. In our world of rapidly changing technologies, questions about their
effects on our daily lives and their resulting long-term impacts continue to emerge. In addition to the impact of
screen time (on smartphones, tablets, computers, and gaming), technology is emerging in our vehicles (such
as GPS and smart cars) and residences (with devices like Alexa or Google Home and doorbell cameras). As
these technologies become integrated into our lives, we are faced with questions about their positive and
negative impacts. Many of us find ourselves with a strong opinion on these issues, only to find the person next
to us bristling with the opposite view.

2Psychological Research

How can we go about finding answers that are supported not by mere opinion, but by evidence that we can all
agree on? The findings of psychological research can help us navigate issues like this.

2.1 Why Is Research Important?
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain how scientific research addresses questions about behavior
• Discuss how scientific research guides public policy
• Appreciate how scientific research can be important in making personal decisions

Scientific research is a critical tool for successfully navigating our complex world. Without it, we would be
forced to rely solely on intuition, other people’s authority, and blind luck. While many of us feel confident in
our abilities to decipher and interact with the world around us, history is filled with examples of how very
wrong we can be when we fail to recognize the need for evidence in supporting claims. At various times in
history, we would have been certain that the sun revolved around a flat earth, that the earth’s continents did
not move, and that mental illness was caused by possession (Figure 2.2). It is through systematic scientific
research that we divest ourselves of our preconceived notions and superstitions and gain an objective
understanding of ourselves and our world.

FIGURE 2.2 Some of our ancestors, across the world and over the centuries, believed that trephination—the
practice of making a hole in the skull, as shown here—allowed evil spirits to leave the body, thus curing mental
illness and other disorders. (credit: “taiproject”/Flickr)

The goal of all scientists is to better understand the world around them. Psychologists focus their attention on
understanding behavior, as well as the cognitive (mental) and physiological (body) processes that underlie
behavior. In contrast to other methods that people use to understand the behavior of others, such as intuition
and personal experience, the hallmark of scientific research is that there is evidence to support a claim.
Scientific knowledge is empirical: It is grounded in objective, tangible evidence that can be observed time and
time again, regardless of who is observing.

While behavior is observable, the mind is not. If someone is crying, we can see behavior. However, the reason
for the behavior is more difficult to determine. Is the person crying due to being sad, in pain, or happy?
Sometimes we can learn the reason for someone’s behavior by simply asking a question, like “Why are you
crying?” However, there are situations in which an individual is either uncomfortable or unwilling to answer
the question honestly, or is incapable of answering. For example, infants would not be able to explain why they
are crying. In such circumstances, the psychologist must be creative in finding ways to better understand
behavior. This chapter explores how scientific knowledge is generated, and how important that knowledge is in
forming decisions in our personal lives and in the public domain.

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Use of Research Information

Trying to determine which theories are and are not accepted by the scientific community can be difficult,
especially in an area of research as broad as psychology. More than ever before, we have an incredible amount
of information at our fingertips, and a simple internet search on any given research topic might result in a
number of contradictory studies. In these cases, we are witnessing the scientific community going through the
process of reaching a consensus, and it could be quite some time before a consensus emerges. For example,
the explosion in our use of technology has led researchers to question whether this ultimately helps or hinders
us. The use and implementation of technology in educational settings has become widespread over the last few
decades. Researchers are coming to different conclusions regarding the use of technology. To illustrate this
point, a study investigating a smartphone app targeting surgery residents (graduate students in surgery
training) found that the use of this app can increase student engagement and raise test scores (Shaw & Tan,
2015). Conversely, another study found that the use of technology in undergraduate student populations had
negative impacts on sleep, communication, and time management skills (Massimini & Peterson, 2009). Until
sufficient amounts of research have been conducted, there will be no clear consensus on the effects that
technology has on a student’s acquisition of knowledge, study skills, and mental health.

In the meantime, we should strive to think critically about the information we encounter by exercising a degree
of healthy skepticism. When someone makes a claim, we should examine the claim from a number of different
perspectives: what is the expertise of the person making the claim, what might they gain if the claim is valid,
does the claim seem justified given the evidence, and what do other researchers think of the claim? This is
especially important when we consider how much information in advertising campaigns and on the internet
claims to be based on “scientific evidence” when in actuality it is a belief or perspective of just a few
individuals trying to sell a product or draw attention to their perspectives.

We should be informed consumers of the information made available to us because decisions based on this
information have significant consequences. One such consequence can be seen in politics and public policy.
Imagine that you have been elected as the governor of your state. One of your responsibilities is to manage the
state budget and determine how to best spend your constituents’ tax dollars. As the new governor, you need to
decide whether to continue funding early intervention programs. These programs are designed to help
children who come from low-income backgrounds, have special needs, or face other disadvantages. These
programs may involve providing a wide variety of services to maximize the children’s development and
position them for optimal levels of success in school and later in life (Blann, 2005). While such programs
sound appealing, you would want to be sure that they also proved effective before investing additional money
in these programs. Fortunately, psychologists and other scientists have conducted vast amounts of research on
such programs and, in general, the programs are found to be effective (Neil & Christensen, 2009; Peters-
Scheffer, Didden, Korzilius, & Sturmey, 2011). While not all programs are equally effective, and the short-term
effects of many such programs are more pronounced, there is reason to believe that many of these programs
produce long-term benefits for participants (Barnett, 2011). If you are committed to being a good steward of
taxpayer money, you would want to look at research. Which programs are most effective? What characteristics
of these programs make them effective? Which programs promote the best outcomes? After examining the
research, you would be best equipped to make decisions about which programs to fund.

LINK TO LEARNING

Watch this video about early childhood program effectiveness (http://openstax.org/l/programeffect) to learn
how scientists evaluate effectiveness and how best to invest money into programs that are most effective.

Ultimately, it is not just politicians who can benefit from using research in guiding their decisions. We all might
look to research from time to time when making decisions in our lives. Imagine you just found out that your
sister Maria’s child, Umberto, was recently diagnosed with autism. There are many treatments for autism that
help decrease the negative impact of autism on the individual. Some examples of treatments for autism are

2.1 • Why Is Research Important? 37

applied behavior analysis (ABA), social communication groups, social skills groups, occupational therapy, and
even medication options. If Maria asked you for advice or guidance, what would you do? You would likely want
to review the research and learn about the efficacy of each treatment so you could best advise your sister.

In the end, research is what makes the difference between facts and opinions. Facts are observable realities,
and opinions are personal judgments, conclusions, or attitudes that may or may not be accurate. In the
scientific community, facts can be established only using evidence collected through empirical research.

NOTABLE RESEARCHERS

Psychological research has a long history involving important figures from diverse backgrounds. While the
introductory chapter discussed several researchers who made significant contributions to the discipline, there
are many more individuals who deserve attention in considering how psychology has advanced as a science
through their work (Figure 2.3). For instance, Margaret Floy Washburn (1871–1939) was the first woman to
earn a PhD in psychology. Her research focused on animal behavior and cognition (Margaret Floy Washburn,
PhD, n.d.). Mary Whiton Calkins (1863–1930) was a preeminent first-generation American psychologist who
opposed the behaviorist movement, conducted significant research into memory, and established one of the
earliest experimental psychology labs in the United States (Mary Whiton Calkins, n.d.).

Francis Sumner (1895–1954) was the first African American to receive a PhD in psychology in 1920. His
dissertation focused on issues related to psychoanalysis. Sumner also had research interests in racial bias and
educational justice. Sumner was one of the founders of Howard University’s department of psychology, and
because of his accomplishments, he is sometimes referred to as the “Father of Black Psychology.” Thirteen
years later, Inez Beverly Prosser (1895–1934) became the first African American woman to receive a PhD in
psychology. Prosser’s research highlighted issues related to education in segregated versus integrated schools,
and ultimately, her work was very influential in the hallmark Brown v. Board of Education Supreme Court
ruling that segregation of public schools was unconstitutional (Ethnicity and Health in America Series:
Featured Psychologists, n.d.).

FIGURE 2.3 (a) Margaret Floy Washburn was the first woman to earn a doctorate degree in psychology. (b) The
outcome of Brown v. Board of Education was influenced by the research of psychologist Inez Beverly Prosser, who
was the first African American woman to earn a PhD in psychology.

Although the establishment of psychology’s scientific roots occurred first in Europe and the United States, it
did not take much time until researchers from around the world began to establish their own laboratories and
research programs. For example, some of the first experimental psychology laboratories in South America
were founded by Horatio Piñero (1869–1919) at two institutions in Buenos Aires, Argentina (Godoy & Brussino,
2010). In India, Gunamudian David Boaz (1908–1965) and Narendra Nath Sen Gupta (1889–1944) established

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the first independent departments of psychology at the University of Madras and the University of Calcutta,
respectively. These developments provided an opportunity for Indian researchers to make important
contributions to the field (Gunamudian David Boaz, n.d.; Narendra Nath Sen Gupta, n.d.).

When the American Psychological Association (APA) was first founded in 1892, all of the members were White
males (Women and Minorities in Psychology, n.d.). However, by 1905, Mary Whiton Calkins was elected as the
first female president of the APA, and by 1946, nearly one-quarter of American psychologists were female.
Psychology became a popular degree option for students enrolled in the nation’s historically Black higher
education institutions, increasing the number of Black Americans who went on to become psychologists. Given
demographic shifts occurring in the United States and increased access to higher educational opportunities
among historically underrepresented populations, there is reason to hope that the diversity of the field will
increasingly match the larger population, and that the research contributions made by the psychologists of the
future will better serve people of all backgrounds (Women and Minorities in Psychology, n.d.).

The Process of Scientific Research

Scientific knowledge is advanced through a process known as the scientific method. Basically, ideas (in the
form of theories and hypotheses) are tested against the real world (in the form of empirical observations), and
those empirical observations lead to more ideas that are tested against the real world, and so on. In this sense,
the scientific process is circular. The types of reasoning within the circle are called deductive and inductive. In
deductive reasoning, ideas are tested in the real world; in inductive reasoning, real-world observations lead
to new ideas (Figure 2.4). These processes are inseparable, like inhaling and exhaling, but different research
approaches place different emphasis on the deductive and inductive aspects.

FIGURE 2.4 Psychological research relies on both inductive and deductive reasoning.

In the scientific context, deductive reasoning begins with a generalization—one hypothesis—that is then used
to reach logical conclusions about the real world. If the hypothesis is correct, then the logical conclusions
reached through deductive reasoning should also be correct. A deductive reasoning argument might go
something like this: All living things require energy to survive (this would be your hypothesis). Ducks are living
things. Therefore, ducks require energy to survive (logical conclusion). In this example, the hypothesis is
correct; therefore, the conclusion is correct as well. Sometimes, however, an incorrect hypothesis may lead to a
logical but incorrect conclusion. Consider this argument: all ducks are born with the ability to see. Quackers is
a duck. Therefore, Quackers was born with the ability to see. Scientists use deductive reasoning to empirically
test their hypotheses. Returning to the example of the ducks, researchers might design a study to test the
hypothesis that if all living things require energy to survive, then ducks will be found to require energy to
survive.

Deductive reasoning starts with a generalization that is tested against real-world observations; however,
inductive reasoning moves in the opposite direction. Inductive reasoning uses empirical observations to

2.1 • Why Is Research Important? 39

construct broad generalizations. Unlike deductive reasoning, conclusions drawn from inductive reasoning
may or may not be correct, regardless of the observations on which they are based. For instance, you may
notice that your favorite fruits—apples, bananas, and oranges—all grow on trees; therefore, you assume that all
fruit must grow on trees. This would be an example of inductive reasoning, and, clearly, the existence of
strawberries, blueberries, and kiwi demonstrate that this generalization is not correct despite it being based
on a number of direct observations. Scientists use inductive reasoning to formulate theories, which in turn
generate hypotheses that are tested with deductive reasoning. In the end, science involves both deductive and
inductive processes.

For example, case studies, which you will read about in the next section, are heavily weighted on the side of
empirical observations. Thus, case studies are closely associated with inductive processes as researchers
gather massive amounts of observations and seek interesting patterns (new ideas) in the data. Experimental
research, on the other hand, puts great emphasis on deductive reasoning.

We’ve stated that theories and hypotheses are ideas, but what sort of ideas are they, exactly? A theory is a well-
developed set of ideas that propose an explanation for observed phenomena. Theories are repeatedly checked
against the world, but they tend to be too complex to be tested all at once; instead, researchers create
hypotheses to test specific aspects of a theory.

A hypothesis is a testable prediction about how the world will behave if our idea is correct, and it is often
worded as an if-then statement (e.g., if I study all night, I will get a passing grade on the test). The hypothesis is
extremely important because it bridges the gap between the realm of ideas and the real world. As specific
hypotheses are tested, theories are modified and refined to reflect and incorporate the result of these tests
Figure 2.5.

FIGURE 2.5 The scientific method involves deriving hypotheses from theories and then testing those hypotheses. If
the results are consistent with the theory, then the theory is supported. If the results are not consistent, then the
theory should be modified and new hypotheses will be generated.

To see how this process works, let’s consider a specific theory and a hypothesis that might be generated from
that theory. As you’ll learn in a later chapter, the James-Lange theory of emotion asserts that emotional
experience relies on the physiological arousal associated with the emotional state. If you walked out of your
home and discovered a very aggressive snake waiting on your doorstep, your heart would begin to race and
your stomach churn. According to the James-Lange theory, these physiological changes would result in your

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feeling of fear. A hypothesis that could be derived from this theory might be that a person who is unaware of
the physiological arousal that the sight of the snake elicits will not feel fear.

A scientific hypothesis is also falsifiable, or capable of being shown to be incorrect. Recall from the
introductory chapter that Sigmund Freud had lots of interesting ideas to explain various human behaviors
(Figure 2.6). However, a major criticism of Freud’s theories is that many of his ideas are not falsifiable; for
example, it is impossible to imagine empirical observations that would disprove the existence of the id, the
ego, and the superego—the three elements of personality described in Freud’s theories. Despite this, Freud’s
theories are widely taught in introductory psychology texts because of their historical significance for
personality psychology and psychotherapy, and these remain the root of all modern forms of therapy.

FIGURE 2.6 Many of the specifics of (a) Freud’s theories, such as (b) his division of the mind into id, ego, and
superego, have fallen out of favor in recent decades because they are not falsifiable. In broader strokes, his views
set the stage for much of psychological thinking today, such as the unconscious nature of the majority of
psychological processes.

In contrast, the James-Lange theory does generate falsifiable hypotheses, such as the one described above.
Some individuals who suffer significant injuries to their spinal columns are unable to feel the bodily changes
that often accompany emotional experiences. Therefore, we could test the hypothesis by determining how
emotional experiences differ between individuals who have the ability to detect these changes in their
physiological arousal and those who do not. In fact, this research has been conducted and while the emotional
experiences of people deprived of an awareness of their physiological arousal may be less intense, they still
experience emotion (Chwalisz, Diener, & Gallagher, 1988).

Scientific research’s dependence on falsifiability allows for great confidence in the information that it
produces. Typically, by the time information is accepted by the scientific community, it has been tested
repeatedly.

2.2 Approaches to Research
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the different research methods used by psychologists
• Discuss the strengths and weaknesses of case studies, naturalistic observation, surveys, and archival research
• Compare longitudinal and cross-sectional approaches to research
• Compare and contrast correlation and causation

There are many research methods available to psychologists in their efforts to understand, describe, and

2.2 • Approaches to Research 41

explain behavior and the cognitive and biological processes that underlie it. Some methods rely on
observational techniques. Other approaches involve interactions between the researcher and the individuals
who are being studied—ranging from a series of simple questions to extensive, in-depth interviews—to well-
controlled experiments.

Each of these research methods has unique strengths and weaknesses, and each method may only be
appropriate for certain types of research questions. For example, studies that rely primarily on observation
produce incredible amounts of information, but the ability to apply this information to the larger population is
somewhat limited because of small sample sizes. Survey research, on the other hand, allows researchers to
easily collect data from relatively large samples. While this allows for results to be generalized to the larger
population more easily, the information that can be collected on any given survey is somewhat limited and
subject to problems associated with any type of self-reported data. Some researchers conduct archival
research by using existing records. While this can be a fairly inexpensive way to collect data that can provide
insight into a number of research questions, researchers using this approach have no control on how or what
kind of data was collected. All of the methods described thus far are correlational in nature. This means that
researchers can speak to important relationships that might exist between two or more variables of interest.
However, correlational data cannot be used to make claims about cause-and-effect relationships.

Correlational research can find a relationship between two variables, but the only way a researcher can claim
that the relationship between the variables is cause and effect is to perform an experiment. In experimental
research, which will be discussed later in this chapter, there is a tremendous amount of control over variables
of interest. While this is a powerful approach, experiments are often conducted in artificial settings. This calls
into question the validity of experimental findings with regard to how they would apply in real-world settings.
In addition, many of the questions that psychologists would like to answer cannot be pursued through
experimental research because of ethical concerns.

Clinical or Case Studies

In 2011, the New York Times published a feature story on Krista and Tatiana Hogan, Canadian twin girls.
These particular twins are unique because Krista and Tatiana are conjoined twins, connected at the head.
There is evidence that the two girls are connected in a part of the brain called the thalamus, which is a major
sensory relay center. Most incoming sensory information is sent through the thalamus before reaching higher
regions of the cerebral cortex for processing.

LINK TO LEARNING

Watch this CBC video about Krista’s and Tatiana’s lives (http://openstax.org/l/hogans) to learn more.

The implications of this potential connection mean that it might be possible for one twin to experience the
sensations of the other twin. For instance, if Krista is watching a particularly funny television program, Tatiana
might smile or laugh even if she is not watching the program. This particular possibility has piqued the
interest of many neuroscientists who seek to understand how the brain uses sensory information.

These twins represent an enormous resource in the study of the brain, and since their condition is very rare, it
is likely that as long as their family agrees, scientists will follow these girls very closely throughout their lives to
gain as much information as possible (Dominus, 2011).

Over time, it has become clear that while Krista and Tatiana share some sensory experiences and motor
control, they remain two distinct individuals, which provides invaluable insight for researchers interested in
the mind and the brain (Egnor, 2017).

In observational research, scientists are conducting a clinical or case study when they focus on one person or
just a few individuals. Indeed, some scientists spend their entire careers studying just 10–20 individuals. Why
would they do this? Obviously, when they focus their attention on a very small number of people, they can gain

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a precious amount of insight into those cases. The richness of information that is collected in clinical or case
studies is unmatched by any other single research method. This allows the researcher to have a very deep
understanding of the individuals and the particular phenomenon being studied.

If clinical or case studies provide so much information, why are they not more frequent among researchers?
As it turns out, the major benefit of this particular approach is also a weakness. As mentioned earlier, this
approach is often used when studying individuals who are interesting to researchers because they have a rare
characteristic. Therefore, the individuals who serve as the focus of case studies are not like most other people.
If scientists ultimately want to explain all behavior, focusing attention on such a special group of people can
make it difficult to generalize any observations to the larger population as a whole. Generalizing refers to the
ability to apply the findings of a particular research project to larger segments of society. Again, case studies
provide enormous amounts of information, but since the cases are so specific, the potential to apply what’s
learned to the average person may be very limited.

Naturalistic Observation

If you want to understand how behavior occurs, one of the best ways to gain information is to simply observe
the behavior in its natural context. However, people might change their behavior in unexpected ways if they
know they are being observed. How do researchers obtain accurate information when people tend to hide their
natural behavior? As an example, imagine that your professor asks everyone in your class to raise their hand if
they always wash their hands after using the restroom. Chances are that almost everyone in the classroom will
raise their hand, but do you think hand washing after every trip to the restroom is really that universal?

This is very similar to the phenomenon mentioned earlier in this chapter: many individuals do not feel
comfortable answering a question honestly. But if we are committed to finding out the facts about hand
washing, we have other options available to us.

Suppose we send a classmate into the restroom to actually watch whether everyone washes their hands after
using the restroom. Will our observer blend into the restroom environment by wearing a white lab coat, sitting
with a clipboard, and staring at the sinks? We want our researcher to be inconspicuous—perhaps standing at
one of the sinks pretending to put in contact lenses while secretly recording the relevant information. This
type of observational study is called naturalistic observation: observing behavior in its natural setting. To
better understand peer exclusion, Suzanne Fanger collaborated with colleagues at the University of Texas to
observe the behavior of preschool children on a playground. How did the observers remain inconspicuous
over the duration of the study? They equipped a few of the children with wireless microphones (which the
children quickly forgot about) and observed while taking notes from a distance. Also, the children in that
particular preschool (a “laboratory preschool”) were accustomed to having observers on the playground
(Fanger, Frankel, & Hazen, 2012).

It is critical that the observer be as unobtrusive and as inconspicuous as possible: when people know they are
being watched, they are less likely to behave naturally. If you have any doubt about this, ask yourself how your
driving behavior might differ in two situations: In the first situation, you are driving down a deserted highway
during the middle of the day; in the second situation, you are being followed by a police car down the same
deserted highway (Figure 2.7).

2.2 • Approaches to Research 43

FIGURE 2.7 Seeing a police car behind you would probably affect your driving behavior. (credit: Michael Gil)

It should be pointed out that naturalistic observation is not limited to research involving humans. Indeed,
some of the best-known examples of naturalistic observation involve researchers going into the field to
observe various kinds of animals in their own environments. As with human studies, the researchers maintain
their distance and avoid interfering with the animal subjects so as not to influence their natural behaviors.
Scientists have used this technique to study social hierarchies and interactions among animals ranging from
ground squirrels to gorillas. The information provided by these studies is invaluable in understanding how
those animals organize socially and communicate with one another. The anthropologist Jane Goodall, for
example, spent nearly five decades observing the behavior of chimpanzees in Africa (Figure 2.8). As an
illustration of the types of concerns that a researcher might encounter in naturalistic observation, some
scientists criticized Goodall for giving the chimps names instead of referring to them by numbers—using
names was thought to undermine the emotional detachment required for the objectivity of the study (McKie,
2010).

FIGURE 2.8 (a) Jane Goodall made a career of conducting naturalistic observations of (b) chimpanzee behavior.
(credit “Jane Goodall”: modification of work by Erik Hersman; “chimpanzee”: modification of work by “Afrika
Force”/Flickr.com)

The greatest benefit of naturalistic observation is the validity, or accuracy, of information collected
unobtrusively in a natural setting. Having individuals behave as they normally would in a given situation
means that we have a higher degree of ecological validity, or realism, than we might achieve with other
research approaches. Therefore, our ability to generalize the findings of the research to real-world situations is
enhanced. If done correctly, we need not worry about people or animals modifying their behavior simply
because they are being observed. Sometimes, people may assume that reality programs give us a glimpse into
authentic human behavior. However, the principle of inconspicuous observation is violated as reality stars are
followed by camera crews and are interviewed on camera for personal confessionals. Given that environment,
we must doubt how natural and realistic their behaviors are.

The major downside of naturalistic observation is that they are often difficult to set up and control. In our
restroom study, what if you stood in the restroom all day prepared to record people’s hand washing behavior
and no one came in? Or, what if you have been closely observing a troop of gorillas for weeks only to find that
they migrated to a new place while you were sleeping in your tent? The benefit of realistic data comes at a cost.
As a researcher you have no control of when (or if) you have behavior to observe. In addition, this type of

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observational research often requires significant investments of time, money, and a good dose of luck.

Sometimes studies involve structured observation. In these cases, people are observed while engaging in set,
specific tasks. An excellent example of structured observation comes from Strange Situation by Mary
Ainsworth (you will read more about this in the chapter on lifespan development). The Strange Situation is a
procedure used to evaluate attachment styles that exist between an infant and caregiver. In this scenario,
caregivers bring their infants into a room filled with toys. The Strange Situation involves a number of phases,
including a stranger coming into the room, the caregiver leaving the room, and the caregiver’s return to the
room. The infant’s behavior is closely monitored at each phase, but it is the behavior of the infant upon being
reunited with the caregiver that is most telling in terms of characterizing the infant’s attachment style with the
caregiver.

Another potential problem in observational research is observer bias. Generally, people who act as observers
are closely involved in the research project and may unconsciously skew their observations to fit their
research goals or expectations. To protect against this type of bias, researchers should have clear criteria
established for the types of behaviors recorded and how those behaviors should be classified. In addition,
researchers often compare observations of the same event by multiple observers, in order to test inter-rater
reliability: a measure of reliability that assesses the consistency of observations by different observers.

Surveys

Often, psychologists develop surveys as a means of gathering data. Surveys are lists of questions to be
answered by research participants, and can be delivered as paper-and-pencil questionnaires, administered
electronically, or conducted verbally (Figure 2.9). Generally, the survey itself can be completed in a short time,
and the ease of administering a survey makes it easy to collect data from a large number of people.

Surveys allow researchers to gather data from larger samples than may be afforded by other research
methods. A sample is a subset of individuals selected from a population, which is the overall group of
individuals that the researchers are interested in. Researchers study the sample and seek to generalize their
findings to the population. Generally, researchers will begin this process by calculating various measures of
central tendency from the data they have collected. These measures provide an overall summary of what a
typical response looks like. There are three measures of central tendency: mode, median, and mean. The
mode is the most frequently occurring response, the median lies at the middle of a given data set, and the
mean is the arithmetic average of all data points. Means tend to be most useful in conducting additional
analyses like those described below; however, means are very sensitive to the effects of outliers, and so one
must be aware of those effects when making assessments of what measures of central tendency tell us about a
data set in question.

FIGURE 2.9 Surveys can be administered in a number of ways, including electronically administered research, like
the survey shown here. (credit: Robert Nyman)

2.2 • Approaches to Research 45

There is both strength and weakness of the survey in comparison to case studies. By using surveys, we can
collect information from a larger sample of people. A larger sample is better able to reflect the actual diversity
of the population, thus allowing better generalizability. Therefore, if our sample is sufficiently large and
diverse, we can assume that the data we collect from the survey can be generalized to the larger population
with more certainty than the information collected through a case study. However, given the greater number of
people involved, we are not able to collect the same depth of information on each person that would be
collected in a case study.

Another potential weakness of surveys is something we touched on earlier in this chapter: People don’t always
give accurate responses. They may lie, misremember, or answer questions in a way that they think makes
them look good. For example, people may report drinking less alcohol than is actually the case.

Any number of research questions can be answered through the use of surveys. One real-world example is the
research conducted by Jenkins, Ruppel, Kizer, Yehl, and Griffin (2012) about the backlash against the US Arab-
American community following the terrorist attacks of September 11, 2001. Jenkins and colleagues wanted to
determine to what extent these negative attitudes toward Arab-Americans still existed nearly a decade after
the attacks occurred. In one study, 140 research participants filled out a survey with 10 questions, including
questions asking directly about the participant’s overt prejudicial attitudes toward people of various
ethnicities. The survey also asked indirect questions about how likely the participant would be to interact with
a person of a given ethnicity in a variety of settings (such as, “How likely do you think it is that you would
introduce yourself to a person of Arab-American descent?”). The results of the research suggested that
participants were unwilling to report prejudicial attitudes toward any ethnic group. However, there were
significant differences between their pattern of responses to questions about social interaction with Arab-
Americans compared to other ethnic groups: they indicated less willingness for social interaction with Arab-
Americans compared to the other ethnic groups. This suggested that the participants harbored subtle forms of
prejudice against Arab-Americans, despite their assertions that this was not the case (Jenkins et al., 2012).

Archival Research

Some researchers gain access to large amounts of data without interacting with a single research participant.
Instead, they use existing records to answer various research questions. This type of research approach is
known as archival research. Archival research relies on looking at past records or data sets to look for
interesting patterns or relationships.

For example, a researcher might access the academic records of all individuals who enrolled in college within
the past ten years and calculate how long it took them to complete their degrees, as well as course loads,
grades, and extracurricular involvement. Archival research could provide important information about who is
most likely to complete their education, and it could help identify important risk factors for struggling
students (Figure 2.10).

FIGURE 2.10 A researcher doing archival research examines records, whether archived as a (a) hardcopy or (b)
electronically. (credit “paper files”: modification of work by “Newtown graffiti”/Flickr; “computer”: modification of
work by INPIVIC Family/Flickr)

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In comparing archival research to other research methods, there are several important distinctions. For one,
the researcher employing archival research never directly interacts with research participants. Therefore, the
investment of time and money to collect data is considerably less with archival research. Additionally,
researchers have no control over what information was originally collected. Therefore, research questions
have to be tailored so they can be answered within the structure of the existing data sets. There is also no
guarantee of consistency between the records from one source to another, which might make comparing and
contrasting different data sets problematic.

Longitudinal and Cross-Sectional Research

Sometimes we want to see how people change over time, as in studies of human development and lifespan.
When we test the same group of individuals repeatedly over an extended period of time, we are conducting
longitudinal research. Longitudinal research is a research design in which data-gathering is administered
repeatedly over an extended period of time. For example, we may survey a group of individuals about their
dietary habits at age 20, retest them a decade later at age 30, and then again at age 40.

Another approach is cross-sectional research. In cross-sectional research, a researcher compares multiple
segments of the population at the same time. Using the dietary habits example above, the researcher might
directly compare different groups of people by age. Instead of studying a group of people for 20 years to see
how their dietary habits changed from decade to decade, the researcher would study a group of 20-year-old
individuals and compare them to a group of 30-year-old individuals and a group of 40-year-old individuals.
While cross-sectional research requires a shorter-term investment, it is also limited by differences that exist
between the different generations (or cohorts) that have nothing to do with age per se, but rather reflect the
social and cultural experiences of different generations of individuals make them different from one another.

To illustrate this concept, consider the following survey findings. In recent years there has been significant
growth in the popular support of same-sex marriage. Many studies on this topic break down survey
participants into different age groups. In general, younger people are more supportive of same-sex marriage
than are those who are older (Jones, 2013). Does this mean that as we age we become less open to the idea of
same-sex marriage, or does this mean that older individuals have different perspectives because of the social
climates in which they grew up? Longitudinal research is a powerful approach because the same individuals
are involved in the research project over time, which means that the researchers need to be less concerned
with differences among cohorts affecting the results of their study.

Often longitudinal studies are employed when researching various diseases in an effort to understand
particular risk factors. Such studies often involve tens of thousands of individuals who are followed for several
decades. Given the enormous number of people involved in these studies, researchers can feel confident that
their findings can be generalized to the larger population. The Cancer Prevention Study-3 (CPS-3) is one of a
series of longitudinal studies sponsored by the American Cancer Society aimed at determining predictive risk
factors associated with cancer. When participants enter the study, they complete a survey about their lives and
family histories, providing information on factors that might cause or prevent the development of cancer. Then
every few years the participants receive additional surveys to complete. In the end, hundreds of thousands of
participants will be tracked over 20 years to determine which of them develop cancer and which do not.

Clearly, this type of research is important and potentially very informative. For instance, earlier longitudinal
studies sponsored by the American Cancer Society provided some of the first scientific demonstrations of the
now well-established links between increased rates of cancer and smoking (American Cancer Society, n.d.)
(Figure 2.11).

2.2 • Approaches to Research 47

FIGURE 2.11 Longitudinal research like the CPS-3 help us to better understand how smoking is associated with
cancer and other diseases. (credit: CDC/Debora Cartagena)

As with any research strategy, longitudinal research is not without limitations. For one, these studies require
an incredible time investment by the researcher and research participants. Given that some longitudinal
studies take years, if not decades, to complete, the results will not be known for a considerable period of time.
In addition to the time demands, these studies also require a substantial financial investment. Many
researchers are unable to commit the resources necessary to see a longitudinal project through to the end.

Research participants must also be willing to continue their participation for an extended period of time, and
this can be problematic. People move, get married and take new names, get ill, and eventually die. Even
without significant life changes, some people may simply choose to discontinue their participation in the
project. As a result, the attrition rates, or reduction in the number of research participants due to dropouts, in
longitudinal studies are quite high and increases over the course of a project. For this reason, researchers
using this approach typically recruit many participants fully expecting that a substantial number will drop out
before the end. As the study progresses, they continually check whether the sample still represents the larger
population, and make adjustments as necessary.

2.3 Analyzing Findings
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain what a correlation coefficient tells us about the relationship between variables
• Recognize that correlation does not indicate a cause-and-effect relationship between variables
• Discuss our tendency to look for relationships between variables that do not really exist
• Explain random sampling and assignment of participants into experimental and control groups
• Discuss how experimenter or participant bias could affect the results of an experiment
• Identify independent and dependent variables

Did you know that as sales in ice cream increase, so does the overall rate of crime? Is it possible that indulging
in your favorite flavor of ice cream could send you on a crime spree? Or, after committing crime do you think
you might decide to treat yourself to a cone? There is no question that a relationship exists between ice cream
and crime (e.g., Harper, 2013), but it would be pretty foolish to decide that one thing actually caused the other
to occur.

It is much more likely that both ice cream sales and crime rates are related to the temperature outside. When
the temperature is warm, there are lots of people out of their houses, interacting with each other, getting
annoyed with one another, and sometimes committing crimes. Also, when it is warm outside, we are more
likely to seek a cool treat like ice cream. How do we determine if there is indeed a relationship between two
things? And when there is a relationship, how can we discern whether it is attributable to coincidence or
causation?

Correlational Research

Correlation means that there is a relationship between two or more variables (such as ice cream consumption
and crime), but this relationship does not necessarily imply cause and effect. When two variables are

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correlated, it simply means that as one variable changes, so does the other. We can measure correlation by
calculating a statistic known as a correlation coefficient. A correlation coefficient is a number from -1 to +1
that indicates the strength and direction of the relationship between variables. The correlation coefficient is
usually represented by the letter r.

The number portion of the correlation coefficient indicates the strength of the relationship. The closer the
number is to 1 (be it negative or positive), the more strongly related the variables are, and the more predictable
changes in one variable will be as the other variable changes. The closer the number is to zero, the weaker the
relationship, and the less predictable the relationships between the variables becomes. For instance, a
correlation coefficient of 0.9 indicates a far stronger relationship than a correlation coefficient of 0.3. If the
variables are not related to one another at all, the correlation coefficient is 0. The example above about ice
cream and crime is an example of two variables that we might expect to have no relationship to each other.

The sign—positive or negative—of the correlation coefficient indicates the direction of the relationship (Figure
2.12). A positive correlation means that the variables move in the same direction. Put another way, it means
that as one variable increases so does the other, and conversely, when one variable decreases so does the other.
A negative correlation means that the variables move in opposite directions. If two variables are negatively
correlated, a decrease in one variable is associated with an increase in the other and vice versa.

The example of ice cream and crime rates is a positive correlation because both variables increase when
temperatures are warmer. Other examples of positive correlations are the relationship between an individual’s
height and weight or the relationship between a person’s age and number of wrinkles. One might expect a
negative correlation to exist between someone’s tiredness during the day and the number of hours they slept
the previous night: the amount of sleep decreases as the feelings of tiredness increase. In a real-world example
of negative correlation, student researchers at the University of Minnesota found a weak negative correlation (r
= -0.29) between the average number of days per week that students got fewer than 5 hours of sleep and their
GPA (Lowry, Dean, & Manders, 2010). Keep in mind that a negative correlation is not the same as no
correlation. For example, we would probably find no correlation between hours of sleep and shoe size.

As mentioned earlier, correlations have predictive value. Imagine that you are on the admissions committee of
a major university. You are faced with a huge number of applications, but you are able to accommodate only a
small percentage of the applicant pool. How might you decide who should be admitted? You might try to
correlate your current students’ college GPA with their scores on standardized tests like the SAT or ACT. By
observing which correlations were strongest for your current students, you could use this information to
predict relative success of those students who have applied for admission into the university.

FIGURE 2.12 Scatterplots are a graphical view of the strength and direction of correlations. The stronger the
correlation, the closer the data points are to a straight line. In these examples, we see that there is (a) a positive
correlation between weight and height, (b) a negative correlation between tiredness and hours of sleep, and (c) no
correlation between shoe size and hours of sleep.

2.3 • Analyzing Findings 49

LINK TO LEARNING

Manipulate this interactive scatterplot (http://openstax.org/l/scatplot) to practice your understanding of
positive and negative correlation.

Correlation Does Not Indicate Causation

Correlational research is useful because it allows us to discover the strength and direction of relationships that
exist between two variables. However, correlation is limited because establishing the existence of a
relationship tells us little about cause and effect. While variables are sometimes correlated because one does
cause the other, it could also be that some other factor, a confounding variable, is actually causing the
systematic movement in our variables of interest. In the ice cream/crime rate example mentioned earlier,
temperature is a confounding variable that could account for the relationship between the two variables.

Even when we cannot point to clear confounding variables, we should not assume that a correlation between
two variables implies that one variable causes changes in another. This can be frustrating when a cause-and-
effect relationship seems clear and intuitive. Think back to our discussion of the research done by the
American Cancer Society and how their research projects were some of the first demonstrations of the link
between smoking and cancer. It seems reasonable to assume that smoking causes cancer, but if we were
limited to correlational research, we would be overstepping our bounds by making this assumption.

Unfortunately, people mistakenly make claims of causation as a function of correlations all the time. Such
claims are especially common in advertisements and news stories. For example, recent research found that
people who eat cereal on a regular basis achieve healthier weights than those who rarely eat cereal (Frantzen,
Treviño, Echon, Garcia-Dominic, & DiMarco, 2013; Barton et al., 2005). Guess how the cereal companies report
this finding. Does eating cereal really cause an individual to maintain a healthy weight, or are there other
possible explanations, such as, someone at a healthy weight is more likely to regularly eat a healthy breakfast
than someone who is obese or someone who avoids meals in an attempt to diet (Figure 2.13)? While
correlational research is invaluable in identifying relationships among variables, a major limitation is the
inability to establish causality. Psychologists want to make statements about cause and effect, but the only way
to do that is to conduct an experiment to answer a research question. The next section describes how scientific
experiments incorporate methods that eliminate, or control for, alternative explanations, which allow
researchers to explore how changes in one variable cause changes in another variable.

FIGURE 2.13 Does eating cereal really cause someone to be a healthy weight? (credit: Tim Skillern)

Illusory Correlations

The temptation to make erroneous cause-and-effect statements based on correlational research is not the only
way we tend to misinterpret data. We also tend to make the mistake of illusory correlations, especially with
unsystematic observations. Illusory correlations, or false correlations, occur when people believe that
relationships exist between two things when no such relationship exists. One well-known illusory correlation
is the supposed effect that the moon’s phases have on human behavior. Many people passionately assert that
human behavior is affected by the phase of the moon, and specifically, that people act strangely when the

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moon is full (Figure 2.14).

FIGURE 2.14 Many people believe that a full moon makes people behave oddly. (credit: Cory Zanker)

There is no denying that the moon exerts a powerful influence on our planet. The ebb and flow of the ocean’s
tides are tightly tied to the gravitational forces of the moon. Many people believe, therefore, that it is logical
that we are affected by the moon as well. After all, our bodies are largely made up of water. A meta-analysis of
nearly 40 studies consistently demonstrated, however, that the relationship between the moon and our
behavior does not exist (Rotton & Kelly, 1985). While we may pay more attention to odd behavior during the full
phase of the moon, the rates of odd behavior remain constant throughout the lunar cycle.

Why are we so apt to believe in illusory correlations like this? Often we read or hear about them and simply
accept the information as valid. Or, we have a hunch about how something works and then look for evidence to
support that hunch, ignoring evidence that would tell us our hunch is false; this is known as confirmation
bias. Other times, we find illusory correlations based on the information that comes most easily to mind, even
if that information is severely limited. And while we may feel confident that we can use these relationships to
better understand and predict the world around us, illusory correlations can have significant drawbacks. For
example, research suggests that illusory correlations—in which certain behaviors are inaccurately attributed to
certain groups—are involved in the formation of prejudicial attitudes that can ultimately lead to discriminatory
behavior (Fiedler, 2004).

Causality: Conducting Experiments and Using the Data

As you’ve learned, the only way to establish that there is a cause-and-effect relationship between two variables
is to conduct a scientific experiment. Experiment has a different meaning in the scientific context than in
everyday life. In everyday conversation, we often use it to describe trying something for the first time, such as
experimenting with a new hair style or a new food. However, in the scientific context, an experiment has
precise requirements for design and implementation.

The Experimental Hypothesis

In order to conduct an experiment, a researcher must have a specific hypothesis to be tested. As you’ve
learned, hypotheses can be formulated either through direct observation of the real world or after careful
review of previous research. For example, if you think that the use of technology in the classroom has negative
impacts on learning, then you have basically formulated a hypothesis—namely, that the use of technology in
the classroom should be limited because it decreases learning. How might you have arrived at this particular
hypothesis? You may have noticed that your classmates who take notes on their laptops perform at lower levels
on class exams than those who take notes by hand, or those who receive a lesson via a computer program
versus via an in-person teacher have different levels of performance when tested (Figure 2.15).

2.3 • Analyzing Findings 51

FIGURE 2.15 How might the use of technology in the classroom impact learning? (credit: modification of work by
Nikolay Georgiev/Pixabay)

These sorts of personal observations are what often lead us to formulate a specific hypothesis, but we cannot
use limited personal observations and anecdotal evidence to rigorously test our hypothesis. Instead, to find out
if real-world data supports our hypothesis, we have to conduct an experiment.

Designing an Experiment

The most basic experimental design involves two groups: the experimental group and the control group. The
two groups are designed to be the same except for one difference— experimental manipulation. The
experimental group gets the experimental manipulation—that is, the treatment or variable being tested (in
this case, the use of technology)—and the control group does not. Since experimental manipulation is the only
difference between the experimental and control groups, we can be sure that any differences between the two
are due to experimental manipulation rather than chance.

In our example of how the use of technology should be limited in the classroom, we have the experimental
group learn algebra using a computer program and then test their learning. We measure the learning in our
control group after they are taught algebra by a teacher in a traditional classroom. It is important for the
control group to be treated similarly to the experimental group, with the exception that the control group does
not receive the experimental manipulation.

We also need to precisely define, or operationalize, how we measure learning of algebra. An operational
definition is a precise description of our variables, and it is important in allowing others to understand exactly
how and what a researcher measures in a particular experiment. In operationalizing learning, we might
choose to look at performance on a test covering the material on which the individuals were taught by the
teacher or the computer program. We might also ask our participants to summarize the information that was
just presented in some way. Whatever we determine, it is important that we operationalize learning in such a
way that anyone who hears about our study for the first time knows exactly what we mean by learning. This
aids peoples’ ability to interpret our data as well as their capacity to repeat our experiment should they choose
to do so.

Once we have operationalized what is considered use of technology and what is considered learning in our
experiment participants, we need to establish how we will run our experiment. In this case, we might have
participants spend 45 minutes learning algebra (either through a computer program or with an in-person
math teacher) and then give them a test on the material covered during the 45 minutes.

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Ideally, the people who score the tests are unaware of who was assigned to the experimental or control group,
in order to control for experimenter bias. Experimenter bias refers to the possibility that a researcher’s
expectations might skew the results of the study. Remember, conducting an experiment requires a lot of
planning, and the people involved in the research project have a vested interest in supporting their
hypotheses. If the observers knew which child was in which group, it might influence how they interpret
ambiguous responses, such as sloppy handwriting or minor computational mistakes. By being blind to which
child is in which group, we protect against those biases. This situation is a single-blind study, meaning that
one of the groups (participants) are unaware as to which group they are in (experiment or control group) while
the researcher who developed the experiment knows which participants are in each group.

In a double-blind study, both the researchers and the participants are blind to group assignments. Why would
a researcher want to run a study where no one knows who is in which group? Because by doing so, we can
control for both experimenter and participant expectations. If you are familiar with the phrase placebo effect,
you already have some idea as to why this is an important consideration. The placebo effect occurs when
people’s expectations or beliefs influence or determine their experience in a given situation. In other words,
simply expecting something to happen can actually make it happen.

The placebo effect is commonly described in terms of testing the effectiveness of a new medication. Imagine
that you work in a pharmaceutical company, and you think you have a new drug that is effective in treating
depression. To demonstrate that your medication is effective, you run an experiment with two groups: The
experimental group receives the medication, and the control group does not. But you don’t want participants
to know whether they received the drug or not.

Why is that? Imagine that you are a participant in this study, and you have just taken a pill that you think will
improve your mood. Because you expect the pill to have an effect, you might feel better simply because you
took the pill and not because of any drug actually contained in the pill—this is the placebo effect.

To make sure that any effects on mood are due to the drug and not due to expectations, the control group
receives a placebo (in this case a sugar pill). Now everyone gets a pill, and once again neither the researcher
nor the experimental participants know who got the drug and who got the sugar pill. Any differences in mood
between the experimental and control groups can now be attributed to the drug itself rather than to
experimenter bias or participant expectations (Figure 2.16).

FIGURE 2.16 Providing the control group with a placebo treatment protects against bias caused by expectancy.
(credit: Elaine and Arthur Shapiro)

Independent and Dependent Variables

In a research experiment, we strive to study whether changes in one thing cause changes in another. To
achieve this, we must pay attention to two important variables, or things that can be changed, in any

2.3 • Analyzing Findings 53

experimental study: the independent variable and the dependent variable. An independent variable is
manipulated or controlled by the experimenter. In a well-designed experimental study, the independent
variable is the only important difference between the experimental and control groups. In our example of how
technology use in the classroom affects learning, the independent variable is the type of learning by
participants in the study (Figure 2.17). A dependent variable is what the researcher measures to see how
much effect the independent variable had. In our example, the dependent variable is the learning exhibited by
our participants.

FIGURE 2.17 In an experiment, manipulations of the independent variable are expected to result in changes in the
dependent variable. (credit: “classroom” modification of work by Nikolay Georgiev/Pixabay; credit “note taking”:
modification of work by KF/Wikimedia)

We expect that the dependent variable will change as a function of the independent variable. In other words,
the dependent variable depends on the independent variable. A good way to think about the relationship
between the independent and dependent variables is with this question: What effect does the independent
variable have on the dependent variable? Returning to our example, what is the effect of being taught a lesson
through a computer program versus through an in-person instructor?

Selecting and Assigning Experimental Participants

Now that our study is designed, we need to obtain a sample of individuals to include in our experiment. Our
study involves human participants so we need to determine who to include. Participants are the subjects of
psychological research, and as the name implies, individuals who are involved in psychological research
actively participate in the process. Often, psychological research projects rely on college students to serve as
participants. In fact, the vast majority of research in psychology subfields has historically involved students as
research participants (Sears, 1986; Arnett, 2008). But are college students truly representative of the general
population? College students tend to be younger, more educated, more liberal, and less diverse than the
general population. Although using students as test subjects is an accepted practice, relying on such a limited
pool of research participants can be problematic because it is difficult to generalize findings to the larger
population.

Our hypothetical experiment involves high school students, and we must first generate a sample of students.
Samples are used because populations are usually too large to reasonably involve every member in our
particular experiment (Figure 2.18). If possible, we should use a random sample (there are other types of

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samples, but for the purposes of this chapter, we will focus on random samples). A random sample is a subset
of a larger population in which every member of the population has an equal chance of being selected.
Random samples are preferred because if the sample is large enough we can be reasonably sure that the
participating individuals are representative of the larger population. This means that the percentages of
characteristics in the sample—sex, ethnicity, socioeconomic level, and any other characteristics that might
affect the results—are close to those percentages in the larger population.

In our example, let’s say we decide our population of interest is algebra students. But all algebra students is a
very large population, so we need to be more specific; instead we might say our population of interest is all
algebra students in a particular city. We should include students from various income brackets, family
situations, races, ethnicities, religions, and geographic areas of town. With this more manageable population,
we can work with the local schools in selecting a random sample of around 200 algebra students who we want
to participate in our experiment.

In summary, because we cannot test all of the algebra students in a city, we want to find a group of about 200
that reflects the composition of that city. With a representative group, we can generalize our findings to the
larger population without fear of our sample being biased in some way.

FIGURE 2.18 Researchers may work with (a) a large population or (b) a sample group that is a subset of the larger
population. (credit “crowd”: modification of work by James Cridland; credit “students”: modification of work by
Laurie Sullivan)

Now that we have a sample, the next step of the experimental process is to split the participants into
experimental and control groups through random assignment. With random assignment, all participants
have an equal chance of being assigned to either group. There is statistical software that will randomly assign
each of the algebra students in the sample to either the experimental or the control group.

Random assignment is critical for sound experimental design. With sufficiently large samples, random
assignment makes it unlikely that there are systematic differences between the groups. So, for instance, it
would be very unlikely that we would get one group composed entirely of males, a given ethnic identity, or a
given religious ideology. This is important because if the groups were systematically different before the
experiment began, we would not know the origin of any differences we find between the groups: Were the
differences preexisting, or were they caused by manipulation of the independent variable? Random
assignment allows us to assume that any differences observed between experimental and control groups
result from the manipulation of the independent variable.

LINK TO LEARNING

Use this online random number generator (http://openstax.org/l/rannumbers) to learn more about random
sampling and assignments.

Issues to Consider

While experiments allow scientists to make cause-and-effect claims, they are not without problems. True

2.3 • Analyzing Findings 55

experiments require the experimenter to manipulate an independent variable, and that can complicate many
questions that psychologists might want to address. For instance, imagine that you want to know what effect
sex (the independent variable) has on spatial memory (the dependent variable). Although you can certainly
look for differences between males and females on a task that taps into spatial memory, you cannot directly
control a person’s sex. We categorize this type of research approach as quasi-experimental and recognize that
we cannot make cause-and-effect claims in these circumstances.

Experimenters are also limited by ethical constraints. For instance, you would not be able to conduct an
experiment designed to determine if experiencing abuse as a child leads to lower levels of self-esteem among
adults. To conduct such an experiment, you would need to randomly assign some experimental participants to
a group that receives abuse, and that experiment would be unethical.

Interpreting Experimental Findings

Once data is collected from both the experimental and the control groups, a statistical analysis is conducted to
find out if there are meaningful differences between the two groups. A statistical analysis determines how
likely any difference found is due to chance (and thus not meaningful). For example, if an experiment is done
on the effectiveness of a nutritional supplement, and those taking a placebo pill (and not the supplement) have
the same result as those taking the supplement, then the experiment has shown that the nutritional
supplement is not effective. Generally, psychologists consider differences to be statistically significant if there
is less than a five percent chance of observing them if the groups did not actually differ from one another.
Stated another way, psychologists want to limit the chances of making “false positive” claims to five percent or
less.

The greatest strength of experiments is the ability to assert that any significant differences in the findings are
caused by the independent variable. This occurs because random selection, random assignment, and a design
that limits the effects of both experimenter bias and participant expectancy should create groups that are
similar in composition and treatment. Therefore, any difference between the groups is attributable to the
independent variable, and now we can finally make a causal statement. If we find that watching a violent
television program results in more violent behavior than watching a nonviolent program, we can safely say
that watching violent television programs causes an increase in the display of violent behavior.

Reporting Research

When psychologists complete a research project, they generally want to share their findings with other
scientists. The American Psychological Association (APA) publishes a manual detailing how to write a paper for
submission to scientific journals. Unlike an article that might be published in a magazine like Psychology
Today, which targets a general audience with an interest in psychology, scientific journals generally publish
peer-reviewed journal articles aimed at an audience of professionals and scholars who are actively involved
in research themselves.

LINK TO LEARNING

The Online Writing Lab (OWL) (http://openstax.org/l/owl) at Purdue University can walk you through the APA
writing guidelines.

A peer-reviewed journal article is read by several other scientists (generally anonymously) with expertise in
the subject matter. These peer reviewers provide feedback—to both the author and the journal
editor—regarding the quality of the draft. Peer reviewers look for a strong rationale for the research being
described, a clear description of how the research was conducted, and evidence that the research was
conducted in an ethical manner. They also look for flaws in the study’s design, methods, and statistical
analyses. They check that the conclusions drawn by the authors seem reasonable given the observations made
during the research. Peer reviewers also comment on how valuable the research is in advancing the

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discipline’s knowledge. This helps prevent unnecessary duplication of research findings in the scientific
literature and, to some extent, ensures that each research article provides new information. Ultimately, the
journal editor will compile all of the peer reviewer feedback and determine whether the article will be
published in its current state (a rare occurrence), published with revisions, or not accepted for publication.

Peer review provides some degree of quality control for psychological research. Poorly conceived or executed
studies can be weeded out, and even well-designed research can be improved by the revisions suggested. Peer
review also ensures that the research is described clearly enough to allow other scientists to replicate it,
meaning they can repeat the experiment using different samples to determine reliability. Sometimes
replications involve additional measures that expand on the original finding. In any case, each replication
serves to provide more evidence to support the original research findings. Successful replications of published
research make scientists more apt to adopt those findings, while repeated failures tend to cast doubt on the
legitimacy of the original article and lead scientists to look elsewhere. For example, it would be a major
advancement in the medical field if a published study indicated that taking a new drug helped individuals
achieve a healthy weight without changing their diet. But if other scientists could not replicate the results, the
original study’s claims would be questioned.

In recent years, there has been increasing concern about a “replication crisis” that has affected a number of
scientific fields, including psychology. Some of the most well-known studies and scientists have produced
research that has failed to be replicated by others (as discussed in Shrout & Rodgers, 2018). In fact, even a
famous Nobel Prize-winning scientist has recently retracted a published paper because she had difficulty
replicating her results (Nobel Prize-winning scientist Frances Arnold retracts paper, 2020 January 3). These
kinds of outcomes have prompted some scientists to begin to work together and more openly, and some would
argue that the current “crisis” is actually improving the ways in which science is conducted and in how its
results are shared with others (Aschwanden, 2018).

The Vaccine-Autism Myth and Retraction of Published Studies
Some scientists have claimed that routine childhood vaccines cause some children to develop autism, and, in
fact, several peer-reviewed publications published research making these claims. Since the initial reports, large-
scale epidemiological research has indicated that vaccinations are not responsible for causing autism and that it
is much safer to have your child vaccinated than not. Furthermore, several of the original studies making this
claim have since been retracted.

A published piece of work can be rescinded when data is called into question because of falsification, fabrication,
or serious research design problems. Once rescinded, the scientific community is informed that there are serious
problems with the original publication. Retractions can be initiated by the researcher who led the study, by
research collaborators, by the institution that employed the researcher, or by the editorial board of the journal in
which the article was originally published. In the vaccine-autism case, the retraction was made because of a
significant conflict of interest in which the leading researcher had a financial interest in establishing a link
between childhood vaccines and autism (Offit, 2008). Unfortunately, the initial studies received so much media
attention that many parents around the world became hesitant to have their children vaccinated (Figure 2.19).
Continued reliance on such debunked studies has significant consequences. For instance, between January and
October of 2019, there were 22 measles outbreaks across the United States and more than a thousand cases of
individuals contracting measles (Patel et al., 2019). This is likely due to the anti-vaccination movements that
have risen from the debunked research. For more information about how the vaccine/autism story unfolded, as
well as the repercussions of this story, take a look at Paul Offit’s book, Autism’s False Prophets: Bad Science,
Risky Medicine, and the Search for a Cure.

DIG DEEPER

2.3 • Analyzing Findings 57

FIGURE 2.19 Some people still think vaccinations cause autism. (credit: modification of work by UNICEF
Sverige)

Reliability and Validity

Reliability and validity are two important considerations that must be made with any type of data collection.
Reliability refers to the ability to consistently produce a given result. In the context of psychological research,
this would mean that any instruments or tools used to collect data do so in consistent, reproducible ways.
There are a number of different types of reliability. Some of these include inter-rater reliability (the degree to
which two or more different observers agree on what has been observed), internal consistency (the degree to
which different items on a survey that measure the same thing correlate with one another), and test-retest
reliability (the degree to which the outcomes of a particular measure remain consistent over multiple
administrations).

Unfortunately, being consistent in measurement does not necessarily mean that you have measured
something correctly. To illustrate this concept, consider a kitchen scale that would be used to measure the
weight of cereal that you eat in the morning. If the scale is not properly calibrated, it may consistently under-
or overestimate the amount of cereal that’s being measured. While the scale is highly reliable in producing
consistent results (e.g., the same amount of cereal poured onto the scale produces the same reading each
time), those results are incorrect. This is where validity comes into play. Validity refers to the extent to which a
given instrument or tool accurately measures what it’s supposed to measure, and once again, there are a
number of ways in which validity can be expressed. Ecological validity (the degree to which research results
generalize to real-world applications), construct validity (the degree to which a given variable actually captures
or measures what it is intended to measure), and face validity (the degree to which a given variable seems valid
on the surface) are just a few types that researchers consider. While any valid measure is by necessity reliable,
the reverse is not necessarily true. Researchers strive to use instruments that are both highly reliable and
valid.

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How Valid Are the SAT and ACT?
Standardized tests like the SAT and ACT are supposed to measure an individual’s aptitude for a college
education, but how reliable and valid are such tests? Research conducted by the College Board suggests that
scores on the SAT have high predictive validity for first-year college students’ GPA (Kobrin, Patterson, Shaw,
Mattern, & Barbuti, 2008). In this context, predictive validity refers to the test’s ability to effectively predict the
GPA of college freshmen. Given that many institutions of higher education require the SAT or ACT for admission,
this high degree of predictive validity might be comforting.

However, the emphasis placed on SAT or ACT scores in college admissions is changing based on a number of
factors. For one, some researchers assert that these tests are biased, and students from historically marginalized
populations are at a disadvantage that unfairly reduces the likelihood of being admitted into a college (Santelices
& Wilson, 2010). Additionally, some research has suggested that the predictive validity of these tests is grossly
exaggerated in how well they are able to predict the GPA of first-year college students. In fact, it has been
suggested that the SAT’s predictive validity may be overestimated by as much as 150% (Rothstein, 2004). Many
institutions of higher education are beginning to consider de-emphasizing the significance of SAT scores in
making admission decisions (Rimer, 2008).

Recent examples of high profile cheating scandals both domestically and abroad have only increased the scrutiny
being placed on these types of tests, and as of March 2019, more than 1000 institutions of higher education have
either relaxed or eliminated the requirements for SAT or ACT testing for admissions (Strauss, 2019, March 19).

2.4 Ethics
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Discuss how research involving human subjects is regulated
• Summarize the processes of informed consent and debriefing
• Explain how research involving animal subjects is regulated

Today, scientists agree that good research is ethical in nature and is guided by a basic respect for human
dignity and safety. However, as you will read in the feature box, this has not always been the case. Modern
researchers must demonstrate that the research they perform is ethically sound. This section presents how
ethical considerations affect the design and implementation of research conducted today.

Research Involving Human Participants

Any experiment involving the participation of human subjects is governed by extensive, strict guidelines
designed to ensure that the experiment does not result in harm. Any research institution that receives federal
support for research involving human participants must have access to an institutional review board (IRB).
The IRB is a committee of individuals often made up of members of the institution’s administration, scientists,
and community members (Figure 2.20). The purpose of the IRB is to review proposals for research that
involves human participants. The IRB reviews these proposals with the principles mentioned above in mind,
and generally, approval from the IRB is required in order for the experiment to proceed.

EVERYDAY CONNECTION

2.4 • Ethics 59

FIGURE 2.20 An institution’s IRB meets regularly to review experimental proposals that involve human
participants. (credit: International Hydropower Association/Flickr)

An institution’s IRB requires several components in any experiment it approves. For one, each participant
must sign an informed consent form before they can participate in the experiment. An informed consent form
provides a written description of what participants can expect during the experiment, including potential risks
and implications of the research. It also lets participants know that their involvement is completely voluntary
and can be discontinued without penalty at any time. Furthermore, the informed consent guarantees that any
data collected in the experiment will remain completely confidential. In cases where research participants are
under the age of 18, the parents or legal guardians are required to sign the informed consent form.

LINK TO LEARNING

View this example of a consent form (http://openstax.org/l/consentform) to learn more.

While the informed consent form should be as honest as possible in describing exactly what participants will
be doing, sometimes deception is necessary to prevent participants’ knowledge of the exact research question
from affecting the results of the study. Deception involves purposely misleading experiment participants in
order to maintain the integrity of the experiment, but not to the point where the deception could be considered
harmful. For example, if we are interested in how our opinion of someone is affected by their attire, we might
use deception in describing the experiment to prevent that knowledge from affecting participants’ responses.
In cases where deception is involved, participants must receive a full debriefing upon conclusion of the
study—complete, honest information about the purpose of the experiment, how the data collected will be used,
the reasons why deception was necessary, and information about how to obtain additional information about
the study.

Ethics and the Tuskegee Syphilis Study
Unfortunately, the ethical guidelines that exist for research today were not always applied in the past. In 1932,
rural, Black men from Tuskegee, Alabama, were recruited to participate in an experiment conducted by the U.S.
Public Health Service, with the aim of studying syphilis in Black men (Figure 2.21). In exchange for free medical
care, meals, and burial insurance, 600 men agreed to participate in the study. A little more than half of the men
tested positive for syphilis, and they served as the experimental group (given that the researchers could not
randomly assign participants to groups, this represents a quasi-experiment). The remaining syphilis-free

DIG DEEPER

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individuals served as the control group. However, those individuals that tested positive for syphilis were never
informed that they had the disease.

While there was no treatment for syphilis when the study began, by 1947 penicillin was recognized as an
effective treatment for the disease. Despite this, no penicillin was administered to the participants in this study,
and the participants were not allowed to seek treatment at any other facilities if they continued in the study. Over
the course of 40 years, many of the participants unknowingly spread syphilis to their wives (and subsequently
their children born from their wives) and eventually died because they never received treatment for the disease.
This study was discontinued in 1972 when the experiment was discovered by the national press (Tuskegee
University, n.d.). The resulting outrage over the experiment led directly to the National Research Act of 1974 and
the strict ethical guidelines for research on humans described in this chapter. Why is this study unethical? How
were the men who participated and their families harmed as a function of this research?

FIGURE 2.21 A participant in the Tuskegee Syphilis Study receives an injection.

LINK TO LEARNING

Visit this website about the Tuskegee Syphilis Study (http://openstax.org/l/tuskegee) to learn more.

Research Involving Animal Subjects

Many psychologists conduct research involving animal subjects. Often, these researchers use rodents (Figure
2.22) or birds as the subjects of their experiments—the APA estimates that 90% of all animal research in
psychology uses these species (American Psychological Association, n.d.). Because many basic processes in
animals are sufficiently similar to those in humans, these animals are acceptable substitutes for research that
would be considered unethical in human participants.

FIGURE 2.22 Rats, like the one shown here, often serve as the subjects of animal research.

This does not mean that animal researchers are immune to ethical concerns. Indeed, the humane and ethical

2.4 • Ethics 61

treatment of animal research subjects is a critical aspect of this type of research. Researchers must design
their experiments to minimize any pain or distress experienced by animals serving as research subjects.

Whereas IRBs review research proposals that involve human participants, animal experimental proposals are
reviewed by an Institutional Animal Care and Use Committee (IACUC). An IACUC consists of institutional
administrators, scientists, veterinarians, and community members. This committee is charged with ensuring
that all experimental proposals require the humane treatment of animal research subjects. It also conducts
semi-annual inspections of all animal facilities to ensure that the research protocols are being followed. No
animal research project can proceed without the committee’s approval.

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Key Terms
archival research method of research using past records or data sets to answer various research questions, or

to search for interesting patterns or relationships
attrition reduction in number of research participants as some drop out of the study over time
cause-and-effect relationship changes in one variable cause the changes in the other variable; can be

determined only through an experimental research design
clinical or case study observational research study focusing on one or a few people
confirmation bias tendency to ignore evidence that disproves ideas or beliefs
confounding variable unanticipated outside factor that affects both variables of interest, often giving the false

impression that changes in one variable causes changes in the other variable, when, in actuality, the
outside factor causes changes in both variables

control group serves as a basis for comparison and controls for chance factors that might influence the
results of the study—by holding such factors constant across groups so that the experimental
manipulation is the only difference between groups

correlation relationship between two or more variables; when two variables are correlated, one variable
changes as the other does

correlation coefficient number from -1 to +1, indicating the strength and direction of the relationship
between variables, and usually represented by r

cross-sectional research compares multiple segments of a population at a single time
debriefing when an experiment involved deception, participants are told complete and truthful information

about the experiment at its conclusion
deception purposely misleading experiment participants in order to maintain the integrity of the experiment
deductive reasoning results are predicted based on a general premise
dependent variable variable that the researcher measures to see how much effect the independent variable

had
double-blind study experiment in which both the researchers and the participants are blind to group

assignments
empirical grounded in objective, tangible evidence that can be observed time and time again, regardless of

who is observing
experimental group group designed to answer the research question; experimental manipulation is the only

difference between the experimental and control groups, so any differences between the two are due to
experimental manipulation rather than chance

experimenter bias researcher expectations skew the results of the study
fact objective and verifiable observation, established using evidence collected through empirical research
falsifiable able to be disproven by experimental results
generalize inferring that the results for a sample apply to the larger population
hypothesis (plural: hypotheses) tentative and testable statement about the relationship between two or more

variables
illusory correlation seeing relationships between two things when in reality no such relationship exists
independent variable variable that is influenced or controlled by the experimenter; in a sound experimental

study, the independent variable is the only important difference between the experimental and control
group

inductive reasoning conclusions are drawn from observations
informed consent process of informing a research participant about what to expect during an experiment,

any risks involved, and the implications of the research, and then obtaining the person’s consent to
participate

Institutional Animal Care and Use Committee (IACUC) committee of administrators, scientists,
veterinarians, and community members that reviews proposals for research involving non-human
animals

2 • Key Terms 63

Institutional Review Board (IRB) committee of administrators, scientists, and community members that
reviews proposals for research involving human participants

inter-rater reliability measure of agreement among observers on how they record and classify a particular
event

longitudinal research studies in which the same group of individuals is surveyed or measured repeatedly
over an extended period of time

naturalistic observation observation of behavior in its natural setting
negative correlation two variables change in different directions, with one becoming larger as the other

becomes smaller; a negative correlation is not the same thing as no correlation
observer bias when observations may be skewed to align with observer expectations
operational definition description of what actions and operations will be used to measure the dependent

variables and manipulate the independent variables
opinion personal judgments, conclusions, or attitudes that may or may not be accurate
participants subjects of psychological research
peer-reviewed journal article article read by several other scientists (usually anonymously) with expertise in

the subject matter, who provide feedback regarding the quality of the manuscript before it is accepted for
publication

placebo effect people’s expectations or beliefs influencing or determining their experience in a given
situation

population overall group of individuals that the researchers are interested in
positive correlation two variables change in the same direction, both becoming either larger or smaller
random assignment method of experimental group assignment in which all participants have an equal

chance of being assigned to either group
random sample subset of a larger population in which every member of the population has an equal chance of

being selected
reliability consistency and reproducibility of a given result
replicate repeating an experiment using different samples to determine the research’s reliability
sample subset of individuals selected from the larger population
single-blind study experiment in which the researcher knows which participants are in the experimental

group and which are in the control group
statistical analysis determines how likely any difference between experimental groups is due to chance
survey list of questions to be answered by research participants—given as paper-and-pencil questionnaires,

administered electronically, or conducted verbally—allowing researchers to collect data from a large
number of people

theory well-developed set of ideas that propose an explanation for observed phenomena
validity accuracy of a given result in measuring what it is designed to measure

Summary
2.1 Why Is Research Important?

Scientists are engaged in explaining and understanding how the world around them works, and they are able
to do so by coming up with theories that generate hypotheses that are testable and falsifiable. Theories that
stand up to their tests are retained and refined, while those that do not are discarded or modified. In this way,
research enables scientists to separate fact from simple opinion. Having good information generated from
research aids in making wise decisions both in public policy and in our personal lives.

2.2 Approaches to Research

The clinical or case study involves studying just a few individuals for an extended period of time. While this
approach provides an incredible depth of information, the ability to generalize these observations to the larger
population is problematic. Naturalistic observation involves observing behavior in a natural setting and allows

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for the collection of valid, true-to-life information from realistic situations. However, naturalistic observation
does not allow for much control and often requires quite a bit of time and money to perform. Researchers
strive to ensure that their tools for collecting data are both reliable (consistent and replicable) and valid
(accurate).

Surveys can be administered in a number of ways and make it possible to collect large amounts of data quickly.
However, the depth of information that can be collected through surveys is somewhat limited compared to a
clinical or case study.

Archival research involves studying existing data sets to answer research questions.

Longitudinal research has been incredibly helpful to researchers who need to collect data on how people
change over time. Cross-sectional research compares multiple segments of a population at a single time.

2.3 Analyzing Findings

A correlation is described with a correlation coefficient, r, which ranges from -1 to 1. The correlation
coefficient tells us about the nature (positive or negative) and the strength of the relationship between two or
more variables. Correlations do not tell us anything about causation—regardless of how strong the relationship
is between variables. In fact, the only way to demonstrate causation is by conducting an experiment. People
often make the mistake of claiming that correlations exist when they really do not.

Researchers can test cause-and-effect hypotheses by conducting experiments. Ideally, experimental
participants are randomly selected from the population of interest. Then, the participants are randomly
assigned to their respective groups. Sometimes, the researcher and the participants are blind to group
membership to prevent their expectations from influencing the results.

In ideal experimental design, the only difference between the experimental and control groups is whether
participants are exposed to the experimental manipulation. Each group goes through all phases of the
experiment, but each group will experience a different level of the independent variable: the experimental
group is exposed to the experimental manipulation, and the control group is not exposed to the experimental
manipulation. The researcher then measures the changes that are produced in the dependent variable in each
group. Once data is collected from both groups, it is analyzed statistically to determine if there are meaningful
differences between the groups.

Psychologists report their research findings in peer-reviewed journal articles. Research published in this
format is checked by several other psychologists who serve as a filter separating ideas that are supported by
evidence from ideas that are not. Replication has an important role in ensuring the legitimacy of published
research. In the long run, only those findings that are capable of being replicated consistently will achieve
consensus in the scientific community.

2.4 Ethics

Ethics in research is an evolving field, and some practices that were accepted or tolerated in the past would be
considered unethical today. Researchers are expected to adhere to basic ethical guidelines when conducting
experiments that involve human participants. Any experiment involving human participants must be
approved by an IRB. Participation in experiments is voluntary and requires informed consent of the
participants. If any deception is involved in the experiment, each participant must be fully debriefed upon the
conclusion of the study.

Animal research is also held to a high ethical standard. Researchers who use animals as experimental subjects
must design their projects so that pain and distress are minimized. Animal research requires the approval of
an IACUC, and all animal facilities are subject to regular inspections to ensure that animals are being treated
humanely.

2 • Summary 65

Review Questions
1. Scientific hypotheses are ________ and falsifiable.

a. observable
b. original
c. provable
d. testable

2. ________ are defined as observable realities.
a. behaviors
b. facts
c. opinions
d. theories

3. Scientific knowledge is ________.
a. intuitive
b. empirical
c. permanent
d. subjective

4. A major criticism of Freud’s early theories involves the fact that his theories ________.
a. were too limited in scope
b. were too outrageous
c. were too broad
d. were not testable

5. Sigmund Freud developed his theory of human personality by conducting in-depth interviews over an
extended period of time with a few clients. This type of research approach is known as a(n): ________.
a. archival research
b. case study
c. naturalistic observation
d. survey

6. ________ involves observing behavior in individuals in their natural environments.
a. archival research
b. case study
c. naturalistic observation
d. survey

7. The major limitation of case studies is ________.
a. the superficial nature of the information collected in this approach
b. the lack of control that the researcher has in this approach
c. the inability to generalize the findings from this approach to the larger population
d. the absence of inter-rater reliability

8. The benefit of naturalistic observation studies is ________.
a. the honesty of the data that is collected in a realistic setting
b. how quick and easy these studies are to perform
c. the researcher’s capacity to make sure that data is collected as efficiently as possible
d. the ability to determine cause and effect in this particular approach

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9. Using existing records to try to answer a research question is known as ________.
a. naturalistic observation
b. survey research
c. longitudinal research
d. archival research

10. ________ involves following a group of research participants for an extended period of time.
a. archival research
b. longitudinal research
c. naturalistic observation
d. cross-sectional research

11. A(n) ________ is a list of questions developed by a researcher that can be administered in paper form.
a. archive
b. case Study
c. naturalistic observation
d. survey

12. Longitudinal research is complicated by high rates of ________.
a. deception
b. observation
c. attrition
d. generalization

13. Height and weight are positively correlated. This means that:
a. There is no relationship between height and weight.
b. Usually, the taller someone is, the thinner they are.
c. Usually, the shorter someone is, the heavier they are.
d. As height increases, typically weight increases.

14. Which of the following correlation coefficients indicates the strongest relationship between two variables?
a. –.90
b. –.50
c. +.80
d. +.25

15. Which statement best illustrates a negative correlation between the number of hours spent watching TV
the week before an exam and the grade on that exam?
a. Watching too much television leads to poor exam performance.
b. Smart students watch less television.
c. Viewing television interferes with a student’s ability to prepare for the upcoming exam.
d. Students who watch more television perform more poorly on their exams.

16. The correlation coefficient indicates the weakest relationship when ________.
a. it is closest to 0
b. it is closest to -1
c. it is positive
d. it is negative

2 • Review Questions 67

17. ________ means that everyone in the population has the same likelihood of being asked to participate in
the study.
a. operationalizing
b. placebo effect
c. random assignment
d. random sampling

18. The ________ is controlled by the experimenter, while the ________ represents the information collected
and statistically analyzed by the experimenter.
a. dependent variable; independent variable
b. independent variable; dependent variable
c. placebo effect; experimenter bias
d. experiment bias; placebo effect

19. Researchers must ________ important concepts in their studies so others would have a clear
understanding of exactly how those concepts were defined.
a. randomly assign
b. randomly select
c. operationalize
d. generalize

20. Sometimes, researchers will administer a(n) ________ to participants in the control group to control for
the effects that participant expectation might have on the experiment.
a. dependent variable
b. independent variable
c. statistical analysis
d. placebo

21. ________ is to animal research as ________ is to human research.
a. informed consent; deception
b. IACUC; IRB
c. IRB; IACUC
d. deception; debriefing

22. Researchers might use ________ when providing participants with the full details of the experiment could
skew their responses.
a. informed consent
b. deception
c. ethics
d. debriefing

23. A person’s participation in a research project must be ________.
a. random
b. rewarded
c. voluntary
d. public

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24. Before participating in an experiment, individuals should read and sign the ________ form.
a. informed consent
b. debriefing
c. IRB
d. ethics

Critical Thinking Questions
25. In this section, there was a discussion about researchers arriving at different conclusions about the use of

technology in certain student populations, with one study determining that a smartphone app for surgery
students seemed effective, but another study finding negative impacts on sleep, communication, and time
management resulting from the use of technology by undergraduates. How might an educational leader
best work through these discrepancies?

26. The scientific method is often described as self-correcting and cyclical. Briefly describe your
understanding of the scientific method with regard to these concepts.

27. In this section, conjoined twins, Krista and Tatiana, were described as being potential participants in a
case study. In what other circumstances would you think that this particular research approach would be
especially helpful and why?

28. Presumably, reality television programs aim to provide a realistic portrayal of the behavior displayed by
the characters featured in such programs. This section pointed out why this is not really the case. What
changes could be made in the way that these programs are produced that would result in more honest
portrayals of realistic behavior?

29. Which of the research methods discussed in this section would be best suited to study the impact of diet
and exercise on the prevalence of a disease such as diabetes? Why?

30. Aside from biomedical research, what other areas of research could greatly benefit by both longitudinal
and archival research?

31. Earlier in this section, we read about research suggesting that there is a correlation between eating cereal
and weight. Cereal companies that present this information in their advertisements could lead someone
to believe that eating more cereal causes healthy weight. Why would they make such a claim and what
arguments could you make to counter this cause-and-effect claim?

32. Recently a study was published in the journal, Nutrition and Cancer, which established a negative
correlation between coffee consumption and breast cancer. Specifically, it was found that women
consuming more than 5 cups of coffee a day were less likely to develop breast cancer than women who
never consumed coffee (Lowcock, Cotterchio, Anderson, Boucher, & El-Sohemy, 2013). Imagine you see a
newspaper story about this research that says, “Coffee Protects Against Cancer.” Why is this headline
misleading and why would a more accurate headline draw less interest?

33. Sometimes, true random sampling can be very difficult to obtain. Many researchers make use of
convenience samples as an alternative. For example, one popular convenience sample would involve
students enrolled in Introduction to Psychology courses. What are the implications of using this sampling
technique?

34. Peer review is an important part of publishing research findings in many scientific disciplines. This
process is normally conducted anonymously; in other words, the author of the article being reviewed does
not know who is reviewing the article, and the reviewers are unaware of the author’s identity. Why would
this be an important part of this process?

2 • Critical Thinking Questions 69

35. Some argue that animal research is inherently flawed in terms of being ethical because unlike human
participants, animals do not consent to be involved in research. Do you agree with this perspective? Given
that animals do not consent to be involved in research projects, what sorts of extra precautions should be
taken to ensure that they receive the most humane treatment possible?

36. At the end of the last section, you were asked to design a basic experiment to answer some question of
interest. What ethical considerations should be made with the study you proposed to ensure that your
experiment would conform to the scientific community’s expectations of ethical research?

Personal Application Questions
37. Healthcare professionals cite an enormous number of health problems related to obesity, and many

people have an understandable desire to attain a healthy weight. There are many diet programs, services,
and products on the market to aid those who wish to lose weight. If a close friend was considering
purchasing or participating in one of these products, programs, or services, how would you make sure
your friend was fully aware of the potential consequences of this decision? What sort of information would
you want to review before making such an investment or lifestyle change yourself?

38. A friend of yours is working part-time in a local pet store. Your friend has become increasingly interested
in how dogs normally communicate and interact with each other, and is thinking of visiting a local
veterinary clinic to see how dogs interact in the waiting room. After reading this section, do you think this
is the best way to better understand such interactions? Do you have any suggestions that might result in
more valid data?

39. As a college student, you are no doubt concerned about the grades that you earn while completing your
coursework. If you wanted to know how overall GPA is related to success in life after college, how would
you choose to approach this question and what kind of resources would you need to conduct this
research?

40. We all have a tendency to make illusory correlations from time to time. Try to think of an illusory
correlation that is held by you, a family member, or a close friend. How do you think this illusory
correlation came about and what can be done in the future to combat them?

41. Are there any questions about human or animal behavior that you would really like to answer? Generate a
hypothesis and briefly describe how you would conduct an experiment to answer your question.

42. Take a few minutes to think about all of the advancements that our society has achieved as a function of
research involving animal subjects. How have you, a friend, or a family member benefited directly from
this kind of research?

70 2 • Personal Application Questions

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FIGURE 3.1 Different brain imaging techniques provide scientists with insight into different aspects of how the
human brain functions. Left to right, PET scan (positron emission tomography), CT scan (computerized tomography),
and fMRI (functional magnetic resonance imaging) are three types of scans. (credit “left”: modification of work by
Health and Human Services Department, National Institutes of Health; credit “center”: modification of work by
“Aceofhearts1968″/Wikimedia Commons; credit “right”: modification of work by Kim J, Matthews NL, Park S.)

INTRODUCTION

CHAPTER OUTLINE
3.1 Human Genetics
3.2 Cells of the Nervous System
3.3 Parts of the Nervous System
3.4 The Brain and Spinal Cord
3.5 The Endocrine System

Have you ever taken a device apart to find out how it works? Many of us have done so,
whether to attempt a repair or simply to satisfy our curiosity. A device’s internal workings are often distinct
from its user interface on the outside. For example, we don’t think about microchips and circuits when we turn
up the volume on a mobile phone; instead, we think about getting the volume just right. Similarly, the inner
workings of the human body are often distinct from the external expression of those workings. It is the job of
psychologists to find the connection between these—for example, to figure out how the firings of millions of
neurons become a thought.

This chapter strives to explain the biological mechanisms that underlie behavior. These physiological and
anatomical foundations are the basis for many areas of psychology. In this chapter, you will learn how genetics
influence both physiological and psychological traits. You will become familiar with the structure and function
of the nervous system. And, finally, you will learn how the nervous system interacts with the endocrine system.

3Biopsychology

3.1 Human Genetics
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain the basic principles of the theory of evolution by natural selection
• Describe the differences between genotype and phenotype
• Discuss how gene-environment interactions are critical for expression of physical and psychological

characteristics

Psychological researchers study genetics in order to better understand the biological factors that contribute to
certain behaviors. While all humans share certain biological mechanisms, we are each unique. And while our
bodies have many of the same parts—brains and hormones and cells with genetic codes—these are expressed
in a wide variety of behaviors, thoughts, and reactions.

Why do two people infected by the same disease have different outcomes: one surviving and one succumbing
to the ailment? How are genetic diseases passed through family lines? Are there genetic components to
psychological disorders, such as depression or schizophrenia? To what extent might there be a psychological
basis to health conditions such as childhood obesity?

To explore these questions, let’s start by focusing on a specific genetic disorder, sickle cell anemia, and how it
might manifest in two affected sisters. Sickle-cell anemia is a genetic condition in which red blood cells, which
are normally round, take on a crescent-like shape (Figure 3.2). The changed shape of these cells affects how
they function: sickle-shaped cells can clog blood vessels and block blood flow, leading to high fever, severe
pain, swelling, and tissue damage.

FIGURE 3.2 Normal blood cells travel freely through the blood vessels, while sickle-shaped cells form blockages
preventing blood flow.

Many people with sickle-cell anemia—and the particular genetic mutation that causes it—die at an early age.
While the notion of “survival of the fittest” may suggest that people with this disorder have a low survival rate
and therefore the disorder will become less common, this is not the case. Despite the negative evolutionary
effects associated with this genetic mutation, the sickle-cell gene remains relatively common among people of
African descent. Why is this? The explanation is illustrated with the following scenario.

Imagine two young women—Luwi and Sena—sisters in rural Zambia, Africa. Luwi carries the gene for sickle-
cell anemia; Sena does not carry the gene. Sickle-cell carriers have one copy of the sickle-cell gene but do not
have full-blown sickle-cell anemia. They experience symptoms only if they are severely dehydrated or are
deprived of oxygen (as in mountain climbing). Carriers are thought to be immune from malaria (an often
deadly disease that is widespread in tropical climates) because changes in their blood chemistry and immune
functioning prevent the malaria parasite from having its effects (Gong, Parikh, Rosenthal, & Greenhouse,
2013). However, full-blown sickle-cell anemia, with two copies of the sickle-cell gene, does not provide
immunity to malaria.

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While walking home from school, both sisters are bitten by mosquitoes carrying the malaria parasite. Luwi is
protected against malaria because she carries the sickle-cell mutation. Sena, on the other hand, develops
malaria and dies just two weeks later. Luwi survives and eventually has children, to whom she may pass on the
sickle-cell mutation.

LINK TO LEARNING

Visit this website about how a mutation in DNA leads to sickle cell anemia (http://openstax.org/l/sickle1) to
learn more.

Malaria is rare in the United States, so the sickle-cell gene benefits nobody: the gene manifests primarily in
minor health problems for carriers with one copy, or a severe full-blown disease with no health benefits for
carriers with two copies. However, the situation is quite different in other parts of the world. In parts of Africa
where malaria is prevalent, having the sickle-cell mutation does provide health benefits for carriers
(protection from malaria).

The story of malaria fits with Charles Darwin’s theory of evolution by natural selection (Figure 3.3). In simple
terms, the theory states that organisms that are better suited for their environment will survive and reproduce,
while those that are poorly suited for their environment will die off. In our example, we can see that, as a
carrier, Luwi’s mutation is highly adaptive in her African homeland; however, if she resided in the United
States (where malaria is rare), her mutation could prove costly—with a high probability of the disease in her
descendants and minor health problems of her own.

FIGURE 3.3 (a) In 1859, Charles Darwin proposed his theory of evolution by natural selection in his book, On the
Origin of Species. (b) The book contains just one illustration: this diagram that shows how species evolve over time
through natural selection.

Two Perspectives on Genetics and Behavior
It’s easy to get confused about two fields that study the interaction of genes and the environment, such as the
fields of evolutionary psychology and behavioral genetics. How can we tell them apart?

In both fields, it is understood that genes not only code for particular traits, but also contribute to certain
patterns of cognition and behavior. Evolutionary psychology focuses on how universal patterns of behavior and
cognitive processes have evolved over time. Therefore, variations in cognition and behavior would make
individuals more or less successful in reproducing and passing those genes on to their offspring. Evolutionary
psychologists study a variety of psychological phenomena that may have evolved as adaptations, including fear

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3.1 • Human Genetics 73

response, food preferences, mate selection, and cooperative behaviors (Confer et al., 2010).

Whereas evolutionary psychologists focus on universal patterns that evolved over millions of years, behavioral
geneticists study how individual differences arise, in the present, through the interaction of genes and the
environment. When studying human behavior, behavioral geneticists often employ twin and adoption studies to
research questions of interest. Twin studies compare the likelihood that a given behavioral trait is shared among
identical and fraternal twins; adoption studies compare those rates among biologically related relatives and
adopted relatives. Both approaches provide some insight into the relative importance of genes and environment
for the expression of a given trait.

LINK TO LEARNING

Watch this interview with renowned evolutionary psychologist David Buss (http://openstax.org/l/buss) to learn
more about how a psychologist approaches evolution and how this approach fits within the social sciences.

Genetic Variation

Genetic variation, the genetic difference between individuals, is what contributes to a species’ adaptation to its
environment. In humans, genetic variation begins with an egg, about 100 million sperm, and fertilization.
Roughly once per month, active ovaries release an egg from follicles. During the egg’s journey from the ovary
through the fallopian tubes, to the uterus, a sperm may fertilize the egg.

The egg and the sperm each contain 23 chromosomes. Chromosomes are long strings of genetic material
known as deoxyribonucleic acid (DNA). DNA is a helix-shaped molecule made up of nucleotide base pairs. In
each chromosome, sequences of DNA make up genes that control or partially control a number of visible
characteristics, known as traits, such as eye color, hair color, and so on. A single gene may have multiple
possible variations, or alleles. An allele is a specific version of a gene. So, a given gene may code for the trait of
hair color, and the different alleles of that gene affect which hair color an individual has.

When a sperm and egg fuse, their 23 chromosomes combine to create a zygote with 46 chromosomes (23
pairs). Therefore, each parent contributes half the genetic information carried by the offspring; the resulting
physical characteristics of the offspring (called the phenotype) are determined by the interaction of genetic
material supplied by the sperm and egg (called the genotype). A person’s genotype is the genetic makeup of
that individual. Phenotype, on the other hand, refers to the individual’s inherited physical characteristics,
which are a combination of genetic and environmental influences (Figure 3.4).

FIGURE 3.4 (a) Genotype refers to the genetic makeup of an individual based on the genetic material (DNA)
inherited from one’s genetic contributors. (b) Phenotype describes an individual’s observable characteristics, such
as hair color, skin color, height, and build. (credit a: modification of work by Caroline Davis; credit b: modification of
work by Cory Zanker)

Note that, in genetics and reproduction, “parent” is often used to describe the individual organisms that

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contribute genetic material to offspring, usually in the form of gamete cells (sperm and egg). The concept of a
genetic parent is distinct from social and legal concepts of parenthood, and may differ from those whom
people consider their parents.

Most traits are controlled by multiple genes, but some traits are controlled by one gene. A characteristic like
cleft chin, for example, is influenced by a single gene from each parent. In this example, we will call the gene
for cleft chin “B,” and the gene for smooth chin “b.” Cleft chin is a dominant trait, which means that having the
dominant allele either from one parent (Bb) or both parents (BB) will always result in the phenotype
associated with the dominant allele. When someone has two copies of the same allele, they are said to be
homozygous for that allele. When someone has a combination of alleles for a given gene, they are said to be
heterozygous. For example, smooth chin is a recessive trait, which means that an individual will only display
the smooth chin phenotype if they are homozygous for that recessive allele (bb).

Imagine that a person with a cleft chin mates with a person with a smooth chin. What type of chin will their
offspring have? The answer to that depends on which alleles each parent carries. If the person with a cleft is
homozygous for cleft chin (BB), their offspring will always have cleft chin. It gets a little more complicated,
however, if the person is heterozygous for this gene (Bb). Since the other person has a smooth chin—therefore
homozygous for the recessive allele (bb)—we can expect the offspring to have a 50% chance of having a cleft
chin and a 50% chance of having a smooth chin (Figure 3.5).

FIGURE 3.5 (a) A Punnett square is a tool used to predict how genes will interact in the production of offspring. The
capital B represents the dominant allele, and the lowercase b represents the recessive allele. In the example of the
cleft chin, where B is cleft chin (dominant allele), wherever a pair contains the dominant allele, B, you can expect a
cleft chin phenotype. You can expect a smooth chin phenotype only when there are two copies of the recessive
allele, bb. (b) A cleft chin, shown here, is an inherited trait.

In sickle cell anemia, heterozygous carriers (like Luwi from the example) can develop blood resistance to
malaria infection while those who are homozygous (like Sena) have a potentially lethal blood disorder. Sickle-
cell anemia is just one of many genetic disorders caused by the pairing of two recessive genes. For example,
phenylketonuria (PKU) is a condition in which individuals lack an enzyme that normally converts harmful
amino acids into harmless byproducts. If someone with this condition goes untreated, they will experience
significant deficits in cognitive function, seizures, and an increased risk of various psychiatric disorders.
Because PKU is a recessive trait, each parent must have at least one copy of the recessive allele in order to
produce a child with the condition (Figure 3.6).

So far, we have discussed traits that involve just one gene, but few human characteristics are controlled by a
single gene. Most traits are polygenic: controlled by more than one gene. Height is one example of a polygenic
trait, as are skin color and weight.

3.1 • Human Genetics 75

FIGURE 3.6 In this Punnett square, N represents the normal allele, and p represents the recessive allele that is
associated with PKU. If two individuals mate who are both heterozygous for the allele associated with PKU, their
offspring have a 25% chance of expressing the PKU phenotype.

Where do harmful genes that contribute to diseases like PKU come from? Gene mutations provide one source
of harmful genes. A mutation is a sudden, permanent change in a gene. While many mutations can be harmful
or lethal, once in a while, a mutation benefits an individual by giving that person an advantage over those who
do not have the mutation. Recall that the theory of evolution asserts that individuals best adapted to their
particular environments are more likely to reproduce and pass on their genes to future generations. In order
for this process to occur, there must be competition—more technically, there must be variability in genes (and
resultant traits) that allow for variation in adaptability to the environment. If a population consisted of
identical individuals, then any dramatic changes in the environment would affect everyone in the same way,
and there would be no variation in selection. In contrast, diversity in genes and associated traits allows some
individuals to perform slightly better than others when faced with environmental change. This creates a
distinct advantage for individuals best suited for their environments in terms of successful reproduction and
genetic transmission.

Human Diversity
This chapter focuses on biology. Later in this course you will learn about social psychology and issues of race,
prejudice, and discrimination. When we focus strictly on biology, race becomes a weak construct. After the
sequencing of the human genome at the turn of the millennium, many scientists began to argue that race was not
a useful variable in genetic research and that its continued use represents a potential source of confusion and
harm. The racial categories that some believed to be helpful in studying genetic diversity in humans are largely
irrelevant. A person’s skin tone, eye color, and hair texture are functions of their genetic makeups, but there is
actually more genetic variation within a given racial category than there is between racial categories. In some
cases, focus on race has led to difficulties with misdiagnoses and/or under-diagnoses of diseases ranging from
sickle cell anemia to cystic fibrosis. Some argue that we need to distinguish between ancestry and race and then
focus on ancestry. This approach would facilitate greater understanding of human genetic diversity (Yudell,
Roberts, DeSalle, & Tishkoff, 2016).

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Gene-Environment Interactions

Genes do not exist in a vacuum. Although we are all biological organisms, we also exist in an environment that
is incredibly important in determining not only when and how our genes express themselves, but also in what
combination. Each of us represents a unique interaction between our genetic makeup and our environment;
range of reaction is one way to describe this interaction. Range of reaction asserts that our genes set the
boundaries within which we can operate, and our environment interacts with the genes to determine where in
that range we will fall. For example, if an individual’s genetic makeup predisposes them to high levels of
intellectual potential and they are reared in a rich, stimulating environment, then they will be more likely to
achieve full potential than if they were raised under conditions of significant deprivation. According to the
concept of range of reaction, genes set definite limits on potential, and environment determines how much of
that potential is achieved. Some disagree with this theory and argue that genes do not set a limit on a person’s
potential with reaction norms being determined by the environment. For example, when individuals
experience neglect or abuse early in life, they are more likely to exhibit adverse psychological and/or physical
conditions that can last throughout their lives. These conditions may develop as a function of the negative
environmental experiences in individuals from dissimilar genetic backgrounds (Miguel, Pereira, Silveira, &
Meaney, 2019; Short & Baram, 2019).

Another perspective on the interaction between genes and the environment is the concept of genetic
environmental correlation. Stated simply, our genes influence our environment, and our environment
influences the expression of our genes (Figure 3.7). Not only do our genes and environment interact, as in
range of reaction, but they also influence one another bidirectionally. For example, the child of an NBA player
would probably be exposed to basketball from an early age. Such exposure might allow the child to realize
their full genetic, athletic potential. Thus, the parents’ genes, which the child shares, influence the child’s
environment, and that environment, in turn, is well suited to support the child’s genetic potential.

FIGURE 3.7 Nature and nurture work together like complex pieces of a human puzzle. The interaction of our
environment and genes makes us the individuals we are. (credit “puzzle”: modification of work by Cory Zanker)

In another approach to gene-environment interactions, the field of epigenetics looks beyond the genotype
itself and studies how the same genotype can be expressed in different ways. In other words, researchers study
how the same genotype can lead to very different phenotypes. As mentioned earlier, gene expression is often
influenced by environmental context in ways that are not entirely obvious. For instance, identical twins share
the same genetic information (identical twins develop from a single fertilized egg that split, so the genetic
material is exactly the same in each; in contrast, fraternal twins usually result from two different eggs
fertilized by different sperm, so the genetic material varies as with non-twin siblings). But even with identical
genes, there remains an incredible amount of variability in how gene expression can unfold over the course of
each twin’s life. Sometimes, one twin will develop a disease and the other will not. In one example, Aliya, an
identical twin, died from cancer at age 7, but her twin, now 19 years old, has never had cancer. Although these
individuals share an identical genotype, their phenotypes differ as a result of how that genetic information is

3.1 • Human Genetics 77

expressed over time and through their unique environmental interactions. The epigenetic perspective is very
different from range of reaction, because here the genotype is not fixed and limited.

LINK TO LEARNING

Watch this video about the epigenetics of twin studies (http://openstax.org/l/twinstudy) to learn more.

Genes affect more than our physical characteristics. Indeed, scientists have found genetic linkages to a
number of behavioral characteristics, ranging from basic personality traits to sexual orientation to spirituality
(for examples, see Mustanski et al., 2005; Comings, Gonzales, Saucier, Johnson, & MacMurray, 2000). Genes are
also associated with temperament and a number of psychological disorders, such as depression and
schizophrenia. So while it is true that genes provide the biological blueprints for our cells, tissues, organs, and
body, they also have a significant impact on our experiences and our behaviors.

Let’s look at the following findings regarding schizophrenia in light of our three views of gene-environment
interactions. Which view do you think best explains this evidence?

In a 2004 study by Tienari and colleagues, adoptees whose biological mothers had schizophrenia and who had
been raised in a disturbed family environment were much more likely to develop schizophrenia or another
psychotic disorder than were any of the other groups in the study:

• Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in
disturbed family environments, 36.8% were likely to develop schizophrenia.

• Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in
healthy family environments, 5.8% were likely to develop schizophrenia.

• Of adoptees with a low genetic risk (whose mothers did not have schizophrenia) and who were raised in
disturbed family environments, 5.3% were likely to develop schizophrenia.

• Of adoptees with a low genetic risk (whose mothers did not have schizophrenia) and who were raised in
healthy family environments, 4.8% were likely to develop schizophrenia.

The study shows that adoptees with high genetic risk were most likely to develop schizophrenia if they were
raised in disturbed home environments. This research lends credibility to the notion that both genetic
vulnerability and environmental stress are necessary for schizophrenia to develop, and that genes alone do not
tell the full tale.

3.2 Cells of the Nervous System
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Identify the basic parts of a neuron
• Describe how neurons communicate with each other
• Explain how drugs act as agonists or antagonists for a given neurotransmitter system

Psychologists striving to understand the human mind may study the nervous system. Learning how the body’s
cells and organs function can help us understand the biological basis of human psychology. The nervous
system is composed of two basic cell types: glial cells (also known as glia) and neurons. Glial cells are
traditionally thought to play a supportive role to neurons, both physically and metabolically. Glial cells provide
scaffolding on which the nervous system is built, help neurons line up closely with each other to allow
neuronal communication, provide insulation to neurons, transport nutrients and waste products, and mediate
immune responses. For years, researchers believed that there were many more glial cells than neurons;
however, more recent work from Suzanna Herculano-Houzel’s laboratory has called this long-standing
assumption into question and has provided important evidence that there may be a nearly 1:1 ratio of glia cells
to neurons. This is important because it suggests that human brains are more similar to other primate brains
than previously thought (Azevedo et al, 2009; Herculano-Houzel, 2012; Herculano-Houzel, 2009). Neurons, on

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the other hand, serve as interconnected information processors that are essential for all of the tasks of the
nervous system. This section briefly describes the structure and function of neurons.

Neuron Structure

Neurons are the central building blocks of the nervous system, 100 billion strong at birth. Like all cells,
neurons consist of several different parts, each serving a specialized function (Figure 3.8). A neuron’s outer
surface is made up of a semipermeable membrane. This membrane allows smaller molecules and molecules
without an electrical charge to pass through it, while stopping larger or highly charged molecules.

FIGURE 3.8 This illustration shows a prototypical neuron, which is being myelinated by a glial cell.

The nucleus of the neuron is located in the soma, or cell body. The soma has branching extensions known as
dendrites. The neuron is a small information processor, and dendrites serve as input sites where signals are
received from other neurons. These signals are transmitted electrically across the soma and down a major
extension from the soma known as the axon, which ends at multiple terminal buttons. The terminal buttons
contain synaptic vesicles that house neurotransmitters, the chemical messengers of the nervous system.

Axons range in length from a fraction of an inch to several feet. In some axons, glial cells form a fatty substance
known as the myelin sheath, which coats the axon and acts as an insulator, increasing the speed at which the
signal travels. The myelin sheath is not continuous and there are small gaps that occur down the length of the
axon. These gaps in the myelin sheath are known as the Nodes of Ranvier. The myelin sheath is crucial for the
normal operation of the neurons within the nervous system: the loss of the insulation it provides can be
detrimental to normal function. To understand how this works, let’s consider an example. PKU, a genetic
disorder discussed earlier, causes a reduction in myelin and abnormalities in white matter cortical and
subcortical structures. The disorder is associated with a variety of issues including severe cognitive deficits,
exaggerated reflexes, and seizures (Anderson & Leuzzi, 2010; Huttenlocher, 2000). Another disorder, multiple
sclerosis (MS), an autoimmune disorder, involves a large-scale loss of the myelin sheath on axons throughout
the nervous system. The resulting interference in the electrical signal prevents the quick transmittal of
information by neurons and can lead to a number of symptoms, such as dizziness, fatigue, loss of motor
control, and sexual dysfunction. While some treatments may help to modify the course of the disease and
manage certain symptoms, there is currently no known cure for multiple sclerosis.

In healthy individuals, the neuronal signal moves rapidly down the axon to the terminal buttons, where
synaptic vesicles release neurotransmitters into the synaptic cleft (Figure 3.9). The synaptic cleft is a very
small space between two neurons and is an important site where communication between neurons occurs.
Once neurotransmitters are released into the synaptic cleft, they travel across it and bind with corresponding
receptors on the dendrite of an adjacent neuron. Receptors, proteins on the cell surface where
neurotransmitters attach, vary in shape, with different shapes “matching” different neurotransmitters.

How does a neurotransmitter “know” which receptor to bind to? The neurotransmitter and the receptor have

3.2 • Cells of the Nervous System 79

what is referred to as a lock-and-key relationship—specific neurotransmitters fit specific receptors similar to
how a key fits a lock. The neurotransmitter binds to any receptor that it fits.

FIGURE 3.9 (a) The synaptic cleft is the space between the terminal button of one neuron and the dendrite of
another neuron. (b) In this pseudo-colored image from a scanning electron microscope, a terminal button (green)
has been opened to reveal the synaptic vesicles (orange and blue) inside. Each vesicle contains about 10,000
neurotransmitter molecules. (credit b: modification of work by Tina Carvalho, NIH-NIGMS; scale-bar data from Matt
Russell)

Neuronal Communication

Now that we have learned about the basic structures of the neuron and the role that these structures play in
neuronal communication, let’s take a closer look at the signal itself—how it moves through the neuron and then
jumps to the next neuron, where the process is repeated.

We begin at the neuronal membrane. The neuron exists in a fluid environment—it is surrounded by
extracellular fluid and contains intracellular fluid (i.e., cytoplasm). The neuronal membrane keeps these two
fluids separate—a critical role because the electrical signal that passes through the neuron depends on the
intra- and extracellular fluids being electrically different. This difference in charge across the membrane,
called the membrane potential, provides energy for the signal.

The electrical charge of the fluids is caused by charged molecules (ions) dissolved in the fluid. The
semipermeable nature of the neuronal membrane somewhat restricts the movement of these charged
molecules, and, as a result, some of the charged particles tend to become more concentrated either inside or
outside the cell.

Between signals, the neuron membrane’s potential is held in a state of readiness, called the resting potential.
Like a rubber band stretched out and waiting to spring into action, ions line up on either side of the cell
membrane, ready to rush across the membrane when the neuron goes active and the membrane opens its
gates. Ions in high-concentration areas are ready to move to low-concentration areas, and positive ions are
ready to move to areas with a negative charge.

In the resting state, sodium (Na+) is at higher concentrations outside the cell, so it will tend to move into the
cell. Potassium (K+), on the other hand, is more concentrated inside the cell, and will tend to move out of the
cell (Figure 3.10). In addition, the inside of the cell is slightly negatively charged compared to the outside, due
to the activity of the sodium-potassium pump. This pump actively transports three sodium ions out of the cell
for every two potassium ions in, creating a net negative charge inside the cell. This provides an additional
force on sodium, causing it to move into the cell.

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FIGURE 3.10 At resting potential, Na+ (blue pentagons) is more highly concentrated outside the cell in the
extracellular fluid (shown in blue), whereas K+ (purple squares) is more highly concentrated near the membrane in
the cytoplasm or intracellular fluid. Other molecules, such as chloride ions (yellow circles) and negatively charged
proteins (brown squares), help contribute to a positive net charge in the extracellular fluid and a negative net charge
in the intracellular fluid.

From this resting potential state, the neuron receives a signal and its state changes abruptly (Figure 3.11).
When a neuron receives signals at the dendrites—due to neurotransmitters from an adjacent neuron binding
to its receptors—small pores, or gates, open on the neuronal membrane, allowing Na+ ions, propelled by both
charge and concentration differences, to move into the cell. With this influx of positive ions, the internal
charge of the cell becomes more positive. If that charge reaches a certain level, called the threshold of
excitation, the neuron becomes active and the action potential begins.

Many additional pores open, causing a massive influx of Na+ ions and a huge positive spike in the membrane
potential, the peak action potential. At the peak of the spike, the sodium gates close and the potassium gates
open. As positively charged potassium ions leave, the cell quickly begins repolarization. At first, it
hyperpolarizes, becoming slightly more negative than the resting potential, and then it levels off, returning to
the resting potential.

FIGURE 3.11 During the action potential, the electrical charge across the membrane changes dramatically.

This positive spike constitutes the action potential: the electrical signal that typically moves from the cell body
down the axon to the axon terminals. The electrical signal moves down the axon with the impulses jumping in
a leapfrog fashion between the Nodes of Ranvier. The Nodes of Ranvier are natural gaps in the myelin sheath.
At each point, some of the sodium ions that enter the cell diffuse to the next section of the axon, raising the
charge past the threshold of excitation and triggering a new influx of sodium ions. The action potential moves

3.2 • Cells of the Nervous System 81

all the way down the axon in this fashion until reaching the terminal buttons.

The action potential is an all-or-none phenomenon. In simple terms, this means that an incoming signal from
another neuron is either sufficient or insufficient to reach the threshold of excitation. There is no in-between,
and there is no turning off an action potential once it starts. Think of it like sending an email or a text message.
You can think about sending it all you want, but the message is not sent until you hit the send button.
Furthermore, once you send the message, there is no stopping it.

Because it is all or none, the action potential is recreated, or propagated, at its full strength at every point along
the axon. Much like the lit fuse of a firecracker, it does not fade away as it travels down the axon. It is this all-or-
none property that explains the fact that your brain perceives an injury to a distant body part like your toe as
equally painful as one to your nose.

As noted earlier, when the action potential arrives at the terminal button, the synaptic vesicles release their
neurotransmitters into the synaptic cleft. The neurotransmitters travel across the synapse and bind to
receptors on the dendrites of the adjacent neuron, and the process repeats itself in the new neuron (assuming
the signal is sufficiently strong to trigger an action potential). Once the signal is delivered, excess
neurotransmitters in the synaptic cleft drift away, are broken down into inactive fragments, or are reabsorbed
in a process known as reuptake. Reuptake involves the neurotransmitter being pumped back into the neuron
that released it, in order to clear the synapse (Figure 3.12). Clearing the synapse serves both to provide a clear
“on” and “off” state between signals and to regulate the production of neurotransmitter (full synaptic vesicles
provide signals that no additional neurotransmitters need to be produced).

FIGURE 3.12 Reuptake involves moving a neurotransmitter from the synapse back into the axon terminal from
which it was released.

Neuronal communication is often referred to as an electrochemical event. The movement of the action
potential down the length of the axon is an electrical event, and movement of the neurotransmitter across the
synaptic space represents the chemical portion of the process. However, there are some specialized
connections between neurons that are entirely electrical. In such cases, the neurons are said to communicate
via an electrical synapse. In these cases, two neurons physically connect to one another via gap junctions,
which allows the current from one cell to pass into the next. There are far fewer electrical synapses in the
brain, but those that do exist are much faster than the chemical synapses that have been described above
(Connors & Long, 2004).

LINK TO LEARNING

Watch this video about neuronal communication (http://openstax.org/l/neuroncom) to learn more.

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Neurotransmitters and Drugs

There are several different types of neurotransmitters released by different neurons, and we can speak in
broad terms about the kinds of functions associated with different neurotransmitters (Table 3.1). Much of what
psychologists know about the functions of neurotransmitters comes from research on the effects of drugs in
psychological disorders. Psychologists who take a biological perspective and focus on the physiological
causes of behavior assert that psychological disorders like depression and schizophrenia are associated with
imbalances in one or more neurotransmitter systems. In this perspective, psychotropic medications can help
improve the symptoms associated with these disorders. Psychotropic medications are drugs that treat
psychiatric symptoms by restoring neurotransmitter balance.

Major Neurotransmitters and How They Affect Behavior

Neurotransmitter Involved in Potential Effect on Behavior

Acetylcholine Muscle action, memory Increased arousal, enhanced cognition

Beta-endorphin Pain, pleasure Decreased anxiety, decreased tension

Dopamine Mood, sleep, learning Increased pleasure, suppressed appetite

Gamma-aminobutyric acid (GABA) Brain function, sleep Decreased anxiety, decreased tension

Glutamate Memory, learning Increased learning, enhanced memory

Norepinephrine Heart, intestines, alertness Increased arousal, suppressed appetite

Serotonin Mood, sleep Modulated mood, suppressed appetite

TABLE 3.1

Psychoactive drugs can act as agonists or antagonists for a given neurotransmitter system. Agonists are
chemicals that mimic a neurotransmitter at the receptor site. An antagonist, on the other hand, blocks or
impedes the normal activity of a neurotransmitter at the receptor. Agonists and antagonists represent drugs
that are prescribed to correct the specific neurotransmitter imbalances underlying a person’s condition. For
example, Parkinson’s disease, a progressive nervous system disorder, is associated with low levels of
dopamine. Therefore, a common treatment strategy for Parkinson’s disease involves using dopamine agonists,
which mimic the effects of dopamine by binding to dopamine receptors.

Certain symptoms of schizophrenia are associated with overactive dopamine neurotransmission. The
antipsychotics used to treat these symptoms are antagonists for dopamine—they block dopamine’s effects by
binding its receptors without activating them. Thus, they prevent dopamine released by one neuron from
signaling information to adjacent neurons.

In contrast to agonists and antagonists, which both operate by binding to receptor sites, reuptake inhibitors
prevent unused neurotransmitters from being transported back to the neuron. This allows neurotransmitters
to remain active in the synaptic cleft for longer durations, increasing their effectiveness. Depression, which
has been consistently linked with reduced serotonin levels, is commonly treated with selective serotonin
reuptake inhibitors (SSRIs). By preventing reuptake, SSRIs strengthen the effect of serotonin, giving it more
time to interact with serotonin receptors on dendrites. Common SSRIs on the market today include Prozac,
Paxil, and Zoloft. The drug LSD is structurally very similar to serotonin, and it affects the same neurons and
receptors as serotonin. Psychotropic drugs are not instant solutions for people suffering from psychological
disorders. Often, an individual must take a drug for several weeks before seeing improvement, and many

3.2 • Cells of the Nervous System 83

psychoactive drugs have significant negative side effects. Furthermore, individuals vary dramatically in how
they respond to the drugs. To improve chances for success, it is not uncommon for people receiving
pharmacotherapy to undergo psychological and/or behavioral therapies as well. Some research suggests that
combining drug therapy with other forms of therapy tends to be more effective than any one treatment alone
(for one such example, see March et al., 2007).

3.3 Parts of the Nervous System
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the difference between the central and peripheral nervous systems
• Explain the difference between the somatic and autonomic nervous systems
• Differentiate between the sympathetic and parasympathetic divisions of the autonomic nervous system

The nervous system can be divided into two major subdivisions: the central nervous system (CNS) and the
peripheral nervous system (PNS), shown in Figure 3.13. The CNS is comprised of the brain and spinal cord;
the PNS connects the CNS to the rest of the body. In this section, we focus on the peripheral nervous system;
later, we look at the brain and spinal cord.

FIGURE 3.13 The nervous system is divided into two major parts: (a) the Central Nervous System and (b) the
Peripheral Nervous System.

Peripheral Nervous System

The peripheral nervous system is made up of thick bundles of axons, called nerves, carrying messages back
and forth between the CNS and the muscles, organs, and senses in the periphery of the body (i.e., everything
outside the CNS). The PNS has two major subdivisions: the somatic nervous system and the autonomic

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nervous system.

The somatic nervous system is associated with activities traditionally thought of as conscious or voluntary. It
is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists of motor
neurons and sensory neurons. Motor neurons, carrying instructions from the CNS to the muscles, are efferent
fibers (efferent means “moving away from”). Sensory neurons, carrying sensory information to the CNS, are
afferent fibers (afferent means “moving toward”). A helpful way to remember this is that efferent = exit and
afferent = arrive. Each nerve is basically a bundle of neurons forming a two-way superhighway, containing
thousands of axons, both efferent and afferent.

The autonomic nervous system controls our internal organs and glands and is generally considered to be
outside the realm of voluntary control. It can be further subdivided into the sympathetic and parasympathetic
divisions (Figure 3.14). The sympathetic nervous system is involved in preparing the body for stress-related
activities; the parasympathetic nervous system is associated with returning the body to routine, day-to-day
operations. The two systems have complementary functions, operating in tandem to maintain the body’s
homeostasis. Homeostasis is a state of equilibrium, or balance, in which biological conditions (such as body
temperature) are maintained at optimal levels.

FIGURE 3.14 The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite
effects on various systems.

The sympathetic nervous system is activated when we are faced with stressful or high-arousal situations. The
activity of this system was adaptive for our ancestors, increasing their chances of survival. Imagine, for
example, that one of our early ancestors, out hunting small game, suddenly disturbs a large bear with her cubs.
At that moment, the hunter’s body undergoes a series of changes—a direct function of sympathetic
activation—preparing them to face the threat. The pupils dilate, the heart rate and blood pressure increase, the
bladder relaxes, and the liver releases glucose; adrenaline surges into the bloodstream. This constellation of

3.3 • Parts of the Nervous System 85

physiological changes, known as the fight or flight response, allows the body access to energy reserves and
heightened sensory capacity so that it might fight off a threat or run away to safety.

LINK TO LEARNING

Watch this video about the Fight Flight Freeze response (http://openstax.org/l/response) to learn more.

While it is clear that such a response would be critical for survival for our ancestors, who lived in a world full of
real physical threats, many of the high-arousal situations we face in the modern world are more psychological
in nature. For example, think about how you feel when you have to stand up and give a presentation in front of
a roomful of people, or right before taking a big test. You are in no real physical danger in those situations, and
yet you have evolved to respond to a perceived threat with the fight or flight response. This kind of response is
not nearly as adaptive in the modern world; in fact, we suffer negative health consequences when faced
constantly with psychological threats that we can neither fight nor flee. Recent research suggests that an
increase in susceptibility to heart disease (Chandola, Brunner, & Marmot, 2006) and impaired function of the
immune system (Glaser & Kiecolt-Glaser, 2005) are among the many negative consequences of persistent and
repeated exposure to stressful situations. Some of this tendency for stress reactivity can be wired by early
experiences of trauma.

Once the threat has been resolved, the parasympathetic nervous system takes over and returns bodily
functions to a relaxed state. Our hunter’s heart rate and blood pressure return to normal, the pupils constrict,
bladder control is restored, and the liver begins to store glucose in the form of glycogen for future use. These
restorative processes are associated with activation of the parasympathetic nervous system.

3.4 The Brain and Spinal Cord
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain the functions of the spinal cord
• Identify the hemispheres and lobes of the brain
• Describe the types of techniques available to clinicians and researchers to image or scan the brain

The brain is a remarkably complex organ comprised of billions of interconnected neurons and glia. It is a
bilateral, or two-sided, structure that can be separated into distinct lobes. Each lobe is associated with certain
types of functions, but, ultimately, all of the areas of the brain interact with one another to provide the
foundation for our thoughts and behaviors. In this section, we discuss the overall organization of the brain and
the functions associated with different brain areas, beginning with what can be seen as an extension of the
brain, the spinal cord.

The Spinal Cord

It can be said that the spinal cord is what connects the brain to the outside world. Because of it, the brain can
act. The spinal cord is like a relay station, but a very smart one. It not only routes messages to and from the
brain, but it also has its own system of automatic processes, called reflexes.

The top of the spinal cord is a bundle of nerves that merges with the brain stem, where the basic processes of
life are controlled, such as breathing and digestion. In the opposite direction, the spinal cord ends just below
the ribs—contrary to what we might expect, it does not extend all the way to the base of the spine.

The spinal cord is functionally organized in 30 segments, corresponding with the vertebrae. Each segment is
connected to a specific part of the body through the peripheral nervous system. Nerves branch out from the
spine at each vertebra. Sensory nerves bring messages in; motor nerves send messages out to the muscles and
organs. Messages travel to and from the brain through every segment.

Some sensory messages are immediately acted on by the spinal cord, without any input from the brain.

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Withdrawal from a hot object and the knee jerk are two examples. When a sensory message meets certain
parameters, the spinal cord initiates an automatic reflex. The signal passes from the sensory nerve to a simple
processing center, which initiates a motor command. Seconds are saved, because messages don’t have to go
the brain, be processed, and get sent back. In matters of survival, the spinal reflexes allow the body to react
extraordinarily fast.

The spinal cord is protected by bony vertebrae and cushioned in cerebrospinal fluid, but injuries still occur.
When the spinal cord is damaged in a particular segment, all lower segments are cut off from the brain,
causing paralysis. Therefore, the lower on the spine damage occurs, the fewer functions an injured individual
will lose.

Neuroplasticity

Bob Woodruff, a reporter for ABC, suffered a traumatic brain injury after a bomb exploded next to the vehicle
he was in while covering a news story in Iraq. As a consequence of these injuries, Woodruff experienced many
cognitive deficits including difficulties with memory and language. However, over time and with the aid of
intensive amounts of cognitive and speech therapy, Woodruff has shown an incredible recovery of function
(Fernandez, 2008, October 16).

One of the factors that made this recovery possible was neuroplasticity. Neuroplasticity refers to how the
nervous system can change and adapt. Neuroplasticity can occur in a variety of ways including personal
experiences, developmental processes, or, as in Woodruff’s case, in response to some sort of damage or injury
that has occurred. Neuroplasticity can involve creation of new synapses, pruning of synapses that are no
longer used, changes in glial cells, and even the birth of new neurons. Because of neuroplasticity, our brains
are constantly changing and adapting, and while our nervous system is most plastic when we are very young,
as Woodruff’s case suggests, it is still capable of remarkable changes later in life.

The Two Hemispheres

The surface of the brain, known as the cerebral cortex, is very uneven, characterized by a distinctive pattern
of folds or bumps, known as gyri (singular: gyrus), and grooves, known as sulci (singular: sulcus), shown in
Figure 3.15. These gyri and sulci form important landmarks that allow us to separate the brain into functional
centers. The most prominent sulcus, known as the longitudinal fissure, is the deep groove that separates the
brain into two halves or hemispheres: the left hemisphere and the right hemisphere.

FIGURE 3.15 The surface of the brain is covered with gyri and sulci. A deep sulcus is called a fissure, such as the
longitudinal fissure that divides the brain into left and right hemispheres. (credit: modification of work by Bruce
Blaus)

There is evidence of specialization of function—referred to as lateralization—in each hemisphere, mainly
regarding differences in language functions. The left hemisphere controls the right half of the body, and the
right hemisphere controls the left half of the body. Decades of research on lateralization of function by Michael

3.4 • The Brain and Spinal Cord 87

Gazzaniga and his colleagues suggest that a variety of functions ranging from cause-and-effect reasoning to
self-recognition may follow patterns that suggest some degree of hemispheric dominance (Gazzaniga, 2005).
For example, the left hemisphere has been shown to be superior for forming associations in memory, selective
attention, and positive emotions. The right hemisphere, on the other hand, has been shown to be superior in
pitch perception, arousal, and negative emotions (Ehret, 2006). However, it should be pointed out that
research on which hemisphere is dominant in a variety of different behaviors has produced inconsistent
results, and therefore, it is probably better to think of how the two hemispheres interact to produce a given
behavior rather than attributing certain behaviors to one hemisphere versus the other (Banich & Heller, 1998).

The two hemispheres are connected by a thick band of neural fibers known as the corpus callosum, consisting
of about 200 million axons. The corpus callosum allows the two hemispheres to communicate with each other
and allows for information being processed on one side of the brain to be shared with the other side.

Normally, we are not aware of the different roles that our two hemispheres play in day-to-day functions, but
there are people who come to know the capabilities and functions of their two hemispheres quite well. In some
cases of severe epilepsy, doctors elect to sever the corpus callosum as a means of controlling the spread of
seizures (Figure 3.16). While this is an effective treatment option, it results in individuals who have “split
brains.” After surgery, these split-brain patients show a variety of interesting behaviors. For instance, a split-
brain patient is unable to name a picture that is shown in the patient’s left visual field because the information
is only available in the largely nonverbal right hemisphere. However, they are able to recreate the picture with
their left hand, which is also controlled by the right hemisphere. When the more verbal left hemisphere sees
the picture that the hand drew, the patient is able to name it (assuming the left hemisphere can interpret what
was drawn by the left hand).

FIGURE 3.16 (a, b) The corpus callosum connects the left and right hemispheres of the brain. (c) A scientist
spreads this dissected sheep brain apart to show the corpus callosum between the hemispheres. (credit c:
modification of work by Aaron Bornstein)

Much of what we know about the functions of different areas of the brain comes from studying changes in the
behavior and ability of individuals who have suffered damage to the brain. For example, researchers study the
behavioral changes caused by strokes to learn about the functions of specific brain areas. A stroke, caused by
an interruption of blood flow to a region in the brain, causes a loss of brain function in the affected region. The
damage can be in a small area, and, if it is, this gives researchers the opportunity to link any resulting
behavioral changes to a specific area. The types of deficits displayed after a stroke will be largely dependent on
where in the brain the damage occurred.

Consider Theona, an intelligent, self-sufficient woman, who is 62 years old. Recently, she suffered a stroke in
the front portion of her right hemisphere. As a result, she has great difficulty moving her left leg. (As you
learned earlier, the right hemisphere controls the left side of the body; also, the brain’s main motor centers are
located at the front of the head, in the frontal lobe.) Theona has also experienced behavioral changes. For
example, while in the produce section of the grocery store, she sometimes eats grapes, strawberries, and
apples directly from their bins before paying for them. This behavior—which would have been very
embarrassing to her before the stroke—is consistent with damage in another region in the frontal lobe—the

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prefrontal cortex, which is associated with judgment, reasoning, and impulse control.

Forebrain Structures

The two hemispheres of the cerebral cortex are part of the forebrain (Figure 3.17), which is the largest part of
the brain. The forebrain contains the cerebral cortex and a number of other structures that lie beneath the
cortex (called subcortical structures): thalamus, hypothalamus, pituitary gland, and the limbic system (a
collection of structures). The cerebral cortex, which is the outer surface of the brain, is associated with higher
level processes such as consciousness, thought, emotion, reasoning, language, and memory. Each cerebral
hemisphere can be subdivided into four lobes, each associated with different functions.

FIGURE 3.17 The brain and its parts can be divided into three main categories: the forebrain, midbrain, and
hindbrain.

Lobes of the Brain

The four lobes of the brain are the frontal, parietal, temporal, and occipital lobes (Figure 3.18). The frontal
lobe is located in the forward part of the brain, extending back to a fissure known as the central sulcus. The
frontal lobe is involved in reasoning, motor control, emotion, and language. It contains the motor cortex,
which is involved in planning and coordinating movement; the prefrontal cortex, which is responsible for
higher-level cognitive functioning; and Broca’s area, which is essential for language production.

FIGURE 3.18 The lobes of the brain are shown.

People who suffer damage to Broca’s area have great difficulty producing language of any form (Figure 3.18).
For example, Padma was an electrical engineer who was socially active and a caring, involved parent. About
twenty years ago, she was in a car accident and suffered damage to her Broca’s area. She completely lost the
ability to speak and form any kind of meaningful language. There is nothing wrong with her mouth or her vocal

3.4 • The Brain and Spinal Cord 89

cords, but she is unable to produce words. She can follow directions but can’t respond verbally, and she can
read but no longer write. She can do routine tasks like running to the market to buy milk, but she could not
communicate verbally if a situation called for it.

Probably the most famous case of frontal lobe damage is that of a man by the name of Phineas Gage. On
September 13, 1848, Gage (age 25) was working as a railroad foreman in Vermont. He and his crew were using
an iron rod to tamp explosives down into a blasting hole to remove rock along the railway’s path.
Unfortunately, the iron rod created a spark and caused the rod to explode out of the blasting hole, into Gage’s
face, and through his skull (Figure 3.19). Although lying in a pool of his own blood with brain matter emerging
from his head, Gage was conscious and able to get up, walk, and speak. But in the months following his
accident, people noticed that his personality had changed. Many of his friends described him as no longer
being himself. Before the accident, it was said that Gage was a well-mannered, soft-spoken man, but he began
to behave in odd and inappropriate ways after the accident. Such changes in personality would be consistent
with loss of impulse control—a frontal lobe function.

Beyond the damage to the frontal lobe itself, subsequent investigations into the rod’s path also identified
probable damage to pathways between the frontal lobe and other brain structures, including the limbic
system. With connections between the planning functions of the frontal lobe and the emotional processes of
the limbic system severed, Gage had difficulty controlling his emotional impulses.

However, there is some evidence suggesting that the dramatic changes in Gage’s personality were exaggerated
and embellished. Gage’s case occurred in the midst of a 19th century debate over localization—regarding
whether certain areas of the brain are associated with particular functions. On the basis of extremely limited
information about Gage, the extent of his injury, and his life before and after the accident, scientists tended to
find support for their own views, on whichever side of the debate they fell (Macmillan, 1999).

FIGURE 3.19 (a) Phineas Gage holds the iron rod that penetrated his skull in an 1848 railroad construction
accident. (b) Gage’s prefrontal cortex was severely damaged in the left hemisphere. The rod entered Gage’s face on
the left side, passed behind his eye, and exited through the top of his skull, before landing about 80 feet away.
(credit a: modification of work by Jack and Beverly Wilgus)

The brain’s parietal lobe is located immediately behind the frontal lobe, and is involved in processing
information from the body’s senses. It contains the somatosensory cortex, which is essential for processing
sensory information from across the body, such as touch, temperature, and pain. The somatosensory cortex is
an area of the brain which processes touch and sensation. The somatosensory cortex is fascinating because
each different area of the cortex processes sensations from a different part of your body. Furthermore, the
larger the surface area of the specific body part and the greater amount of nerves in that body part, the larger
the area dedicated to processing sensation from that body part in the somatosensory cortex. For example,

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fingers take up a lot more space than toes. As you can notice from (Figure 3.20), the amount of space to process
sensation from fingers is much greater than that of toes.

LINK TO LEARNING

One fascinating example of neuroplasticity involves reorganization of the somatosensory cortex following limb
amputation. Check out this NPR segment about amputees’ experiences of “phantom limbs” following
amputation (http://openstax.org/l/phantomlimb) to learn more.

FIGURE 3.20 Spatial relationships in the body are mirrored in the organization of the somatosensory cortex.

The temporal lobe is located on the side of the head (temporal means “near the temples”), and is associated
with hearing, memory, emotion, and some aspects of language. The auditory cortex, the main area
responsible for processing auditory information, is located within the temporal lobe. Wernicke’s area,
important for speech comprehension, is also located here. Whereas individuals with damage to Broca’s area
have difficulty producing language, those with damage to Wernicke’s area can produce sensible language, but
they are unable to understand it (Figure 3.21).

FIGURE 3.21 Damage to either Broca’s area or Wernicke’s area can result in language deficits. The types of deficits
are very different, however, depending on which area is affected.

The occipital lobe is located at the very back of the brain, and contains the primary visual cortex, which is
responsible for interpreting incoming visual information. The occipital cortex is organized retinotopically,

3.4 • The Brain and Spinal Cord 91

which means there is a close relationship between the position of an object in a person’s visual field and the
position of that object’s representation on the cortex. You will learn much more about how visual information
is processed in the occipital lobe when you study sensation and perception.

Other Areas of the Forebrain

Other areas of the forebrain, located beneath the cerebral cortex, include the thalamus and the limbic system.
The thalamus is a sensory relay for the brain. All of our senses, with the exception of smell, are routed through
the thalamus before being directed to other areas of the brain for processing (Figure 3.22).

FIGURE 3.22 The thalamus serves as the relay center of the brain where most senses are routed for processing.

The limbic system is involved in processing both emotion and memory. Interestingly, the sense of smell
projects directly to the limbic system; therefore, not surprisingly, smell can evoke emotional responses in ways
that other sensory modalities cannot. The limbic system is made up of a number of different structures, but
three of the most important are the hippocampus, the amygdala, and the hypothalamus (Figure 3.23). The
hippocampus is an essential structure for learning and memory. The amygdala is involved in our experience
of emotion and in tying emotional meaning to our memories. The hypothalamus regulates a number of
homeostatic processes, including the regulation of body temperature, appetite, and blood pressure. The
hypothalamus also serves as an interface between the nervous system and the endocrine system and in the
regulation of sexual motivation and behavior.

FIGURE 3.23 The limbic system is involved in mediating emotional response and memory.

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The Case of Henry Molaison (H.M.)

In 1953, Henry Gustav Molaison (H. M.) was a 27-year-old man who experienced severe seizures. In an attempt
to control his seizures, H. M. underwent brain surgery to remove his hippocampus and amygdala. Following
the surgery, H.M’s seizures became much less severe, but he also suffered some unexpected—and
devastating—consequences of the surgery: he lost his ability to form many types of new memories. For
example, he was unable to learn new facts, such as who was president of the United States. He was able to learn
new skills, but afterward he had no recollection of learning them. For example, while he might learn to use a
computer, he would have no conscious memory of ever having used one. He could not remember new faces,
and he was unable to remember events, even immediately after they occurred. Researchers were fascinated by
his experience, and he is considered one of the most studied cases in medical and psychological history
(Hardt, Einarsson, & Nader, 2010; Squire, 2009). Indeed, his case has provided tremendous insight into the
role that the hippocampus plays in the consolidation of new learning into explicit memory.

LINK TO LEARNING

Clive Wearing, an accomplished musician, lost the ability to form new memories when his hippocampus was
damaged through illness. Check out the first few minutes of this documentary video about this man and his
condition (http://openstax.org/l/wearing) to learn more.

Midbrain and Hindbrain Structures

The midbrain is comprised of structures located deep within the brain, between the forebrain and the
hindbrain. The reticular formation is centered in the midbrain, but it actually extends up into the forebrain
and down into the hindbrain. The reticular formation is important in regulating the sleep/wake cycle, arousal,
alertness, and motor activity.

The substantia nigra (Latin for “black substance”) and the ventral tegmental area (VTA) are also located in
the midbrain (Figure 3.24). Both regions contain cell bodies that produce the neurotransmitter dopamine, and
both are critical for movement. Degeneration of the substantia nigra and VTA is involved in Parkinson’s
disease. In addition, these structures are involved in mood, reward, and addiction (Berridge & Robinson, 1998;
Gardner, 2011; George, Le Moal, & Koob, 2012).

FIGURE 3.24 The substantia nigra and ventral tegmental area (VTA) are located in the midbrain.

The hindbrain is located at the back of the head and looks like an extension of the spinal cord. It contains the
medulla, pons, and cerebellum (Figure 3.25). The medulla controls the automatic processes of the autonomic
nervous system, such as breathing, blood pressure, and heart rate. The word pons literally means “bridge,”

3.4 • The Brain and Spinal Cord 93

and as the name suggests, the pons serves to connect the hindbrain to the rest of the brain. It also is involved
in regulating brain activity during sleep. The medulla, pons, and various structures are known as the
brainstem, and aspects of the brainstem span both the midbrain and the hindbrain.

FIGURE 3.25 The pons, medulla, and cerebellum make up the hindbrain.

The cerebellum (Latin for “little brain”) receives messages from muscles, tendons, joints, and structures in
our ear to control balance, coordination, movement, and motor skills. The cerebellum is also thought to be an
important area for processing some types of memories. In particular, procedural memory, or memory involved
in learning and remembering how to perform tasks, is thought to be associated with the cerebellum. Recall
that H. M. was unable to form new explicit memories, but he could learn new tasks. This is likely due to the fact
that H. M.’s cerebellum remained intact.

Brain Dead and on Life Support
What would you do if your spouse or loved one was declared brain dead but their body was being kept alive by
medical equipment? Whose decision should it be to remove a feeding tube? Should medical care costs be a
factor?

On February 25, 1990, a Florida woman named Terri Schiavo went into cardiac arrest, apparently triggered by a
bulimic episode. She was eventually revived, but her brain had been deprived of oxygen for a long time. Brain
scans indicated that there was no activity in her cerebral cortex, and she suffered from severe and permanent
cerebral atrophy. Basically, Schiavo was in a vegetative state. Medical professionals determined that she would
never again be able to move, talk, or respond in any way. To remain alive, she required a feeding tube, and there
was no chance that her situation would ever improve.

On occasion, Schiavo’s eyes would move, and sometimes she would groan. Despite the doctors’ insistence to the
contrary, her parents believed that these were signs that she was trying to communicate with them.

After 12 years, Schiavo’s husband argued that his wife would not have wanted to be kept alive with no feelings,
sensations, or brain activity. Her parents, however, were very much against removing her feeding tube.
Eventually, the case made its way to the courts, both in the state of Florida and at the federal level. By 2005, the
courts found in favor of Schiavo’s husband, and the feeding tube was removed on March 18, 2005. Schiavo died
13 days later.

Why did Schiavo’s eyes sometimes move, and why did she groan? Although the parts of her brain that control

WHAT DO YOU THINK?

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thought, voluntary movement, and feeling were completely damaged, her brainstem was still intact. Her medulla
and pons maintained her breathing and caused involuntary movements of her eyes and the occasional groans.
Over the 15-year period that she was on a feeding tube, Schiavo’s medical costs may have topped $7 million
(Arnst, 2003).

These questions were brought to popular conscience decades ago in the case of Terri Schiavo, and they have
persisted. In 2013, a 13-year-old girl who suffered complications after tonsil surgery was declared brain dead.
There was a battle between her family, who wanted her to remain on life support, and the hospital’s policies
regarding persons declared brain dead. In another complicated 2013–14 case in Texas, a pregnant EMT
professional declared brain dead was kept alive for weeks, despite her spouse’s directives, which were based on
her wishes should this situation arise. In this case, state laws designed to protect an unborn fetus came into
consideration until doctors determined the fetus unviable.

Decisions surrounding the medical response to patients declared brain dead are complex. What do you think
about these issues?

Brain Imaging

You have learned how brain injury can provide information about the functions of different parts of the brain.
Increasingly, however, we are able to obtain that information using brain imaging techniques on individuals
who have not suffered brain injury. In this section, we take a more in-depth look at some of the techniques that
are available for imaging the brain, including techniques that rely on radiation, magnetic fields, or electrical
activity within the brain.

Techniques Involving Radiation

A computerized tomography (CT) scan involves taking a number of x-rays of a particular section of a person’s
body or brain (Figure 3.26). The x-rays pass through tissues of different densities at different rates, allowing a
computer to construct an overall image of the area of the body being scanned. A CT scan is often used to
determine whether someone has a tumor or significant brain atrophy.

FIGURE 3.26 A CT scan can be used to show brain tumors. (a) The image on the left shows a healthy brain, whereas
(b) the image on the right indicates a brain tumor in the left frontal lobe. (credit a: modification of work by
“Aceofhearts1968″/Wikimedia Commons; credit b: modification of work by Roland Schmitt et al)

Positron emission tomography (PET) scans create pictures of the living, active brain (Figure 3.27). An
individual receiving a PET scan drinks or is injected with a mildly radioactive substance, called a tracer. Once
in the bloodstream, the amount of tracer in any given region of the brain can be monitored. As a brain area
becomes more active, more blood flows to that area. A computer monitors the movement of the tracer and
creates a rough map of active and inactive areas of the brain during a given behavior. PET scans show little
detail, are unable to pinpoint events precisely in time, and require that the brain be exposed to radiation;
therefore, this technique has been replaced by the fMRI as an alternative diagnostic tool. However, combined

3.4 • The Brain and Spinal Cord 95

with CT, PET technology is still being used in certain contexts. For example, CT/PET scans allow better imaging
of the activity of neurotransmitter receptors and open new avenues in schizophrenia research. In this hybrid
CT/PET technology, CT contributes clear images of brain structures, while PET shows the brain’s activity.

FIGURE 3.27 A PET scan is helpful for showing activity in different parts of the brain. (credit: Health and Human
Services Department, National Institutes of Health)

Techniques Involving Magnetic Fields

In magnetic resonance imaging (MRI), a person is placed inside a machine that generates a strong magnetic
field. The magnetic field causes the hydrogen atoms in the body’s cells to move. When the magnetic field is
turned off, the hydrogen atoms emit electromagnetic signals as they return to their original positions. Tissues
of different densities give off different signals, which a computer interprets and displays on a monitor.
Functional magnetic resonance imaging (fMRI) operates on the same principles, but it shows changes in
brain activity over time by tracking blood flow and oxygen levels. The fMRI provides more detailed images of
the brain’s structure, as well as better accuracy in time, than is possible in PET scans (Figure 3.28). With their
high level of detail, MRI and fMRI are often used to compare the brains of healthy individuals to the brains of
individuals diagnosed with psychological disorders. This comparison helps determine what structural and
functional differences exist between these populations.

FIGURE 3.28 An fMRI shows activity in the brain over time. This image represents a single frame from an fMRI.
(credit: modification of work by Kim J, Matthews NL, Park S.)

LINK TO LEARNING

Visit this virtual lab about MRI and fMRI (http://openstax.org/l/mri) to learn more.

Techniques Involving Electrical Activity

In some situations, it is helpful to gain an understanding of the overall activity of a person’s brain, without
needing information on the actual location of the activity. Electroencephalography (EEG) serves this purpose
by providing a measure of a brain’s electrical activity. An array of electrodes is placed around a person’s head

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(Figure 3.29). The signals received by the electrodes result in a printout of the electrical activity of their brain,
or brainwaves, showing both the frequency (number of waves per second) and amplitude (height) of the
recorded brainwaves, with an accuracy within milliseconds. Such information is especially helpful to
researchers studying sleep patterns among individuals with sleep disorders.

FIGURE 3.29 Using caps with electrodes, modern EEG research can study the precise timing of overall brain
activities. (credit: SMI Eye Tracking)

3.5 The Endocrine System
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Identify the major glands of the endocrine system
• Identify the hormones secreted by each gland
• Describe each hormone’s role in regulating bodily functions

The endocrine system consists of a series of glands that produce chemical substances known as hormones
(Figure 3.30). Like neurotransmitters, hormones are chemical messengers that must bind to a receptor in
order to send their signal. However, unlike neurotransmitters, which are released in close proximity to cells
with their receptors, hormones are secreted into the bloodstream and travel throughout the body, affecting any
cells that contain receptors for them. Thus, whereas neurotransmitters’ effects are localized, the effects of
hormones are widespread. Also, hormones are slower to take effect, and tend to be longer lasting.

3.5 • The Endocrine System 97

FIGURE 3.30 The major glands of the endocrine system are shown.

Hormones are involved in regulating all sorts of bodily functions, and they are ultimately controlled through
interactions between the hypothalamus (in the central nervous system) and the pituitary gland (in the
endocrine system). Imbalances in hormones are related to a number of disorders. This section explores some
of the major glands that make up the endocrine system and the hormones secreted by these glands (Table 3.2).

Major Glands

The pituitary gland descends from the hypothalamus at the base of the brain, and acts in close association
with it. The pituitary is often referred to as the “master gland” because its messenger hormones control all the
other glands in the endocrine system, although it mostly carries out instructions from the hypothalamus. In
addition to messenger hormones, the pituitary also secretes growth hormone, endorphins for pain relief, and a
number of key hormones that regulate fluid levels in the body.

Located in the neck, the thyroid gland releases hormones that regulate growth, metabolism, and appetite. In
hyperthyroidism, or Grave’s disease, the thyroid secretes too much of the hormone thyroxine, causing
agitation, bulging eyes, and weight loss. In hypothyroidism, reduced hormone levels cause sufferers to
experience tiredness, and they often complain of feeling cold. Fortunately, thyroid disorders are often treatable
with medications that help reestablish a balance in the hormones secreted by the thyroid.

The adrenal glands sit atop our kidneys and secrete hormones involved in the stress response, such as
epinephrine (adrenaline) and norepinephrine (noradrenaline). The pancreas is an internal organ that secretes
hormones that regulate blood sugar levels: insulin and glucagon. These pancreatic hormones are essential for
maintaining stable levels of blood sugar throughout the day by lowering blood glucose levels (insulin) or
raising them (glucagon). People who suffer from diabetes do not produce enough insulin; therefore, they must
take medications that stimulate or replace insulin production, and they must closely control the amount of
sugars and carbohydrates they consume.

The gonads secrete sexual hormones, which are important in reproduction, and mediate both sexual
motivation and behavior. The female gonads are the ovaries; the male gonads are the testes. Ovaries secrete
estrogens and progesterone, and the testes secrete androgens, such as testosterone.

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Major Endocrine Glands and Associated Hormone Functions

Endocrine
Gland

Associated Hormones Function

Pituitary
Growth hormone, releasing and inhibiting hormones (such as
thyroid stimulating hormone)

Regulate growth, regulate hormone
release

Thyroid Thyroxine, triiodothyronine Regulate metabolism and appetite

Pineal Melatonin
Regulate some biological rhythms
such as sleep cycles

Adrenal Epinephrine, norepinephrine
Stress response, increase metabolic
activities

Pancreas Insulin, glucagon Regulate blood sugar levels

Ovaries Estrogen, progesterone
Mediate sexual motivation and
behavior, reproduction

Testes Androgens, such as testosterone
Mediate sexual motivation and
behavior, reproduction

TABLE 3.2

Athletes and Anabolic Steroids
Although it is against Federal laws and many professional athletic associations (The National Football League, for
example) have banned their use, anabolic steroid drugs continue to be used by amateur and professional
athletes. The drugs are believed to enhance athletic performance. Anabolic steroid drugs mimic the effects of the
body’s own steroid hormones, like testosterone and its derivatives. These drugs have the potential to provide a
competitive edge by increasing muscle mass, strength, and endurance, although not all users may experience
these results. Moreover, use of performance-enhancing drugs (PEDs) does not come without risks. Anabolic
steroid use has been linked with a wide variety of potentially negative outcomes, ranging in severity from largely
cosmetic (acne) to life threatening (heart attack). Furthermore, use of these substances can result in profound
changes in mood and can increase aggressive behavior (National Institute on Drug Abuse, 2001).

Baseball player Alex Rodriguez (A-Rod) spent the latter part of his playing career at the center of a media storm
regarding his use of illegal PEDs. Rodriguez excelled while using the drugs; his success played a large role in
negotiating a contract that made him the highest paid player in professional baseball. A subsequent scandal and
suspension tarnished his reputation and, according to a statement he made once retired, cost him over $40
million. Even lower-profile athletes, particularly in cycling and Olympic sports, have been revealed as steroid
users. What are your thoughts on athletes and doping? Why or why not should the use of PEDs be banned? What
advice would you give an athlete who was considering using PEDs?

DIG DEEPER

3.5 • The Endocrine System 99

Key Terms
action potential electrical signal that moves down the neuron’s axon
adrenal gland sits atop our kidneys and secretes hormones involved in the stress response
agonist drug that mimics or strengthens the effects of a neurotransmitter
all-or-none phenomenon that incoming signal from another neuron is either sufficient or insufficient to reach

the threshold of excitation
allele specific version of a gene
amygdala structure in the limbic system involved in our experience of emotion and tying emotional meaning

to our memories
antagonist drug that blocks or impedes the normal activity of a given neurotransmitter
auditory cortex strip of cortex in the temporal lobe that is responsible for processing auditory information
autonomic nervous system controls our internal organs and glands
axon major extension of the soma
biological perspective view that psychological disorders like depression and schizophrenia are associated

with imbalances in one or more neurotransmitter systems
Broca’s area region in the left hemisphere that is essential for language production
central nervous system (CNS) brain and spinal cord
cerebellum hindbrain structure that controls our balance, coordination, movement, and motor skills, and it is

thought to be important in processing some types of memory
cerebral cortex surface of the brain that is associated with our highest mental capabilities
chromosome long strand of genetic information
computerized tomography (CT) scan imaging technique in which a computer coordinates and integrates

multiple x-rays of a given area
corpus callosum thick band of neural fibers connecting the brain’s two hemispheres
dendrite branch-like extension of the soma that receives incoming signals from other neurons
deoxyribonucleic acid (DNA) helix-shaped molecule made of nucleotide base pairs
diabetes disease related to insufficient insulin production
dominant allele allele whose phenotype will be expressed in an individual that possesses that allele
electroencephalography (EEG) recording the electrical activity of the brain via electrodes on the scalp
endocrine system series of glands that produce chemical substances known as hormones
epigenetics study of gene-environment interactions, such as how the same genotype leads to different

phenotypes
fight or flight response activation of the sympathetic division of the autonomic nervous system, allowing

access to energy reserves and heightened sensory capacity so that we might fight off a given threat or run
away to safety

forebrain largest part of the brain, containing the cerebral cortex, the thalamus, and the limbic system,
among other structures

fraternal twins twins who develop from two different eggs fertilized by different sperm, so their genetic
material varies the same as in non-twin siblings

frontal lobe part of the cerebral cortex involved in reasoning, motor control, emotion, and language; contains
motor cortex

functional magnetic resonance imaging (fMRI) MRI that shows changes in metabolic activity over time
gene sequence of DNA that controls or partially controls physical characteristics
genetic environmental correlation view of gene-environment interaction that asserts our genes affect our

environment, and our environment influences the expression of our genes
genotype genetic makeup of an individual
glial cell nervous system cell that provides physical and metabolic support to neurons, including neuronal

insulation and communication, and nutrient and waste transport
gonad secretes sexual hormones, which are important for successful reproduction, and mediate both sexual

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motivation and behavior
gyrus (plural: gyri) bump or ridge on the cerebral cortex
hemisphere left or right half of the brain
heterozygous consisting of two different alleles
hindbrain division of the brain containing the medulla, pons, and cerebellum
hippocampus structure in the temporal lobe associated with learning and memory
homeostasis state of equilibrium—biological conditions, such as body temperature, are maintained at optimal

levels
homozygous consisting of two identical alleles
hormone chemical messenger released by endocrine glands
hypothalamus forebrain structure that regulates sexual motivation and behavior and a number of

homeostatic processes; serves as an interface between the nervous system and the endocrine system
identical twins twins that develop from the same sperm and egg
lateralization concept that each hemisphere of the brain is associated with specialized functions
limbic system collection of structures involved in processing emotion and memory
longitudinal fissure deep groove in the brain’s cortex
magnetic resonance imaging (MRI) magnetic fields used to produce a picture of the tissue being imaged
medulla hindbrain structure that controls automated processes like breathing, blood pressure, and heart rate
membrane potential difference in charge across the neuronal membrane
midbrain division of the brain located between the forebrain and the hindbrain; contains the reticular

formation
motor cortex strip of cortex involved in planning and coordinating movement
mutation sudden, permanent change in a gene
myelin sheath fatty substance that insulates axons
neuron cells in the nervous system that act as interconnected information processors, which are essential for

all of the tasks of the nervous system
neuroplasticity nervous system’s ability to change
neurotransmitter chemical messenger of the nervous system
Nodes of Ranvier open spaces that are found in the myelin sheath that encases the axon
occipital lobe part of the cerebral cortex associated with visual processing; contains the primary visual cortex
pancreas secretes hormones that regulate blood sugar
parasympathetic nervous system associated with routine, day-to-day operations of the body
parietal lobe part of the cerebral cortex involved in processing various sensory and perceptual information;

contains the primary somatosensory cortex
peripheral nervous system (PNS) connects the brain and spinal cord to the muscles, organs and senses in

the periphery of the body
phenotype individual’s inheritable physical characteristics
pituitary gland secretes a number of key hormones, which regulate fluid levels in the body, and a number of

messenger hormones, which direct the activity of other glands in the endocrine system
polygenic multiple genes affecting a given trait
pons hindbrain structure that connects the brain and spinal cord; involved in regulating brain activity during

sleep
positron emission tomography (PET) scan involves injecting individuals with a mildly radioactive substance

and monitoring changes in blood flow to different regions of the brain
prefrontal cortex area in the frontal lobe responsible for higher-level cognitive functioning
psychotropic medication drugs that treat psychiatric symptoms by restoring neurotransmitter balance
range of reaction asserts our genes set the boundaries within which we can operate, and our environment

interacts with the genes to determine where in that range we will fall
receptor protein on the cell surface where neurotransmitters attach
recessive allele allele whose phenotype will be expressed only if an individual is homozygous for that allele

3 • Key Terms 101

resting potential the state of readiness of a neuron membrane’s potential between signals
reticular formation midbrain structure important in regulating the sleep/wake cycle, arousal, alertness, and

motor activity
reuptake neurotransmitter is pumped back into the neuron that released it
semipermeable membrane cell membrane that allows smaller molecules or molecules without an electrical

charge to pass through it, while stopping larger or highly charged molecules
soma cell body
somatic nervous system relays sensory and motor information to and from the CNS
somatosensory cortex essential for processing sensory information from across the body, such as touch,

temperature, and pain
substantia nigra midbrain structure where dopamine is produced; involved in control of movement
sulcus (plural: sulci) depressions or grooves in the cerebral cortex
sympathetic nervous system involved in stress-related activities and functions
synaptic cleft small gap between two neurons where communication occurs
synaptic vesicle storage site for neurotransmitters
temporal lobe part of cerebral cortex associated with hearing, memory, emotion, and some aspects of

language; contains primary auditory cortex
terminal button axon terminal containing synaptic vesicles
thalamus sensory relay for the brain
theory of evolution by natural selection states that organisms that are better suited for their environments

will survive and reproduce compared to those that are poorly suited for their environments
threshold of excitation level of charge in the membrane that causes the neuron to become active
thyroid secretes hormones that regulate growth, metabolism, and appetite
ventral tegmental area (VTA) midbrain structure where dopamine is produced: associated with mood,

reward, and addiction
Wernicke’s area important for speech comprehension

Summary
3.1 Human Genetics

Genes are sequences of DNA that code for a particular trait. Different versions of a gene are called
alleles—sometimes alleles can be classified as dominant or recessive. A dominant allele always results in the
dominant phenotype. In order to exhibit a recessive phenotype, an individual must be homozygous for the
recessive allele. Genes affect both physical and psychological characteristics. Ultimately, how and when a gene
is expressed, and what the outcome will be—in terms of both physical and psychological characteristics—is a
function of the interaction between our genes and our environments.

3.2 Cells of the Nervous System

Glia and neurons are the two cell types that make up the nervous system. While glia generally play supporting
roles, the communication between neurons is fundamental to all of the functions associated with the nervous
system. Neuronal communication is made possible by the neuron’s specialized structures. The soma contains
the cell nucleus, and the dendrites extend from the soma in tree-like branches. The axon is another major
extension of the cell body; axons are often covered by a myelin sheath, which increases the speed of
transmission of neural impulses. At the end of the axon are terminal buttons that contain synaptic vesicles
filled with neurotransmitters.

Neuronal communication is an electrochemical event. The dendrites contain receptors for neurotransmitters
released by nearby neurons. If the signals received from other neurons are sufficiently strong, an action
potential will travel down the length of the axon to the terminal buttons, resulting in the release of
neurotransmitters into the synaptic cleft. Action potentials operate on the all-or-none principle and involve

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the movement of Na+ and K+ across the neuronal membrane.

Different neurotransmitters are associated with different functions. Often, psychological disorders involve
imbalances in a given neurotransmitter system. Therefore, psychotropic drugs are prescribed in an attempt to
bring the neurotransmitters back into balance. Drugs can act either as agonists or as antagonists for a given
neurotransmitter system.

3.3 Parts of the Nervous System

The brain and spinal cord make up the central nervous system. The peripheral nervous system is comprised of
the somatic and autonomic nervous systems. The somatic nervous system transmits sensory and motor
signals to and from the central nervous system. The autonomic nervous system controls the function of our
organs and glands, and can be divided into the sympathetic and parasympathetic divisions. Sympathetic
activation prepares us for fight or flight, while parasympathetic activation is associated with normal
functioning under relaxed conditions.

3.4 The Brain and Spinal Cord

The brain consists of two hemispheres, each controlling the opposite side of the body. Each hemisphere can be
subdivided into different lobes: frontal, parietal, temporal, and occipital. In addition to the lobes of the
cerebral cortex, the forebrain includes the thalamus (sensory relay) and limbic system (emotion and memory
circuit). The midbrain contains the reticular formation, which is important for sleep and arousal, as well as the
substantia nigra and ventral tegmental area. These structures are important for movement, reward, and
addictive processes. The hindbrain contains the structures of the brainstem (medulla, pons, and midbrain),
which control automatic functions like breathing and blood pressure. The hindbrain also contains the
cerebellum, which helps coordinate movement and certain types of memories.

Individuals with brain damage have been studied extensively to provide information about the role of different
areas of the brain, and recent advances in technology allow us to glean similar information by imaging brain
structure and function. These techniques include CT, PET, MRI, fMRI, and EEG.

3.5 The Endocrine System

The glands of the endocrine system secrete hormones to regulate normal body functions. The hypothalamus
serves as the interface between the nervous system and the endocrine system, and it controls the secretions of
the pituitary. The pituitary serves as the master gland, controlling the secretions of all other glands. The
thyroid secretes thyroxine, which is important for basic metabolic processes and growth; the adrenal glands
secrete hormones involved in the stress response; the pancreas secretes hormones that regulate blood sugar
levels; and the ovaries and testes produce sex hormones that regulate sexual motivation and behavior.

Review Questions
1. A(n) ________ is a sudden, permanent change in a sequence of DNA.

a. allele
b. chromosome
c. epigenetic
d. mutation

2. ________ refers to a person’s genetic makeup, while ________ refers to a person’s physical characteristics.
a. Phenotype; genotype
b. Genotype; phenotype
c. DNA; gene
d. Gene; DNA

3 • Review Questions 103

3. ________ is the field of study that focuses on genes and their expression.
a. Social psychology
b. Evolutionary psychology
c. Epigenetics
d. Behavioral neuroscience

4. Humans have ________ pairs of chromosomes.
a. 15
b. 23
c. 46
d. 78

5. The ________ receive(s) incoming signals from other neurons.
a. soma
b. terminal buttons
c. myelin sheath
d. dendrites

6. A(n) ________ facilitates or mimics the activity of a given neurotransmitter system.
a. axon
b. SSRI
c. agonist
d. antagonist

7. Multiple sclerosis involves a breakdown of the ________.
a. soma
b. myelin sheath
c. synaptic vesicles
d. dendrites

8. An action potential involves Na+ moving ________ the cell and K+ moving ________ the cell.
a. inside; outside
b. outside; inside
c. inside; inside
d. outside; outside

9. Our ability to make our legs move as we walk across the room is controlled by the ________ nervous
system.
a. autonomic
b. somatic
c. sympathetic
d. parasympathetic

10. If your ________ is activated, you will feel relatively at ease.
a. somatic nervous system
b. sympathetic nervous system
c. parasympathetic nervous system
d. spinal cord

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11. The central nervous system is comprised of ________.
a. sympathetic and parasympathetic nervous systems
b. organs and glands
c. somatic and autonomic nervous systems
d. brain and spinal cord

12. Sympathetic activation is associated with ________.
a. pupil dilation
b. storage of glucose in the liver
c. increased heart rate
d. both A and C

13. The ________ is a sensory relay station where all sensory information, except for smell, goes before being
sent to other areas of the brain for further processing.
a. amygdala
b. hippocampus
c. hypothalamus
d. thalamus

14. Damage to the ________ disrupts one’s ability to comprehend language, but it leaves one’s ability to
produce words intact.
a. amygdala
b. Broca’s Area
c. Wernicke’s Area
d. occipital lobe

15. A(n) ________ uses magnetic fields to create pictures of a given tissue.
a. EEG
b. MRI
c. PET scan
d. CT scan

16. Which of the following is not a structure of the forebrain?
a. thalamus
b. hippocampus
c. amygdala
d. substantia nigra

17. The two major hormones secreted from the pancreas are:
a. estrogen and progesterone
b. norepinephrine and epinephrine
c. thyroxine and oxytocin
d. glucagon and insulin

18. The ________ secretes messenger hormones that direct the function of the rest of the endocrine glands.
a. ovary
b. thyroid
c. pituitary
d. pancreas

3 • Review Questions 105

19. The ________ gland secretes epinephrine.
a. adrenal
b. thyroid
c. pituitary
d. master

20. The ________ secretes hormones that regulate the body’s fluid levels.
a. adrenal
b. pituitary
c. testes
d. thyroid

Critical Thinking Questions
21. The theory of evolution by natural selection requires variability of a given trait. Why is variability

necessary and where does it come from?

22. Cocaine has two effects on synaptic transmission: it impairs reuptake of dopamine and it causes more
dopamine to be released into the synaptic cleft. Would cocaine be classified as an agonist or antagonist?
Why?

23. Drugs such as lidocaine and novocaine act as Na+ channel blockers. In other words, they prevent sodium
from moving across the neuronal membrane. Why would this particular effect make these drugs such
effective local anesthetics?

24. What are the implications of compromised immune function as a result of exposure to chronic stress?

25. Examine Figure 3.14, illustrating the effects of sympathetic nervous system activation. How would all of
these things play into the fight or flight response?

26. Before the advent of modern imaging techniques, scientists and clinicians relied on autopsies of people
who suffered brain injury with resultant change in behavior to determine how different areas of the brain
were affected. What are some of the limitations associated with this kind of approach?

27. Which of the techniques discussed would be viable options for you to determine how activity in the
reticular formation is related to sleep and wakefulness? Why?

28. Hormone secretion is often regulated through a negative feedback mechanism, which means that once a
hormone is secreted it will cause the hypothalamus and pituitary to shut down the production of signals
necessary to secrete the hormone in the first place. Most oral contraceptives are made of small doses of
estrogen and/or progesterone. Why would this be an effective means of contraception?

29. Chemical messengers are used in both the nervous system and the endocrine system. What properties do
these two systems share? What properties are different? Which one would be faster? Which one would
result in long-lasting changes?

Personal Application Questions
30. You share half of your genetic makeup with each of your parents, but you are no doubt very different from

both of them. Spend a few minutes jotting down the similarities and differences between you and your
parents. How do you think your unique environment and experiences have contributed to some of the
differences you see?

31. Have you or someone you know ever been prescribed a psychotropic medication? If so, what side effects
were associated with the treatment?

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32. Hopefully, you do not face real physical threats from potential predators on a daily basis. However, you
probably have your fair share of stress. What situations are your most common sources of stress? What
can you do to try to minimize the negative consequences of these particular stressors in your life?

33. You read about H. M.’s memory deficits following the bilateral removal of his hippocampus and amygdala.
Have you encountered a character in a book, television program, or movie that suffered memory deficits?
How was that character similar to and different from H. M.?

34. Given the negative health consequences associated with the use of anabolic steroids, what kinds of
considerations might be involved in a person’s decision to use them?

3 • Personal Application Questions 107

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FIGURE 4.1 Sleep, which we all experience, is a quiet and mysterious pause in our daily lives. Two sleeping children
are depicted in this 1895 oil painting titled Zwei schlafende Mädchen auf der Ofenbank, which translates as “two
sleeping girls on the stove,” by Swiss painter Albert Anker.

INTRODUCTION

CHAPTER OUTLINE
4.1 What Is Consciousness?
4.2 Sleep and Why We Sleep
4.3 Stages of Sleep
4.4 Sleep Problems and Disorders
4.5 Substance Use and Abuse
4.6 Other States of Consciousness

Our lives involve regular, dramatic changes in the degree to which we are aware of our
surroundings and our internal states. While awake, we feel alert and aware of the many important things going
on around us. Our experiences change dramatically while we are in deep sleep and once again when we are
dreaming. Some people also experience altered states of consciousness through meditation, hypnosis, or
alcohol and other drugs.

This chapter will discuss states of consciousness with a particular emphasis on sleep. The different stages of
sleep will be identified, and sleep disorders will be described. The chapter will close with discussions of altered
states of consciousness produced by psychoactive drugs, hypnosis, and meditation.

4States of Consciousness

4.1 What Is Consciousness?
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Understand what is meant by consciousness
• Explain how circadian rhythms are involved in regulating the sleep-wake cycle, and how circadian cycles can be

disrupted
• Discuss the concept of sleep debt

Consciousness describes our awareness of internal and external stimuli. Awareness of internal stimuli
includes feeling pain, hunger, thirst, sleepiness, and being aware of our thoughts and emotions. Awareness of
external stimuli includes experiences such as seeing the light from the sun, feeling the warmth of a room, and
hearing the voice of a friend.

We experience different states of consciousness and different levels of awareness on a regular basis. We might
even describe consciousness as a continuum that ranges from full awareness to a deep sleep. Sleep is a state
marked by relatively low levels of physical activity and reduced sensory awareness that is distinct from periods
of rest that occur during wakefulness. Wakefulness is characterized by high levels of sensory awareness,
thought, and behavior. Beyond being awake or asleep, there are many other states of consciousness people
experience. These include daydreaming, intoxication, and unconsciousness due to anesthesia. We might also
experience unconscious states of being via drug-induced anesthesia for medical purposes. Often, we are not
completely aware of our surroundings, even when we are fully awake. For instance, have you ever daydreamed
while driving home from work or school without really thinking about the drive itself? You were capable of
engaging in the all of the complex tasks involved with operating a motor vehicle even though you were not
aware of doing so. Many of these processes, like much of psychological behavior, are rooted in our biology.

Biological Rhythms

Biological rhythms are internal rhythms of biological activity. A woman’s menstrual cycle is an example of a
biological rhythm—a recurring, cyclical pattern of bodily changes. One complete menstrual cycle takes about
28 days—a lunar month—but many biological cycles are much shorter. For example, body temperature
fluctuates cyclically over a 24-hour period (Figure 4.2). Alertness is associated with higher body temperatures,
and sleepiness with lower body temperatures.

FIGURE 4.2 This chart illustrates the circadian change in body temperature over 28 hours in a group of eight young
men. Body temperature rises throughout the waking day, peaking in the afternoon, and falls during sleep with the
lowest point occurring during the very early morning hours.

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This pattern of temperature fluctuation, which repeats every day, is one example of a circadian rhythm. A
circadian rhythm is a biological rhythm that takes place over a period of about 24 hours. Our sleep-wake
cycle, which is linked to our environment’s natural light-dark cycle, is perhaps the most obvious example of a
circadian rhythm, but we also have daily fluctuations in heart rate, blood pressure, blood sugar, and body
temperature. Some circadian rhythms play a role in changes in our state of consciousness.

If we have biological rhythms, then is there some sort of biological clock? In the brain, the hypothalamus,
which lies above the pituitary gland, is a main center of homeostasis. Homeostasis is the tendency to maintain
a balance, or optimal level, within a biological system.

The brain’s clock mechanism is located in an area of the hypothalamus known as the suprachiasmatic
nucleus (SCN). The axons of light-sensitive neurons in the retina provide information to the SCN based on the
amount of light present, allowing this internal clock to be synchronized with the outside world (Klein, Moore, &
Reppert, 1991; Welsh, Takahashi, & Kay, 2010) (Figure 4.3).

FIGURE 4.3 The suprachiasmatic nucleus (SCN) serves as the brain’s clock mechanism. The clock sets itself with
light information received through projections from the retina.

Problems With Circadian Rhythms

Generally, and for most people, our circadian cycles are aligned with the outside world. For example, most
people sleep during the night and are awake during the day. One important regulator of sleep-wake cycles is
the hormone melatonin. The pineal gland, an endocrine structure located inside the brain that releases
melatonin, is thought to be involved in the regulation of various biological rhythms and of the immune system
during sleep (Hardeland, Pandi-Perumal, & Cardinali, 2006). Melatonin release is stimulated by darkness and
inhibited by light.

There are individual differences in regard to our sleep-wake cycle. For instance, some people would say they
are morning people, while others would consider themselves to be night owls. These individual differences in
circadian patterns of activity are known as a person’s chronotype, and research demonstrates that morning
larks and night owls differ with regard to sleep regulation (Taillard, Philip, Coste, Sagaspe, & Bioulac, 2003).
Sleep regulation refers to the brain’s control of switching between sleep and wakefulness as well as
coordinating this cycle with the outside world.

LINK TO LEARNING

Watch this brief video about circadian rhythms and how they affect sleep (http://openstax.org/l/circadian) to
learn more.

4.1 • What Is Consciousness? 111

Disruptions of Normal Sleep

Whether lark, owl, or somewhere in between, there are situations in which a person’s circadian clock gets out
of synchrony with the external environment. One way that this happens involves traveling across multiple time
zones. When we do this, we often experience jet lag. Jet lag is a collection of symptoms that results from the
mismatch between our internal circadian cycles and our environment. These symptoms include fatigue,
sluggishness, irritability, and insomnia (i.e., a consistent difficulty in falling or staying asleep for at least three
nights a week over a month’s time) (Roth, 2007).

Individuals who do rotating shift work are also likely to experience disruptions in circadian cycles. Rotating
shift work refers to a work schedule that changes from early to late on a daily or weekly basis. For example, a
person may work from 7:00 a.m. to 3:00 p.m. on Monday, 3:00 a.m. to 11:00 a.m. on Tuesday, and 11:00 a.m. to
7:00 p.m. on Wednesday. In such instances, the individual’s schedule changes so frequently that it becomes
difficult for a normal circadian rhythm to be maintained. This often results in sleeping problems, and it can
lead to signs of depression and anxiety. These kinds of schedules are common for individuals working in
health care professions and service industries, and they are associated with persistent feelings of exhaustion
and agitation that can make someone more prone to making mistakes on the job (Gold et al., 1992; Presser,
1995).

Rotating shift work has pervasive effects on the lives and experiences of individuals engaged in that kind of
work, which is clearly illustrated in stories reported in a qualitative study that researched the experiences of
middle-aged nurses who worked rotating shifts (West, Boughton & Byrnes, 2009). Several of the nurses
interviewed commented that their work schedules affected their relationships with their family. One of the
nurses said,

If you’ve had a partner who does work regular job 9 to 5 office hours . . . the ability to spend time, good
time with them when you’re not feeling absolutely exhausted . . . that would be one of the problems
that I’ve encountered. (West et al., 2009, p. 114)

While disruptions in circadian rhythms can have negative consequences, there are things we can do to help us
realign our biological clocks with the external environment. Some of these approaches, such as using a bright
light as shown in Figure 4.4, have been shown to alleviate some of the problems experienced by individuals
suffering from jet lag or from the consequences of rotating shift work. Because the biological clock is driven by
light, exposure to bright light during working shifts and dark exposure when not working can help combat
insomnia and symptoms of anxiety and depression (Huang, Tsai, Chen, & Hsu, 2013).

FIGURE 4.4 Devices like this are designed to provide exposure to bright light to help people maintain a regular
circadian cycle. They can be helpful for people working night shifts or for people affected by seasonal variations in
light.

LINK TO LEARNING

Watch this video about overcoming jet lag (http://openstax.org/l/jetlag) to learn some tips.

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Insufficient Sleep

When people have difficulty getting sleep due to their work or the demands of day-to-day life, they accumulate
a sleep debt. A person with a sleep debt does not get sufficient sleep on a chronic basis. The consequences of
sleep debt include decreased levels of alertness and mental efficiency. Interestingly, since the advent of
electric light, the amount of sleep that people get has declined. While we certainly welcome the convenience of
having the darkness lit up, we also suffer the consequences of reduced amounts of sleep because we are more
active during the nighttime hours than our ancestors were. As a result, many of us sleep less than 7–8 hours a
night and accrue a sleep debt. While there is tremendous variation in any given individual’s sleep needs, the
National Sleep Foundation (n.d.) cites research to estimate that newborns require the most sleep (between 12
and 18 hours a night) and that this amount declines to just 7–9 hours by the time we are adults.

If you lie down to take a nap and fall asleep very easily, chances are you may have sleep debt. Given that college
students are notorious for suffering from significant sleep debt (Hicks, Fernandez, & Pellegrini, 2001; Hicks,
Johnson, & Pellegrini, 1992; Miller, Shattuck, & Matsangas, 2010), chances are you and your classmates deal
with sleep debt-related issues on a regular basis. In 2015, the National Sleep Foundation updated their sleep
duration hours, to better accommodate individual differences. Table 4.1 shows the new recommendations,
which describe sleep durations that are “recommended”, “may be appropriate”, and “not recommended”.

Sleep Needs at Different Ages

Age Recommended May be appropriate Not recommended

0–3 months 14–17 hours
11–13 hours
18–19 hours

Fewer than 11 hours
More than 19 hours

4–11 months 12–15 hours
10–11 hours
16–18 hours

Fewer than 10 hours
More than 18 hours

1–2 years 11–14 hours
9–10 hours
15–16 hours

Fewer than 9 hours
More than 16 hours

3–5 years 10–13 hours
8–9 hours
14 hours

Fewer than 8 hours
More than 14 hours

6–13 years 9–11 hours
7–8 hours
12 hours

Fewer than 7 hours
More than 12 hours

14–17 years 8–10 hours
7 hours
11 hours

Fewer than 7 hours
More than 11 hours

18–25 years 7–9 hours
6 hours
10–11 hours

Fewer than 6 hours
More than 11 hours

26–64 years 7–9 hours
6 hours
10 hours

Fewer than 6 hours
More than 10 hours

≥65 years 7–8 hours
5–6 hours
9 hours

Fewer than 5 hours
More than 9 hours

TABLE 4.1

Sleep debt and sleep deprivation have significant negative psychological and physiological consequences
Figure 4.5. As mentioned earlier, lack of sleep can result in decreased mental alertness and cognitive function.

4.1 • What Is Consciousness? 113

In addition, sleep deprivation often results in depression-like symptoms. These effects can occur as a function
of accumulated sleep debt or in response to more acute periods of sleep deprivation. It may surprise you to
know that sleep deprivation is associated with obesity, increased blood pressure, increased levels of stress
hormones, and reduced immune functioning (Banks & Dinges, 2007). A sleep deprived individual generally
will fall asleep more quickly than if they were not sleep deprived. Some sleep-deprived individuals have
difficulty staying awake when they stop moving (example sitting and watching television or driving a car). That
is why individuals suffering from sleep deprivation can also put themselves and others at risk when they put
themselves behind the wheel of a car or work with dangerous machinery. Some research suggests that sleep
deprivation affects cognitive and motor function as much as, if not more than, alcohol intoxication (Williamson
& Feyer, 2000). Research shows that the most severe effects of sleep deprivation occur when a person stays
awake for more than 24 hours (Killgore & Weber, 2014; Killgore et al., 2007), or following repeated nights with
fewer than four hours in bed (Wickens, Hutchins, Lauk, Seebook, 2015). For example, irritability, distractibility,
and impairments in cognitive and moral judgment can occur with fewer than four hours of sleep. If someone
stays awake for 48 consecutive hours, they could start to hallucinate.

FIGURE 4.5 This figure illustrates some of the negative consequences of sleep deprivation. While cognitive deficits
may be the most obvious, many body systems are negatively impacted by lack of sleep. (credit: modification of work
by Mikael Häggström)

LINK TO LEARNING

Read this article about sleep needs (http://openstax.org/l/sleephabits) to assess your own sleeping habits.

The amount of sleep we get varies across the lifespan. When we are very young, we spend up to 16 hours a day
sleeping. As we grow older, we sleep less. In fact, a meta-analysis, which is a study that combines the results of
many related studies, conducted within the last decade indicates that by the time we are 65 years old, we
average fewer than 7 hours of sleep per day (Ohayon, Carskadon, Guilleminault, & Vitiello, 2004).

4.2 Sleep and Why We Sleep
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe areas of the brain involved in sleep
• Understand hormone secretions associated with sleep
• Describe several theories aimed at explaining the function of sleep
• Name and describe three theories about why we dream

We spend approximately one-third of our lives sleeping. Given the average life expectancy for U.S. citizens falls

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between 73 and 79 years old (Singh & Siahpush, 2006), we can expect to spend approximately 25 years of our
lives sleeping. Some animals never sleep (e.g., some fish and amphibian species); other animals sleep very
little without apparent negative consequences (e.g., giraffes); yet some animals (e.g., rats) die after two weeks
of sleep deprivation (Siegel, 2008). Why do we devote so much time to sleeping? Is it absolutely essential that
we sleep? This section will consider these questions and explore various explanations for why we sleep.

What is Sleep?

You have read that sleep is distinguished by low levels of physical activity and reduced sensory awareness. As
discussed by Siegel (2008), a definition of sleep must also include mention of the interplay of the circadian and
homeostatic mechanisms that regulate sleep. Homeostatic regulation of sleep is evidenced by sleep rebound
following sleep deprivation. Sleep rebound refers to the fact that a sleep-deprived individual will fall asleep
more quickly during subsequent opportunities for sleep. Sleep is characterized by certain patterns of activity
of the brain that can be visualized using electroencephalography (EEG), and different phases of sleep can be
differentiated using EEG as well.

Sleep-wake cycles seem to be controlled by multiple brain areas acting in conjunction with one another. Some
of these areas include the thalamus, the hypothalamus, and the pons. As already mentioned, the
hypothalamus contains the SCN—the biological clock of the body—in addition to other nuclei that, in
conjunction with the thalamus, regulate slow-wave sleep. The pons is important for regulating rapid eye
movement (REM) sleep (National Institutes of Health, n.d.).

Sleep is also associated with the secretion and regulation of a number of hormones from several endocrine
glands including: melatonin, follicle stimulating hormone (FSH), luteinizing hormone (LH), and growth
hormone (National Institutes of Health, n.d.). You have read that the pineal gland releases melatonin during
sleep (Figure 4.6). Melatonin is thought to be involved in the regulation of various biological rhythms and the
immune system (Hardeland et al., 2006). During sleep, the pituitary gland secretes both FSH and LH which are
important in regulating the reproductive system (Christensen et al., 2012; Sofikitis et al., 2008). The pituitary
gland also secretes growth hormone, during sleep, which plays a role in physical growth and maturation as
well as other metabolic processes (Bartke, Sun, & Longo, 2013).

FIGURE 4.6 The pineal and pituitary glands secrete a number of hormones during sleep.

Why Do We Sleep?

Given the central role that sleep plays in our lives and the number of adverse consequences that have been
associated with sleep deprivation, one would think that we would have a clear understanding of why it is that
we sleep. Unfortunately, this is not the case; however, several hypotheses have been proposed to explain the
function of sleep.

4.2 • Sleep and Why We Sleep 115

Adaptive Function of Sleep

One popular hypothesis of sleep incorporates the perspective of evolutionary psychology. Evolutionary
psychology is a discipline that studies how universal patterns of behavior and cognitive processes have
evolved over time as a result of natural selection. Variations and adaptations in cognition and behavior make
individuals more or less successful in reproducing and passing their genes to their offspring. One hypothesis
from this perspective might argue that sleep is essential to restore resources that are expended during the day.
Just as bears hibernate in the winter when resources are scarce, perhaps people sleep at night to reduce their
energy expenditures. While this is an intuitive explanation of sleep, there is little research that supports this
explanation. In fact, it has been suggested that there is no reason to think that energetic demands could not be
addressed with periods of rest and inactivity (Frank, 2006; Rial et al., 2007), and some research has actually
found a negative correlation between energetic demands and the amount of time spent sleeping (Capellini,
Barton, McNamara, Preston, & Nunn, 2008).

Another evolutionary hypothesis of sleep holds that our sleep patterns evolved as an adaptive response to
predatory risks, which increase in darkness. Thus we sleep in safe areas to reduce the chance of harm. Again,
this is an intuitive and appealing explanation for why we sleep. Perhaps our ancestors spent extended periods
of time asleep to reduce attention to themselves from potential predators. Comparative research indicates,
however, that the relationship that exists between predatory risk and sleep is very complex and equivocal.
Some research suggests that species that face higher predatory risks sleep fewer hours than other species
(Capellini et al., 2008), while other researchers suggest there is no relationship between the amount of time a
given species spends in deep sleep and its predation risk (Lesku, Roth, Amlaner, & Lima, 2006).

It is quite possible that sleep serves no single universally adaptive function, and different species have evolved
different patterns of sleep in response to their unique evolutionary pressures. While we have discussed the
negative outcomes associated with sleep deprivation, it should be pointed out that there are many benefits that
are associated with adequate amounts of sleep. A few such benefits listed by the National Sleep Foundation
(n.d.) include maintaining healthy weight, lowering stress levels, improving mood, and increasing motor
coordination, as well as a number of benefits related to cognition and memory formation.

Cognitive Function of Sleep

Another theory regarding why we sleep involves sleep’s importance for cognitive function and memory
formation (Rattenborg, Lesku, Martinez-Gonzalez, & Lima, 2007). Indeed, we know sleep deprivation results in
disruptions in cognition and memory deficits (Brown, 2012), leading to impairments in our abilities to
maintain attention, make decisions, and recall long-term memories. Moreover, these impairments become
more severe as the amount of sleep deprivation increases (Alhola & Polo-Kantola, 2007). Furthermore, slow-
wave sleep after learning a new task can improve resultant performance on that task (Huber, Ghilardi,
Massimini, & Tononi, 2004) and seems essential for effective memory formation (Stickgold, 2005).
Understanding the impact of sleep on cognitive function should help you understand that cramming all night
for a test may be not effective and can even prove counterproductive.

LINK TO LEARNING

Watch this brief video that gives sleep tips for college students (http://openstax.org/l/sleeptips) to learn more.

Getting the optimal amount of sleep has also been associated with other cognitive benefits. Research indicates
that included among these possible benefits are increased capacities for creative thinking (Cai, Mednick,
Harrison, Kanady, & Mednick, 2009; Wagner, Gais, Haider, Verleger, & Born, 2004), language learning (Fenn,
Nusbaum, & Margoliash, 2003; Gómez, Bootzin, & Nadel, 2006), and inferential judgments (Ellenbogen, Hu,
Payne, Titone, & Walker, 2007). It is possible that even the processing of emotional information is influenced by
certain aspects of sleep (Walker, 2009).

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LINK TO LEARNING

Watch this brief video about the relationship between sleep and memory (http://openstax.org/l/sleepmemory)
to learn more.

4.3 Stages of Sleep
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Differentiate between REM and non-REM sleep
• Describe the differences between the three stages of non-REM sleep
• Understand the role that REM and non-REM sleep play in learning and memory

Sleep is not a uniform state of being. Instead, sleep is composed of several different stages that can be
differentiated from one another by the patterns of brain wave activity that occur during each stage. While
awake, our brain wave activity is dominated by beta waves. As compared to the brain wave patterns while
asleep, beta waves have the highest frequency (13–30 Hz) and lowest amplitude, and they tend to show more
variability. As we begin to fall asleep, our brain wave activity changes. These changes can be visualized using
an EEG and are distinguished from one another by both the frequency and amplitude of the brain wave. The
frequency of a brain wave is how many brain waves occur in a second, and frequency is measured in Hertz
(Hz). Amplitude is the height of the brain wave (Figure 4.7). Sleep can be divided into two different general
phases: REM sleep and non-REM (NREM) sleep. Rapid eye movement (REM) sleep is characterized by darting
movements of the eyes under closed eyelids. Brain waves during REM sleep appear very similar to brain waves
during wakefulness. In contrast, non-REM (NREM) sleep is subdivided into three stages distinguished from
each other and from wakefulness by characteristic patterns of brain waves. The first three stages of sleep are
NREM sleep, typically followed by REM sleep. In this section, we will discuss each of these stages of sleep and
their associated patterns of brain wave activity.

FIGURE 4.7 Brainwave activity changes dramatically across the different stages of sleep. (credit “sleeping”:
modification of work by Ryan Vaarsi)

NREM Stages of Sleep

As we begin to fall asleep, we enter NREM sleep, and brain wave patterns decrease in frequency and increase
in amplitude. The first stage of NREM sleep is known as stage 1 sleep. Stage 1 sleep is a transitional phase that
occurs between wakefulness and sleep, the period during which we drift off to sleep. During this time, there is
a slowdown in both the rates of respiration and heartbeat. In addition, stage 1 sleep involves a marked

4.3 • Stages of Sleep 117

decrease in both overall muscle tension and core body temperature.

In terms of brain wave activity, stage 1 sleep is associated with both alpha and theta waves. The early portion of
stage 1 sleep produces alpha waves. These patterns of electrical activity (waves) resemble that of someone
who is very relaxed, yet awake, but they have less variability (are more synchronized) and are relatively lower
in frequency (8–12 Hz) and higher in amplitude than beta waves (Figure 4.8). As an individual continues
through stage 1 sleep, there is an increase in theta wave activity. Theta waves are even lower frequency (4–7
Hz), and higher in amplitude, than the alpha wave patterns. It is relatively easy to wake someone from stage 1
sleep; in fact, people often report that they have not been asleep if they are awoken during stage 1 sleep.

FIGURE 4.8 Brainwave activity changes dramatically across the different stages of sleep.

As we move into stage 2 sleep, the body goes into a state of deep relaxation. Theta waves still dominate the
activity of the brain, but they are interrupted by brief bursts of activity known as sleep spindles (Figure 4.9). A
sleep spindle is a rapid burst of higher frequency brain waves that may be important for learning and memory
(Fogel & Smith, 2011; Poe, Walsh, & Bjorness, 2010). In addition, the appearance of K-complexes is often
associated with stage 2 sleep. A K-complex is a very high amplitude pattern of brain activity that may in some
cases occur in response to environmental stimuli. Thus, K-complexes might serve as a bridge to higher levels
of arousal in response to what is going on in our environments (Halász, 1993; Steriade & Amzica, 1998).

FIGURE 4.9 Stage 2 sleep is characterized by the appearance of both sleep spindles and K-complexes.

NREM stage 3 sleep is often referred to as deep sleep or slow-wave sleep because this stage is characterized by
low frequency (less than 3 Hz), high amplitude delta waves (Figure 4.10). These delta waves have the lowest
frequency and highest amplitude of our sleeping brain wave patterns. During this time, an individual’s heart
rate and respiration slow dramatically, and it is much more difficult to awaken someone from sleep during

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stage 3 than during earlier stages. Interestingly, individuals who have increased levels of alpha brain wave
activity (more often associated with wakefulness and transition into stage 1 sleep) during stage 3 often report
that they do not feel refreshed upon waking, regardless of how long they slept (Stone, Taylor, McCrae, Kalsekar,
& Lichstein, 2008).

FIGURE 4.10 (a) Delta waves, which are low frequency and high amplitude, characterize (b) slow-wave stage 3 and
REM sleep.

REM Sleep

As mentioned earlier, REM sleep is marked by rapid movements of the eyes. The brain waves associated with
this stage of sleep are very similar to those observed when a person is awake, as shown in Figure 4.11, and this
is the period of sleep in which dreaming occurs. It is also associated with paralysis of muscle systems in the
body with the exception of those that make circulation and respiration possible. Therefore, no movement of
voluntary muscles occurs during REM sleep in a normal individual; REM sleep is often referred to as
paradoxical sleep because of this combination of high brain activity and lack of muscle tone. Like NREM sleep,
REM has been implicated in various aspects of learning and memory (Wagner, Gais, & Born, 2001; Siegel,
2001).

FIGURE 4.11 (a) A period of rapid eye movement is marked by the short red line segment. The brain waves
associated with REM sleep, outlined in the red box in (a), look very similar to those seen (b) during wakefulness.

If people are deprived of REM sleep and then allowed to sleep without disturbance, they will spend more time
in REM sleep in what would appear to be an effort to recoup the lost time in REM. This is known as the REM
rebound, and it suggests that REM sleep is also homeostatically regulated. Aside from the role that REM sleep
may play in processes related to learning and memory, REM sleep may also be involved in emotional

4.3 • Stages of Sleep 119

processing and regulation. In such instances, REM rebound may actually represent an adaptive response to
stress in nondepressed individuals by suppressing the emotional salience of aversive events that occurred in
wakefulness (Suchecki, Tiba, & Machado, 2012). Sleep deprivation in general is associated with a number of
negative consequences (Brown, 2012).

The hypnogram below (Figure 4.12) shows a person’s passage through the stages of sleep.

FIGURE 4.12 A hypnogram is a diagram of the stages of sleep as they occur during a period of sleep. This
hypnogram illustrates how an individual moves through the various stages of sleep.

LINK TO LEARNING

View this video about sleep stages (http://openstax.org/l/sleepstages) to learn more.

Dreams

Dreams and their associated meanings vary across different cultures and periods of time. By the late 19th
century, Austrian psychiatrist Sigmund Freud had become convinced that dreams represented an opportunity
to gain access to the unconscious. By analyzing dreams, Freud thought people could increase self-awareness
and gain valuable insight to help them deal with the problems they faced in their lives. Freud made
distinctions between the manifest content and the latent content of dreams. Manifest content is the actual
content, or storyline, of a dream. Latent content, on the other hand, refers to the hidden meaning of a dream.
For instance, if a woman dreams about being chased by a snake, Freud might have argued that this represents
the woman’s fear of sexual intimacy, with the snake serving as a symbol of a man’s penis.

Freud was not the only theorist to focus on the content of dreams. The 20th century Swiss psychiatrist Carl
Jung believed that dreams allowed us to tap into the collective unconscious. The collective unconscious, as
described by Jung, is a theoretical repository of information he believed to be shared by everyone. According
to Jung, certain symbols in dreams reflected universal archetypes with meanings that are similar for all people
regardless of culture or location.

The sleep and dreaming researcher Rosalind Cartwright, however, believes that dreams simply reflect life
events that are important to the dreamer. Unlike Freud and Jung, Cartwright’s ideas about dreaming have
found empirical support. For example, she and her colleagues published a study in which women going
through divorce were asked several times over a five month period to report the degree to which their former
spouses were on their minds. These same women were awakened during REM sleep in order to provide a
detailed account of their dream content. There was a significant positive correlation between the degree to
which women thought about their former spouses during waking hours and the number of times their former
spouses appeared as characters in their dreams (Cartwright, Agargun, Kirkby, & Friedman, 2006). Recent
research (Horikawa, Tamaki, Miyawaki, & Kamitani, 2013) has uncovered new techniques by which

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researchers may effectively detect and classify the visual images that occur during dreaming by using fMRI for
neural measurement of brain activity patterns, opening the way for additional research in this area.

Alan Hobson, a neuroscientist, is credited for developing activation-synthesis theory of dreaming. Early
versions of this theory proposed that dreams were not the meaning-filled representations of angst proposed by
Freud and others, but were rather the result of our brain attempting to make sense of (“synthesize”) the neural
activity (“activation”) that was happening during REM sleep. Recent adaptations (e.g., Hobson, 2002) continue
to update the theory based on accumulating evidence. For example, Hobson (2009) suggests that dreaming
may represent a state of protoconsciousness. In other words, dreaming involves constructing a virtual reality
in our heads that we might use to help us during wakefulness. Among a variety of neurobiological evidence,
John Hobson cites research on lucid dreams as an opportunity to better understand dreaming in general.
Lucid dreams are dreams in which certain aspects of wakefulness are maintained during a dream state. In a
lucid dream, a person becomes aware of the fact that they are dreaming, and as such, they can control the
dream’s content (LaBerge, 1990).

4.4 Sleep Problems and Disorders
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the symptoms and treatments of insomnia
• Recognize the symptoms of several parasomnias
• Describe the symptoms and treatments for sleep apnea
• Recognize risk factors associated with sudden infant death syndrome (SIDS) and steps to prevent it
• Describe the symptoms and treatments for narcolepsy

Many people experience disturbances in their sleep at some point in their lives. Depending on the population
and sleep disorder being studied, between 30% and 50% of the population suffers from a sleep disorder at
some point in their lives (Bixler, Kales, Soldatos, Kaels, & Healey, 1979; Hossain & Shapiro, 2002; Ohayon,
1997, 2002; Ohayon & Roth, 2002). This section will describe several sleep disorders as well as some of their
treatment options.

Insomnia

Insomnia, a consistent difficulty in falling or staying asleep, is the most common of the sleep disorders.
Individuals with insomnia often experience long delays between the times that they go to bed and actually fall
asleep. In addition, these individuals may wake up several times during the night only to find that they have
difficulty getting back to sleep. As mentioned earlier, one of the criteria for insomnia involves experiencing
these symptoms for at least three nights a week for at least one month’s time (Roth, 2007).

It is not uncommon for people suffering from insomnia to experience increased levels of anxiety about their
inability to fall asleep. This becomes a self-perpetuating cycle because increased anxiety leads to increased
arousal, and higher levels of arousal make the prospect of falling asleep even more unlikely. Chronic insomnia
is almost always associated with feeling overtired and may be associated with symptoms of depression.

There may be many factors that contribute to insomnia, including age, drug use, exercise, mental status, and
bedtime routines. Not surprisingly, insomnia treatment may take one of several different approaches. People
who suffer from insomnia might limit their use of stimulant drugs (such as caffeine) or increase their amount
of physical exercise during the day. Some people might turn to over-the-counter (OTC) or prescribed sleep
medications to help them sleep, but this should be done sparingly because many sleep medications result in
dependence and alter the nature of the sleep cycle, and they can increase insomnia over time. Those who
continue to have insomnia, particularly if it affects their quality of life, should seek professional treatment.

Some forms of psychotherapy, such as cognitive-behavioral therapy, can help sufferers of insomnia.
Cognitive-behavioral therapy is a type of psychotherapy that focuses on cognitive processes and problem

4.4 • Sleep Problems and Disorders 121

behaviors. The treatment of insomnia likely would include stress management techniques and changes in
problematic behaviors that could contribute to insomnia (e.g., spending more waking time in bed). Cognitive-
behavioral therapy has been demonstrated to be quite effective in treating insomnia (Savard, Simard, Ivers, &
Morin, 2005; Williams, Roth, Vatthauer, & McCrae, 2013).

Solutions to Support Healthy Sleep
Has something like this ever happened to you? My sophomore college housemate got so stressed out during
finals sophomore year he drank almost a whole bottle of Nyquil to try to fall asleep. When he told me, I made him
go see the college therapist.

Many college students struggle getting the recommended 7–9 hours of sleep each night. However, for some, it’s
not because of all-night partying or late-night study sessions. It’s simply that they feel so overwhelmed and
stressed that they cannot fall asleep or stay asleep. One or two nights of sleep difficulty is not unusual, but if you
experience anything more than that, you should seek a doctor’s advice.

Here are some tips to maintain healthy sleep:

• Stick to a sleep schedule, even on the weekends. Try going to bed and waking up at the same time every day
to keep your biological clock in sync so your body gets in the habit of sleeping every night.

• Avoid anything stimulating for an hour before bed. That includes exercise and bright light from devices.
• Exercise daily.
• Avoid naps.
• Keep your bedroom temperature between 60 and 67 degrees. People sleep better in cooler temperatures.
• Avoid alcohol, cigarettes, caffeine, and heavy meals before bed. It may feel like alcohol helps you sleep, but

it actually disrupts REM sleep and leads to frequent awakenings. Heavy meals may make you sleepy, but
they can also lead to frequent awakenings due to gastric distress.

• If you cannot fall asleep, leave your bed and do something else until you feel tired again. Train your body to
associate the bed with sleeping rather than other activities like studying, eating, or watching television
shows.

Parasomnias

A parasomnia is one of a group of sleep disorders in which unwanted, disruptive motor activity and/or
experiences during sleep play a role. Parasomnias can occur in either REM or NREM phases of sleep.
Sleepwalking, restless leg syndrome, and night terrors are all examples of parasomnias (Mahowald & Schenck,
2000).

Sleepwalking

In sleepwalking, or somnambulism, the sleeper engages in relatively complex behaviors ranging from
wandering about to driving an automobile. During periods of sleepwalking, sleepers often have their eyes
open, but they are not responsive to attempts to communicate with them. Sleepwalking most often occurs
during slow-wave sleep, but it can occur at any time during a sleep period in some affected individuals
(Mahowald & Schenck, 2000).

Historically, somnambulism has been treated with a variety of pharmacotherapies ranging from
benzodiazepines to antidepressants. However, the success rate of such treatments is questionable.
Guilleminault et al. (2005) found that sleepwalking was not alleviated with the use of benzodiazepines.
However, all of their somnambulistic patients who also suffered from sleep-related breathing problems
showed a marked decrease in sleepwalking when their breathing problems were effectively treated.

EVERYDAY CONNECTION

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A Sleepwalking Defense?
On January 16, 1997, Scott Falater sat down to dinner with his wife and children and told them about difficulties
he was experiencing on a project at work. After dinner, he prepared some materials to use in leading a church
youth group the following morning, and then he attempted to repair the family’s swimming pool pump before
retiring to bed. The following morning, he awoke to barking dogs and unfamiliar voices from downstairs. As he
went to investigate what was going on, he was met by a group of police officers who arrested him for the murder
of his wife (Cartwright, 2004; CNN, 1999).

Yarmila Falater’s body was found in the family’s pool with 44 stab wounds. A neighbor called the police after
witnessing Falater standing over his wife’s body before dragging her into the pool. Upon a search of the premises,
police found blood-stained clothes and a bloody knife in the trunk of Falater’s car, and he had blood stains on his
neck.

Remarkably, Falater insisted that he had no recollection of hurting his wife in any way. His children and his wife’s
parents all agreed that Falater had an excellent relationship with his wife and they couldn’t think of a reason that
would provide any sort of motive to murder her (Cartwright, 2004).

Scott Falater had a history of regular episodes of sleepwalking as a child, and he had even behaved violently
toward his sister once when she tried to prevent him from leaving their home in his pajamas during a
sleepwalking episode. He suffered from no apparent anatomical brain anomalies or psychological disorders. It
appeared that Scott Falater had killed his wife in his sleep, or at least, that is the defense he used when he was
tried for his wife’s murder (Cartwright, 2004; CNN, 1999). In Falater’s case, a jury found him guilty of first degree
murder in June of 1999 (CNN, 1999); however, there are other murder cases where the sleepwalking defense
has been used successfully. As scary as it sounds, many sleep researchers believe that homicidal sleepwalking is
possible in individuals suffering from the types of sleep disorders described below (Broughton et al., 1994;
Cartwright, 2004; Mahowald, Schenck, & Cramer Bornemann, 2005; Pressman, 2007).

REM Sleep Behavior Disorder (RBD)

REM sleep behavior disorder (RBD) occurs when the muscle paralysis associated with the REM sleep phase
does not occur. Individuals who suffer from RBD have high levels of physical activity during REM sleep,
especially during disturbing dreams. These behaviors vary widely, but they can include kicking, punching,
scratching, yelling, and behaving like an animal that has been frightened or attacked. People who suffer from
this disorder can injure themselves or their sleeping partners when engaging in these behaviors. Furthermore,
these types of behaviors ultimately disrupt sleep, although affected individuals have no memories that these
behaviors have occurred (Arnulf, 2012).

This disorder is associated with a number of neurodegenerative diseases such as Parkinson’s disease. In fact,
this relationship is so robust that some view the presence of RBD as a potential aid in the diagnosis and
treatment of a number of neurodegenerative diseases (Ferini-Strambi, 2011). Clonazepam, an anti-anxiety
medication with sedative properties, is most often used to treat RBD. It is administered alone or in conjunction
with doses of melatonin (the hormone secreted by the pineal gland). As part of treatment, the sleeping
environment is often modified to make it a safer place for those suffering from RBD (Zangini, Calandra-
Buonaura, Grimaldi, & Cortelli, 2011).

Other Parasomnias

A person with restless leg syndrome has uncomfortable sensations in the legs during periods of inactivity or
when trying to fall asleep. This discomfort is relieved by deliberately moving the legs, which, not surprisingly,
contributes to difficulty in falling or staying asleep. Restless leg syndrome is quite common and has been

DIG DEEPER

4.4 • Sleep Problems and Disorders 123

associated with a number of other medical diagnoses, such as chronic kidney disease and diabetes (Mahowald
& Schenck, 2000). There are a variety of drugs that treat restless leg syndrome: benzodiazepines, opiates, and
anticonvulsants (Restless Legs Syndrome Foundation, n.d.).

Night terrors result in a sense of panic in the sufferer and are often accompanied by screams and attempts to
escape from the immediate environment (Mahowald & Schenck, 2000). Although individuals suffering from
night terrors appear to be awake, they generally have no memories of the events that occurred, and attempts to
console them are ineffective. Typically, individuals suffering from night terrors will fall back asleep again
within a short time. Night terrors apparently occur during the NREM phase of sleep (Provini, Tinuper, Bisulli, &
Lagaresi, 2011). Generally, treatment for night terrors is unnecessary unless there is some underlying medical
or psychological condition that is contributing to the night terrors (Mayo Clinic, n.d.).

Sleep Apnea

Sleep apnea is defined by episodes during which a sleeper’s breathing stops. These episodes can last 10–20
seconds or longer and often are associated with brief periods of arousal. While individuals suffering from sleep
apnea may not be aware of these repeated disruptions in sleep, they do experience increased levels of fatigue.
Many individuals diagnosed with sleep apnea first seek treatment because their sleeping partners indicate
that they snore loudly and/or stop breathing for extended periods of time while sleeping (Henry & Rosenthal,
2013). Sleep apnea is much more common in overweight people and is often associated with loud snoring.
Surprisingly, sleep apnea may exacerbate cardiovascular disease (Sánchez-de-la-Torre, Campos-Rodriguez, &
Barbé, 2012). While sleep apnea is less common in thin people, anyone, regardless of their weight, who snores
loudly or gasps for air while sleeping, should be checked for sleep apnea.

While people are often unaware of their sleep apnea, they are keenly aware of some of the adverse
consequences of insufficient sleep. Consider a patient who believed that as a result of his sleep apnea he “had
three car accidents in six weeks. They were ALL my fault. Two of them I didn’t even know I was involved in
until afterwards” (Henry & Rosenthal, 2013, p. 52). It is not uncommon for people suffering from undiagnosed
or untreated sleep apnea to fear that their careers will be affected by the lack of sleep, illustrated by this
statement from another patient, “I’m in a job where there’s a premium on being mentally alert. I was really
sleepy… and having trouble concentrating…. It was getting to the point where it was kind of scary” (Henry &
Rosenthal, 2013, p. 52).

There are two types of sleep apnea: obstructive sleep apnea and central sleep apnea. Obstructive sleep apnea
occurs when an individual’s airway becomes blocked during sleep, and air is prevented from entering the
lungs. In central sleep apnea, disruption in signals sent from the brain that regulate breathing cause periods
of interrupted breathing (White, 2005).

One of the most common treatments for sleep apnea involves the use of a special device during sleep. A
continuous positive airway pressure (CPAP) device includes a mask that fits over the sleeper’s nose and
mouth, which is connected to a pump that pumps air into the person’s airways, forcing them to remain open,
as shown in Figure 4.13. Some newer CPAP masks are smaller and cover only the nose. This treatment option
has proven to be effective for people suffering from mild to severe cases of sleep apnea (McDaid et al., 2009).
However, alternative treatment options are being explored because consistent compliance by users of CPAP
devices is a problem. Recently, a new EPAP (expiratory positive air pressure) device has shown promise in
double-blind trials as one such alternative (Berry, Kryger, & Massie, 2011).

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FIGURE 4.13 (a) A typical CPAP device used in the treatment of sleep apnea is (b) affixed to the head with straps,
and a mask that covers the nose and mouth.

SIDS

In sudden infant death syndrome (SIDS) an infant stops breathing during sleep and dies. Infants younger
than 12 months appear to be at the highest risk for SIDS, and boys have a greater risk than girls. A number of
risk factors have been associated with SIDS including premature birth, smoking within the home, and
hyperthermia. There may also be differences in both brain structure and function in infants that die from SIDS
(Berkowitz, 2012; Mage & Donner, 2006; Thach, 2005).

The substantial amount of research on SIDS has led to a number of recommendations to parents to protect
their children (Figure 4.14). For one, research suggests that infants should be placed on their backs when put
down to sleep, and their cribs should not contain any items which pose suffocation threats, such as blankets,
pillows or padded crib bumpers (cushions that cover the bars of a crib). Infants should not have caps placed on
their heads when put down to sleep in order to prevent overheating, and people in the child’s household should
abstain from smoking in the home. Recommendations like these have helped to decrease the number of infant
deaths from SIDS in recent years (Mitchell, 2009; Task Force on Sudden Infant Death Syndrome, 2011).

FIGURE 4.14 The Safe to Sleep campaign educates the public about how to minimize risk factors associated with
SIDS. This campaign is sponsored in part by the National Institute of Child Health and Human Development.

Narcolepsy

Unlike the other sleep disorders described in this section, a person with narcolepsy cannot resist falling
asleep at inopportune times. These sleep episodes are often associated with cataplexy, which is a lack of
muscle tone or muscle weakness, and in some cases involves complete paralysis of the voluntary muscles.
This is similar to the kind of paralysis experienced by healthy individuals during REM sleep (Burgess &
Scammell, 2012; Hishikawa & Shimizu, 1995; Luppi et al., 2011). Narcoleptic episodes take on other features
of REM sleep. For example, around one third of individuals diagnosed with narcolepsy experience vivid,
dream-like hallucinations during narcoleptic attacks (Chokroverty, 2010).

Surprisingly, narcoleptic episodes are often triggered by states of heightened arousal or stress. The typical
episode can last from a minute or two to half an hour. Once awakened from a narcoleptic attack, people report
that they feel refreshed (Chokroverty, 2010). Obviously, regular narcoleptic episodes could interfere with the
ability to perform one’s job or complete schoolwork, and in some situations, narcolepsy can result in
significant harm and injury (e.g., driving a car or operating machinery or other potentially dangerous
equipment).

4.4 • Sleep Problems and Disorders 125

Generally, narcolepsy is treated using psychomotor stimulant drugs, such as amphetamines (Mignot, 2012).
These drugs promote increased levels of neural activity. Narcolepsy is associated with reduced levels of the
signaling molecule hypocretin in some areas of the brain (De la Herrán-Arita & Drucker-Colín, 2012; Han,
2012), and the traditional stimulant drugs do not have direct effects on this system. Therefore, it is quite likely
that new medications that are developed to treat narcolepsy will be designed to target the hypocretin system.

There is a tremendous amount of variability among sufferers, both in terms of how symptoms of narcolepsy
manifest and the effectiveness of currently available treatment options. This is illustrated by McCarty’s (2010)
case study of a 50-year-old woman who sought help for the excessive sleepiness during normal waking hours
that she had experienced for several years. She indicated that she had fallen asleep at inappropriate or
dangerous times, including while eating, while socializing with friends, and while driving her car. During
periods of emotional arousal, the woman complained that she felt some weakness in the right side of her body.
Although she did not experience any dream-like hallucinations, she was diagnosed with narcolepsy as a result
of sleep testing. In her case, the fact that her cataplexy was confined to the right side of her body was quite
unusual. Early attempts to treat her condition with a stimulant drug alone were unsuccessful. However, when a
stimulant drug was used in conjunction with a popular antidepressant, her condition improved dramatically.

4.5 Substance Use and Abuse
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the diagnostic criteria for substance use disorders
• Identify the neurotransmitter systems impacted by various categories of drugs
• Describe how different categories of drugs affect behavior and experience

While we all experience altered states of consciousness in the form of sleep on a regular basis, some people
use drugs and other substances that result in altered states of consciousness as well. This section will present
information relating to the use of various psychoactive drugs and problems associated with such use. This will
be followed by brief descriptions of the effects of some of the more well-known drugs commonly used today.

Substance Use Disorders

The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) is used by
clinicians to diagnose individuals suffering from various psychological disorders. Drug use disorders are
addictive disorders, and the criteria for specific substance (drug) use disorders are described in DSM-5. A
person who has a substance use disorder often uses more of the substance than they originally intended to and
continues to use that substance despite experiencing significant adverse consequences. In individuals
diagnosed with a substance use disorder, there is a compulsive pattern of drug use that is often associated with
both physical and psychological dependence.

Physical dependence involves changes in normal bodily functions—the user will experience withdrawal from
the drug upon cessation of use. In contrast, a person who has psychological dependence has an emotional,
rather than physical, need for the drug and may use the drug to relieve psychological distress. Tolerance is
linked to physiological dependence, and it occurs when a person requires more and more drug to achieve
effects previously experienced at lower doses. Tolerance can cause the user to increase the amount of drug
used to a dangerous level—even to the point of overdose and death.

Drug withdrawal includes a variety of negative symptoms experienced when drug use is discontinued. These
symptoms usually are opposite of the effects of the drug. For example, withdrawal from sedative drugs often
produces unpleasant arousal and agitation. In addition to withdrawal, many individuals who are diagnosed
with substance use disorders will also develop tolerance to these substances. Psychological dependence, or
drug craving, is a recent addition to the diagnostic criteria for substance use disorder in DSM-5. This is an
important factor because we can develop tolerance and experience withdrawal from any number of drugs that
we do not abuse. In other words, physical dependence in and of itself is of limited utility in determining

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whether or not someone has a substance use disorder.

Drug Categories

The effects of all psychoactive drugs occur through their interactions with our endogenous neurotransmitter
systems. Many of these drugs, and their relationships, are shown in Table 4.2. As you have learned, drugs can
act as agonists or antagonists of a given neurotransmitter system. An agonist facilitates the activity of a
neurotransmitter system, and antagonists impede neurotransmitter activity.

Drugs and Their Effects

Class of Drug Examples
Effects on
the Body

Effects When Used
Psychologically

Addicting?

Stimulants

Cocaine,
amphetamines
(including some
ADHD medications
such as Adderall),
methamphetamines,
MDMA (“Ecstasy” or
“Molly”)

Increased
heart rate,
blood
pressure,
body
temperature

Increased alertness, mild euphoria,
decreased appetite in low doses. High
doses increase agitation, paranoia, can
cause hallucinations. Some can cause
heightened sensitivity to physical
stimuli. High doses of MDMA can
cause brain toxicity and death.

Yes

Sedative-
Hypnotics
(“Depressants”)

Alcohol,
barbiturates (e.g.,
secobarbital,
pentobarbital),
Benzodiazepines
(e.g., Xanax)

Decreased
heart rate,
blood
pressure

Low doses increase relaxation,
decrease inhibitions. High doses can
induce sleep, cause motor
disturbance, memory loss, decreased
respiratory function, and death.

Yes

Opiates

Opium, Heroin,
Fentanyl, Morphine,
Oxycodone, Vicodin,
methadone, and
other prescription
pain relievers

Decreased
pain, pupil
dilation,
decreased
gut motility,
decreased
respiratory
function

Pain relief, euphoria, sleepiness. High
doses can cause death due to
respiratory depression.

Yes

Hallucinogens

Marijuana, LSD,
Peyote, mescaline,
DMT, dissociative
anesthetics
including ketamine
and PCP

Increased
heart rate
and blood
pressure
that may
dissipate
over time

Mild to intense perceptual changes
with high variability in effects based on
strain, method of ingestion, and
individual differences

Yes

TABLE 4.2

Alcohol and Other Depressants

Ethanol, which we commonly refer to as alcohol, is in a class of psychoactive drugs known as depressants

4.5 • Substance Use and Abuse 127

(Figure 4.15). A depressant is a drug that tends to suppress central nervous system activity. Other depressants
include barbiturates and benzodiazepines. These drugs share in common their ability to serve as agonists of
the gamma-Aminobutyric acid (GABA) neurotransmitter system. Because GABA has a quieting effect on the
brain, GABA agonists also have a quieting effect; these types of drugs are often prescribed to treat both anxiety
and insomnia.

FIGURE 4.15 The GABA-gated chloride (Cl–) channel is embedded in the cell membrane of certain neurons. The
channel has multiple receptor sites where alcohol, barbiturates, and benzodiazepines bind to exert their effects. The
binding of these molecules opens the chloride channel, allowing negatively-charged chloride ions (Cl–) into the
neuron’s cell body. Changing its charge in a negative direction pushes the neuron away from firing; thus, activating a
GABA neuron has a quieting effect on the brain.

Acute alcohol administration results in a variety of changes to consciousness. At rather low doses, alcohol use
is associated with feelings of euphoria. As the dose increases, people report feeling sedated. Generally, alcohol
is associated with decreases in reaction time and visual acuity, lowered levels of alertness, and reduction in
behavioral control. With excessive alcohol use, a person might experience a complete loss of consciousness
and/or difficulty remembering events that occurred during a period of intoxication (McKim & Hancock, 2013).
In addition, if a pregnant person consumes alcohol, their infant may be born with a cluster of birth defects and
symptoms collectively called fetal alcohol spectrum disorder (FASD) or fetal alcohol syndrome (FAS).

With repeated use of many central nervous system depressants, such as alcohol, a person becomes physically
dependent upon the substance and will exhibit signs of both tolerance and withdrawal. Psychological
dependence on these drugs is also possible. Therefore, the abuse potential of central nervous system
depressants is relatively high.

Drug withdrawal is usually an aversive experience, and it can be a life-threatening process in individuals who
have a long history of very high doses of alcohol and/or barbiturates. This is of such concern that people who
are trying to overcome addiction to these substances should only do so under medical supervision.

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Stimulants

Stimulants are drugs that tend to increase overall levels of neural activity. Many of these drugs act as agonists
of the dopamine neurotransmitter system. Dopamine activity is often associated with reward and craving;
therefore, drugs that affect dopamine neurotransmission often have abuse liability. Drugs in this category
include cocaine, amphetamines (including methamphetamine), cathinones (i.e., bath salts), MDMA (ecstasy),
nicotine, and caffeine.

Cocaine can be taken in multiple ways. While many users snort cocaine, intravenous injection and inhalation
(smoking) are also common. The freebase version of cocaine, known as crack, is a potent, smokable version of
the drug. Like many other stimulants, cocaine agonizes the dopamine neurotransmitter system by blocking
the reuptake of dopamine in the neuronal synapse.

Methamphetamine
Methamphetamine in its smokable form, often called “crystal meth” due to its resemblance to rock crystal
formations, is highly addictive. The smokable form reaches the brain very quickly to produce an intense euphoria
that dissipates almost as fast as it arrives, prompting users to continuing taking the drug. Users often consume
the drug every few hours across days-long binges called “runs,” in which the user forgoes food and sleep. The
availability of potent and inexpensive forms of methamphetamine, coupled with a lower risk of overdose than
with opiate drugs, is making crystal meth a popular choice among drug users today (NIDA, 2019). Using crystal
meth poses a number of serious long-term health issues, including dental problems (often called “meth mouth”),
skin abrasions caused by excessive scratching, memory loss, sleep problems, violent behavior, paranoia, and
hallucinations. Methamphetamine addiction produces an intense craving that is difficult to treat.

Amphetamines have a mechanism of action quite similar to cocaine in that they block the reuptake of
dopamine in addition to stimulating its release (Figure 4.16). While amphetamines are often abused, they are
also commonly prescribed to people diagnosed with attention deficit hyperactivity disorder (ADHD). It may
seem counterintuitive that stimulant medications are prescribed to treat a disorder that involves hyperactivity,
but the therapeutic effect comes from increases in neurotransmitter activity within certain areas of the brain
associated with impulse control. These brain areas include the prefrontal cortex and basal ganglia.

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4.5 • Substance Use and Abuse 129

FIGURE 4.16 As one of their mechanisms of action, cocaine and amphetamines block the reuptake of dopamine
from the synapse into the presynaptic cell.

In recent years, methamphetamine (meth) use has become increasingly widespread. Methamphetamine is a
type of amphetamine that can be made from ingredients that are readily available (e.g., medications
containing pseudoephedrine, a compound found in many over-the-counter cold and flu remedies). Despite
recent changes in laws designed to make obtaining pseudoephedrine more difficult, methamphetamine
continues to be an easily accessible and relatively inexpensive drug option (Shukla, Crump, & Chrisco, 2012).

Stimulant users seek a euphoric high, feelings of intense elation and pleasure, especially in those users who
take the drug via intravenous injection or smoking. MDMA (3.4-methelynedioxy-methamphetamine,
commonly known as “ecstasy” or “Molly”) is a mild stimulant with perception-altering effects. It is typically
consumed in pill form. Users experience increased energy, feelings of pleasure, and emotional warmth.
Repeated use of these stimulants can have significant adverse consequences. Users can experience physical
symptoms that include nausea, elevated blood pressure, and increased heart rate. In addition, these drugs can
cause feelings of anxiety, hallucinations, and paranoia (Fiorentini et al., 2011). Normal brain functioning is
altered after repeated use of these drugs. For example, repeated use can lead to overall depletion among the
monoamine neurotransmitters (dopamine, norepinephrine, and serotonin). Depletion of certain
neurotransmitters can lead to mood dysphoria, cognitive problems, and other factors. This can lead to people
compulsively using stimulants such as cocaine and amphetamines, in part to try to reestablish the person’s
physical and psychological pre-use baseline. (Jayanthi & Ramamoorthy, 2005; Rothman, Blough, & Baumann,
2007).

Caffeine is another stimulant drug. While it is probably the most commonly used drug in the world, the
potency of this particular drug pales in comparison to the other stimulant drugs described in this section.
Generally, people use caffeine to maintain increased levels of alertness and arousal. Caffeine is found in many
common medicines (such as weight loss drugs), beverages, foods, and even cosmetics (Herman & Herman,
2013). While caffeine may have some indirect effects on dopamine neurotransmission, its primary
mechanism of action involves antagonizing adenosine activity (Porkka-Heiskanen, 2011). Adenosine is a

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neurotransmitter that promotes sleep. Caffeine is an adenosine antagonist, so caffeine inhibits the adenosine
receptors, thus decreasing sleepiness and promoting wakefulness.

While caffeine is generally considered a relatively safe drug, high blood levels of caffeine can result in
insomnia, agitation, muscle twitching, nausea, irregular heartbeat, and even death (Reissig, Strain, & Griffiths,
2009; Wolt, Ganetsky, & Babu, 2012). In 2012, Kromann and Nielson reported on a case study of a 40-year-old
woman who suffered significant ill effects from her use of caffeine. The woman used caffeine in the past to
boost her mood and to provide energy, but over the course of several years, she increased her caffeine
consumption to the point that she was consuming three liters of soda each day. Although she had been taking a
prescription antidepressant, her symptoms of depression continued to worsen and she began to suffer
physically, displaying significant warning signs of cardiovascular disease and diabetes. Upon admission to an
outpatient clinic for treatment of mood disorders, she met all of the diagnostic criteria for substance
dependence and was advised to dramatically limit her caffeine intake. Once she was able to limit her use to
less than 12 ounces of soda a day, both her mental and physical health gradually improved. Despite the
prevalence of caffeine use and the large number of people who confess to suffering from caffeine addiction,
this was the first published description of soda dependence appearing in scientific literature.

Nicotine is highly addictive, and the use of tobacco products is associated with increased risks of heart disease,
stroke, and a variety of cancers. Nicotine exerts its effects through its interaction with acetylcholine receptors.
Acetylcholine functions as a neurotransmitter in motor neurons. In the central nervous system, it plays a role
in arousal and reward mechanisms. Nicotine is most commonly used in the form of tobacco products like
cigarettes or chewing tobacco; therefore, there is a tremendous interest in developing effective smoking
cessation techniques. To date, people have used a variety of nicotine replacement therapies in addition to
various psychotherapeutic options in an attempt to discontinue their use of tobacco products. In general,
smoking cessation programs may be effective in the short term, but it is unclear whether these effects persist
(Cropley, Theadom, Pravettoni, & Webb, 2008; Levitt, Shaw, Wong, & Kaczorowski, 2007; Smedslund, Fisher,
Boles, & Lichtenstein, 2004). Vaping as a means to deliver nicotine is becoming increasingly popular,
especially among teens and young adults. Vaping uses battery-powered devices, sometimes called e-cigarettes,
that deliver liquid nicotine and flavorings as a vapor. Originally reported as a safe alternative to the known
cancer-causing agents found in cigarettes, vaping is now known to be very dangerous and has led to serious
lung disease and death in users (Shmerling, 2019).

Opioids

An opioid is one of a category of drugs that includes heroin, morphine, methadone, and codeine. Opioids have
analgesic properties; that is, they decrease pain. Humans have an endogenous opioid neurotransmitter
system—the body makes small quantities of opioid compounds that bind to opioid receptors reducing pain and
producing euphoria. Thus, opioid drugs, which mimic this endogenous painkilling mechanism, have an
extremely high potential for abuse. Natural opioids, called opiates, are derivatives of opium, which is a
naturally occurring compound found in the poppy plant. There are now several synthetic versions of opiate
drugs (correctly called opioids) that have very potent painkilling effects, and they are often abused. For
example, the National Institutes of Drug Abuse has sponsored research that suggests the misuse and abuse of
the prescription pain killers hydrocodone and oxycodone are significant public health concerns (Maxwell,
2006). In 2013, the U.S. Food and Drug Administration recommended tighter controls on their medical use.

Historically, heroin has been a major opioid drug of abuse (Figure 4.17). Heroin can be snorted, smoked, or
injected intravenously. Heroin produces intense feelings of euphoria and pleasure, which are amplified when
the heroin is injected intravenously. Following the initial “rush,” users experience 4–6 hours of “going on the
nod,” alternating between conscious and semiconscious states. Heroin users often shoot the drug directly into
their veins. Some people who have injected many times into their arms will show “track marks,” while other
users will inject into areas between their fingers or between their toes, so as not to show obvious track marks
and, like all abusers of intravenous drugs, have an increased risk for contraction of both tuberculosis and HIV.

4.5 • Substance Use and Abuse 131

FIGURE 4.17 (a) Common paraphernalia for heroin preparation and use are shown here in a needle exchange kit.
(b) Heroin is cooked on a spoon over a candle. (credit a: modification of work by Todd Huffman)

Aside from their utility as analgesic drugs, opioid-like compounds are often found in cough suppressants, anti-
nausea, and anti-diarrhea medications. Given that withdrawal from a drug often involves an experience
opposite to the effect of the drug, it should be no surprise that opioid withdrawal resembles a severe case of the
flu. While opioid withdrawal can be extremely unpleasant, it is not life-threatening (Julien, 2005). Still, people
experiencing opioid withdrawal may be given methadone to make withdrawal from the drug less difficult.
Methadone is a synthetic opioid that is less euphorigenic than heroin and similar drugs. Methadone clinics
help people who previously struggled with opioid addiction manage withdrawal symptoms through the use of
methadone. Other drugs, including the opioid buprenorphine, have also been used to alleviate symptoms of
opiate withdrawal.

Codeine is an opioid with relatively low potency. It is often prescribed for minor pain, and it is available over-
the-counter in some other countries. Like all opioids, codeine does have abuse potential. In fact, abuse of
prescription opioid medications is becoming a major concern worldwide (Aquina, Marques-Baptista,
Bridgeman, & Merlin, 2009; Casati, Sedefov, & Pfeiffer-Gerschel, 2012).

The Opioid Crisis
Few people in the United States remain untouched by the recent opioid epidemic. It seems like everyone knows
a friend, family member, or neighbor who has died of an overdose. Opioid addiction reached crisis levels in the
United States such that by 2019, an average of 130 people died each day of an opioid overdose (NIDA, 2019).

The crisis actually began in the 1990s, when pharmaceutical companies began mass-marketing pain-relieving
opioid drugs like OxyContin with the promise (now known to be false) that they were non-addictive. Increased
prescriptions led to greater rates of misuse, along with greater incidence of addiction, even among patients who
used these drugs as prescribed. Physiologically, the body can become addicted to opiate drugs in less than a
week, including when taken as prescribed. Withdrawal from opioids includes pain, which patients often
misinterpret as pain caused by the problem that led to the original prescription, and which motivates patients to
continue using the drugs.

The FDA’s 2013 recommendation for tighter controls on opiate prescriptions left many patients addicted to
prescription drugs like OxyContin unable to obtain legitimate prescriptions. This created a black market for the
drug, where prices soared to $80 or more for a single pill. To prevent withdrawal, many people turned to cheaper
heroin, which could be bought for $5 a dose or less. To keep heroin affordable, many dealers began adding more
potent synthetic opioids including fentanyl and carfentanyl to increase the effects of heroin. These synthetic
drugs are so potent that even small doses can cause overdose and death.

Large-scale public health campaigns by the National Institutes of Health and the National Institute of Drug Abuse
have led to recent declines in the opioid crisis. These initiatives include increasing access to treatment and

EVERYDAY CONNECTION

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recovery services, increasing access to overdose-reversal drugs like Naloxone, and implementing better public
health monitoring systems (NIDA, 2019).

Hallucinogens

A hallucinogen is one of a class of drugs that results in profound alterations in sensory and perceptual
experiences (Figure 4.18). In some cases, users experience vivid visual hallucinations. It is also common for
these types of drugs to cause hallucinations of body sensations (e.g., feeling as if you are a giant) and a skewed
perception of the passage of time.

FIGURE 4.18 Psychedelic images like this are often associated with hallucinogenic compounds. (credit:
modification of work by “new 1lluminati”/Flickr)

As a group, hallucinogens are incredibly varied in terms of the neurotransmitter systems they affect.
Mescaline and LSD are serotonin agonists, and PCP (angel dust) and ketamine (an animal anesthetic) act as
antagonists of the NMDA glutamate receptor. In general, these drugs are not thought to possess the same sort
of abuse potential as other classes of drugs discussed in this section.

LINK TO LEARNING

To learn more about some of the most commonly abused prescription and street drugs, check out the
Commonly Abused Drugs Chart (http://openstax.org/l/drugabuse) and the Commonly Abused Prescription
Drugs Chart (http://openstax.org/l/Rxabuse) from the National Institute on Drug Abuse.

Medical Marijuana
The decade from 2010–2019 brought many changes in laws regarding marijuana. While the possession and use
of marijuana remains illegal in many states, it is now legal to possess limited quantities of marijuana for
recreational use in eleven states: Alaska, California, Colorado, Illinois, Maine, Massachusetts, Michigan, Nevada,
Oregon, Vermont, and Washington. Medical marijuana is legal in over half of the United States and in the District
of Columbia (Figure 4.19). Medical marijuana is marijuana that is prescribed by a doctor for the treatment of a
health condition. For example, people who undergo chemotherapy will often be prescribed marijuana to
stimulate their appetites and prevent excessive weight loss resulting from the side effects of chemotherapy
treatment. Marijuana may also have some promise in the treatment of a variety of medical conditions (Mather,
Rauwendaal, Moxham-Hall, & Wodak, 2013; Robson, 2014; Schicho & Storr, 2014).

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4.5 • Substance Use and Abuse 133

FIGURE 4.19 Medical marijuana shops are becoming more and more common in the United States. (credit:
Laurie Avocado)

While medical marijuana laws have been passed on a state-by-state basis, federal laws still classify this as an
illicit substance, making conducting research on the potentially beneficial medicinal uses of marijuana
problematic. There is quite a bit of controversy within the scientific community as to the extent to which
marijuana might have medicinal benefits due to a lack of large-scale, controlled research (Bostwick, 2012). As a
result, many scientists have urged the federal government to allow for relaxation of current marijuana laws and
classifications in order to facilitate a more widespread study of the drug’s effects (Aggarwal et al., 2009;
Bostwick, 2012; Kogan & Mechoulam, 2007).

Until recently, the United States Department of Justice routinely arrested people involved and seized marijuana
used in medicinal settings. In the latter part of 2013, however, the United States Department of Justice issued
statements indicating that they would not continue to challenge state medical marijuana laws. This shift in policy
may be in response to the scientific community’s recommendations and/or reflect changing public opinion
regarding marijuana.

4.6 Other States of Consciousness
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Define hypnosis and meditation
• Understand the similarities and differences of hypnosis and meditation

Our states of consciousness change as we move from wakefulness to sleep. We also alter our consciousness
through the use of various psychoactive drugs. This final section will consider hypnotic and meditative states
as additional examples of altered states of consciousness experienced by some individuals.

Hypnosis

Hypnosis is a state of extreme self-focus and attention in which minimal attention is given to external stimuli.
In the therapeutic setting, a clinician may use relaxation and suggestion in an attempt to alter the thoughts
and perceptions of a patient. Hypnosis has also been used to draw out information believed to be buried deeply
in someone’s memory. For individuals who are especially open to the power of suggestion, hypnosis can prove
to be a very effective technique, and brain imaging studies have demonstrated that hypnotic states are
associated with global changes in brain functioning (Del Casale et al., 2012; Guldenmund, Vanhaudenhuyse,
Boly, Laureys, & Soddu, 2012).

Historically, hypnosis has been viewed with some suspicion because of its portrayal in popular media and
entertainment (Figure 4.20). Therefore, it is important to make a distinction between hypnosis as an
empirically based therapeutic approach versus as a form of entertainment. Contrary to popular belief,
individuals undergoing hypnosis usually have clear memories of the hypnotic experience and are in control of
their own behaviors. While hypnosis may be useful in enhancing memory or a skill, such enhancements are
very modest in nature (Raz, 2011).

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FIGURE 4.20 Popular portrayals of hypnosis have led to some widely-held misconceptions.

How exactly does a hypnotist bring a participant to a state of hypnosis? While there are variations, there are
four parts that appear consistent in bringing people into the state of suggestibility associated with hypnosis
(National Research Council, 1994). These components include:

• The participant is guided to focus on one thing, such as the hypnotist’s words or a ticking watch.
• The participant is made comfortable and is directed to be relaxed and sleepy.
• The participant is told to be open to the process of hypnosis, trust the hypnotist and let go.
• The participant is encouraged to use their imagination.

These steps are conducive to being open to the heightened suggestibility of hypnosis.

People vary in terms of their ability to be hypnotized, but a review of available research suggests that most
people are at least moderately hypnotizable (Kihlstrom, 2013). Hypnosis in conjunction with other techniques
is used for a variety of therapeutic purposes and has shown to be at least somewhat effective for pain
management, treatment of depression and anxiety, smoking cessation, and weight loss (Alladin, 2012; Elkins,
Johnson, & Fisher, 2012; Golden, 2012; Montgomery, Schnur, & Kravits, 2012).

How does hypnosis work? Two theories attempt to answer this question: One theory views hypnosis as
dissociation and the other theory views it as the performance of a social role. According to the dissociation
view, hypnosis is effectively a dissociated state of consciousness, much like our earlier example where you may
drive to work, but you are only minimally aware of the process of driving because your attention is focused
elsewhere. This theory is supported by Ernest Hilgard’s research into hypnosis and pain. In Hilgard’s
experiments, he induced participants into a state of hypnosis, and placed their arms into ice water.
Participants were told they would not feel pain, but they could press a button if they did; while they reported
not feeling pain, they did, in fact, press the button, suggesting a dissociation of consciousness while in the
hypnotic state (Hilgard & Hilgard, 1994).

Taking a different approach to explain hypnosis, the social-cognitive theory of hypnosis sees people in
hypnotic states as performing the social role of a hypnotized person. As you will learn when you study social
roles, people’s behavior can be shaped by their expectations of how they should act in a given situation. Some
view a hypnotized person’s behavior not as an altered or dissociated state of consciousness, but as their
fulfillment of the social expectations for that role (Coe, 2009; Coe & Sarbin, 1966).

4.6 • Other States of Consciousness 135

Meditation

Meditation is the act of focusing on a single target (such as the breath or a repeated sound) to increase
awareness of the moment. While hypnosis is generally achieved through the interaction of a therapist and the
person being treated, an individual can perform meditation alone. Often, however, people wishing to learn to
meditate receive some training in techniques to achieve a meditative state.

Although there are a number of different techniques in use, the central feature of all meditation is clearing the
mind in order to achieve a state of relaxed awareness and focus (Chen et al., 2013; Lang et al., 2012).
Mindfulness meditation has recently become popular. In the variation of mindful meditation, the meditator’s
attention is focused on some internal process or an external object (Zeidan, Grant, Brown, McHaffie, & Coghill,
2012).

Meditative techniques have their roots in religious practices (Figure 4.21), but their use has grown in
popularity among practitioners of alternative medicine. Research indicates that meditation may help reduce
blood pressure, and the American Heart Association suggests that meditation might be used in conjunction
with more traditional treatments as a way to manage hypertension, although there is not sufficient data for a
recommendation to be made (Brook et al., 2013). Like hypnosis, meditation also shows promise in stress
management, sleep quality (Caldwell, Harrison, Adams, Quin, & Greeson, 2010), treatment of mood and
anxiety disorders (Chen et al., 2013; Freeman et al., 2010; Vøllestad, Nielsen, & Nielsen, 2012), and pain
management (Reiner, Tibi, & Lipsitz, 2013).

FIGURE 4.21 (a) This is a statue of a meditating Buddha, representing one of the many religious traditions of which
meditation plays a part. (b) People practicing meditation may experience an alternate state of consciousness. (credit
a: modification of work by Jim Epler; credit b: modification of work by Caleb Roenigk)

LINK TO LEARNING

Feeling stressed? Think meditation might help? Watch this instructional video about using Buddhist
meditation techniques to alleviate stress (http://openstax.org/l/meditate) to learn more.

LINK TO LEARNING

Watch this video about the results of a brain imaging study in individuals who underwent specific mindfulness
meditative techniques (http://openstax.org/l/brainimaging) to learn more.

136 4 • States of Consciousness

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Key Terms
alpha wave type of rbrain wave characteristic during the early part of NREM stage 1 sleep, which has fairly low

amplitude and a frequency of 8–12 Hz
beta wave type of brain wave characteristic during wakefulness, which has a very low amplitude and a

frequency of 13–30 Hz
biological rhythm internal cycle of biological activity
cataplexy lack of muscle tone or muscle weakness, and in some cases complete paralysis of the voluntary

muscles
central sleep apnea sleep disorder with periods of interrupted breathing due to a disruption in signals sent

from the brain that regulate breathing
circadian rhythm biological rhythm that occurs over approximately 24 hours
codeine opiate with relatively low potency often prescribed for minor pain
cognitive-behavioral therapy psychotherapy that focuses on cognitive processes and problem behaviors that

is sometimes used to treat sleep disorders such as insomnia
collective unconscious theoretical repository of information shared by all people across cultures, as

described by Carl Jung
consciousness awareness of internal and external stimuli
continuous positive airway pressure (CPAP) device used to treat sleep apnea; includes a mask that fits over

the sleeper’s nose and mouth, which is connected to a pump that pumps air into the person’s airways,
forcing them to remain open

delta wave type of brain wave characteristic during stage 3 NREM sleep, which has a high amplitude and low
frequency of less than 3 Hz

depressant drug that tends to suppress central nervous system activity
euphoric high feelings of intense elation and pleasure from drug use
evolutionary psychology discipline that studies how universal patterns of behavior and cognitive processes

have evolved over time as a result of natural selection
hallucinogen one of a class of drugs that results in profound alterations in sensory and perceptual

experiences, often with vivid hallucinations
homeostasis tendency to maintain a balance, or optimal level, within a biological system
hypnosis state of extreme self-focus and attention in which minimal attention is given to external stimuli
insomnia consistent difficulty in falling or staying asleep for at least three nights a week over a month’s time
jet lag collection of symptoms brought on by travel from one time zone to another that results from the

mismatch between our internal circadian cycles and our environment
K-complex very high amplitude pattern of brain activity associated with stage 2 sleep that may occur in

response to environmental stimuli
latent content hidden meaning of a dream, per Sigmund Freud’s view of the function of dreams
lucid dream people become aware that they are dreaming and can control the dream’s content
manifest content storyline of events that occur during a dream, per Sigmund Freud’s view of the function of

dreams
meditation clearing the mind in order to achieve a state of relaxed awareness and focus
melatonin hormone secreted by the endocrine gland that serves as an important regulator of the sleep-wake

cycle
meta-analysis study that combines the results of several related studies
methadone synthetic opioid that is less euphorigenic than heroin and similar drugs; used to manage

withdrawal symptoms in opiate users
methadone clinic uses methadone to treat withdrawal symptoms in opiate users
methamphetamine type of amphetamine that can be made from pseudoephedrine, an over-the-counter drug;

widely manufactured and abused
narcolepsy sleep disorder in which the sufferer cannot resist falling to sleep at inopportune times

4 • Key Terms 137

night terror sleep disorder in which the sleeper experiences a sense of panic and may scream or attempt to
escape from the immediate environment

non-REM (NREM) period of sleep outside periods of rapid eye movement (REM) sleep
obstructive sleep apnea sleep disorder defined by episodes when breathing stops during sleep as a result of

blockage of the airway
opiate/opioid one of a category of drugs that has strong analgesic properties; opiates are produced from the

resin of the opium poppy; includes heroin, morphine, methadone, and codeine
parasomnia one of a group of sleep disorders characterized by unwanted, disruptive motor activity and/or

experiences during sleep
physical dependence changes in normal bodily functions that cause a drug user to experience withdrawal

symptoms upon cessation of use
pineal gland endocrine structure located inside the brain that releases melatonin
psychological dependence emotional, rather than a physical, need for a drug which may be used to relieve

psychological distress
rapid eye movement (REM) sleep period of sleep characterized by brain waves very similar to those during

wakefulness and by darting movements of the eyes under closed eyelids
REM sleep behavior disorder (RBD) sleep disorder in which the muscle paralysis associated with the REM

sleep phase does not occur; sleepers have high levels of physical activity during REM sleep, especially
during disturbing dreams

restless leg syndrome sleep disorder in which the sufferer has uncomfortable sensations in the legs when
trying to fall asleep that are relieved by moving the legs

rotating shift work work schedule that changes from early to late on a daily or weekly basis
sleep state marked by relatively low levels of physical activity and reduced sensory awareness that is distinct

from periods of rest that occur during wakefulness
sleep apnea sleep disorder defined by episodes during which breathing stops during sleep
sleep debt result of insufficient sleep on a chronic basis
sleep rebound sleep-deprived individuals will experience shorter sleep latencies during subsequent

opportunities for sleep
sleep regulation brain’s control of switching between sleep and wakefulness as well as coordinating this cycle

with the outside world
sleep spindle rapid burst of high frequency brain waves during stage 2 sleep that may be important for

learning and memory
sleepwalking (also, somnambulism) sleep disorder in which the sleeper engages in relatively complex

behaviors
stage 1 sleep first stage of sleep; transitional phase that occurs between wakefulness and sleep; the period

during which a person drifts off to sleep
stage 2 sleep second stage of sleep; the body goes into deep relaxation; characterized by the appearance of

sleep spindles
stage 3 sleep third stage of sleep; deep sleep characterized by low frequency, high amplitude delta waves
stimulant drug that tends to increase overall levels of neural activity; includes caffeine, nicotine,

amphetamines, and cocaine
sudden infant death syndrome (SIDS) infant (one year old or younger) with no apparent medical condition

suddenly dies during sleep
suprachiasmatic nucleus (SCN) area of the hypothalamus in which the body’s biological clock is located
theta wave type of brain wave characteristic of the end of stage 1 NREM sleep, which has a moderately low

amplitude and a frequency of 4–7 Hz
tolerance state of requiring increasing quantities of the drug to gain the desired effect
wakefulness characterized by high levels of sensory awareness, thought, and behavior
withdrawal variety of negative symptoms experienced when drug use is discontinued

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Summary
4.1 What Is Consciousness?

States of consciousness vary over the course of the day and throughout our lives. Important factors in these
changes are the biological rhythms, and, more specifically, the circadian rhythms generated by the
suprachiasmatic nucleus (SCN). Typically, our biological clocks are aligned with our external environment,
and light tends to be an important cue in setting this clock. When people travel across multiple time zones or
work rotating shifts, they can experience disruptions of their circadian cycles that can lead to insomnia,
sleepiness, and decreased alertness. Bright light therapy has shown to be promising in dealing with circadian
disruptions. If people go extended periods of time without sleep, they will accrue a sleep debt and potentially
experience a number of adverse psychological and physiological consequences.

4.2 Sleep and Why We Sleep

We devote a very large portion of time to sleep, and our brains have complex systems that control various
aspects of sleep. Several hormones important for physical growth and maturation are secreted during sleep.
While the reason we sleep remains something of a mystery, there is some evidence to suggest that sleep is very
important to learning and memory.

4.3 Stages of Sleep

The different stages of sleep are characterized by the patterns of brain waves associated with each stage. As a
person transitions from being awake to falling asleep, alpha waves are replaced by theta waves. Sleep spindles
and K-complexes emerge in stage 2 sleep. Stage 3 and stage 4 are described as slow-wave sleep that is marked
by a predominance of delta waves. REM sleep involves rapid movements of the eyes, paralysis of voluntary
muscles, and dreaming. Both NREM and REM sleep appear to play important roles in learning and memory.
Dreams may represent life events that are important to the dreamer. Alternatively, dreaming may represent a
state of protoconsciousness, or a virtual reality, in the mind that helps a person during consciousness.

4.4 Sleep Problems and Disorders

Many individuals suffer from some type of sleep disorder or disturbance at some point in their lives. Insomnia
is a common experience in which people have difficulty falling or staying asleep. Parasomnias involve
unwanted motor behavior or experiences throughout the sleep cycle and include RBD, sleepwalking, restless
leg syndrome, and night terrors. Sleep apnea occurs when individuals stop breathing during their sleep, and in
the case of sudden infant death syndrome, infants will stop breathing during sleep and die. Narcolepsy
involves an irresistible urge to fall asleep during waking hours and is often associated with cataplexy and
hallucination.

4.5 Substance Use and Abuse

Substance use disorder is defined in DSM-5 as a compulsive pattern of drug use despite negative
consequences. Both physical and psychological dependence are important parts of this disorder. Alcohol,
barbiturates, and benzodiazepines are central nervous system depressants that affect GABA
neurotransmission. Cocaine, amphetamine, cathinones, and MDMA are all central nervous stimulants that
agonize dopamine neurotransmission, while nicotine and caffeine affect acetylcholine and adenosine,
respectively. Opiate drugs serve as powerful analgesics through their effects on the endogenous opioid
neurotransmitter system, and hallucinogenic drugs cause pronounced changes in sensory and perceptual
experiences. The hallucinogens are variable with regards to the specific neurotransmitter systems they affect.

4.6 Other States of Consciousness

Hypnosis is a focus on the self that involves suggested changes of behavior and experience. Meditation
involves relaxed, yet focused, awareness. Both hypnotic and meditative states may involve altered states of
consciousness that have potential application for the treatment of a variety of physical and psychological

4 • Summary 139

disorders.

Review Questions
1. The body’s biological clock is located in the ________.

a. hippocampus
b. thalamus
c. hypothalamus
d. pituitary gland

2. ________ occurs when there is a chronic deficiency in sleep.
a. jet lag
b. rotating shift work
c. circadian rhythm
d. sleep debt

3. ________ cycles occur roughly once every 24 hours.
a. biological
b. circadian
c. rotating
d. conscious

4. ________ is one way in which people can help reset their biological clocks.
a. Light-dark exposure
b. coffee consumption
c. alcohol consumption
d. napping

5. Growth hormone is secreted by the ________ while we sleep.
a. pineal gland
b. thyroid
c. pituitary gland
d. pancreas

6. The ________ plays a role in controlling slow-wave sleep.
a. hypothalamus
b. thalamus
c. pons
d. both a and b

7. ________ is a hormone secreted by the pineal gland that plays a role in regulating biological rhythms and
immune function.
a. growth hormone
b. melatonin
c. LH
d. FSH

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8. ________ appears to be especially important for enhanced performance on recently learned tasks.
a. melatonin
b. slow-wave sleep
c. sleep deprivation
d. growth hormone

9. ________ is(are) described as slow-wave sleep.
a. stage 1
b. stage 2
c. stage 3 and stage 4
d. REM sleep

10. Sleep spindles and K-complexes are most often associated with ________ sleep.
a. stage 1
b. stage 2
c. stage 3 and stage 4
d. REM

11. Symptoms of ________ may be improved by REM deprivation.
a. schizophrenia
b. Parkinson’s disease
c. depression
d. generalized anxiety disorder

12. The ________ content of a dream refers to the true meaning of the dream.
a. latent
b. manifest
c. collective unconscious
d. important

13. ________ is loss of muscle tone or control that is often associated with narcolepsy.
a. RBD
b. CPAP
c. cataplexy
d. insomnia

14. An individual may suffer from ________ if there is a disruption in the brain signals that are sent to the
muscles that regulate breathing.
a. central sleep apnea
b. obstructive sleep apnea
c. narcolepsy
d. SIDS

15. The most common treatment for ________ involves the use of amphetamine-like medications.
a. sleep apnea
b. RBD
c. SIDS
d. narcolepsy

4 • Review Questions 141

16. ________ is another word for sleepwalking.
a. insomnia
b. somnambulism
c. cataplexy
d. narcolepsy

17. ________ occurs when a drug user requires more and more of a given drug in order to experience the
same effects of the drug.
a. withdrawal
b. psychological dependence
c. tolerance
d. reuptake

18. Cocaine blocks the reuptake of ________.
a. GABA
b. glutamate
c. acetylcholine
d. dopamine

19. ________ refers to drug craving.
a. psychological dependence
b. antagonism
c. agonism
d. physical dependence

20. LSD affects ________ neurotransmission.
a. dopamine
b. serotonin
c. acetylcholine
d. norepinephrine

21. ________ is most effective in individuals that are very open to the power of suggestion.
a. hypnosis
b. meditation
c. mindful awareness
d. cognitive therapy

22. ________ has its roots in religious practice.
a. hypnosis
b. meditation
c. cognitive therapy
d. behavioral therapy

23. Meditation may be helpful in ________.
a. pain management
b. stress control
c. treating the flu
d. both a and b

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24. Research suggests that cognitive processes, such as learning, may be affected by ________.
a. hypnosis
b. meditation
c. mindful awareness
d. progressive relaxation

Critical Thinking Questions
25. Healthcare professionals often work rotating shifts. Why is this problematic? What can be done to deal

with potential problems?

26. Generally, humans are considered diurnal which means we are awake during the day and asleep during
the night. Many rodents, on the other hand, are nocturnal. Why do you think different animals have such
different sleep-wake cycles?

27. If theories that assert sleep is necessary for restoration and recovery from daily energetic demands are
correct, what do you predict about the relationship that would exist between individuals’ total sleep
duration and their level of activity?

28. How could researchers determine if given areas of the brain are involved in the regulation of sleep?

29. Differentiate the evolutionary theories of sleep and make a case for the one with the most compelling
evidence.

30. Freud believed that dreams provide important insight into the unconscious mind. He maintained that a
dream’s manifest content could provide clues into an individual’s unconscious. What potential criticisms
exist for this particular perspective?

31. Some people claim that sleepwalking and talking in your sleep involve individuals acting out their dreams.
Why is this particular explanation unlikely?

32. One of the recommendations that therapists will make to people who suffer from insomnia is to spend less
waking time in bed. Why do you think spending waking time in bed might interfere with the ability to fall
asleep later?

33. How is narcolepsy with cataplexy similar to and different from REM sleep?

34. The negative health consequences of both alcohol and tobacco products are well-documented. A drug like
marijuana, on the other hand, is generally considered to be as safe, if not safer than these legal drugs. Why
do you think marijuana use continues to be illegal in many parts of the United States?

35. Why are programs designed to educate people about the dangers of using tobacco products just as
important as developing tobacco cessation programs?

36. What advantages exist for researching the potential health benefits of hypnosis?

37. What types of studies would be most convincing regarding the effectiveness of meditation in the
treatment for some type of physical or mental disorder?

Personal Application Questions
38. We experience shifts in our circadian clocks in the fall and spring of each year with time changes

associated with daylight saving time. Is springing ahead or falling back easier for you to adjust to, and why
do you think that is?

39. What do you do to adjust to the differences in your daily schedule throughout the week? Are you running a
sleep debt when daylight saving time begins or ends?

4 • Critical Thinking Questions 143

40. Have you (or someone you know) ever experienced significant periods of sleep deprivation because of
simple insomnia, high levels of stress, or as a side effect from a medication? What were the consequences
of missing out on sleep?

41. Researchers believe that one important function of sleep is to facilitate learning and memory. How does
knowing this help you in your college studies? What changes could you make to your study and sleep
habits to maximize your mastery of the material covered in class?

42. What factors might contribute to your own experiences with insomnia?

43. Many people experiment with some sort of psychoactive substance at some point in their lives. Why do
you think people are motivated to use substances that alter consciousness?

44. Under what circumstances would you be willing to consider hypnosis and/or meditation as a treatment
option? What kind of information would you need before you made a decision to use these techniques?

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FIGURE 5.1 If you were standing in the midst of this street scene, you would be absorbing and processing
numerous pieces of sensory input. (credit: modification of work by Cory Zanker)

INTRODUCTION

CHAPTER OUTLINE
5.1 Sensation versus Perception
5.2 Waves and Wavelengths
5.3 Vision
5.4 Hearing
5.5 The Other Senses
5.6 Gestalt Principles of Perception

Imagine standing on a city street corner. You might be struck by movement everywhere as
cars and people go about their business, by the sound of a street musician’s melody or a horn honking in the
distance, by the smell of exhaust fumes or of food being sold by a nearby vendor, and by the sensation of hard
pavement under your feet.

We rely on our sensory systems to provide important information about our surroundings. We use this
information to successfully navigate and interact with our environment so that we can find nourishment, seek
shelter, maintain social relationships, and avoid potentially dangerous situations.

This chapter will provide an overview of how sensory information is received and processed by the nervous
system and how that affects our conscious experience of the world. We begin by learning the distinction
between sensation and perception. Then we consider the physical properties of light and sound stimuli, along
with an overview of the basic structure and function of the major sensory systems. The chapter will close with
a discussion of a historically important theory of perception called Gestalt.

5Sensation and Perception

5.1 Sensation versus Perception
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Distinguish between sensation and perception
• Describe the concepts of absolute threshold and difference threshold
• Discuss the roles attention, motivation, and sensory adaptation play in perception

Sensation

What does it mean to sense something? Sensory receptors are specialized neurons that respond to specific
types of stimuli. When sensory information is detected by a sensory receptor, sensation has occurred. For
example, light that enters the eye causes chemical changes in cells that line the back of the eye. These cells
relay messages, in the form of action potentials (as you learned when studying biopsychology), to the central
nervous system. The conversion from sensory stimulus energy to action potential is known as transduction.

You have probably known since elementary school that we have five senses: vision, hearing (audition), smell
(olfaction), taste (gustation), and touch (somatosensation). It turns out that this notion of five senses is
oversimplified. We also have sensory systems that provide information about balance (the vestibular sense),
body position and movement (proprioception and kinesthesia), pain (nociception), and temperature
(thermoception).

The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold.
Absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to
be detected 50% of the time. Another way to think about this is by asking how dim can a light be or how soft
can a sound be and still be detected half of the time. The sensitivity of our sensory receptors can be quite
amazing. It has been estimated that on a clear night, the most sensitive sensory cells in the back of the eye can
detect a candle flame 30 miles away (Okawa & Sampath, 2007). Under quiet conditions, the hair cells (the
receptor cells of the inner ear) can detect the tick of a clock 20 feet away (Galanter, 1962).

It is also possible for us to get messages that are presented below the threshold for conscious awareness—these
are called subliminal messages. A stimulus reaches a physiological threshold when it is strong enough to
excite sensory receptors and send nerve impulses to the brain: This is an absolute threshold. A message below
that threshold is said to be subliminal: We receive it, but we are not consciously aware of it. Over the years
there has been a great deal of speculation about the use of subliminal messages in advertising, rock music, and
self-help audio programs. Research evidence shows that in laboratory settings, people can process and
respond to information outside of awareness. But this does not mean that we obey these messages like
zombies; in fact, hidden messages have little effect on behavior outside the laboratory (Kunst-Wilson & Zajonc,
1980; Rensink, 2004; Nelson, 2008; Radel, Sarrazin, Legrain, & Gobancé, 2009; Loersch, Durso, & Petty, 2013).

Absolute thresholds are generally measured under incredibly controlled conditions in situations that are
optimal for sensitivity. Sometimes, we are more interested in how much difference in stimuli is required to
detect a difference between them. This is known as the just noticeable difference ( jnd) or difference
threshold. Unlike the absolute threshold, the difference threshold changes depending on the stimulus
intensity. As an example, imagine yourself in a very dark movie theater. If an audience member were to receive
a text message that caused the cell phone screen to light up, chances are that many people would notice the
change in illumination in the theater. However, if the same thing happened in a brightly lit arena during a
basketball game, very few people would notice. The cell phone brightness does not change, but its ability to be
detected as a change in illumination varies dramatically between the two contexts. Ernst Weber proposed this
theory of change in difference threshold in the 1830s, and it has become known as Weber’s law: The difference
threshold is a constant fraction of the original stimulus, as the example illustrates.

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Perception

While our sensory receptors are constantly collecting information from the environment, it is ultimately how
we interpret that information that affects how we interact with the world. Perception refers to the way sensory
information is organized, interpreted, and consciously experienced. Perception involves both bottom-up and
top-down processing. Bottom-up processing refers to sensory information from a stimulus in the
environment driving a process, and top-down processing refers to knowledge and expectancy driving a
process, as shown in Figure 5.2 (Egeth & Yantis, 1997; Fine & Minnery, 2009; Yantis & Egeth, 1999).

FIGURE 5.2 Top-down and bottom-up are ways we process our perceptions.

Imagine that you and some friends are sitting in a crowded restaurant eating lunch and talking. It is very noisy,
and you are concentrating on your friend’s face to hear what they are saying, then the sound of breaking glass
and clang of metal pans hitting the floor rings out. The server dropped a large tray of food. Although you were
attending to your meal and conversation, that crashing sound would likely get through your attentional filters
and capture your attention. You would have no choice but to notice it. That attentional capture would be caused
by the sound from the environment: it would be bottom-up.

Alternatively, top-down processes are generally goal directed, slow, deliberate, effortful, and under your
control (Fine & Minnery, 2009; Miller & Cohen, 2001; Miller & D’Esposito, 2005). For instance, if you misplaced
your keys, how would you look for them? If you had a yellow key fob, you would probably look for yellowness of
a certain size in specific locations, such as on the counter, coffee table, and other similar places. You would not
look for yellowness on your ceiling fan, because you know keys are not normally lying on top of a ceiling fan.
That act of searching for a certain size of yellowness in some locations and not others would be top-
down—under your control and based on your experience.

One way to think of this concept is that sensation is a physical process, whereas perception is psychological.
For example, upon walking into a kitchen and smelling the scent of baking cinnamon rolls, the sensation is the
scent receptors detecting the odor of cinnamon, but the perception may be “Mmm, this smells like the bread
Grandma used to bake when the family gathered for holidays.”

Although our perceptions are built from sensations, not all sensations result in perception. In fact, we often
don’t perceive stimuli that remain relatively constant over prolonged periods of time. This is known as
sensory adaptation. Imagine going to a city that you have never visited. You check in to the hotel, but when
you get to your room, there is a road construction sign with a bright flashing light outside your window.
Unfortunately, there are no other rooms available, so you are stuck with a flashing light. You decide to watch
television to unwind. The flashing light was extremely annoying when you first entered your room. It was as if
someone was continually turning a bright yellow spotlight on and off in your room, but after watching
television for a short while, you no longer notice the light flashing. The light is still flashing and filling your
room with yellow light every few seconds, and the photoreceptors in your eyes still sense the light, but you no
longer perceive the rapid changes in lighting conditions. That you no longer perceive the flashing light
demonstrates sensory adaptation and shows that while closely associated, sensation and perception are
different.

5.1 • Sensation versus Perception 147

There is another factor that affects sensation and perception: attention. Attention plays a significant role in
determining what is sensed versus what is perceived. Imagine you are at a party full of music, chatter, and
laughter. You get involved in an interesting conversation with a friend, and you tune out all the background
noise. If someone interrupted you to ask what song had just finished playing, you would probably be unable to
answer that question.

LINK TO LEARNING

See for yourself how inattentional blindness works by checking out this selective attention test
(http://openstax.org/l/blindness) from Simons and Chabris (1999).

One of the most interesting demonstrations of how important attention is in determining our perception of the
environment occurred in a famous study conducted by Daniel Simons and Christopher Chabris (1999). In this
study, participants watched a video of people dressed in black and white passing basketballs. Participants
were asked to count the number of times the team dressed in white passed the ball. During the video, a person
dressed in a black gorilla costume walks among the two teams. You would think that someone would notice the
gorilla, right? Nearly half of the people who watched the video didn’t notice the gorilla at all, despite the fact
that he was clearly visible for nine seconds. Because participants were so focused on the number of times the
team dressed in white was passing the ball, they completely tuned out other visual information. Inattentional
blindness is the failure to notice something that is completely visible because the person was actively
attending to something else and did not pay attention to other things (Mack & Rock, 1998; Simons & Chabris,
1999).

In a similar experiment, researchers tested inattentional blindness by asking participants to observe images
moving across a computer screen. They were instructed to focus on either white or black objects, disregarding
the other color. When a red cross passed across the screen, about one third of subjects did not notice it (Figure
5.3) (Most, Simons, Scholl, & Chabris, 2000).

FIGURE 5.3 Nearly one third of participants in a study did not notice that a red cross passed on the screen because
their attention was focused on the black or white figures. (credit: Cory Zanker)

Motivation can also affect perception. Have you ever been expecting a really important phone call and, while
taking a shower, you think you hear the phone ringing, only to discover that it is not? If so, then you have
experienced how motivation to detect a meaningful stimulus can shift our ability to discriminate between a
true sensory stimulus and background noise. The ability to identify a stimulus when it is embedded in a
distracting background is called signal detection theory. This might also explain why a mother is awakened
by a quiet murmur from her baby but not by other sounds that occur while she is asleep. Signal detection
theory has practical applications, such as increasing air traffic controller accuracy. Controllers need to be able
to detect planes among many signals (blips) that appear on the radar screen and follow those planes as they
move through the sky. In fact, the original work of the researcher who developed signal detection theory was
focused on improving the sensitivity of air traffic controllers to plane blips (Swets, 1964).

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Our perceptions can also be affected by our beliefs, values, prejudices, expectations, and life experiences. As
you will see later in this chapter, individuals who are deprived of the experience of binocular vision during
critical periods of development have trouble perceiving depth (Fawcett, Wang, & Birch, 2005). The shared
experiences of people within a given cultural context can have pronounced effects on perception. For example,
Marshall Segall, Donald Campbell, and Melville Herskovits (1963) published the results of a multinational
study in which they demonstrated that individuals from Western cultures were more prone to experience
certain types of visual illusions than individuals from non-Western cultures, and vice versa. One such illusion
that Westerners were more likely to experience was the Müller-Lyer illusion (Figure 5.4): The lines appear to be
different lengths, but they are actually the same length.

FIGURE 5.4 In the Müller-Lyer illusion, lines appear to be different lengths although they are identical. (a) Arrows at
the ends of lines may make the line on the right appear longer, although the lines are the same length. (b) When
applied to a three-dimensional image, the line on the right again may appear longer although both black lines are
the same length.

These perceptual differences were consistent with differences in the types of environmental features
experienced on a regular basis by people in a given cultural context. People in Western cultures, for example,
have a perceptual context of buildings with straight lines, what Segall’s study called a carpentered world (Segall
et al., 1966). In contrast, people from certain non-Western cultures with an uncarpentered view, such as the
Zulu of South Africa, whose villages are made up of round huts arranged in circles, are less susceptible to this
illusion (Segall et al., 1999). It is not just vision that is affected by cultural factors. Indeed, research has
demonstrated that the ability to identify an odor, and rate its pleasantness and its intensity, varies cross-
culturally (Ayabe-Kanamura, Saito, Distel, Martínez-Gómez, & Hudson, 1998).

Children described as thrill seekers are more likely to show taste preferences for intense sour flavors (Liem,
Westerbeek, Wolterink, Kok, & de Graaf, 2004), which suggests that basic aspects of personality might affect
perception. Furthermore, individuals who hold positive attitudes toward reduced-fat foods are more likely to
rate foods labeled as reduced fat as tasting better than people who have less positive attitudes about these
products (Aaron, Mela, & Evans, 1994).

5.2 Waves and Wavelengths
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe important physical features of wave forms
• Show how physical properties of light waves are associated with perceptual experience
• Show how physical properties of sound waves are associated with perceptual experience

Visual and auditory stimuli both occur in the form of waves. Although the two stimuli are very different in
terms of composition, wave forms share similar characteristics that are especially important to our visual and

5.2 • Waves and Wavelengths 149

auditory perceptions. In this section, we describe the physical properties of the waves as well as the perceptual
experiences associated with them.

Amplitude and Wavelength

Two physical characteristics of a wave are amplitude and wavelength (Figure 5.5). The amplitude of a wave is
the distance from the center line to the top point of the crest or the bottom point of the trough. Wavelength
refers to the length of a wave from one peak to the next.

FIGURE 5.5 The amplitude or height of a wave is measured from the peak to the trough. The wavelength is
measured from peak to peak.

Wavelength is directly related to the frequency of a given wave form. Frequency refers to the number of waves
that pass a given point in a given time period and is often expressed in terms of hertz (Hz), or cycles per
second. Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies
(Figure 5.6).

FIGURE 5.6 This figure illustrates waves of differing wavelengths/frequencies. At the top of the figure, the red wave
has a long wavelength/short frequency. Moving from top to bottom, the wavelengths decrease and frequencies
increase.

Light Waves

The visible spectrum is the portion of the larger electromagnetic spectrum that we can see. As Figure 5.7
shows, the electromagnetic spectrum encompasses all of the electromagnetic radiation that occurs in our
environment and includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and
radio waves. The visible spectrum in humans is associated with wavelengths that range from 380 to 740 nm—a
very small distance, since a nanometer (nm) is one billionth of a meter. Other species can detect other portions
of the electromagnetic spectrum. For instance, honeybees can see light in the ultraviolet range (Wakakuwa,
Stavenga, & Arikawa, 2007), and some snakes can detect infrared radiation in addition to more traditional
visual light cues (Chen, Deng, Brauth, Ding, & Tang, 2012; Hartline, Kass, & Loop, 1978).

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FIGURE 5.7 Light that is visible to humans makes up only a small portion of the electromagnetic spectrum.

In humans, light wavelength is associated with perception of color (Figure 5.8). Within the visible spectrum,
our experience of red is associated with longer wavelengths, greens are intermediate, and blues and violets are
shorter in wavelength. (An easy way to remember this is the mnemonic ROYGBIV: red, orange, yellow, green,
blue, indigo, violet.) The amplitude of light waves is associated with our experience of brightness or intensity of
color, with larger amplitudes appearing brighter.

FIGURE 5.8 Different wavelengths of light are associated with our perception of different colors. (credit:
modification of work by Johannes Ahlmann)

Sound Waves

Like light waves, the physical properties of sound waves are associated with various aspects of our perception
of sound. The frequency of a sound wave is associated with our perception of that sound’s pitch. High-
frequency sound waves are perceived as high-pitched sounds, while low-frequency sound waves are perceived
as low-pitched sounds. The audible range of sound frequencies is between 20 and 20000 Hz, with greatest
sensitivity to those frequencies that fall in the middle of this range.

As was the case with the visible spectrum, other species show differences in their audible ranges. For instance,
chickens have a very limited audible range, from 125 to 2000 Hz. Mice have an audible range from 1000 to
91000 Hz, and the beluga whale’s audible range is from 1000 to 123000 Hz. Our pet dogs and cats have audible
ranges of about 70–45000 Hz and 45–64000 Hz, respectively (Strain, 2003).

The loudness of a given sound is closely associated with the amplitude of the sound wave. Higher amplitudes
are associated with louder sounds. Loudness is measured in terms of decibels (dB), a logarithmic unit of
sound intensity. A typical conversation would correlate with 60 dB; a rock concert might check in at 120 dB
(Figure 5.9). A whisper 5 feet away or rustling leaves are at the low end of our hearing range; sounds like a
window air conditioner, a normal conversation, and even heavy traffic or a vacuum cleaner are within a
tolerable range. However, there is the potential for hearing damage from about 80 dB to 130 dB: These are
sounds of a food processor, power lawnmower, heavy truck (25 feet away), subway train (20 feet away), live

5.2 • Waves and Wavelengths 151

rock music, and a jackhammer. About one-third of all hearing loss is due to noise exposure, and the louder the
sound, the shorter the exposure needed to cause hearing damage (Le, Straatman, Lea, & Westerberg, 2017).
Listening to music through earbuds at maximum volume (around 100–105 decibels) can cause noise-induced
hearing loss after 15 minutes of exposure. Although listening to music at maximum volume may not seem to
cause damage, it increases the risk of age-related hearing loss (Kujawa & Liberman, 2006). The threshold for
pain is about 130 dB, a jet plane taking off or a revolver firing at close range (Dunkle, 1982).

FIGURE 5.9 This figure illustrates the loudness of common sounds. (credit “planes”: modification of work by Max
Pfandl; credit “crowd”: modification of work by Christian Holmér; credit: “earbuds”: modification of work by “Skinny
Guy Lover_Flickr”/Flickr; credit “traffic”: modification of work by “quinntheislander_Pixabay”/Pixabay; credit
“talking”: modification of work by Joi Ito; credit “leaves”: modification of work by Aurelijus Valeiša)

Although wave amplitude is generally associated with loudness, there is some interaction between frequency
and amplitude in our perception of loudness within the audible range. For example, a 10 Hz sound wave is
inaudible no matter the amplitude of the wave. A 1000 Hz sound wave, on the other hand, would vary
dramatically in terms of perceived loudness as the amplitude of the wave increased.

LINK TO LEARNING

Watch this brief video about our perception of frequency and amplitude (http://openstax.org/l/frequency) to
learn more.

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Of course, different musical instruments can play the same musical note at the same level of loudness, yet they
still sound quite different. This is known as the timbre of a sound. Timbre refers to a sound’s purity, and it is
affected by the complex interplay of frequency, amplitude, and timing of sound waves.

5.3 Vision
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the basic anatomy of the visual system
• Discuss how rods and cones contribute to different aspects of vision
• Describe how monocular and binocular cues are used in the perception of depth

The visual system constructs a mental representation of the world around us (Figure 5.10). This contributes to
our ability to successfully navigate through physical space and interact with important individuals and objects
in our environments. This section will provide an overview of the basic anatomy and function of the visual
system. In addition, we will explore our ability to perceive color and depth.

FIGURE 5.10 Our eyes take in sensory information that helps us understand the world around us. (credit “top left”:
modification of work by “rajkumar1220″/Flickr”; credit “top right”: modification of work by Thomas Leuthard; credit
“middle left”: modification of work by Demietrich Baker; credit “middle right”: modification of work by
“kaybee07″/Flickr; credit “bottom left”: modification of work by “Isengardt”/Flickr; credit “bottom right”:
modification of work by Willem Heerbaart)

Anatomy of the Visual System

The eye is the major sensory organ involved in vision (Figure 5.11). Light waves are transmitted across the
cornea and enter the eye through the pupil. The cornea is the transparent covering over the eye. It serves as a
barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the
eye. The pupil is the small opening in the eye through which light passes, and the size of the pupil can change
as a function of light levels as well as emotional arousal. When light levels are low, the pupil will become
dilated, or expanded, to allow more light to enter the eye. When light levels are high, the pupil will constrict, or
become smaller, to reduce the amount of light that enters the eye. The pupil’s size is controlled by muscles that
are connected to the iris, which is the colored portion of the eye.

5.3 • Vision 153

FIGURE 5.11 The anatomy of the eye is illustrated in this diagram.

After passing through the pupil, light crosses the lens, a curved, transparent structure that serves to provide
additional focus. The lens is attached to muscles that can change its shape to aid in focusing light that is
reflected from near or far objects. In a normal-sighted individual, the lens will focus images perfectly on a
small indentation in the back of the eye known as the fovea, which is part of the retina, the light-sensitive
lining of the eye. The fovea contains densely packed specialized photoreceptor cells (Figure 5.12). These
photoreceptor cells, known as cones, are light-detecting cells. The cones are specialized types of
photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide
tremendous spatial resolution. They also are directly involved in our ability to perceive color.

While cones are concentrated in the fovea, where images tend to be focused, rods, another type of
photoreceptor, are located throughout the remainder of the retina. Rods are specialized photoreceptors that
work well in low light conditions, and while they lack the spatial resolution and color function of the cones,
they are involved in our vision in dimly lit environments as well as in our perception of movement on the
periphery of our visual field.

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FIGURE 5.12 The two types of photoreceptors are shown in this image. Cones are colored green and rods are blue.

We have all experienced the different sensitivities of rods and cones when making the transition from a
brightly lit environment to a dimly lit environment. Imagine going to see a blockbuster movie on a clear
summer day. As you walk from the brightly lit lobby into the dark theater, you notice that you immediately have
difficulty seeing much of anything. After a few minutes, you begin to adjust to the darkness and can see the
interior of the theater. In the bright environment, your vision was dominated primarily by cone activity. As you
move to the dark environment, rod activity dominates, but there is a delay in transitioning between the phases.
If your rods do not transform light into nerve impulses as easily and efficiently as they should, you will have
difficulty seeing in dim light, a condition known as night blindness.

Rods and cones are connected (via several interneurons) to retinal ganglion cells. Axons from the retinal
ganglion cells converge and exit through the back of the eye to form the optic nerve. The optic nerve carries
visual information from the retina to the brain. There is a point in the visual field called the blind spot: Even
when light from a small object is focused on the blind spot, we do not see it. We are not consciously aware of
our blind spots for two reasons: First, each eye gets a slightly different view of the visual field; therefore, the
blind spots do not overlap. Second, our visual system fills in the blind spot so that although we cannot respond
to visual information that occurs in that portion of the visual field, we are also not aware that information is
missing.

The optic nerve from each eye merges just below the brain at a point called the optic chiasm. As Figure 5.13
shows, the optic chiasm is an X-shaped structure that sits just below the cerebral cortex at the front of the
brain. At the point of the optic chiasm, information from the right visual field (which comes from both eyes) is
sent to the left side of the brain, and information from the left visual field is sent to the right side of the brain.

5.3 • Vision 155

FIGURE 5.13 This illustration shows the optic chiasm at the front of the brain and the pathways to the occipital lobe
at the back of the brain, where visual sensations are processed into meaningful perceptions.

Once inside the brain, visual information is sent via a number of structures to the occipital lobe at the back of
the brain for processing. Visual information might be processed in parallel pathways which can generally be
described as the “what pathway” and the “where/how” pathway. The “what pathway” is involved in object
recognition and identification, while the “where/how pathway” is involved with location in space and how one
might interact with a particular visual stimulus (Milner & Goodale, 2008; Ungerleider & Haxby, 1994). For
example, when you see a ball rolling down the street, the “what pathway” identifies what the object is, and the
“where/how pathway” identifies its location or movement in space.

The Ethics of Research Using Animals
David Hubel and Torsten Wiesel were awarded the Nobel Prize in Medicine in 1981 for their research on the
visual system. They collaborated for more than twenty years and made significant discoveries about the
neurology of visual perception (Hubel & Wiesel, 1959, 1962, 1963, 1970; Wiesel & Hubel, 1963). They studied
animals, mostly cats and monkeys. Although they used several techniques, they did considerable single unit
recordings, during which tiny electrodes were inserted in the animal’s brain to determine when a single cell was
activated. Among their many discoveries, they found that specific brain cells respond to lines with specific
orientations (called ocular dominance), and they mapped the way those cells are arranged in areas of the visual
cortex known as columns and hypercolumns.

In some of their research, they sutured one eye of newborn kittens closed and followed the development of the
kittens’ vision. They discovered there was a critical period of development for vision. If kittens were deprived of
input from one eye, other areas of their visual cortex filled in the area that was normally used by the eye that was
sewn closed. In other words, neural connections that exist at birth can be lost if they are deprived of sensory
input.

What do you think about sewing a kitten’s eye closed for research? To many animal advocates, this would seem
brutal, abusive, and unethical. What if you could do research that would help ensure babies and children born
with certain conditions could develop full vision instead of becoming blind? Would you want that research done?
Would you conduct that research, even if it meant causing some harm to cats? Would you think the same way if

WHAT DO YOU THINK?

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you were the parent of such a child? What if you worked at the animal shelter?

Like virtually every other industrialized nation, the United States permits medical experimentation on animals,
with few limitations (assuming sufficient scientific justification). The goal of any laws that exist is not to ban such
tests but rather to limit unnecessary animal suffering by establishing standards for the humane treatment and
housing of animals in laboratories.

As explained by Stephen Latham, the director of the Interdisciplinary Center for Bioethics at Yale (2012),
possible legal and regulatory approaches to animal testing vary on a continuum from strong government
regulation and monitoring of all experimentation at one end, to a self-regulated approach that depends on the
ethics of the researchers at the other end. The United Kingdom has the most significant regulatory scheme,
whereas Japan uses the self-regulation approach. The U.S. approach is somewhere in the middle, the result of a
gradual blending of the two approaches.

There is no question that medical research is a valuable and important practice. The question is whether the use
of animals is a necessary or even best practice for producing the most reliable results. Alternatives include the
use of patient-drug databases, virtual drug trials, computer models and simulations, and noninvasive imaging
techniques such as magnetic resonance imaging and computed tomography scans (“Animals in Science/
Alternatives,” n.d.). Other techniques, such as microdosing, use humans not as test animals but as a means to
improve the accuracy and reliability of test results. In vitro methods based on human cell and tissue cultures,
stem cells, and genetic testing methods are also increasingly available.

Today, at the local level, any facility that uses animals and receives federal funding must have an Institutional
Animal Care and Use Committee (IACUC) that ensures that the NIH guidelines are being followed. The IACUC
must include researchers, administrators, a veterinarian, and at least one person with no ties to the institution:
that is, a concerned citizen. This committee also performs inspections of laboratories and protocols.

Color and Depth Perception

We do not see the world in black and white; neither do we see it as two-dimensional (2-D) or flat (just height
and width, no depth). Let’s look at how color vision works and how we perceive three dimensions (height,
width, and depth).

Color Vision

Normal-sighted individuals have three different types of cones that mediate color vision. Each of these cone
types is maximally sensitive to a slightly different wavelength of light. According to the trichromatic theory of
color vision, shown in Figure 5.14, all colors in the spectrum can be produced by combining red, green, and
blue. The three types of cones are each receptive to one of the colors.

5.3 • Vision 157

FIGURE 5.14 This figure illustrates the different sensitivities for the three cone types found in a normal-sighted
individual. (credit: modification of work by Vanessa Ezekowitz)

Colorblindness: A Personal Story
Several years ago, I dressed to go to a public function and walked into the kitchen where my 7-year-old daughter
sat. She looked up at me, and in her most stern voice, said, “You can’t wear that.” I asked, “Why not?” and she
informed me the colors of my clothes did not match. She had complained frequently that I was bad at matching my
shirts, pants, and ties, but this time, she sounded especially alarmed. As a single father with no one else to ask at
home, I drove us to the nearest convenience store and asked the store clerk if my clothes matched. She said my
pants were a bright green color, my shirt was a reddish orange, and my tie was brown. She looked at my quizzically
and said, “No way do your clothes match.” Over the next few days, I started asking my coworkers and friends if my
clothes matched. After several days of being told that my coworkers just thought I had “a really unique style,” I
made an appointment with an eye doctor and was tested (Figure 5.15). It was then that I found out that I was
colorblind. I cannot differentiate between most greens, browns, and reds. Fortunately, other than unknowingly
being badly dressed, my colorblindness rarely harms my day-to-day life.

FIGURE 5.15 The Ishihara test evaluates color perception by assessing whether individuals can discern numbers
that appear in a circle of dots of varying colors and sizes.

Some forms of color deficiency are rare. Seeing in grayscale (only shades of black and white) is extremely rare, and
people who do so only have rods, which means they have very low visual acuity and cannot see very well. The most
common X-linked inherited abnormality is red-green color blindness (Birch, 2012). Approximately 8% of males with
European Caucasian decent, 5% of Asian males, 4% of African males, and less than 2% of indigenous American
males, Australian males, and Polynesian males have red-green color deficiency (Birch, 2012). Comparatively, only

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about 0.4% in females from European Caucasian descent have red-green color deficiency (Birch, 2012).

The trichromatic theory of color vision is not the only theory—another major theory of color vision is known as
the opponent-process theory. According to this theory, color is coded in opponent pairs: black-white, yellow-
blue, and green-red. The basic idea is that some cells of the visual system are excited by one of the opponent
colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be
inhibited by wavelengths associated with red, and vice versa. One of the implications of opponent processing is
that we do not experience greenish-reds or yellowish-blues as colors. Another implication is that this leads to
the experience of negative afterimages. An afterimage describes the continuation of a visual sensation after
removal of the stimulus. For example, when you stare briefly at the sun and then look away from it, you may
still perceive a spot of light although the stimulus (the sun) has been removed. When color is involved in the
stimulus, the color pairings identified in the opponent-process theory lead to a negative afterimage. You can
test this concept using the flag in Figure 5.16.

FIGURE 5.16 Stare at the white dot for 30–60 seconds and then move your eyes to a blank piece of white paper.
What do you see? This is known as a negative afterimage, and it provides empirical support for the opponent-
process theory of color vision.

But these two theories—the trichromatic theory of color vision and the opponent-process theory—are not
mutually exclusive. Research has shown that they just apply to different levels of the nervous system. For
visual processing on the retina, trichromatic theory applies: the cones are responsive to three different
wavelengths that represent red, blue, and green. But once the signal moves past the retina on its way to the
brain, the cells respond in a way consistent with opponent-process theory (Land, 1959; Kaiser, 1997).

LINK TO LEARNING

Watch this video about color perception (http://openstax.org/l/colorvision) to learn more.

Depth Perception

Our ability to perceive spatial relationships in three-dimensional (3-D) space is known as depth perception.
With depth perception, we can describe things as being in front, behind, above, below, or to the side of other
things.

Our world is three-dimensional, so it makes sense that our mental representation of the world has three-
dimensional properties. We use a variety of cues in a visual scene to establish our sense of depth. Some of
these are binocular cues, which means that they rely on the use of both eyes. One example of a binocular
depth cue is binocular disparity, the slightly different view of the world that each of our eyes receives. To
experience this slightly different view, do this simple exercise: extend your arm fully and extend one of your

5.3 • Vision 159

fingers and focus on that finger. Now, close your left eye without moving your head, then open your left eye and
close your right eye without moving your head. You will notice that your finger seems to shift as you alternate
between the two eyes because of the slightly different view each eye has of your finger.

A 3-D movie works on the same principle: the special glasses you wear allow the two slightly different images
projected onto the screen to be seen separately by your left and your right eye. As your brain processes these
images, you have the illusion that the leaping animal or running person is coming right toward you.

Although we rely on binocular cues to experience depth in our 3-D world, we can also perceive depth in 2-D
arrays. Think about all the paintings and photographs you have seen. Generally, you pick up on depth in these
images even though the visual stimulus is 2-D. When we do this, we are relying on a number of monocular
cues, or cues that require only one eye. If you think you can’t see depth with one eye, note that you don’t bump
into things when using only one eye while walking—and, in fact, we have more monocular cues than binocular
cues.

An example of a monocular cue would be what is known as linear perspective. Linear perspective refers to the
fact that we perceive depth when we see two parallel lines that seem to converge in an image (Figure 5.17).
Some other monocular depth cues are interposition, the partial overlap of objects, and the relative size and
closeness of images to the horizon.

FIGURE 5.17 We perceive depth in a two-dimensional figure like this one through the use of monocular cues like
linear perspective, like the parallel lines converging as the road narrows in the distance. (credit: Marc Dalmulder)

Stereoblindness
Bruce Bridgeman was born with an extreme case of lazy eye that resulted in him being stereoblind, or unable to
respond to binocular cues of depth. He relied heavily on monocular depth cues, but he never had a true
appreciation of the 3-D nature of the world around him. This all changed one night in 2012 while Bruce was
seeing a movie with his wife.

The movie the couple was going to see was shot in 3-D, and even though he thought it was a waste of money,
Bruce paid for the 3-D glasses when he purchased his ticket. As soon as the film began, Bruce put on the glasses
and experienced something completely new. For the first time in his life he appreciated the true depth of the
world around him. Remarkably, his ability to perceive depth persisted outside of the movie theater.

There are cells in the nervous system that respond to binocular depth cues. Normally, these cells require
activation during early development in order to persist, so experts familiar with Bruce’s case (and others like his)

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assume that at some point in his development, Bruce must have experienced at least a fleeting moment of
binocular vision. It was enough to ensure the survival of the cells in the visual system tuned to binocular cues.
The mystery now is why it took Bruce nearly 70 years to have these cells activated (Peck, 2012).

5.4 Hearing
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the basic anatomy and function of the auditory system
• Explain how we encode and perceive pitch
• Discuss how we localize sound

Our auditory system converts pressure waves into meaningful sounds. This translates into our ability to hear
the sounds of nature, to appreciate the beauty of music, and to communicate with one another through spoken
language. This section will provide an overview of the basic anatomy and function of the auditory system. It
will include a discussion of how the sensory stimulus is translated into neural impulses, where in the brain
that information is processed, how we perceive pitch, and how we know where sound is coming from.

Anatomy of the Auditory System

The ear can be separated into multiple sections. The outer ear includes the pinna, which is the visible part of
the ear that protrudes from our heads, the auditory canal, and the tympanic membrane, or eardrum. The
middle ear contains three tiny bones known as the ossicles, which are named the malleus (or hammer), incus
(or anvil), and the stapes (or stirrup). The inner ear contains the semi-circular canals, which are involved in
balance and movement (the vestibular sense), and the cochlea. The cochlea is a fluid-filled, snail-shaped
structure that contains the sensory receptor cells (hair cells) of the auditory system (Figure 5.18).

FIGURE 5.18 The ear is divided into outer (pinna and tympanic membrane), middle (the three ossicles: malleus,
incus, and stapes), and inner (cochlea and basilar membrane) divisions.

Sound waves travel along the auditory canal and strike the tympanic membrane, causing it to vibrate. This
vibration results in movement of the three ossicles. As the ossicles move, the stapes presses into a thin
membrane of the cochlea known as the oval window. As the stapes presses into the oval window, the fluid
inside the cochlea begins to move, which in turn stimulates hair cells, which are auditory receptor cells of the
inner ear embedded in the basilar membrane. The basilar membrane is a thin strip of tissue within the
cochlea.

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The activation of hair cells is a mechanical process: the stimulation of the hair cell ultimately leads to
activation of the cell. As hair cells become activated, they generate neural impulses that travel along the
auditory nerve to the brain. Auditory information is shuttled to the inferior colliculus, the medial geniculate
nucleus of the thalamus, and finally to the auditory cortex in the temporal lobe of the brain for processing. Like
the visual system, there is also evidence suggesting that information about auditory recognition and
localization is processed in parallel streams (Rauschecker & Tian, 2000; Renier et al., 2009).

Pitch Perception

Different frequencies of sound waves are associated with differences in our perception of the pitch of those
sounds. Low-frequency sounds are lower pitched, and high-frequency sounds are higher pitched. How does
the auditory system differentiate among various pitches?

Several theories have been proposed to account for pitch perception. We’ll discuss two of them here: temporal
theory and place theory. The temporal theory of pitch perception asserts that frequency is coded by the
activity level of a sensory neuron. This would mean that a given hair cell would fire action potentials related to
the frequency of the sound wave. While this is a very intuitive explanation, we detect such a broad range of
frequencies (20–20,000 Hz) that the frequency of action potentials fired by hair cells cannot account for the
entire range. Because of properties related to sodium channels on the neuronal membrane that are involved in
action potentials, there is a point at which a cell cannot fire any faster (Shamma, 2001).

The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to
sounds of different frequencies. More specifically, the base of the basilar membrane responds best to high
frequencies and the tip of the basilar membrane responds best to low frequencies. Therefore, hair cells that
are in the base portion would be labeled as high-pitch receptors, while those in the tip of basilar membrane
would be labeled as low-pitch receptors (Shamma, 2001).

In reality, both theories explain different aspects of pitch perception. At frequencies up to about 4000 Hz, it is
clear that both the rate of action potentials and place contribute to our perception of pitch. However, much
higher frequency sounds can only be encoded using place cues (Shamma, 2001).

Sound Localization

The ability to locate sound in our environments is an important part of hearing. Localizing sound could be
considered similar to the way that we perceive depth in our visual fields. Like the monocular and binocular
cues that provided information about depth, the auditory system uses both monaural (one-eared) and
binaural (two-eared) cues to localize sound.

Each pinna interacts with incoming sound waves differently, depending on the sound’s source relative to our
bodies. This interaction provides a monaural cue that is helpful in locating sounds that occur above or below
and in front or behind us. The sound waves received by your two ears from sounds that come from directly
above, below, in front, or behind you would be identical; therefore, monaural cues are essential (Grothe, Pecka,
& McAlpine, 2010).

Binaural cues, on the other hand, provide information on the location of a sound along a horizontal axis by
relying on differences in patterns of vibration of the eardrum between our two ears. If a sound comes from an
off-center location, it creates two types of binaural cues: interaural level differences and interaural timing
differences. Interaural level difference refers to the fact that a sound coming from the right side of your body
is more intense at your right ear than at your left ear because of the attenuation of the sound wave as it passes
through your head. Interaural timing difference refers to the small difference in the time at which a given
sound wave arrives at each ear (Figure 5.19). Certain brain areas monitor these differences to construct where
along a horizontal axis a sound originates (Grothe et al., 2010).

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FIGURE 5.19 Localizing sound involves the use of both monaural and binaural cues. (credit “plane”: modification of
work by Max Pfandl)

Hearing Loss

Deafness is the partial or complete inability to hear. Some people are born without hearing, which is known as
congenital deafness. Other people suffer from conductive hearing loss, which is due to a problem delivering
sound energy to the cochlea. Causes for conductive hearing loss include blockage of the ear canal, a hole in the
tympanic membrane, problems with the ossicles, or fluid in the space between the eardrum and cochlea.
Another group of people suffer from sensorineural hearing loss, which is the most common form of hearing
loss. Sensorineural hearing loss can be caused by many factors, such as aging, head or acoustic trauma,
infections and diseases (such as measles or mumps), medications, environmental effects such as noise
exposure (noise-induced hearing loss, as shown in Figure 5.20), tumors, and toxins (such as those found in
certain solvents and metals).

FIGURE 5.20 Environmental factors that can lead to sensorineural hearing loss include regular exposure to loud
music or construction equipment. (a) Musical performers and (b) construction workers are at risk for this type of
hearing loss. (credit a: modification of work by “GillyBerlin_Flickr”/Flickr; credit b: modification of work by Nick
Allen)

Given the mechanical nature by which the sound wave stimulus is transmitted from the eardrum through the
ossicles to the oval window of the cochlea, some degree of hearing loss is inevitable. With conductive hearing

5.4 • Hearing 163

loss, hearing problems are associated with a failure in the vibration of the eardrum and/or movement of the
ossicles. These problems are often dealt with through devices like hearing aids that amplify incoming sound
waves to make vibration of the eardrum and movement of the ossicles more likely to occur.

When the hearing problem is associated with a failure to transmit neural signals from the cochlea to the brain,
it is called sensorineural hearing loss. One disease that results in sensorineural hearing loss is Ménière’s
disease. Although not well understood, Ménière’s disease results in a degeneration of inner ear structures that
can lead to hearing loss, tinnitus (constant ringing or buzzing), vertigo (a sense of spinning), and an increase
in pressure within the inner ear (Semaan & Megerian, 2011). This kind of loss cannot be treated with hearing
aids, but some individuals might be candidates for a cochlear implant as a treatment option. Cochlear
implants are electronic devices that consist of a microphone, a speech processor, and an electrode array. The
device receives incoming sound information and directly stimulates the auditory nerve to transmit
information to the brain.

LINK TO LEARNING

Watch this video about cochlear implant surgeries (http://openstax.org/l/cochlear) to learn more.

Deaf Culture
In the United States and other places around the world, deaf people have their own language, schools, and
customs. This is called deaf culture. In the United States, deaf individuals often communicate using American
Sign Language (ASL); ASL has no verbal component and is based entirely on visual signs and gestures. The
primary mode of communication is signing. One of the values of deaf culture is to continue traditions like using
sign language rather than teaching deaf children to try to speak, read lips, or have cochlear implant surgery.

When a child is diagnosed as deaf, parents have difficult decisions to make. Should the child be enrolled in
mainstream schools and taught to verbalize and read lips? Or should the child be sent to a school for deaf
children to learn ASL and have significant exposure to deaf culture? Do you think there might be differences in
the way that parents approach these decisions depending on whether or not they are also deaf?

5.5 The Other Senses
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Describe the basic functions of the chemical senses
• Explain the basic functions of the somatosensory, nociceptive, and thermoceptive sensory systems
• Describe the basic functions of the vestibular, proprioceptive, and kinesthetic sensory systems

Vision and hearing have received an incredible amount of attention from researchers over the years. While
there is still much to be learned about how these sensory systems work, we have a much better understanding
of them than of our other sensory modalities. In this section, we will explore our chemical senses (taste and
smell) and our body senses (touch, temperature, pain, balance, and body position).

The Chemical Senses

Taste (gustation) and smell (olfaction) are called chemical senses because both have sensory receptors that
respond to molecules in the food we eat or in the air we breathe. There is a pronounced interaction between
our chemical senses. For example, when we describe the flavor of a given food, we are really referring to both
gustatory and olfactory properties of the food working in combination.

WHAT DO YOU THINK?

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Taste (Gustation)

You have learned since elementary school that there are four basic groupings of taste: sweet, salty, sour, and
bitter. Research demonstrates, however, that we have at least six taste groupings. Umami is our fifth taste.
Umami is actually a Japanese word that roughly translates to yummy, and it is associated with a taste for
monosodium glutamate (Kinnamon & Vandenbeuch, 2009). There is also a growing body of experimental
evidence suggesting that we possess a taste for the fatty content of a given food (Mizushige, Inoue, & Fushiki,
2007).

Molecules from the food and beverages we consume dissolve in our saliva and interact with taste receptors on
our tongue and in our mouth and throat. Taste buds are formed by groupings of taste receptor cells with hair-
like extensions that protrude into the central pore of the taste bud (Figure 5.21). Taste buds have a life cycle of
ten days to two weeks, so even destroying some by burning your tongue won’t have any long-term effect; they
just grow right back. Taste molecules bind to receptors on this extension and cause chemical changes within
the sensory cell that result in neural impulses being transmitted to the brain via different nerves, depending
on where the receptor is located. Taste information is transmitted to the medulla, thalamus, and limbic
system, and to the gustatory cortex, which is tucked underneath the overlap between the frontal and temporal
lobes (Maffei, Haley, & Fontanini, 2012; Roper, 2013).

FIGURE 5.21 (a) Taste buds are composed of a number of individual taste receptors cells that transmit information
to nerves. (b) This micrograph shows a close-up view of the tongue’s surface. (credit a: modification of work by
Jonas Töle; credit b: scale-bar data from Matt Russell)

Smell (Olfaction)

Olfactory receptor cells are located in a mucous membrane at the top of the nose. Small hair-like extensions
from these receptors serve as the sites for odor molecules dissolved in the mucus to interact with chemical
receptors located on these extensions (Figure 5.22). Once an odor molecule has bound a given receptor,
chemical changes within the cell result in signals being sent to the olfactory bulb: a bulb-like structure at the
tip of the frontal lobe where the olfactory nerves begin. From the olfactory bulb, information is sent to regions
of the limbic system and to the primary olfactory cortex, which is located very near the gustatory cortex
(Lodovichi & Belluscio, 2012; Spors et al., 2013).

5.5 • The Other Senses 165

FIGURE 5.22 Olfactory receptors are the hair-like parts that extend from the olfactory bulb into the mucous
membrane of the nasal cavity.

There is tremendous variation in the sensitivity of the olfactory systems of different species. We often think of
dogs as having far superior olfactory systems than our own, and indeed, dogs can do some remarkable things
with their noses. There is some evidence to suggest that dogs can “smell” dangerous drops in blood glucose
levels as well as cancerous tumors (Wells, 2010). Dogs’ extraordinary olfactory abilities may be due to the
increased number of functional genes for olfactory receptors (between 800 and 1200), compared to the fewer
than 400 observed in humans and other primates (Niimura & Nei, 2007).

Many species respond to chemical messages, known as pheromones, sent by another individual (Wysocki &
Preti, 2004). Pheromonal communication often involves providing information about the reproductive status
of a potential mate. So, for example, when a female rat is ready to mate, it secretes pheromonal signals that
draw attention from nearby male rats. Pheromonal activation is actually an important component in eliciting
sexual behavior in the male rat (Furlow, 1996, 2012; Purvis & Haynes, 1972; Sachs, 1997). There has also been
a good deal of research (and controversy) about pheromones in humans (Comfort, 1971; Russell, 1976;
Wolfgang-Kimball, 1992; Weller, 1998).

Touch, Thermoception, and Nociception

A number of receptors are distributed throughout the skin to respond to various touch-related stimuli (Figure
5.23). These receptors include Meissner’s corpuscles, Pacinian corpuscles, Merkel’s disks, and Ruffini
corpuscles. Meissner’s corpuscles respond to pressure and lower frequency vibrations, and Pacinian
corpuscles detect transient pressure and higher frequency vibrations. Merkel’s disks respond to light
pressure, while Ruffini corpuscles detect stretch (Abraira & Ginty, 2013).

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FIGURE 5.23 There are many types of sensory receptors located in the skin, each attuned to specific touch-related
stimuli.

In addition to the receptors located in the skin, there are also a number of free nerve endings that serve
sensory functions. These nerve endings respond to a variety of different types of touch-related stimuli and
serve as sensory receptors for both thermoception (temperature perception) and nociception (a signal
indicating potential harm and maybe pain) (Garland, 2012; Petho & Reeh, 2012; Spray, 1986). Sensory
information collected from the receptors and free nerve endings travels up the spinal cord and is transmitted
to regions of the medulla, thalamus, and ultimately to somatosensory cortex, which is located in the
postcentral gyrus of the parietal lobe.

Pain Perception

Pain is an unpleasant experience that involves both physical and psychological components. Feeling pain is
quite adaptive because it makes us aware of an injury, and it motivates us to remove ourselves from the cause
of that injury. In addition, pain also makes us less likely to suffer additional injury because we will be gentler
with our injured body parts.

Generally speaking, pain can be considered to be neuropathic or inflammatory in nature. Pain that signals
some type of tissue damage is known as inflammatory pain. In some situations, pain results from damage to
neurons of either the peripheral or central nervous system. As a result, pain signals that are sent to the brain
get exaggerated. This type of pain is known as neuropathic pain. Multiple treatment options for pain relief
range from relaxation therapy to the use of analgesic medications to deep brain stimulation. The most effective
treatment option for a given individual will depend on a number of considerations, including the severity and
persistence of the pain and any medical/psychological conditions.

Some individuals are born without the ability to feel pain. This very rare genetic disorder is known as
congenital insensitivity to pain (or congenital analgesia). While those with congenital analgesia can detect
differences in temperature and pressure, they cannot experience pain. As a result, they often suffer significant
injuries. Young children have serious mouth and tongue injuries because they have bitten themselves
repeatedly. Not surprisingly, individuals suffering from this disorder have much shorter life expectancies due
to their injuries and secondary infections of injured sites (U.S. National Library of Medicine, 2013).

LINK TO LEARNING

Watch this video about congenital insensitivity to pain (http://openstax.org/l/congenital) to learn more.

The Vestibular Sense, Proprioception, and Kinesthesia

The vestibular sense contributes to our ability to maintain balance and body posture. As Figure 5.24 shows,
the major sensory organs (utricle, saccule, and the three semicircular canals) of this system are located next to
the cochlea in the inner ear. The vestibular organs are fluid-filled and have hair cells, similar to the ones found

5.5 • The Other Senses 167

in the auditory system, which respond to movement of the head and gravitational forces. When these hair cells
are stimulated, they send signals to the brain via the vestibular nerve. Although we may not be consciously
aware of our vestibular system’s sensory information under normal circumstances, its importance is apparent
when we experience motion sickness and/or dizziness related to infections of the inner ear (Khan & Chang,
2013).

FIGURE 5.24 The major sensory organs of the vestibular system are located next to the cochlea in the inner ear.
These include the utricle, saccule, and the three semicircular canals (posterior, superior, and horizontal).

In addition to maintaining balance, the vestibular system collects information critical for controlling
movement and the reflexes that move various parts of our bodies to compensate for changes in body position.
Therefore, both proprioception (perception of body position) and kinesthesia (perception of the body’s
movement through space) interact with information provided by the vestibular system.

These sensory systems also gather information from receptors that respond to stretch and tension in muscles,
joints, skin, and tendons (Lackner & DiZio, 2005; Proske, 2006; Proske & Gandevia, 2012). Proprioceptive and
kinesthetic information travels to the brain via the spinal column. Several cortical regions in addition to the
cerebellum receive information from and send information to the sensory organs of the proprioceptive and
kinesthetic systems.

5.6 Gestalt Principles of Perception
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain the figure-ground relationship
• Define Gestalt principles of grouping
• Describe how perceptual set is influenced by an individual’s characteristics and mental state

In the early part of the 20th century, Max Wertheimer published a paper demonstrating that individuals
perceived motion in rapidly flickering static images—an insight that came to him as he used a child’s toy
tachistoscope. Wertheimer, and his assistants Wolfgang Köhler and Kurt Koffka, who later became his
partners, believed that perception involved more than simply combining sensory stimuli. This belief led to a
new movement within the field of psychology known as Gestalt psychology. The word gestalt literally means
form or pattern, but its use reflects the idea that the whole is different from the sum of its parts. In other words,
the brain creates a perception that is more than simply the sum of available sensory inputs, and it does so in
predictable ways. Gestalt psychologists translated these predictable ways into principles by which we organize
sensory information. As a result, Gestalt psychology has been extremely influential in the area of sensation

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and perception (Rock & Palmer, 1990).

One Gestalt principle is the figure-ground relationship. According to this principle, we tend to segment our
visual world into figure and ground. Figure is the object or person that is the focus of the visual field, while the
ground is the background. As Figure 5.25 shows, our perception can vary tremendously, depending on what is
perceived as figure and what is perceived as ground. Presumably, our ability to interpret sensory information
depends on what we label as figure and what we label as ground in any particular case, although this
assumption has been called into question (Peterson & Gibson, 1994; Vecera & O’Reilly, 1998).

FIGURE 5.25 The concept of figure-ground relationship explains why this image can be perceived either as a vase
or as a pair of faces.

Another Gestalt principle for organizing sensory stimuli into meaningful perception is proximity. This
principle asserts that things that are close to one another tend to be grouped together, as Figure 5.26
illustrates.

FIGURE 5.26 The Gestalt principle of proximity suggests that you see (a) one block of dots on the left side and (b)
three columns on the right side.

How we read something provides another illustration of the proximity concept. For example, we read this
sentence like this, notl iket hiso rt hat. We group the letters of a given word together because there are no
spaces between the letters, and we perceive words because there are spaces between each word. Here are
some more examples: Cany oum akes enseo ft hiss entence? What doth es e wor dsmea n?

We might also use the principle of similarity to group things in our visual fields. According to this principle,
things that are alike tend to be grouped together (Figure 5.27). For example, when watching a football game, we
tend to group individuals based on the colors of their uniforms. When watching an offensive drive, we can get a

5.6 • Gestalt Principles of Perception 169

sense of the two teams simply by grouping along this dimension.

FIGURE 5.27 When looking at this array of dots, we likely perceive alternating rows of colors. We are grouping these
dots according to the principle of similarity.

Two additional Gestalt principles are the law of continuity (or good continuation) and closure. The law of
continuity suggests that we are more likely to perceive continuous, smooth flowing lines rather than jagged,
broken lines (Figure 5.28). The principle of closure states that we organize our perceptions into complete
objects rather than as a series of parts (Figure 5.29).

FIGURE 5.28 Good continuation would suggest that we are more likely to perceive this as two overlapping lines,
rather than four lines meeting in the center.

FIGURE 5.29 Closure suggests that we will perceive a complete circle and rectangle rather than a series of
segments.

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LINK TO LEARNING

Watch this video showing real world examples of Gestalt principles (http://openstax.org/l/gestalt) to learn
more.

According to Gestalt theorists, pattern perception, or our ability to discriminate among different figures and
shapes, occurs by following the principles described above. You probably feel fairly certain that your
perception accurately matches the real world, but this is not always the case. Our perceptions are based on
perceptual hypotheses: educated guesses that we make while interpreting sensory information. These
hypotheses are informed by a number of factors, including our personalities, experiences, and expectations.
We use these hypotheses to generate our perceptual set. For instance, research has demonstrated that those
who are given verbal priming produce a biased interpretation of complex ambiguous figures (Goolkasian &
Woodbury, 2010).

The Depths of Perception: Bias, Prejudice, and Cultural Factors
In this chapter, you have learned that perception is a complex process. Built from sensations, but influenced by
our own experiences, biases, prejudices, and cultures, perceptions can be very different from person to person.
Research suggests that implicit racial prejudice and stereotypes affect perception. For instance, several studies
have demonstrated that non-Black participants identify weapons faster and are more likely to identify non-
weapons as weapons when the image of the weapon is paired with the image of a Black person (Payne, 2001;
Payne, Shimizu, & Jacoby, 2005). Furthermore, White individuals’ decisions to shoot an armed target in a video
game is made more quickly when the target is Black (Correll, Park, Judd, & Wittenbrink, 2002; Correll, Urland, &
Ito, 2006). This research is important, considering the number of very high-profile cases in the last few decades
in which Black people were killed by people who claimed to believe that the unarmed individuals were armed
and/or represented some threat to their personal safety.

DIG DEEPER

5.6 • Gestalt Principles of Perception 171

Key Terms
absolute threshold minimum amount of stimulus energy that must be present for the stimulus to be detected

50% of the time
afterimage continuation of a visual sensation after removal of the stimulus
amplitude height of a wave
basilar membrane thin strip of tissue within the cochlea that contains the hair cells which serve as the

sensory receptors for the auditory system
binaural cue two-eared cue to localize sound
binocular cue cue that relies on the use of both eyes
binocular disparity slightly different view of the world that each eye receives
blind spot point where we cannot respond to visual information in that portion of the visual field
bottom-up processing system in which perceptions are built from sensory input
closure organizing our perceptions into complete objects rather than as a series of parts
cochlea fluid-filled, snail-shaped structure that contains the sensory receptor cells of the auditory system
cochlear implant electronic device that consists of a microphone, a speech processor, and an electrode array

to directly stimulate the auditory nerve to transmit information to the brain
conductive hearing loss failure in the vibration of the eardrum and/or movement of the ossicles
cone specialized photoreceptor that works best in bright light conditions and detects color
congenital deafness deafness from birth
congenital insensitivity to pain (congenital analgesia) genetic disorder that results in the inability to

experience pain
cornea transparent covering over the eye
deafness partial or complete inability to hear
decibel (dB) logarithmic unit of sound intensity
depth perception ability to perceive depth
electromagnetic spectrum all the electromagnetic radiation that occurs in our environment
figure-ground relationship segmenting our visual world into figure and ground
fovea small indentation in the retina that contains cones
frequency number of waves that pass a given point in a given time period
Gestalt psychology field of psychology based on the idea that the whole is different from the sum of its parts
good continuation (also, continuity) we are more likely to perceive continuous, smooth flowing lines rather

than jagged, broken lines
hair cell auditory receptor cell of the inner ear
hertz (Hz) cycles per second; measure of frequency
inattentional blindness failure to notice something that is completely visible because of a lack of attention
incus middle ear ossicle; also known as the anvil
inflammatory pain signal that some type of tissue damage has occurred
interaural level difference sound coming from one side of the body is more intense at the closest ear because

of the attenuation of the sound wave as it passes through the head
interaural timing difference small difference in the time at which a given sound wave arrives at each ear
iris colored portion of the eye
just noticeable difference difference in stimuli required to detect a difference between the stimuli
kinesthesia perception of the body’s movement through space
lens curved, transparent structure that provides additional focus for light entering the eye
linear perspective perceive depth in an image when two parallel lines seem to converge
malleus middle ear ossicle; also known as the hammer
Meissner’s corpuscle touch receptor that responds to pressure and lower frequency vibrations
Ménière’s disease results in a degeneration of inner ear structures that can lead to hearing loss, tinnitus,

vertigo, and an increase in pressure within the inner ear

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Merkel’s disk touch receptor that responds to light touch
monaural cue one-eared cue to localize sound
monocular cue cue that requires only one eye
neuropathic pain pain from damage to neurons of either the peripheral or central nervous system
nociception sensory signal indicating potential harm and maybe pain
olfactory bulb bulb-like structure at the tip of the frontal lobe, where the olfactory nerves begin
olfactory receptor sensory cell for the olfactory system
opponent-process theory of color perception color is coded in opponent pairs: black-white, yellow-blue, and

red-green
optic chiasm X-shaped structure that sits just below the brain’s ventral surface; represents the merging of the

optic nerves from the two eyes and the separation of information from the two sides of the visual field to
the opposite side of the brain

optic nerve carries visual information from the retina to the brain
Pacinian corpuscle touch receptor that detects transient pressure and higher frequency vibrations
pattern perception ability to discriminate among different figures and shapes
peak (also, crest) highest point of a wave
perception way that sensory information is interpreted and consciously experienced
perceptual hypothesis educated guess used to interpret sensory information
pheromone chemical message sent by another individual
photoreceptor light-detecting cell
pinna visible part of the ear that protrudes from the head
pitch perception of a sound’s frequency
place theory of pitch perception different portions of the basilar membrane are sensitive to sounds of

different frequencies
principle of closure organize perceptions into complete objects rather than as a series of parts
proprioception perception of body position
proximity things that are close to one another tend to be grouped together
pupil small opening in the eye through which light passes
retina light-sensitive lining of the eye
rod specialized photoreceptor that works well in low light conditions
Ruffini corpuscle touch receptor that detects stretch
sensation what happens when sensory information is detected by a sensory receptor
sensorineural hearing loss failure to transmit neural signals from the cochlea to the brain
sensory adaptation not perceiving stimuli that remain relatively constant over prolonged periods of time
signal detection theory change in stimulus detection as a function of current mental state
similarity things that are alike tend to be grouped together
stapes middle ear ossicle; also known as the stirrup
subliminal message message presented below the threshold of conscious awareness
taste bud grouping of taste receptor cells with hair-like extensions that protrude into the central pore of the

taste bud
temporal theory of pitch perception sound’s frequency is coded by the activity level of a sensory neuron
thermoception temperature perception
timbre sound’s purity
top-down processing interpretation of sensations is influenced by available knowledge, experiences, and

thoughts
transduction conversion from sensory stimulus energy to action potential
trichromatic theory of color perception color vision is mediated by the activity across the three groups of

cones
trough lowest point of a wave
tympanic membrane eardrum

5 • Key Terms 173

umami taste for monosodium glutamate
vertigo spinning sensation
vestibular sense contributes to our ability to maintain balance and body posture
visible spectrum portion of the electromagnetic spectrum that we can see
wavelength length of a wave from one peak to the next peak

Summary
5.1 Sensation versus Perception

Sensation occurs when sensory receptors detect sensory stimuli. Perception involves the organization,
interpretation, and conscious experience of those sensations. All sensory systems have both absolute and
difference thresholds, which refer to the minimum amount of stimulus energy or the minimum amount of
difference in stimulus energy required to be detected about 50% of the time, respectively. Sensory adaptation,
selective attention, and signal detection theory can help explain what is perceived and what is not. In addition,
our perceptions are affected by a number of factors, including beliefs, values, prejudices, culture, and life
experiences.

5.2 Waves and Wavelengths

Both light and sound can be described in terms of wave forms with physical characteristics like amplitude,
wavelength, and timbre. Wavelength and frequency are inversely related so that longer waves have lower
frequencies, and shorter waves have higher frequencies. In the visual system, a light wave’s wavelength is
generally associated with color, and its amplitude is associated with brightness. In the auditory system, a
sound’s frequency is associated with pitch, and its amplitude is associated with loudness.

5.3 Vision

Light waves cross the cornea and enter the eye at the pupil. The eye’s lens focuses this light so that the image is
focused on a region of the retina known as the fovea. The fovea contains cones that possess high levels of
visual acuity and operate best in bright light conditions. Rods are located throughout the retina and operate
best under dim light conditions. Visual information leaves the eye via the optic nerve. Information from each
visual field is sent to the opposite side of the brain at the optic chiasm. Visual information then moves through
a number of brain sites before reaching the occipital lobe, where it is processed.

Two theories explain color perception. The trichromatic theory asserts that three distinct cone groups are
tuned to slightly different wavelengths of light, and it is the combination of activity across these cone types that
results in our perception of all the colors we see. The opponent-process theory of color vision asserts that color
is processed in opponent pairs and accounts for the interesting phenomenon of a negative afterimage. We
perceive depth through a combination of monocular and binocular depth cues.

5.4 Hearing

Sound waves are funneled into the auditory canal and cause vibrations of the eardrum; these vibrations move
the ossicles. As the ossicles move, the stapes presses against the oval window of the cochlea, which causes fluid
inside the cochlea to move. As a result, hair cells embedded in the basilar membrane become enlarged, which
sends neural impulses to the brain via the auditory nerve.

Pitch perception and sound localization are important aspects of hearing. Our ability to perceive pitch relies
on both the firing rate of the hair cells in the basilar membrane as well as their location within the membrane.
In terms of sound localization, both monaural and binaural cues are used to locate where sounds originate in
our environment.

Individuals can be born deaf, or they can develop deafness as a result of age, genetic predisposition, and/or
environmental causes. Hearing loss that results from a failure of the vibration of the eardrum or the resultant
movement of the ossicles is called conductive hearing loss. Hearing loss that involves a failure of the

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transmission of auditory nerve impulses to the brain is called sensorineural hearing loss.

5.5 The Other Senses

Taste (gustation) and smell (olfaction) are chemical senses that employ receptors on the tongue and in the
nose that bind directly with taste and odor molecules in order to transmit information to the brain for
processing. Our ability to perceive touch, temperature, and pain is mediated by a number of receptors and free
nerve endings that are distributed throughout the skin and various tissues of the body. The vestibular sense
helps us maintain a sense of balance through the response of hair cells in the utricle, saccule, and semi-
circular canals that respond to changes in head position and gravity. Our proprioceptive and kinesthetic
systems provide information about body position and body movement through receptors that detect stretch
and tension in the muscles, joints, tendons, and skin of the body.

5.6 Gestalt Principles of Perception

Gestalt theorists have been incredibly influential in the areas of sensation and perception. Gestalt principles
such as figure-ground relationship, grouping by proximity or similarity, the law of good continuation, and
closure are all used to help explain how we organize sensory information. Our perceptions are not infallible,
and they can be influenced by bias, prejudice, and other factors.

Review Questions
1. ________ refers to the minimum amount of stimulus energy required to be detected 50% of the time.

a. absolute threshold
b. difference threshold
c. just noticeable difference
d. transduction

2. Decreased sensitivity to an unchanging stimulus is known as ________.
a. transduction
b. difference threshold
c. sensory adaptation
d. inattentional blindness

3. ________ involves the conversion of sensory stimulus energy into neural impulses.
a. sensory adaptation
b. inattentional blindness
c. difference threshold
d. transduction

4. ________ occurs when sensory information is organized, interpreted, and consciously experienced.
a. sensation
b. perception
c. transduction
d. sensory adaptation

5. Which of the following correctly matches the pattern in our perception of color as we move from short
wavelengths to long wavelengths?
a. red to orange to yellow
b. yellow to orange to red
c. yellow to red to orange
d. orange to yellow to red

5 • Review Questions 175

6. The visible spectrum includes light that ranges from about ________.
a. 400–700 nm
b. 200–900 nm
c. 20–20000 Hz
d. 10–20 dB

7. The electromagnetic spectrum includes ________.
a. radio waves
b. x-rays
c. infrared light
d. all of the above

8. The audible range for humans is ________.
a. 380–740 Hz
b. 10–20 dB
c. less than 300 dB
d. 20-20,000 Hz

9. The quality of a sound that is affected by frequency, amplitude, and timing of the sound wave is known as
________.
a. pitch
b. tone
c. electromagnetic
d. timbre

10. The ________ is a small indentation of the retina that contains cones.
a. optic chiasm
b. optic nerve
c. fovea
d. iris

11. ________ operate best under bright light conditions.
a. cones
b. rods
c. retinal ganglion cells
d. striate cortex

12. ________ depth cues require the use of both eyes.
a. monocular
b. binocular
c. linear perspective
d. accommodating

13. If you were to stare at a green dot for a relatively long period of time and then shift your gaze to a blank
white screen, you would see a ________ negative afterimage.
a. blue
b. yellow
c. black
d. red

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14. Hair cells located near the base of the basilar membrane respond best to ________ sounds.
a. low-frequency
b. high-frequency
c. low-amplitude
d. high-amplitude

15. The three ossicles of the middle ear are known as ________.
a. malleus, incus, and stapes
b. hammer, anvil, and stirrup
c. pinna, cochlea, and utricle
d. both a and b

16. Hearing aids might be effective for treating ________.
a. Ménière’s disease
b. sensorineural hearing loss
c. conductive hearing loss
d. interaural time differences

17. Cues that require two ears are referred to as ________ cues.
a. monocular
b. monaural
c. binocular
d. binaural

18. Chemical messages often sent between two members of a species to communicate something about
reproductive status are called ________.
a. hormones
b. pheromones
c. Merkel’s disks
d. Meissner’s corpuscles

19. Which taste is associated with monosodium glutamate?
a. sweet
b. bitter
c. umami
d. sour

20. ________ serve as sensory receptors for temperature and pain stimuli.
a. free nerve endings
b. Pacinian corpuscles
c. Ruffini corpuscles
d. Meissner’s corpuscles

21. Which of the following is involved in maintaining balance and body posture?
a. auditory nerve
b. nociceptors
c. olfactory bulb
d. vestibular system

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22. According to the principle of ________, objects that occur close to one another tend to be grouped
together.
a. similarity
b. good continuation
c. proximity
d. closure

23. Our tendency to perceive things as complete objects rather than as a series of parts is known as the
principle of ________.
a. closure
b. good continuation
c. proximity
d. similarity

24. According to the law of ________, we are more likely to perceive smoothly flowing lines rather than
choppy or jagged lines.
a. closure
b. good continuation
c. proximity
d. similarity

25. The main point of focus in a visual display is known as the ________.
a. closure
b. perceptual set
c. ground
d. figure

Critical Thinking Questions
26. Not everything that is sensed is perceived. Do you think there could ever be a case where something could

be perceived without being sensed?

27. Please generate a novel example of how just noticeable difference can change as a function of stimulus
intensity.

28. Why do you think other species have such different ranges of sensitivity for both visual and auditory
stimuli compared to humans?

29. Why do you think humans are especially sensitive to sounds with frequencies that fall in the middle
portion of the audible range?

30. Compare the two theories of color perception. Are they completely different?

31. Color is not a physical property of our environment. What function (if any) do you think color vision
serves?

32. Given what you’ve read about sound localization, from an evolutionary perspective, how does sound
localization facilitate survival?

33. How can temporal and place theories both be used to explain our ability to perceive the pitch of sound
waves with frequencies up to 4000 Hz?

34. Many people experience nausea while traveling in a car, plane, or boat. How might you explain this as a
function of sensory interaction?

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35. If you heard someone say that they would do anything not to feel the pain associated with significant
injury, how would you respond given what you’ve just read?

36. Do you think a person’s sex influences the way they experience pain? Why do you think this is?

37. The central tenet of Gestalt psychology is that the whole is different from the sum of its parts. What does
this mean in the context of perception?

38. Take a look at the following figure. How might you influence whether people see a duck or a rabbit?

FIGURE 5.30

Personal Application Questions
39. Think about a time when you failed to notice something around you because your attention was focused

elsewhere. If someone pointed it out, were you surprised that you hadn’t noticed it right away?

40. If you grew up with a family pet, then you have surely noticed that they often seem to hear things that you
don’t hear. Now that you’ve read this section, you probably have some insight as to why this may be. How
would you explain this to a friend who never had the opportunity to take a class like this?

41. Take a look at a few of your photos or personal works of art. Can you find examples of linear perspective as
a potential depth cue?

42. If you had to choose to lose either your vision or your hearing, which would you choose and why?

43. As mentioned earlier, a food’s flavor represents an interaction of both gustatory and olfactory information.
Think about the last time you were seriously congested due to a cold or the flu. What changes did you
notice in the flavors of the foods that you ate during this time?

44. Have you ever listened to a song on the radio and sung along only to find out later that you have been
singing the wrong lyrics? Once you found the correct lyrics, did your perception of the song change?

5 • Personal Application Questions 179

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FIGURE 6.1 Loggerhead sea turtle hatchlings are born knowing how to find the ocean and how to swim. Unlike the
sea turtle, humans must learn how to swim (and surf). (credit “turtle”: modification of work by Becky Skiba, USFWS;
credit “surfer”: modification of work by Mike Baird)

INTRODUCTION

CHAPTER OUTLINE
6.1 What Is Learning?
6.2 Classical Conditioning
6.3 Operant Conditioning
6.4 Observational Learning (Modeling)

The summer sun shines brightly on a deserted stretch of beach. Suddenly, a tiny grey head
emerges from the sand, then another and another. Soon the beach is teeming with loggerhead sea turtle
hatchlings (Figure 6.1). Although only minutes old, the hatchlings know exactly what to do. Their flippers are
not very efficient for moving across the hot sand, yet they continue onward, instinctively. Some are quickly
snapped up by gulls circling overhead and others become lunch for hungry ghost crabs that dart out of their
holes. Despite these dangers, the hatchlings are driven to leave the safety of their nest and find the ocean.

Not far down this same beach, Ben and his son, Julian, paddle out into the ocean on surfboards. A wave
approaches. Julian crouches on his board, then jumps up and rides the wave for a few seconds before losing
his balance. He emerges from the water in time to watch his father ride the face of the wave.

Unlike baby sea turtles, which know how to find the ocean and swim with no help from their parents, we are
not born knowing how to swim (or surf). Yet we humans pride ourselves on our ability to learn. In fact, over
thousands of years and across cultures, we have created institutions devoted entirely to learning. But have you
ever asked yourself how exactly it is that we learn? What processes are at work as we come to know what we
know? This chapter focuses on the primary ways in which learning occurs.

6Learning

6.1 What Is Learning?
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain how learned behaviors are different from instincts and reflexes
• Define learning
• Recognize and define three basic forms of learning—classical conditioning, operant conditioning, and

observational learning

Birds build nests and migrate as winter approaches. Infants suckle for nurishment. Dogs shake water off wet
fur. Salmon swim upstream to spawn, and spiders spin intricate webs. What do these seemingly unrelated
behaviors have in common? They all are unlearned behaviors. Both instincts and reflexes are innate
(unlearned) behaviors that organisms are born with. Reflexes are a motor or neural reaction to a specific
stimulus in the environment. They tend to be simpler than instincts, involve the activity of specific body parts
and systems (e.g., the knee-jerk reflex and the contraction of the pupil in bright light), and involve more
primitive centers of the central nervous system (e.g., the spinal cord and the medulla). In contrast, instincts
are innate behaviors that are triggered by a broader range of events, such as maturation and the change of
seasons. They are more complex patterns of behavior, involve movement of the organism as a whole (e.g.,
sexual activity and migration), and involve higher brain centers.

Both reflexes and instincts help an organism adapt to its environment and do not have to be learned. For
example, every healthy human baby has a sucking reflex, present at birth. Babies are born knowing how to
suck on a nipple, whether artificial (from a bottle) or human. Nobody teaches the baby to suck, just as no one
teaches a sea turtle hatchling to move toward the ocean. Learning, like reflexes and instincts, allows an
organism to adapt to its environment. But unlike instincts and reflexes, learned behaviors involve change and
experience: learning is a relatively permanent change in behavior or knowledge that results from experience.
In contrast to the innate behaviors discussed above, learning involves acquiring knowledge and skills through
experience. Looking back at our surfing scenario, Julian will have to spend much more time training with his
surfboard before he learns how to ride the waves like his father.

Learning to surf, as well as any complex learning process (e.g., learning about the discipline of psychology),
involves a complex interaction of conscious and unconscious processes. Learning has traditionally been
studied in terms of its simplest components—the associations our minds automatically make between events.
Our minds have a natural tendency to connect events that occur closely together or in sequence. Associative
learning occurs when an organism makes connections between stimuli or events that occur together in the
environment. You will see that associative learning is central to all three basic learning processes discussed in
this chapter; classical conditioning tends to involve unconscious processes, operant conditioning tends to
involve conscious processes, and observational learning adds social and cognitive layers to all the basic
associative processes, both conscious and unconscious. These learning processes will be discussed in detail
later in the chapter, but it is helpful to have a brief overview of each as you begin to explore how learning is
understood from a psychological perspective.

In classical conditioning, also known as Pavlovian conditioning, organisms learn to associate events—or
stimuli—that repeatedly happen together. We experience this process throughout our daily lives. For example,
you might see a flash of lightning in the sky during a storm and then hear a loud boom of thunder. The sound of
the thunder naturally makes you jump (loud noises have that effect by reflex). Because lightning reliably
predicts the impending boom of thunder, you may associate the two and jump when you see lightning.
Psychological researchers study this associative process by focusing on what can be seen and
measured—behaviors. Researchers ask if one stimulus triggers a reflex, can we train a different stimulus to
trigger that same reflex? In operant conditioning, organisms learn, again, to associate events—a behavior and
its consequence (reinforcement or punishment). A pleasant consequence encourages more of that behavior in
the future, whereas a punishment deters the behavior. Imagine you are teaching your dog, Hodor, to sit. You

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tell Hodor to sit, and give him a treat when he does. After repeated experiences, Hodor begins to associate the
act of sitting with receiving a treat. He learns that the consequence of sitting is that he gets a doggie biscuit
(Figure 6.2). Conversely, if the dog is punished when exhibiting a behavior, it becomes conditioned to avoid
that behavior (e.g., receiving a small shock when crossing the boundary of an invisible electric fence).

FIGURE 6.2 In operant conditioning, a response is associated with a consequence. This dog has learned that
certain behaviors result in receiving a treat. (credit: Crystal Rolfe)

Observational learning extends the effective range of both classical and operant conditioning. In contrast to
classical and operant conditioning, in which learning occurs only through direct experience, observational
learning is the process of watching others and then imitating what they do. A lot of learning among humans
and other animals comes from observational learning. To get an idea of the extra effective range that
observational learning brings, consider Ben and his son Julian from the introduction. How might observation
help Julian learn to surf, as opposed to learning by trial and error alone? By watching his father, he can imitate
the moves that bring success and avoid the moves that lead to failure. Can you think of something you have
learned how to do after watching someone else?

All of the approaches covered in this chapter are part of a particular tradition in psychology, called
behaviorism, which we discuss in the next section. However, these approaches do not represent the entire
study of learning. Separate traditions of learning have taken shape within different fields of psychology, such
as memory and cognition, so you will find that other chapters will round out your understanding of the topic.
Over time these traditions tend to converge. For example, in this chapter you will see how cognition has come
to play a larger role in behaviorism, whose more extreme adherents once insisted that behaviors are triggered
by the environment with no intervening thought.

6.2 Classical Conditioning
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Explain how classical conditioning occurs
• Summarize the processes of acquisition, extinction, spontaneous recovery, generalization, and discrimination

Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you
have heard of Pavlov and his famous dogs.

Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his
experiments in classical conditioning (Figure 6.3). As we discussed briefly in the previous section, classical
conditioning is a process by which we learn to associate stimuli and, consequently, to anticipate events.

6.2 • Classical Conditioning 183

FIGURE 6.3 Ivan Pavlov’s research on the digestive system of dogs unexpectedly led to his discovery of the learning
process now known as classical conditioning.

Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist,
not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of
cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). In
his studies with dogs, Pavlov measured the amount of saliva produced in response to various foods. Over time,
Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food,
at the sight of an empty food bowl, and even at the sound of the laboratory assistants’ footsteps. Salivating to
food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of
an empty bowl or the sound of footsteps.

These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs’
“psychic secretions” (Pavlov, 1927). To explore this phenomenon in an objective manner, Pavlov designed a
series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to
train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a
bell, a light, and a touch on the leg. Through his experiments, Pavlov realized that an organism has two types of
responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned
(learned) responses.

In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder
in this situation was an unconditioned stimulus (UCS): a stimulus that elicits a reflexive response in an
organism. The dogs’ salivation was an unconditioned response (UCR): a natural (unlearned) reaction to a
given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:

In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus.
Pavlov would sound a tone (like ringing a bell) and then give the dogs the meat powder (Figure 6.4). The tone
was the neutral stimulus (NS), which is a stimulus that does not naturally elicit a response. Prior to
conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for
the dogs.

When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the
tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned
stimulus (CS), which is a stimulus that elicits a response after repeatedly being paired with an unconditioned
stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the
sound of the assistants’ footsteps. The behavior caused by the conditioned stimulus is called the conditioned
response (CR). In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they
began to salivate (CR) in anticipation of food.

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FIGURE 6.4 Before conditioning, an unconditioned stimulus (food) produces an unconditioned response
(salivation), and a neutral stimulus (bell) does not produce a response. During conditioning, the unconditioned
stimulus (food) is presented repeatedly just after the presentation of the neutral stimulus (bell). After conditioning,
the neutral stimulus alone produces a conditioned response (salivation), thus becoming a conditioned stimulus.

LINK TO LEARNING

View this video about Pavlov and his dogs (http://openstax.org/l/pavlov2) to learn more.

Real World Application of Classical Conditioning

How does classical conditioning work in the real world? Consider the case of Moisha, who was diagnosed with
cancer. When she received her first chemotherapy treatment, she vomited shortly after the chemicals were
injected. In fact, every trip to the doctor for chemotherapy treatment shortly after the drugs were injected, she
vomited. Moisha’s treatment was a success and her cancer went into remission. Now, when she visits her
oncologist’s office every 6 months for a check-up, she becomes nauseous. In this case, the chemotherapy drugs
are the unconditioned stimulus (UCS), vomiting is the unconditioned response (UCR), the doctor’s office is the
conditioned stimulus (CS) after being paired with the UCS, and nausea is the conditioned response (CR). Let’s
assume that the chemotherapy drugs that Moisha takes are given through a syringe injection. After entering
the doctor’s office, Moisha sees a syringe, and then gets her medication. In addition to the doctor’s office,
Moisha will learn to associate the syringe with the medication and will respond to syringes with nausea. This is
an example of higher-order (or second-order) conditioning, when the conditioned stimulus (the doctor’s office)
serves to condition another stimulus (the syringe). It is hard to achieve anything above second-order
conditioning. For example, if someone rang a bell every time Moisha received a syringe injection of
chemotherapy drugs in the doctor’s office, Moisha likely will never get sick in response to the bell.

Consider another example of classical conditioning. Let’s say you have a cat named Tiger, who is quite spoiled.
You keep her food in a separate cabinet, and you also have a special electric can opener that you use only to
open cans of cat food. For every meal, Tiger hears the distinctive sound of the electric can opener (“zzhzhz”)
and then gets her food. Tiger quickly learns that when she hears “zzhzhz” she is about to get fed. What do you
think Tiger does when she hears the electric can opener? She will likely get excited and run to where you are

6.2 • Classical Conditioning 185

preparing her food. This is an example of classical conditioning. In this case, what are the UCS, CS, UCR, and
CR?

What if the cabinet holding Tiger’s food becomes squeaky? In that case, Tiger hears “squeak” (the cabinet),
“zzhzhz” (the electric can opener), and then she gets her food. Tiger will learn to get excited when she hears
the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus
(“zzhzhz”) is called higher-order conditioning, or second-order conditioning. This means you are using the
conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet (Figure 6.5). It is
hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet
(“squeak”), use the can opener (“zzhzhz”), and then feed Tiger, Tiger will likely never get excited when hearing
the bell alone.

FIGURE 6.5 In higher-order conditioning, an established conditioned stimulus is paired with a new neutral stimulus
(the second-order stimulus), so that eventually the new stimulus also elicits the conditioned response, without the
initial conditioned stimulus being presented.

Classical Conditioning at Stingray City
Kate and her spouse recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where
they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary
stingrays have become accustomed to interacting with humans. About 40 years ago, people began to clean fish

EVERYDAY CONNECTION

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and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays
would swim in to eat (unconditioned response) what the people threw into the water; this continued for years. By
the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them
by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs.
When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know
that they will get to eat (conditioned response).

As soon as they reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped
into the water with bags of squid, the stingrays’ favorite treat. The swarm of stingrays bumped and rubbed up
against their legs like hungry cats (Figure 6.6). Kate was able to feed, pet, and even kiss (for luck) these amazing
creatures. Then all the squid was gone, and so were the stingrays.

FIGURE 6.6 Kate holds a southern stingray at Stingray City in the Cayman Islands. These stingrays have been
classically conditioned to associate the sound of a boat motor with food provided by tourists. (credit: Kathryn
Dumper)

Classical conditioning also applies to humans, even babies. For example, Elan buys formula in blue canisters
for their six-month-old daughter, Angelina. Whenever Elan takes out a formula container, Angelina gets
excited, tries to reach toward the food, and most likely salivates. Why does Angelina get excited when she sees
the formula canister? What are the UCS, CS, UCR, and CR here?

So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be
fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small
electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the
unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the
discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set
boundaries. In this example, the edge of the yard elicits fear and anxiety in the dog. Fear and anxiety are the
conditioned response.

LINK TO LEARNING

Watch this video clip from the television show, The Office, for a humorous look at conditioning
(http://openstax.org/l/theoffice) in which Jim conditions Dwight to expect a breath mint every time Jim’s
computer makes a specific sound.

6.2 • Classical Conditioning 187

General Processes in Classical Conditioning

Now that you know how classical conditioning works and have seen several examples, let’s take a look at some
of the general processes involved. In classical conditioning, the initial period of learning is known as
acquisition, when an organism learns to connect a neutral stimulus and an unconditioned stimulus. During
acquisition, the neutral stimulus begins to elicit the conditioned response, and eventually the neutral stimulus
becomes a conditioned stimulus capable of eliciting the conditioned response by itself. Timing is important for
conditioning to occur. Typically, there should only be a brief interval between presentation of the conditioned
stimulus and the unconditioned stimulus. Depending on what is being conditioned, sometimes this interval is
as little as five seconds (Chance, 2009). However, with other types of conditioning, the interval can be up to
several hours.

Taste aversion is a type of conditioning in which an interval of several hours may pass between the
conditioned stimulus (something ingested) and the unconditioned stimulus (nausea or illness). Here’s how it
works. Between classes, you and a friend grab a quick lunch from a food cart on campus. You share a dish of
chicken curry and head off to your next class. A few hours later, you feel nauseous and become ill. Although
your friend is fine and you determine that you have intestinal flu (the food is not the culprit), you’ve developed
a taste aversion; the next time you are at a restaurant and someone orders curry, you immediately feel ill.
While the chicken dish is not what made you sick, you are experiencing taste aversion: you’ve been
conditioned to be averse to a food after a single, bad experience.

How does this occur—conditioning based on a single instance and involving an extended time lapse between
the event and the negative stimulus? Research into taste aversion suggests that this response may be an
evolutionary adaptation designed to help organisms quickly learn to avoid harmful foods (Garcia & Rusiniak,
1980; Garcia & Koelling, 1966). Not only may this contribute to species survival via natural selection, but it
may also help us develop strategies for challenges such as helping cancer patients through the nausea induced
by certain treatments (Holmes, 1993; Jacobsen et al., 1993; Hutton, Baracos, & Wismer, 2007; Skolin et al.,
2006). Garcia and Koelling (1966) showed not only that taste aversions could be conditioned, but also that
there were biological constraints to learning. In their study, separate groups of rats were conditioned to
associate either a flavor with illness, or lights and sounds with illness. Results showed that all rats exposed to
flavor-illness pairings learned to avoid the flavor, but none of the rats exposed to lights and sounds with illness
learned to avoid lights or sounds. This added evidence to the idea that classical conditioning could contribute
to species survival by helping organisms learn to avoid stimuli that posed real dangers to health and welfare.

Robert Rescorla demonstrated how powerfully an organism can learn to predict the UCS from the CS. Take, for
example, the following two situations. Ari’s dad always has dinner on the table every day at 6:00. Soraya’s mom
switches it up so that some days they eat dinner at 6:00, some days they eat at 5:00, and other days they eat at
7:00. For Ari, 6:00 reliably and consistently predicts dinner, so Ari will likely start feeling hungry every day
right before 6:00, even if he’s had a late snack. Soraya, on the other hand, will be less likely to associate 6:00
with dinner, since 6:00 does not always predict that dinner is coming. Rescorla, along with his colleague at Yale
University, Alan Wagner, developed a mathematical formula that could be used to calculate the probability that
an association would be learned given the ability of a conditioned stimulus to predict the occurrence of an
unconditioned stimulus and other factors; today this is known as the Rescorla-Wagner model (Rescorla &
Wagner, 1972)

Once we have established the connection between the unconditioned stimulus and the conditioned stimulus,
how do we break that connection and get the dog, cat, or child to stop responding? In Tiger’s case, imagine
what would happen if you stopped using the electric can opener for her food and began to use it only for
human food. Now, Tiger would hear the can opener, but she would not get food. In classical conditioning terms,
you would be giving the conditioned stimulus, but not the unconditioned stimulus. Pavlov explored this
scenario in his experiments with dogs: sounding the tone without giving the dogs the meat powder. Soon the
dogs stopped responding to the tone. Extinction is the decrease in the conditioned response when the

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unconditioned stimulus is no longer presented with the conditioned stimulus. When presented with the
conditioned stimulus alone, the dog, cat, or other organism would show a weaker and weaker response, and
finally no response. In classical conditioning terms, there is a gradual weakening and disappearance of the
conditioned response.

What happens when learning is not used for a while—when what was learned lies dormant? As we just
discussed, Pavlov found that when he repeatedly presented the bell (conditioned stimulus) without the meat
powder (unconditioned stimulus), extinction occurred; the dogs stopped salivating to the bell. However, after a
couple of hours of resting from this extinction training, the dogs again began to salivate when Pavlov rang the
bell. What do you think would happen with Tiger’s behavior if your electric can opener broke, and you did not
use it for several months? When you finally got it fixed and started using it to open Tiger’s food again, Tiger
would remember the association between the can opener and her food—she would get excited and run to the
kitchen when she heard the sound. The behavior of Pavlov’s dogs and Tiger illustrates a concept Pavlov called
spontaneous recovery: the return of a previously extinguished conditioned response following a rest period
(Figure 6.7).

FIGURE 6.7 This is the curve of acquisition, extinction, and spontaneous recovery. The rising curve shows the
conditioned response quickly getting stronger through the repeated pairing of the conditioned stimulus and the
unconditioned stimulus (acquisition). Then the curve decreases, which shows how the conditioned response
weakens when only the conditioned stimulus is presented (extinction). After a break or pause from conditioning, the
conditioned response reappears (spontaneous recovery).

Of course, these processes also apply in humans. For example, let’s say that every day when you walk to
campus, an ice cream truck passes your route. Day after day, you hear the truck’s music (neutral stimulus), so
you finally stop and purchase a chocolate ice cream bar. You take a bite (unconditioned stimulus) and then
your mouth waters (unconditioned response). This initial period of learning is known as acquisition, when you
begin to connect the neutral stimulus (the sound of the truck) and the unconditioned stimulus (the taste of the
chocolate ice cream in your mouth). During acquisition, the conditioned response gets stronger and stronger
through repeated pairings of the conditioned stimulus and unconditioned stimulus. Several days (and ice
cream bars) later, you notice that your mouth begins to water (conditioned response) as soon as you hear the
truck’s musical jingle—even before you bite into the ice cream bar. Then one day you head down the street. You
hear the truck’s music (conditioned stimulus), and your mouth waters (conditioned response). However, when
you get to the truck, you discover that they are all out of ice cream. You leave disappointed. The next few days
you pass by the truck and hear the music, but don’t stop to get an ice cream bar because you’re running late for
class. You begin to salivate less and less when you hear the music, until by the end of the week, your mouth no
longer waters when you hear the tune. This illustrates extinction. The conditioned response weakens when
only the conditioned stimulus (the sound of the truck) is presented, without being followed by the
unconditioned stimulus (chocolate ice cream in the mouth). Then the weekend comes. You don’t have to go to

6.2 • Classical Conditioning 189

class, so you don’t pass the truck. Monday morning arrives and you take your usual route to campus. You
round the corner and hear the truck again. What do you think happens? Your mouth begins to water again.
Why? After a break from conditioning, the conditioned response reappears, which indicates spontaneous
recovery.

Acquisition and extinction involve the strengthening and weakening, respectively, of a learned association.
Two other learning processes—stimulus discrimination and stimulus generalization—are involved in
determining which stimuli will trigger learned responses. Animals (including humans) need to distinguish
between stimuli—for example, between sounds that predict a threatening event and sounds that do not—so that
they can respond appropriately (such as running away if the sound is threatening). When an organism learns
to respond differently to various stimuli that are similar, it is called stimulus discrimination. In classical
conditioning terms, the organism demonstrates the conditioned response only to the conditioned stimulus.
Pavlov’s dogs discriminated between the basic tone that sounded before they were fed and other tones (e.g.,
the doorbell), because the other sounds did not predict the arrival of food. Similarly, Tiger, the cat,
discriminated between the sound of the can opener and the sound of the electric mixer. When the electric
mixer is going, Tiger is not about to be fed, so she does not come running to the kitchen looking for food. In our
other example, Moisha, the cancer patient, discriminated between oncologists and other types of doctors. She
learned not to feel ill when visiting doctors for other types of appointments, such as her annual physical.

On the other hand, when an organism demonstrates the conditioned response to stimuli that are similar to the
condition stimulus, it is called stimulus generalization, the opposite of stimulus discrimination. The more
similar a stimulus is to the condition stimulus, the more likely the organism is to give the conditioned
response. For instance, if the electric mixer sounds very similar to the electric can opener, Tiger may come
running after hearing its sound. But if you do not feed her following the electric mixer sound, and you continue
to feed her consistently after the electric can opener sound, she will quickly learn to discriminate between the
two sounds (provided they are sufficiently dissimilar that she can tell them apart). In our other example,
Moisha continued to feel ill whenever visiting other oncologists or other doctors in the same building as her
oncologist.

Behaviorism

John B. Watson, shown in Figure 6.8, is considered the founder of behaviorism. Behaviorism is a school of
thought that arose during the first part of the 20th century, which incorporates elements of Pavlov’s classical
conditioning (Hunt, 2007). In stark contrast with Freud, who considered the reasons for behavior to be hidden
in the unconscious, Watson championed the idea that all behavior can be studied as a simple stimulus-
response reaction, without regard for internal processes. Watson argued that in order for psychology to
become a legitimate science, it must shift its concern away from internal mental processes because mental
processes cannot be seen or measured. Instead, he asserted that psychology must focus on outward
observable behavior that can be measured.

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FIGURE 6.8 John B. Watson used the principles of classical conditioning in the study of human emotion.

Watson’s ideas were influenced by Pavlov’s work. According to Watson, human behavior, just like animal
behavior, is primarily the result of conditioned responses. Whereas Pavlov’s work with dogs involved the
conditioning of reflexes, Watson believed the same principles could be extended to the conditioning of human
emotions (Watson, 1919).

In 1920, while chair of the psychology department at Johns Hopkins University, Watson and his graduate
student, Rosalie Rayner, conducted research on a baby nicknamed Little Albert. Rayner and Watson’s
experiments with Little Albert demonstrated how fears can be conditioned using classical conditioning.
Through these experiments, Little Albert was exposed to and conditioned to fear certain things. Initially he was
presented with various neutral stimuli, including a rabbit, a dog, a monkey, masks, cotton wool, and a white
rat. He was not afraid of any of these things. Then Watson, with the help of Rayner, conditioned Little Albert to
associate these stimuli with an emotion—fear. For example, Watson handed Little Albert the white rat, and
Little Albert enjoyed playing with it. Then Watson made a loud sound, by striking a hammer against a metal
bar hanging behind Little Albert’s head, each time Little Albert touched the rat. Little Albert was frightened by
the sound—demonstrating a reflexive fear of sudden loud noises—and began to cry. Watson repeatedly paired
the loud sound with the white rat. Soon Little Albert became frightened by the white rat alone. In this case,
what are the UCS, CS, UCR, and CR? Days later, Little Albert demonstrated stimulus generalization—he became
afraid of other furry things: a rabbit, a furry coat, and even a Santa Claus mask (Figure 6.9). Watson had
succeeded in conditioning a fear response in Little Albert, thus demonstrating that emotions could become
conditioned responses. It had been Watson’s intention to produce a phobia—a persistent, excessive fear of a
specific object or situation— through conditioning alone, thus countering Freud’s view that phobias are caused
by deep, hidden conflicts in the mind. However, there is no evidence that Little Albert experienced phobias in
later years. Little Albert’s mother moved away, ending the experiment. While Watson’s research provided new
insight into conditioning, it would be considered unethical by today’s standards.

FIGURE 6.9 Through stimulus generalization, Little Albert came to fear furry things, including Watson in a Santa
Claus mask.

6.2 • Classical Conditioning 191

LINK TO LEARNING

View scenes from this video on John Watson’s experiment in which Little Albert was conditioned to respond in
fear to furry objects (http://openstax.org/l/Watson1) to learn more.

As you watch the video, look closely at Little Albert’s reactions and the manner in which Watson and Rayner
present the stimuli before and after conditioning. Based on what you see, would you come to the same
conclusions as the researchers?

Advertising and Associative Learning
Advertising executives are pros at applying the principles of associative learning. Think about the car
commercials you have seen on television. Many of them feature an attractive model. By associating the model
with the car being advertised, you come to see the car as being desirable (Cialdini, 2008). You may be asking
yourself, does this advertising technique actually work? According to Cialdini (2008), men who viewed a car
commercial that included an attractive model later rated the car as being faster, more appealing, and better
designed than did men who viewed an advertisement for the same car minus the model.

Have you ever noticed how quickly advertisers cancel contracts with a famous athlete following a scandal? As far
as the advertiser is concerned, that athlete is no longer associated with positive feelings; therefore, the athlete
cannot be used as an unconditioned stimulus to condition the public to associate positive feelings (the
unconditioned response) with their product (the conditioned stimulus).

Now that you are aware of how associative learning works, see if you can find examples of these types of
advertisements on television, in magazines, or on the Internet.

6.3 Operant Conditioning
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Define operant conditioning
• Explain the difference between reinforcement and punishment
• Distinguish between reinforcement schedules

The previous section of this chapter focused on the type of associative learning known as classical
conditioning. Remember that in classical conditioning, something in the environment triggers a reflex
automatically, and researchers train the organism to react to a different stimulus. Now we turn to the second
type of associative learning, operant conditioning. In operant conditioning, organisms learn to associate a
behavior and its consequence (Table 6.1). A pleasant consequence makes that behavior more likely to be
repeated in the future. For example, Spirit, a dolphin at the National Aquarium in Baltimore, does a flip in the
air when her trainer blows a whistle. The consequence is that she gets a fish.

EVERYDAY CONNECTION

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Classical and Operant Conditioning Compared

Classical Conditioning Operant Conditioning

Conditioning
approach

An unconditioned stimulus (such as food) is paired
with a neutral stimulus (such as a bell). The neutral
stimulus eventually becomes the conditioned
stimulus, which brings about the conditioned
response (salivation).

The target behavior is followed by
reinforcement or punishment to either
strengthen or weaken it, so that the
learner is more likely to exhibit the desired
behavior in the future.

Stimulus
timing

The stimulus occurs immediately before the
response.

The stimulus (either reinforcement or
punishment) occurs soon after the
response.

TABLE 6.1

Psychologist B. F. Skinner saw that classical conditioning is limited to existing behaviors that are reflexively
elicited, and it doesn’t account for new behaviors such as riding a bike. He proposed a theory about how such
behaviors come about. Skinner believed that behavior is motivated by the consequences we receive for the
behavior: the reinforcements and punishments. His idea that learning is the result of consequences is based
on the law of effect, which was first proposed by psychologist Edward Thorndike. According to the law of
effect, behaviors that are followed by consequences that are satisfying to the organism are more likely to be
repeated, and behaviors that are followed by unpleasant consequences are less likely to be repeated
(Thorndike, 1911). Essentially, if an organism does something that brings about a desired result, the organism
is more likely to do it again. If an organism does something that does not bring about a desired result, the
organism is less likely to do it again. An example of the law of effect is in employment. One of the reasons (and
often the main reason) we show up for work is because we get paid to do so. If we stop getting paid, we will
likely stop showing up—even if we love our job.

Working with Thorndike’s law of effect as his foundation, Skinner began conducting scientific experiments on
animals (mainly rats and pigeons) to determine how organisms learn through operant conditioning (Skinner,
1938). He placed these animals inside an operant conditioning chamber, which has come to be known as a
“Skinner box” (Figure 6.10). A Skinner box contains a lever (for rats) or disk (for pigeons) that the animal can
press or peck for a food reward via the dispenser. Speakers and lights can be associated with certain behaviors.
A recorder counts the number of responses made by the animal.

FIGURE 6.10 (a) B. F. Skinner developed operant conditioning for systematic study of how behaviors are
strengthened or weakened according to their consequences. (b) In a Skinner box, a rat presses a lever in an operant
conditioning chamber to receive a food reward. (credit a: modification of work by “Silly rabbit”/Wikimedia
Commons)

6.3 • Operant Conditioning 193

LINK TO LEARNING

Watch this brief video to see Skinner’s interview and a demonstration of operant conditioning of pigeons
(http://openstax.org/l/skinner1) to learn more.

In discussing operant conditioning, we use several everyday words—positive, negative, reinforcement, and
punishment—in a specialized manner. In operant conditioning, positive and negative do not mean good and
bad. Instead, positive means you are adding something, and negative means you are taking something away.
Reinforcement means you are increasing a behavior, and punishment means you are decreasing a behavior.
Reinforcement can be positive or negative, and punishment can also be positive or negative. All reinforcers
(positive or negative) increase the likelihood of a behavioral response. All punishers (positive or negative)
decrease the likelihood of a behavioral response. Now let’s combine these four terms: positive reinforcement,
negative reinforcement, positive punishment, and negative punishment (Table 6.2).

Positive and Negative Reinforcement and Punishment

Reinforcement Punishment

Positive
Something is added to increase the likelihood of a
behavior.

Something is added to decrease the likelihood of a
behavior.

Negative
Something is removed to increase the likelihood
of a behavior.

Something is removed to decrease the likelihood
of a behavior.

TABLE 6.2

Reinforcement

The most effective way to teach a person or animal a new behavior is with positive reinforcement. In positive
reinforcement, a desirable stimulus is added to increase a behavior.

For example, you tell your five-year-old son, Jerome, that if he cleans his room, he will get a toy. Jerome quickly
cleans his room because he wants a new art set. Let’s pause for a moment. Some people might say, “Why
should I reward my child for doing what is expected?” But in fact we are constantly and consistently rewarded
in our lives. Our paychecks are rewards, as are high grades and acceptance into our preferred school. Being
praised for doing a good job and for passing a driver’s test is also a reward. Positive reinforcement as a
learning tool is extremely effective. It has been found that one of the most effective ways to increase
achievement in school districts with below-average reading scores was to pay the children to read. Specifically,
second-grade students in Dallas were paid $2 each time they read a book and passed a short quiz about the
book. The result was a significant increase in reading comprehension (Fryer, 2010). What do you think about
this program? If Skinner were alive today, he would probably think this was a great idea. He was a strong
proponent of using operant conditioning principles to influence students’ behavior at school. In fact, in
addition to the Skinner box, he also invented what he called a teaching machine that was designed to reward
small steps in learning (Skinner, 1961)—an early forerunner of computer-assisted learning. His teaching
machine tested students’ knowledge as they worked through various school subjects. If students answered
questions correctly, they received immediate positive reinforcement and could continue; if they answered
incorrectly, they did not receive any reinforcement. The idea was that students would spend additional time
studying the material to increase their chance of being reinforced the next time (Skinner, 1961).

In negative reinforcement, an undesirable stimulus is removed to increase a behavior. For example, car
manufacturers use the principles of negative reinforcement in their seatbelt systems, which go “beep, beep,
beep” until you fasten your seatbelt. The annoying sound stops when you exhibit the desired behavior,

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increasing the likelihood that you will buckle up in the future. Negative reinforcement is also used frequently
in horse training. Riders apply pressure—by pulling the reins or squeezing their legs—and then remove the
pressure when the horse performs the desired behavior, such as turning or speeding up. The pressure is the
negative stimulus that the horse wants to remove.

Punishment

Many people confuse negative reinforcement with punishment in operant conditioning, but they are two very
different mechanisms. Remember that reinforcement, even when it is negative, always increases a behavior. In
contrast, punishment always decreases a behavior. In positive punishment, you add an undesirable stimulus
to decrease a behavior. An example of positive punishment is scolding a student to get the student to stop
texting in class. In this case, a stimulus (the reprimand) is added in order to decrease the behavior (texting in
class). In negative punishment, you remove a pleasant stimulus to decrease behavior. For example, when a
child misbehaves, a parent can take away a favorite toy. In this case, a stimulus (the toy) is removed in order to
decrease the behavior.

Punishment, especially when it is immediate, is one way to decrease undesirable behavior. For example,
imagine your four-year-old son, Brandon, hit his younger brother. You have Brandon write 100 times “I will not
hit my brother” (positive punishment). Chances are he won’t repeat this behavior. While strategies like this are
common today, in the past children were often subject to physical punishment, such as spanking. It’s
important to be aware of some of the drawbacks in using physical punishment on children. First, punishment
may teach fear. Brandon may become fearful of the street, but he also may become fearful of the person who
delivered the punishment—you, his parent. Similarly, children who are punished by teachers may come to fear
the teacher and try to avoid school (Gershoff et al., 2010). Consequently, most schools in the United States have
banned corporal punishment. Second, punishment may cause children to become more aggressive and prone
to antisocial behavior and delinquency (Gershoff, 2002). They see their parents resort to spanking when they
become angry and frustrated, so, in turn, they may act out this same behavior when they become angry and
frustrated. For example, because you spank Brenda when you are angry with her for her misbehavior, she
might start hitting her friends when they won’t share their toys.

While positive punishment can be effective in some cases, Skinner suggested that the use of punishment
should be weighed against the possible negative effects. Today’s psychologists and parenting experts favor
reinforcement over punishment—they recommend that you catch your child doing something good and reward
them for it.

Shaping

In his operant conditioning experiments, Skinner often used an approach called shaping. Instead of rewarding
only the target behavior, in shaping, we reward successive approximations of a target behavior. Why is shaping
needed? Remember that in order for reinforcement to work, the organism must first display the behavior.
Shaping is needed because it is extremely unlikely that an organism will display anything but the simplest of
behaviors spontaneously. In shaping, behaviors are broken down into many small, achievable steps. The
specific steps used in the process are the following:

1. Reinforce any response that resembles the desired behavior.
2. Then reinforce the response that more closely resembles the desired behavior. You will no longer reinforce

the previously reinforced response.
3. Next, begin to reinforce the response that even more closely resembles the desired behavior.
4. Continue to reinforce closer and closer approximations of the desired behavior.
5. Finally, only reinforce the desired behavior.

Shaping is often used in teaching a complex behavior or chain of behaviors. Skinner used shaping to teach
pigeons not only such relatively simple behaviors as pecking a disk in a Skinner box, but also many unusual
and entertaining behaviors, such as turning in circles, walking in figure eights, and even playing ping pong; the

6.3 • Operant Conditioning 195

technique is commonly used by animal trainers today. An important part of shaping is stimulus
discrimination. Recall Pavlov’s dogs—he trained them to respond to the tone of a bell, and not to similar tones
or sounds. This discrimination is also important in operant conditioning and in shaping behavior.

LINK TO LEARNING

Watch this brief video of Skinner’s pigeons playing ping pong (http://openstax.org/l/pingpong) to learn more.

It’s easy to see how shaping is effective in teaching behaviors to animals, but how does shaping work with
humans? Let’s consider parents whose goal is to have their child learn to clean his room. They use shaping to
help him master steps toward the goal. Instead of performing the entire task, they set up these steps and
reinforce each step. First, he cleans up one toy. Second, he cleans up five toys. Third, he chooses whether to
pick up ten toys or put his books and clothes away. Fourth, he cleans up everything except two toys. Finally, he
cleans his entire room.

Primary and Secondary Reinforcers

Rewards such as stickers, praise, money, toys, and more can be used to reinforce learning. Let’s go back to
Skinner’s rats again. How did the rats learn to press the lever in the Skinner box? They were rewarded with
food each time they pressed the lever. For animals, food would be an obvious reinforcer.

What would be a good reinforcer for humans? For your child Chris, it was the promise of a toy when they
cleaned their room. How about Sydney, the soccer player? If you gave Sydney a piece of candy every time
Sydney scored a goal, you would be using a primary reinforcer. Primary reinforcers are reinforcers that have
innate reinforcing qualities. These kinds of reinforcers are not learned. Water, food, sleep, shelter, sex, and
touch, among others, are primary reinforcers. Pleasure is also a primary reinforcer. Organisms do not lose
their drive for these things. For most people, jumping in a cool lake on a very hot day would be reinforcing and
the cool lake would be innately reinforcing—the water would cool the person off (a physical need), as well as
provide pleasure.

A secondary reinforcer has no inherent value and only has reinforcing qualities when linked with a primary
reinforcer. Praise, linked to affection, is one example of a secondary reinforcer, as when you called out “Great
shot!” every time Sydney made a goal. Another example, money, is only worth something when you can use it
to buy other things—either things that satisfy basic needs (food, water, shelter—all primary reinforcers) or
other secondary reinforcers. If you were on a remote island in the middle of the Pacific Ocean and you had
stacks of money, the money would not be useful if you could not spend it. What about the stickers on the
behavior chart? They also are secondary reinforcers.

Sometimes, instead of stickers on a sticker chart, a token is used. Tokens, which are also secondary
reinforcers, can then be traded in for rewards and prizes. Entire behavior management systems, known as
token economies, are built around the use of these kinds of token reinforcers. Token economies have been
found to be very effective at modifying behavior in a variety of settings such as schools, prisons, and mental
hospitals. For example, a study by Adibsereshki and Abkenar (2014) found that use of a token economy
increased appropriate social behaviors and reduced inappropriate behaviors in a group of eight grade
students. Similar studies show demonstrable gains on behavior and academic achievement for groups ranging
from first grade to high school, and representing a wide array of abilities and disabilities. For example, during
studies involving younger students, when children in the study exhibited appropriate behavior (not hitting or
pinching), they received a “quiet hands” token. When they hit or pinched, they lost a token. The children could
then exchange specified amounts of tokens for minutes of playtime.

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Behavior Modification in Children
Parents and teachers often use behavior modification to change a child’s behavior. Behavior modification uses
the principles of operant conditioning to accomplish behavior change so that undesirable behaviors are switched
for more socially acceptable ones. Some teachers and parents create a sticker chart, in which several behaviors
are listed (Figure 6.11). Sticker charts are a form of token economies, as described in the text. Each time children
perform the behavior, they get a sticker, and after a certain number of stickers, they get a prize, or reinforcer. The
goal is to increase acceptable behaviors and decrease misbehavior. Remember, it is best to reinforce desired
behaviors, rather than to use punishment. In the classroom, the teacher can reinforce a wide range of behaviors,
from students raising their hands, to walking quietly in the hall, to turning in their homework. At home, parents
might create a behavior chart that rewards children for things such as putting away toys, brushing their teeth,
and helping with dinner. In order for behavior modification to be effective, the reinforcement needs to be
connected with the behavior; the reinforcement must matter to the child and be done consistently.

FIGURE 6.11 Sticker charts are a form of positive reinforcement and a tool for behavior modification. Once this
child earns a certain number of stickers for demonstrating a desired behavior, she will be rewarded with a trip to
the ice cream parlor. (credit: Abigail Batchelder)

Time-out is another popular technique used in behavior modification with children. It operates on the principle of
negative punishment. When a child demonstrates an undesirable behavior, they are removed from the desirable
activity at hand (Figure 6.12). For example, say that Sophia and her brother Mario are playing with building
blocks. Sophia throws some blocks at her brother, so you give her a warning that she will go to time-out if she
does it again. A few minutes later, she throws more blocks at Mario. You remove Sophia from the room for a few
minutes. When she comes back, she doesn’t throw blocks.

There are several important points that you should know if you plan to implement time-out as a behavior
modification technique. First, make sure the child is being removed from a desirable activity and placed in a less
desirable location. If the activity is something undesirable for the child, this technique will backfire because it is
more enjoyable for the child to be removed from the activity. Second, the length of the time-out is important. The
general rule of thumb is one minute for each year of the child’s age. Sophia is five; therefore, she sits in a time-
out for five minutes. Setting a timer helps children know how long they have to sit in time-out. Finally, as a
caregiver, keep several guidelines in mind over the course of a time-out: remain calm when directing your child to
time-out; ignore your child during time-out (because caregiver attention may reinforce misbehavior); and give the
child a hug or a kind word when time-out is over.

EVERYDAY CONNECTION

6.3 • Operant Conditioning 197

FIGURE 6.12 Time-out is a popular form of negative punishment used by caregivers. When a child misbehaves,
they are removed from a desirable activity in an effort to decrease the unwanted behavior. For example, (a) a
child might be playing on the playground with friends and push another child; (b) the child who misbehaved
would then be removed from the activity for a short period of time. (credit a: modification of work by Simone
Ramella; credit b: modification of work by “Spring Dew”/Flickr)

Reinforcement Schedules

Remember, the best way to teach a person or animal a behavior is to use positive reinforcement. For example,
Skinner used positive reinforcement to teach rats to press a lever in a Skinner box. At first, the rat might
randomly hit the lever while exploring the box, and out would come a pellet of food. After eating the pellet,
what do you think the hungry rat did next? It hit the lever again, and received another pellet of food. Each time
the rat hit the lever, a pellet of food came out. When an organism receives a reinforcer each time it displays a
behavior, it is called continuous reinforcement. This reinforcement schedule is the quickest way to teach
someone a behavior, and it is especially effective in training a new behavior. Let’s look back at the dog that was
learning to sit earlier in the chapter. Now, each time he sits, you give him a treat. Timing is important here: you
will be most successful if you present the reinforcer immediately after he sits, so that he can make an
association between the target behavior (sitting) and the consequence (getting a treat).

LINK TO LEARNING

Watch this video clip of veterinarian Dr. Sophia Yin shaping a dog’s behavior using the steps outlined above
(http://openstax.org/l/sueyin) to learn more.

Once a behavior is trained, researchers and trainers often turn to another type of reinforcement
schedule—partial reinforcement. In partial reinforcement, also referred to as intermittent reinforcement, the
person or animal does not get reinforced every time they perform the desired behavior. There are several
different types of partial reinforcement schedules (Table 6.3). These schedules are described as either fixed or
variable, and as either interval or ratio. Fixed refers to the number of responses between reinforcements, or
the amount of time between reinforcements, which is set and unchanging. Variable refers to the number of
responses or amount of time between reinforcements, which varies or changes. Interval means the schedule is
based on the time between reinforcements, and ratio means the schedule is based on the number of responses
between reinforcements.

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Reinforcement Schedules

Reinforcement
Schedule

Description Result Example

Fixed interval
Reinforcement is delivered at
predictable time intervals (e.g., after 5,
10, 15, and 20 minutes).

Moderate response
rate with significant
pauses after
reinforcement

Hospital patient uses
patient-controlled, doctor-
timed pain relief

Variable
interval

Reinforcement is delivered at
unpredictable time intervals (e.g.,
after 5, 7, 10, and 20 minutes).

Moderate yet steady
response rate

Checking social media

Fixed ratio
Reinforcement is delivered after a
predictable number of responses (e.g.,
after 2, 4, 6, and 8 responses).

High response rate
with pauses after
reinforcement

Piecework—factory worker
getting paid for every x
number of items
manufactured

Variable ratio
Reinforcement is delivered after an
unpredictable number of responses
(e.g., after 1, 4, 5, and 9 responses).

High and steady
response rate

Gambling

TABLE 6.3

Now let’s combine these four terms. A fixed interval reinforcement schedule is when behavior is rewarded
after a set amount of time. For example, June undergoes major surgery in a hospital. During recovery, they are
expected to experience pain and will require prescription medications for pain relief. June is given an IV drip
with a patient-controlled painkiller. Their doctor sets a limit: one dose per hour. June pushes a button when
pain becomes difficult, and they receive a dose of medication. Since the reward (pain relief) only occurs on a
fixed interval, there is no point in exhibiting the behavior when it will not be rewarded.

With a variable interval reinforcement schedule, the person or animal gets the reinforcement based on
varying amounts of time, which are unpredictable. Say that Manuel is the manager at a fast-food restaurant.
Every once in a while someone from the quality control division comes to Manuel’s restaurant. If the restaurant
is clean and the service is fast, everyone on that shift earns a $20 bonus. Manuel never knows when the quality
control person will show up, so he always tries to keep the restaurant clean and ensures that his employees
provide prompt and courteous service. His productivity regarding prompt service and keeping a clean
restaurant are steady because he wants his crew to earn the bonus.

With a fixed ratio reinforcement schedule, there are a set number of responses that must occur before the
behavior is rewarded. Carla sells glasses at an eyeglass store, and she earns a commission every time she sells
a pair of glasses. She always tries to sell people more pairs of glasses, including prescription sunglasses or a
backup pair, so she can increase her commission. She does not care if the person really needs the prescription
sunglasses, Carla just wants her bonus. The quality of what Carla sells does not matter because her
commission is not based on quality; it’s only based on the number of pairs sold. This distinction in the quality
of performance can help determine which reinforcement method is most appropriate for a particular
situation. Fixed ratios are better suited to optimize the quantity of output, whereas a fixed interval, in which
the reward is not quantity based, can lead to a higher quality of output.

In a variable ratio reinforcement schedule, the number of responses needed for a reward varies. This is the
most powerful partial reinforcement schedule. An example of the variable ratio reinforcement schedule is

6.3 • Operant Conditioning 199

gambling. Imagine that Sarah—generally a smart, thrifty woman—visits Las Vegas for the first time. She is not a
gambler, but out of curiosity she puts a quarter into the slot machine, and then another, and another. Nothing
happens. Two dollars in quarters later, her curiosity is fading, and she is just about to quit. But then, the
machine lights up, bells go off, and Sarah gets 50 quarters back. That’s more like it! Sarah gets back to
inserting quarters with renewed interest, and a few minutes later she has used up all her gains and is $10 in
the hole. Now might be a sensible time to quit. And yet, she keeps putting money into the slot machine because
she never knows when the next reinforcement is coming. She keeps thinking that with the next quarter she
could win $50, or $100, or even more. Because the reinforcement schedule in most types of gambling has a
variable ratio schedule, people keep trying and hoping that the next time they will win big. This is one of the
reasons that gambling is so addictive—and so resistant to extinction.

In operant conditioning, extinction of a reinforced behavior occurs at some point after reinforcement stops,
and the speed at which this happens depends on the reinforcement schedule. In a variable ratio schedule, the
point of extinction comes very slowly, as described above. But in the other reinforcement schedules, extinction
may come quickly. For example, if June presses the button for the pain relief medication before the allotted
time the doctor has approved, no medication is administered. They are on a fixed interval reinforcement
schedule (dosed hourly), so extinction occurs quickly when reinforcement doesn’t come at the expected time.
Among the reinforcement schedules, variable ratio is the most productive and the most resistant to extinction.
Fixed interval is the least productive and the easiest to extinguish (Figure 6.13).

FIGURE 6.13 The four reinforcement schedules yield different response patterns. The variable ratio schedule is
unpredictable and yields high and steady response rates, with little if any pause after reinforcement (e.g., gambler).
A fixed ratio schedule is predictable and produces a high response rate, with a short pause after reinforcement (e.g.,
eyeglass saleswoman). The variable interval schedule is unpredictable and produces a moderate, steady response
rate (e.g., restaurant manager). The fixed interval schedule yields a scallop-shaped response pattern, reflecting a
significant pause after reinforcement (e.g., surgery patient).

Gambling and the Brain
Skinner (1953) stated, “If the gambling establishment cannot persuade a patron to turn over money with no return,
it may achieve the same effect by returning part of the patron’s money on a variable-ratio schedule” (p. 397).

Skinner uses gambling as an example of the power of the variable-ratio reinforcement schedule for maintaining
behavior even during long periods without any reinforcement. In fact, Skinner was so confident in his knowledge of
gambling addiction that he even claimed he could turn a pigeon into a pathological gambler (“Skinner’s Utopia,”
1971). It is indeed true that variable-ratio schedules keep behavior quite persistent—just imagine the frequency of a
child’s tantrums if a parent gives in even once to the behavior. The occasional reward makes it almost impossible to
stop the behavior.

Recent research in rats has failed to support Skinner’s idea that training on variable-ratio schedules alone causes

CONNECT THE CONCEPTS

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pathological gambling (Laskowski et al., 2019). However, other research suggests that gambling does seem to work
on the brain in the same way as most addictive drugs, and so there may be some combination of brain chemistry
and reinforcement schedule that could lead to problem gambling (Figure 6.14). Specifically, modern research shows
the connection between gambling and the activation of the reward centers of the brain that use the
neurotransmitter (brain chemical) dopamine (Murch & Clark, 2016). Interestingly, gamblers don’t even have to win
to experience the “rush” of dopamine in the brain. “Near misses,” or almost winning but not actually winning, also
have been shown to increase activity in the ventral striatum and other brain reward centers that use dopamine
(Chase & Clark, 2010). These brain effects are almost identical to those produced by addictive drugs like cocaine
and heroin (Murch & Clark, 2016). Based on the neuroscientific evidence showing these similarities, the DSM-5 now
considers gambling an addiction, while earlier versions of the DSM classified gambling as an impulse control
disorder.

FIGURE 6.14 Some research suggests that pathological gamblers use gambling to compensate for abnormally low
levels of the hormone norepinephrine, which is associated with stress and is secreted in moments of arousal and
thrill. (credit: Ted Murphy)

In addition to dopamine, gambling also appears to involve other neurotransmitters, including norepinephrine and
serotonin (Potenza, 2013). Norepinephrine is secreted when a person feels stress, arousal, or thrill. It may be that
pathological gamblers use gambling to increase their levels of this neurotransmitter. Deficiencies in serotonin might
also contribute to compulsive behavior, including a gambling addiction (Potenza, 2013).

It may be that pathological gamblers’ brains are different than those of other people, and perhaps this difference
may somehow have led to their gambling addiction, as these studies seem to suggest. However, it is very difficult to
ascertain the cause because it is impossible to conduct a true experiment (it would be unethical to try to turn
randomly assigned participants into problem gamblers). Therefore, it may be that causation actually moves in the
opposite direction—perhaps the act of gambling somehow changes neurotransmitter levels in some gamblers’
brains. It also is possible that some overlooked factor, or confounding variable, played a role in both the gambling
addiction and the differences in brain chemistry.

Cognition and Latent Learning

Strict behaviorists like Watson and Skinner focused exclusively on studying behavior rather than cognition
(such as thoughts and expectations). In fact, Skinner was such a staunch believer that cognition didn’t matter
that his ideas were considered radical behaviorism. Skinner considered the mind a “black box”—something
completely unknowable—and, therefore, something not to be studied. However, another behaviorist, Edward C.
Tolman, had a different opinion. Tolman’s experiments with rats demonstrated that organisms can learn even
if they do not receive immediate reinforcement (Tolman & Honzik, 1930; Tolman, Ritchie, & Kalish, 1946). This
finding was in conflict with the prevailing idea at the time that reinforcement must be immediate in order for
learning to occur, thus suggesting a cognitive aspect to learning.

6.3 • Operant Conditioning 201

In the experiments, Tolman placed hungry rats in a maze with no reward for finding their way through it. He
also studied a comparison group that was rewarded with food at the end of the maze. As the unreinforced rats
explored the maze, they developed a cognitive map: a mental picture of the layout of the maze (Figure 6.15).
After 10 sessions in the maze without reinforcement, food was placed in a goal box at the end of the maze. As
soon as the rats became aware of the food, they were able to find their way through the maze quickly, just as
quickly as the comparison group, which had been rewarded with food all along. This is known as latent
learning: learning that occurs but is not observable in behavior until there is a reason to demonstrate it.

FIGURE 6.15 Psychologist Edward Tolman found that rats use cognitive maps to navigate through a maze. Have you
ever worked your way through various levels on a video game? You learned when to turn left or right, move up or
down. In that case you were relying on a cognitive map, just like the rats in a maze. (credit: modification of work by
“FutUndBeidl”/Flickr)

Latent learning also occurs in humans. Children may learn by watching the actions of their parents but only
demonstrate it at a later date, when the learned material is needed. For example, suppose that Ravi’s dad
drives him to school every day. In this way, Ravi learns the route from his house to his school, but he’s never
driven there himself, so he has not had a chance to demonstrate that he’s learned the way. One morning Ravi’s
dad has to leave early for a meeting, so he can’t drive Ravi to school. Instead, Ravi follows the same route on his
bike that his dad would have taken in the car. This demonstrates latent learning. Ravi had learned the route to
school, but had no need to demonstrate this knowledge earlier.

This Place Is Like a Maze
Have you ever gotten lost in a building and couldn’t find your way back out? While that can be frustrating, you’re

EVERYDAY CONNECTION

202 6 • Learning

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not alone. At one time or another we’ve all gotten lost in places like a museum, hospital, or university library.
Whenever we go someplace new, we build a mental representation—or cognitive map—of the location, as
Tolman’s rats built a cognitive map of their maze. However, some buildings are confusing because they include
many areas that look alike or have short lines of sight. Because of this, it’s often difficult to predict what’s around
a corner or decide whether to turn left or right to get out of a building. Psychologist Laura Carlson (2010)
suggests that what we place in our cognitive map can impact our success in navigating through the environment.
She suggests that paying attention to specific features upon entering a building, such as a picture on the wall, a
fountain, a statue, or an escalator, adds information to our cognitive map that can be used later to help find our
way out of the building.

LINK TO LEARNING

Watch this video about Carlson’s studies on cognitive maps and navigation in buildings (http://openstax.org/l/
carlsonmaps) to learn more.

6.4 Observational Learning (Modeling)
LEARNING OBJECTIVES
By the end of this section, you will be able to:

• Define observational learning
• Discuss the steps in the modeling process
• Explain the prosocial and antisocial effects of observational learning

Previous sections of this chapter focused on classical and operant conditioning, which are forms of associative
learning. In observational learning, we learn by watching others and then imitating, or modeling, what they
do or say. For instance, have you ever gone to YouTube to find a video showing you how to do something? The
individuals performing the imitated behavior are called models. Research suggests that this imitative learning
involves a specific type of neuron, called a mirror neuron (Hickock, 2010; Rizzolatti, Fadiga, Fogassi, & Gallese,
2002; Rizzolatti, Fogassi, & Gallese, 2006).