Forty Studies that Changed Psychology

FORTY STUDIES THAT C H A N G E D PSYCHOLOGY

L

FORTY STUDIES THAT C H A N G E D PSYCHOLOGY Explorations into the History of Psychological Research Sixth Edition

Roger R. Hock, Ph.D. Mendocino College

Pearson Education International

VP/Editorial Director: Leah Jewell Executive Editor/Project Manager: Jessica Mosher Editorial Assistant: Amanda Bacher Associate Managing Editor: Maureen Richardson Production Liaison: Shelly Kupperman Senior Operations Supervisor: Sherry Lewis Director of Marketing: Brandy Dawson Senior Marketing Manager: Kate Mitchell Marketing Assistant: Jennifer Lang

AV Project Manager: Maria Piper Associate Supplements Editor: Virginia Livsey Director, Cover Design: Jayne Conte Cover Designer: Studio Indigo Cover Image: Getty Images, Inc. Composition and Full-Service Project Management: Aptara, Inc./Puneet Lamba Printer/Binder: R.R. Donnelley & Sons Cover Printer: Phoenix Color Corp.

Credits and acknowledgments borrowed from other sources and reproduced, with permission, in this textbook appear on the appropriate page of appearance within text. If you purchased this book within the United States or Canada you should be aware that it has been wrongfully imported without the approval of the Publisher or the Author. Copyright © 2009, 2005, 2002, 1999, 1996 by Pearson Education, Inc., Upper Saddle River, New Jersey, 07458. All rights reserved. Printed in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to: Rights and Permissions Department. Pearson Prentice Hall™ is a trademark of Pearson Education, Inc. Pearson* is a registered trademark of Pearson pic Prentice Hall* is a registered trademark of Pearson Education, Inc. Pearson Pearson Pearson Pearson Pearson

Education Ltd., London Education Singapore, Pte. Ltd Education Canada, Inc. Education-Japan Education Australia PTY, Limited

Pearson Education North Asia Ltd., Hong Kong Pearson Educación de Mexico, S.A. de CV. Pearson Education Malaysia, Pte. Ltd. Pearson Education Upper Saddle River, New Jersey

PEARSON 10 ISBN-13: ISBN-ID:

9

8

7

6

5

4

17Ö-D-13-S0M507-7 G-13-5tmsa7-X

For Diane Perin Hock and Caroline Mei Perin Hock

CONTENTS

PREFACE

xi

CHAPTER I BIOLOGY AND HUMAN BEHAVIOR 1 READING 1: O N E BRAIN OR T W O ? 1 Gazzaniga, M. S. (1967). The split brain in man. Scientific American, 217(2), 24-29. READING 2: MORE EXPERIENCE = BIGGER BRAIN 11 Rosenzweig, M. R., Bennett, E. L., & Diamond, M. C. (1972). Brain changes in response to experience. Scientific American, 226(2), 2 2 - 2 9 . READING 3: ARE Y O U A "NATURAL?" 19 Bouchard, T., Lykken, D., McGue, M., Segal, N., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250, 223-229. READING 4: WATCH O U T FOR THE VISUAL C L I F F ! 27 Gibson, E. J . , & Walk, R. D. (1960). The "visual cliff." Scientific American, 202(4), 67-71.

CHAPTER II

PERCEPTION AND CONSCIOUSNESS

35

READING 5: TAKE A L O N G L O O K 36 Fantz, R. L. (1961). The origin of form perception. Scientific American, 204(May), 61-72. READING 6 : T O SLEEP, N O D O U B T T O DREAM . . . 42 Aserinsky, E., & Kleitman, N. (1953). Regularly occurring periods of eye mobility and concomitant phenomena during sleep. Science, 118, 273-274. Dement, W. (1960). The effect of dream deprivation. Science, 131, 1705-1707. READING 7: U N R O M A N C I N G THE DREAM 49 Hobson, J. A., & McCarley, R. W. (1977). The brain as a dream-state generator: An activation-synthesis hypothesis of the dream process. American Journal of Psychiatry, 134, 1335-1348. READING 8: A C T I N G AS IF Y O U ARE H Y P N O T I Z E D 56 Spanos, N. R (1982). Hypnotic behavior: A cognitive, social, psychological perspective. Research Communications in Psychology, Psychiatry, and Behavior, 7, 199-213. vii

viii

Contents

CHAPTER III LEARNING AND CONDITIONING 65 READING 9: IT'S NOT JUST A B O U T SALIVATING D O G S ! 65 Pavlov, I. P. (1927). Conditioned reflexes. London: Oxford University Press. READING 10: LITTLE EMOTIONAL ALBERT 72 Watson, J. B., & Rayner, R. (1920). Conditioned emotional responses. Journal of Experimental Psychology, 3, 1-14. READING 11: K N O C K W O O D ! 78 Skinner, B. F. (1948). Superstition in the pigeon. Journal of Experimental Psychology, 38, 168-172. READING 12: SEE A G G R E S S I O N . . . D O A G G R E S S I O N ! 8 5 Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. Journal of Abnormal and Social Psychology, 63, 575-582.

CHAPTER IV

INTELLIGENCE, COGNITION, AND MEMORY

93

READING 13: WHAT Y O U EXPECT IS WHAT Y O U G E T 93 Rosenthal, R., & Jacobson, L. (1966). Teachers' expectancies: Determinates of pupils' IQ gains. Psychological Reports, 19, 115-118. R E A D I N G 14: JUST H O W ARE Y O U INTELLIGENT? 100 Gardner, H. (1983) Frames of mind: The theory of multiple intelligences. New York: Basic Books. READING 15: MAPS IN Y O U R MIND 110 Tolman, E. C. (1948). Cognitive maps in rats and men. Psychological Review, 55, 189-208. READING 16: THANKS FOR THE MEMORIES! 11 7 Loftus, E. F. (1975). Leading questions and the eyewitness report. Cognitive Psychology, 7, 560-572.

CHAPTER V HUMAN DEVELOPMENT 126 READING 17: D I S C O V E R I N G L O V E 126 Harlow, H. F. (1958). The nature of love. American Psychologist, 13, 673-685. READING 18: O U T OF SIGHT, BUT N O T O U T OF MIND 1 34 Piaget, J. (1954). The development of object concept. In J. Piaget, The construction of reality in the child (pp. 3 - 9 6 ) . New York: Basic Books. READING 19: H O W MORAL ARE Y O U ? 143 Kohlberg, L. (1963). The development of children's orientations toward a moral order: Sequence in the development of moral thought. Vita Humana, 6, 11-33. READING 20: IN C O N T R O L A N D G L A D OF IT! 150 Langer, E. J . , & Rodin, J. (1976). The effects of choice and enhanced personal responsibility for the aged: A field experiment in an institutional setting. Journal of Personality and Social Psychology, 34, 191-198.

Contents

CHAPTER VI

EMOTION AND MOTIVATION

ix

158

READING 21: A SEXUAL MOTIVATION . . . 158 Masters, W. H., & Johnson, V. E. (1966). Human sexual response. Boston: Little, Brown. READING 22:1 C A N SEE IT ALL OVER Y O U R FACE! 1 68 Ekman, P., & Friesen, W. V. (1971). Constants across cultures in the face and emotion. Journal of Personality and Social Psychology, 17, 124—129. READING 23: LIFE, C H A N G E , A N D STRESS 1 75 Holmes, T. H., & Rahe, R. H. (1967). The Social Readjustment Rating Scale. Journal of Psychosomatic Research, 11,213-218. READING 24: T H O U G H T S O U T O F T U N E 183 Festinger, L., & Carlsmith, J. M. (1959). Cognitive consequences of forced compliance. Journal of Abnormal and Social Psychology, 58, 203-210.

CHAPTER VII

PERSONALITY

191

READING 25: ARE Y O U THE MASTER OF Y O U R FATE? 192 Rotter, J. B. (1966). Generalized expectancies for internal versus external control of reinforcement. Psychological Monographs, 80, 1-28. READING 26: MASCULINE O R FEMININE . . . O R B O T H ? 199 Bem, S. L. (1974). The measurement of psychological androgyny. Journal of Consulting and Clinical Psychology, 42, 155-162. READING 27: RACING AGAINST Y O U R HEART 210 Friedman, M., & Rosenman, R. H. (1959). Association of specific overt behavior pattern with blood and cardiovascular findings. Journal of the American Medical Association, 169, 1286-1296. READING 28: THE O N E , THE MANY 217 Triandis, H., Bontempo, R., Villareal, M., Asai, M., & Lucca, N. (1988). Individualism and collectivism: Cross-cultural perspectives on self-ingroup relationships. Journal of Personality and Social Psychology, 54, 323-338.

CHAPTER VIII PSYCHOPATHOLOGY 2 2 7 READING 29: W H O ' S CRAZY HERE, ANYWAY? 227 Rosenhan, D. L. (1973). On being sane in insane places. Science, 179, 250-258. READING 30: Y O U ' R E G E T T I N G DEFENSIVE A G A I N ! 2 3 5 Freud, A. (1946). The ego and the mechanisms of defense. New York: International Universities Press. READING 31: LEARNING TO BE DEPRESSED 2 4 2 Seligman, M. E. P., & Maier, S. F. (1967). Failure to escape traumatic shock. Journal of Experimental Psychology, 74, 1-9.

x

Contents

R E A D I N G 32: C R O W D I N G I N T O THE BEHAVIORAL SINK 249 Calhoun, J. B. (1962). Population density and social pathology. Scientific American, 206(3), 139-148.

CHAPTER IX

PSYCHOTHERAPY

258

READING 33: C H O O S I N G Y O U R PSYCHOTHERAPIST 258 Smith, M. L., & Glass, G. V. (1977). Meta-analysis of psychotherapy outcome studies. American Psychologist, 32, 752-760. R E A D I N G 34: RELAXING Y O U R FEARS AWAY 264 Wolpe, J. (1961). The systematic desensitization treatment of neuroses. Journal of Nervous and Mental Diseases, 132, 180-203. READING 35: PROJECTIONS O F W H O Y O U ARE 271 Rorschach, H. (1942). Psychodiagnostics: A diagnostic test based on perception. New York: Grune & Stratton. READING 36: PICTURE THIS! 278 Murray, H. A. (1938). Explorations in personality (pp. 5 3 1 - 5 4 5 ) . New York: Oxford University Press.

CHAPTER X

SOCIAL PSYCHOLOGY

286

READING 37: A PRISON BY ANY OTHER NAME . . . 287 Zimbardo, P. G. (1972). The pathology of imprisonment. Society, 9(6), 4-8. Haney, C, Banks, W. C, & Zimbardo, P. G. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology & Penology, 1, 69-97. R E A D I N G 38: THE POWER O F C O N F O R M I T Y 295 Asch, S. E. (1955). Opinions and social pressure. Scientific American, 193(5), 31-35. READING 39: T O HELP O R N O T T O HELP 300 Darley, J. M., & Latané, B. (1968). Bystander intervention in emergencies: Diffusion of responsibility. Journal of Personality and Social Psychology, 8, 377-383. READING 40: O B E Y AT ANY C O S T ? 308 Milgram, S. (1963). Behavioral study of obedience. Journal of Abnormal and Social Psychology, 67, 371-378.

A U T H O R INDEX SUBJECT INDEX

318 322

PREFACE

T

he publication of this sixth edition of Forty Studies marks the 18th anniversary of its original release. T h e majority of the studies included in this edition are the same ones that m a d e up a large part of the first edition. This demonstrates how these landmark studies continue to e x e r t their influence over psychological thought and research today. These original studies and the ones that have been added over the past 18 years provide a fascinating glimpse into the birth and growth of the science of psychology, and into the insights we have acquired into the complexities of human nature. Many studies of h u m a n behavior have m a d e remarkable and lasting impacts on the various disciplines that comprise the vast field of psychology. T h e findings generated from these studies have c h a n g e d o u r knowledge of human behavior, a n d they have set the stage for coundess subsequent p r o jects and research programs. Even when the results of some of these pivotal studies have later been drawn into controversy and question, their effect a n d influence in a historical c o n t e x t never diminish. They continue to be cited in new articles; they continue to be the topic of a c a d e m i c discussion; they continue to form the foundation for hundreds of textbook chapters; and they continue to hold a special place in the minds of psychologists. T h e c o n c e p t for this book originated from my many years of teaching psychology. Psychology textbooks a r e based on key studies that have shaped the science of psychology over its relatively brief history. Textbooks, however, seldom give the original, c o r e studies the attention they richly deserve. T h e original research processes a n d findings often a r e summarized a n d diluted to the point that little of the life and e x c i t e m e n t of the discoveries remain. Sometimes, research results a r e r e p o r t e d in ways that may even mislead the r e a d e r about the study's real impact a n d influence about what we know a n d how we know it. This is in no way a criticism of the textbook writers who work u n d e r length constraints and must make many difficult choices about what gets included and in how m u c h detail. T h e situation is, however, unfortunate, because the foundation of all of psychology is scientific research, a n d through over a century of ingenious a n d elegant studies o u r knowledge a n d understanding of h u m a n behavior have been e x p a n d e d a n d refined to the advanced level of sophistication that exists today. This book is an attempt to fill the gap between the psychology textbooks and the research that m a d e them possible. It is a j o u r n e y through the

xi

xii

Preface

headline history of psychology. My h o p e is that the way the 40 chosen studies a r e presented will bring every o n e of t h e m back to life so that you can experie n c e them for yourself. This book is intended for anyone who wishes a g r e a t e r understanding of the t r u e roots of psychology.

C H O O S I N G THE STUDIES T h e studies included in this book have b e e n carefully chosen from those found in psychology texts a n d j o u r n a l s a n d from those suggested by leading authorities in the many b r a n c h e s of psychology. As the studies were selected, 40 seemed to be a realistic n u m b e r both from a historical point of view a n d in terms of length. T h e studies chosen are arguably the most famous, the most important, or the most influential in the history of psychology. I use the word arguably because many who r e a d this book may wish to dispute some of the choices. O n e thing is sure: no single list of 40 studies would satisfy everyone. However, the studies included h e r e continue to be cited most frequently, stirred up the most controversy when they were published, sparked the most subsequent related research, o p e n e d new fields of psychological exploration, or c h a n g e d most dramatically o u r knowledge of h u m a n behavior. T h e s e studies a r e organized by c h a p t e r a c c o r d i n g to the major psychology branches into which they best fit: Biology a n d H u m a n Behavior; Perception a n d Consciousness; Learning; Intelligence, Cognition, a n d Memory; H u m a n Development; E m o t i o n a n d Motivation; Personality; Psychopathology; Psychotherapy; and Social Psychology.

PRESENTING THE STUDIES T h e original studies a r e n o t included in their entirety in this book. Instead, I have discussed a n d summarized them in a consistent f o r m a t t h r o u g h o u t the book to p r o m o t e a clear understanding of the studies presented. E a c h reading contains the following: 1. An e x a c t , readily available reference for where the original study can be found 2. A brief introduction summarizing the b a c k g r o u n d in the field leading up to the study a n d the reasons the r e s e a r c h e r c a r r i e d out the project 3. T h e theoretical propositions or hypotheses on which the research rests 4. A detailed a c c o u n t of the experimental design a n d m e t h o d s used to c a r r y out the research, including, where appropriate, who the participants were and how they were recruited; descriptions of any apparatus a n d materials used; a n d the actual p r o c e d u r e s followed in carrying out the research 5. A s u m m a r y of the results of the study in clear, understandable, nontechnical, nonstatistical, n o j a r g o n language 6. An interpretation of the meaning of the findings based on the author's own discussion in the original article

Preface

xiii

7. T h e significance of the study to the field of psychology 8. A brief discussion of supportive or c o n t r a d i c t o r y follow-up r e s e a r c h findings a n d subsequent questioning or criticism from o t h e r s in t h e field 9. A sampling of r e c e n t applications a n d citations of the study in others' articles to demonstrate its continuing influence 10. References for additional and updated reading relating to the study Often, scientists speak in languages that a r e n o t easily u n d e r s t o o d (even by o t h e r scientists). T h e p r i m a r y goal of this b o o k is to m a k e these discoveries meaningful a n d accessible to t h e r e a d e r a n d to allow you to exp e r i e n c e the e x c i t e m e n t a n d d r a m a o f these r e m a r k a b l e a n d i m p o r t a n t discoveries. W h e r e possible a n d a p p r o p r i a t e , I have edited a n d simplified s o m e o f t h e studies p r e s e n t e d h e r e for ease o f r e a d i n g a n d u n d e r s t a n d i n g . However, this has b e e n d o n e carefully, so that t h e m e a n i n g a n d e l e g a n c e of the work a r e p r e s e r v e d a n d the i m p a c t of t h e r e s e a r c h is distilled a n d clarified.

NEW TO THE SIXTH E D I T I O N This sixth edition of Forty Studies offers n u m e r o u s noteworthy a n d substantive changes and additions. I have a d d e d two of the most influential studies in the history of psychology about how we perceive the world. T h e first is R o b e r t Fantz's revolutionary discovery of an ingenious m e t h o d to allow us to study what very young infants "know" (from 1 9 6 1 ) . T h e second, Philip Zimbardo's famous Stanford Prison Study (from the early 1 9 7 0 s ) focuses on the powerful and controlling forces some situations can e x e r t over o u r behavior. In addition, the R e c e n t Applications sections n e a r the e n d of the readings have been updated. These sections sample the n u m e r o u s r e c e n t citations of the 40 studies into the 21st century. T h e 40 studies discussed in this book are referred to in over 1 0 0 0 research articles every year! A small sampling of those articles is briefly summarized t h r o u g h o u t this edition to allow you to e x p e r i e n c e the ongoing influence of these 40 studies that c h a n g e d psychology. All these recently cited studies a r e fully referenced at the e n d of each reading along with o t h e r relevant sources. As you r e a d through them, you will be able to appreciate the breadth a n d richness of the contributions still being m a d e by the 40 studies that comprise this book. Over the three years since completing the fifth edition, I have continued to enjoy numerous conversations with, and helpful suggestions from, colleagues in many branches of psychological research about potential changes in the selection of studies for this new edition. Two studies I have for some time considered including have been mentioned frequently by fellow researchers, so I have added them in this edition. E a c h of these two newly incorporated studies, in

xiv

Preface

their own significant ways, e x p a n d e d o u r p e r c e p t i o n s of two very basic aspects o f h u m a n n a t u r e a n d a d d e d t o o u r knowledge o f the complexity a n d diversity o f the h u m a n e x p e r i e n c e . O n e of the newly a d d e d studies in this edition provided a window into the p e r c e p t u a l a n d thinking abilities of infants. Of c o u r s e , behavioral scientists have known for d e c a d e s that infants' behaviors in relation to the world a r o u n d t h e m c h a n g e a n d develop quickly in many ways. But just what do babies know? How do they think? H o w skilled a r e they at perceiving a n d processing events in their e n v i r o n m e n t ? You c a n imagine this is a difficult r e s e a r c h challenge to o v e r c o m e because infants c a n n o t talk to you about what is going on in their brains. Instead, r e s e a r c h e r s must infer what infants perceive a n d how they think from their observable behaviors. In essence, this was how the famous Swiss psychologist, J e a n Piaget, who is discussed in C h a p t e r V of this book, f o r m e d his theories of early cognitive dev e l o p m e n t in preverbal infants. In the early 1 9 6 0 s , R o b e r t L. Fantz discovered a new way of allowing us to p e e r inside the p e r c e p t i o n s of infants: looking at what they a r e looking at. It turns out that even very young infants prefer to look at certain objects or events over others. By measuring this behavior, r e f e r r e d to as preferential looking, r e s e a r c h e r s have b e e n able to study infants' knowledge a n d p e r c e p t i o n in many a n d varied contexts. This methodology, along with s o m e e n h a n c e m e n t s to it (also p i o n e e r e d by F a n t z ) , r e m a i n s today, nearly 50 years later, the most widely employed technique when psychologists a n d others wish to study the perceiving, thinking, a n d knowing processes of infants. T h e second study added to this new edition is o n e of the most wellknown research undertakings in the history of psychology. Many would argue, a n d rightly so, that perhaps it should have been a mainstay of this book f r c m the beginning. It is Philip Zimbardo's famous "Stanford Prison Study." T h a t said, the historical timing is perfect to include this study now because a renewed interest has arisen in this study a n d the inferences drawn from it over the past several years, due to the high news-profile prisoner scandals in Iraq a n d various U.S. prisoner policies relating to the "War on Terror." In basic psychological theory, two forces d e t e r m i n e o u r behavior in a given situation: o u r internal, dispositional factors (that is, who we a r e ) and the influences of the situation in which we a r e behaving. In his simulated prison study, Zimbardo set out to e x a m i n e how o r d i n a r y people's behavior might c h a n g e when placed in a situation that carries with it a great deal of inherent power, in this case, a prison. All the studies, regardless of vintage, discussed in the upcoming pages have o n e issue in c o m m o n : research ethics. O n e of the most important building blocks of psychological science is a strict understanding a n d a d h e r e n c e to a clear set of professional ethical guidelines in any r e s e a r c h involving humans or animals. Let's consider briefly the ethical principles social scientists work diligently to follow as they make their discoveries.

Preface

xv

T H E ETHICS O F RESEARCH I N V O L V I N G H U M A N O R ANIMAL PARTICIPANTS Without subjects, scientific research is virtually impossible. In physics, the subjects are m a t t e r and energy; in botany, they a r e plants; in chemistry, they are atoms and molecules; and in psychology, the participants are people. Sometimes, certain types of research do not p e r m i t the use of h u m a n participants, so animal subjects are substituted. However, typically, the ultimate goal of animal research is to understand h u m a n behavior better, not just to study the animals themselves. In this book, you will be reading about research involving both h u m a n and animal subjects. S o m e of the studies may cause you to question the ethics of the researchers in r e g a r d to the p r o c e d u r e s used with the subjects. W h e n painful or stressful p r o c e d u r e s a r e part of a study, usually the question of ethics is noted in the chapter. However, because this is such a volatile and topical issue, a brief discussion of the ethical guidelines followed by present-day psychologists in all research is included h e r e in advance of the specific studies described in this book.

Research with Human Participants T h e American Psychological Association (APA) has issued strict and clear guidelines that researchers must follow when carrying out e x p e r i m e n t s involving h u m a n participants. A portion of the introduction to those guidelines reads as follows: Psychologists strive to benefit those with whom they work and take care to do no harm. In their professional actions, psychologists seek to safeguard the welfare and rights of those with whom they interact. . . . When conflicts occur among psychologists' obligations or concerns, they attempt to resolve these conflicts in a responsible fashion that avoids or minimizes harm. . . . Psychologists uphold professional standards of conduct, clarify their professional roles and obligations, accept appropriate responsibility for their behavior, and seek to manage conflicts of interest that could lead to exploitation or harm.. . . Psychologists respect the dignity and worth of all people, and the rights of individuals to privacy, confidentiality, and self-determination, (excerpted from Ethical Principles of Psychologists and Code of Conduct, 2003; see http://apa.org/ethics). Researchers today take great c a r e to a d h e r e to those principles by following basic ethical principles in carrying out all studies involving h u m a n participants. These principles may be summarized as follows: 1. Informed consent. A researcher must explain to potential participants what the experiment is about and what procedures will be used so that the individual is able to make an informed decision about whether or not to participate. If the person then agrees to participate, this is called informed consent. As you will see in this book, sometimes the true purposes of an experiment cannot be revealed because this would alter the behavior of the participants and contaminate the results. In such cases, when deception is used, a subject still must be given adequate information for informed

xvi

Preface consent, and the portions of the experiment that are hidden must be both justifiable based on the importance of the potential findings and revealed to the participants at the end of their involvement in the study. In research involving children or minors, parent or guardian consent is required and the same ethical guidelines apply.

2. Freedom to withdraw at any time. Part of informed consent is the principle that all h u m a n participants in all research projects must be aware that they may withdraw freely from the study at any time. This may appear to be an unnecessary rule, because it would seem obvious that any subject who is t o o uncomfortable with the p r o c e d u r e s can simply leave. However, this is n o t always so straightforward. F o r e x a m p l e , undergraduate students a r e often given course credit for participating as participants in psychological experiments. If they feel that withdrawing will influe n c e the credit they need, they may not feel free to do so. W h e n participants a r e paid to participate, if they a r e m a d e to feel that their completion of the e x p e r i m e n t is a r e q u i r e m e n t for payment, this could p r o d u c e an unethical i n d u c e m e n t to avoid withdrawing if they wish to do so. To avoid this problem, participants should be given credit or paid at the beginning of the p r o c e d u r e just for showing up. 3. Confidentiality. All results based on participants in experiments should be kept in c o m p l e t e confidence unless specific agreements have been m a d e with the participants. This does not m e a n that results c a n n o t be r e p o r t e d a n d published, but this is d o n e in such a way that individual data c a n n o t be identified. Often, no identifying information is even acquired from participants, a n d all data a r e c o m b i n e d to arrive at average differences a m o n g groups. 4. Debriefing and protedion from harm. Experimenters have the responsibility to protect their participants from all physical and psychological harm that might result from the research procedures. Most psychological research involves methods that are completely harmless, both during and after the study. However, even seemingly harmless procedures can sometimes produce negative effects, such as frustration, embarrassment, or concern. O n e c o m m o n safeguard against those effects is the ethical requirement of debriefing. After participants have completed an experiment, especially o n e involving any form of deception, they should be debriefed. During debriefing, the true purpose and goals of the experiment are explained to them, and they a r e given the opportunity to ask any questions about their experiences. If there is any possibility of lingering aftereffects from the experiment, the researchers should provide participants with contact information if participants might have any concerns in the future. As you read through the studies included in this book, you may find a few studies that a p p e a r to have violated some of these ethical principles. T h o s e studies were carried out long before formal ethical guidelines existed a n d could not be replicated u n d e r today's ethical principles. T h e lack of

Preface

xvii

guidelines, however, does not excuse past researchers for abuses. J u d g m e n t of those investigators must now be m a d e by e a c h of us individually, a n d we must learn, as psychologists have, from past mistakes.

Research with Animal Subjects O n e of the hottest topics of discussion inside and outside the scientific c o m munity is the question of the ethics of animal research. Animal-rights groups are growing in n u m b e r and are becoming increasingly vocal and militant. More controversy exists today over animal subjects than h u m a n participants, probably because animals c a n n o t be protected, as humans can, with informed consent, freedom to withdraw, or debriefing. In addition, the most radical animal rights activists take the view that all living things a r e o r d e r e d in value by their ability to sense pain. In this conceptualization, animals are equal in value to humans and, therefore, any use of animals by humans is seen as unethical. This use includes eating a chicken, wearing leather, and owning pets (which, according to some animal-rights activists, is a form of slavery). At o n e end of the spectrum, many people believe that research with animals is i n h u m a n e and unethical and should be prohibited. However, nearly all scientists and most Americans believe that the limited a n d h u m a n e use of animals in scientific research is necessary a n d beneficial. Many lifesaving drugs and medical techniques have been developed through the use of animal experimental subjects. Animals have also often been subjects in psychological research to study issues such as depression, brain development, overcrowding, and learning processes. T h e primary reason animals a r e used in research is that to c a r r y out similar research on h u m a n s clearly would be unethical. F o r example, suppose you wanted to study the effect on brain development and intelligence of raising infants in an e n r i c h e d environment with many activities and toys, versus an impoverished e n v i r o n m e n t with little to do. To assign h u m a n infants to these different conditions would simply not be possible. However, most people would a g r e e that rats could be studied without major ethical c o n c e r n s to reveal findings potentially i m p o r t a n t to humans (see Reading 2 on research by Rosenzweig a n d B e n n e t t ) . T h e APA, in addition to its guidelines on h u m a n participants, has strict rules governing research with animal subjects that are designed to ensure hum a n e treatment. These rules require that research animals receive p r o p e r housing, feeding, cleanliness, a n d health c a r e . All unnecessary pain to the animal is prohibited. A portion of the APA's Guidelines for the Ethical Conduct in the Care and Use of Animals ( 2 0 0 4 ) reads as follows: Animals are to be provided with humane care and healthful conditions during their stay in the facility.... Psychologists are encouraged to consider enriching the environments of their laboratory animals and should keep abreast of literature on well-being and enrichment for the species with which they work.... When alternative behavioral procedures are available, those that minimize discomfort to the animal should be used. When using aversive conditions, psychologists should adjust

xviii

Preface the parameters of stimulation to levels that appear minimal, though compatible with the aims of the research. Psychologists are encouraged to test painful stimuli on themselves, whenever reasonable, (see http://apa.org/science/ anguide.html).

In this book, several studies involve animal subjects. In addition to the ethical considerations of such research, difficulties also arise in generalizing from animal findings to humans. T h e s e issues a r e discussed in this book within e a c h reading that includes animal research. E a c h individual, whether a r e s e a r c h e r or a student of psychology, must make his or h e r own decisions about animal research in general a n d the justifiability of using animal subj e c t s in any specific instance. If you allow for the idea that animal research is acceptable u n d e r some circumstances, then, for e a c h study involving animals in this book, you must decide if the value of the study's findings supports the m e t h o d s used. O n e final n o t e related to this issue involves a development in animal research that is a response to public c o n c e r n s about potential mistreatment. T h e city of C a m b r i d g e , Massachusetts, o n e of the major research centers of the world a n d h o m e to institutions such as H a r v a r d University a n d the Massachusetts Institute of Technology ( M I T ) , c r e a t e d the position of Commissioner of L a b o r a t o r y Animals within the C a m b r i d g e Health Department (see http://www.cambridgepublichealth.org/services/regulatory-activities/ lab-animals/lab-animals-overview.php). This was the first such governmental position in the United States. C a m b r i d g e is h o m e to 44 research laboratories that house over 2 0 0 , 0 0 0 animals. T h e commissioner's c h a r g e is to ensure hum a n e a n d p r o p e r t r e a t m e n t of all animal subjects in all aspects of the research process, from the animals' living quarters to the methods used in administering the research protocols. If a lab is found to be in violation of Cambridge's strict laws c o n c e r n i n g the h u m a n e care of lab animals, the commissioner is authorized to impose fines of up to $ 3 0 0 per day. As of this writing, only o n e such fine has been imposed; it a m o u n t e d to $ 4 0 , 0 0 0 (for 1 3 3 days in violation) on a facility that appeared to have deliberately disregarded animal treatment laws (Dr. Julie Medley, Commissioner of Laboratory Animals, e-mail, April 5, 2 0 0 7 ) . In all o t h e r cases, any facility that has been found in violation willingly a n d quickly corrects the problem. T h e studies you are about to experie n c e in this book have benefited all of humankind in many ways and to varying degrees. T h e history of psychological research is a relatively short one, but it is brimming with the richness and excitement of discovering h u m a n nature.

ACKNOWLEDGMENTS I would like to express my sincere gratitude to Charlyce J o n e s Owen, Publisher, who supported a n d believed in this project from its inception. Many thanks to L e a h Jewell, Editorial Director of the Humanities Division at Pearson Prentice Hall, for h e r ongoing c o m m i t m e n t to and support of this book. I am also very grateful to Jessica Mosher, Editor in Chief of Psychology

Preface

xix

at Pearson Prentice Hall for h e r support and continuing, talented assistance on this project. I must offer my personal appreciation to B r u c e Kenselaar for lending his c o n s i d e r a b l e talents in designing the c o v e r of this a n d past editions. T h a n k you to my psychology colleagues in the field who have taken the time, interest, and effort to c o m m u n i c a t e to me their c o m m e n t s , suggestions, and wisdom relating to this and previous editions of Forty Studies. I have attempted at every opportunity to incorporate their valued insights into each edition. To my family, my friends, and my students who have participated in the history of this book in so many tangible and intangible ways over the past 18 years (you know who you a r e ) , I extend my continuing best wishes and heartfelt thanks. ROGER R. HOCK

BIOLOGY AND HUMAN BEHAVIOR Reading 1 O N E B R A I N O R T W O ? Reading 2 M O R E E X P E R I E N C E = B I G G E R B R A I N Reading 3 A R E Y O U A "NATURAL?" Reading 4 W A T C H O U T F O R T H E V I S U A L C L I F F !

early all general psychology texts begin with chapters relating to the biology of 11 human behavior. This is due not simply to convention but rather because basic biological processes underlie all behavior. T h e various branches of psychology rest, to varying degrees, on this biological foundation. T h e area of psychology that studies these biological functions is typically called psychobiology or biological psychology. This field focuses on the actions of your brain and nervous system; the processes of receiving stimulation and information from the environment through your senses; the ways your brain organizes sensory information to create your perceptions of the world; and how all of this affects your body and behavior. T h e studies chosen to represent this basic c o m p o n e n t of psychological research include a wide range of research and are a m o n g the most influential and most often cited. T h e first study discusses a famous research p r o g r a m on right-brain/left-brain specialization that shaped m u c h of o u r present knowledge about how the brain functions. N e x t is a study that surprised the scientific community by demonstrating how a stimulating "childhood" might result in a m o r e highly developed brain. T h e third study represents a fundamental c h a n g e in the thinking of many psychologists about the basic causes of h u m a n behavior, personality, a n d social interaction—namely, a new appreciation for the significance of your genes. F o u r t h is the invention of the famous visual cliff m e t h o d of studying infants' abilities to perceive depth. All these studies, along with several others in this book, also address an issue that underlies a n d connects nearly all areas of psychology a n d provides the fuel for an ongoing a n d fascinating debate: the n a t u r e - n u r t u r e controversy.

Reading 1: ONE BRAIN OR TWO? Gazzaniga, M. S. (1967). The split brain in man. Scientific American, 217(2), 24-29. You are probably aware that the two halves of your brain a r e not the same a n d that they p e r f o r m different functions. F o r e x a m p l e , in general the left side of your brain is responsible for m o v e m e n t in the right side of your body, a n d vice 1

2

Chapter I

Biology and Human Behavior

versa. Beyond this, though, the two brain hemispheres appear to have m u c h g r e a t e r specialized abilities. It has c o m e to be r a t h e r c o m m o n knowledge that, for most of us, the left brain controls o u r ability to use language while the right is involved in spatial relationships, such as those n e e d e d for artistic activities. Stroke or head-injury patients who suffer d a m a g e to the left side of the brain will usually lose, to varying degrees, their ability to speak (often this skill returns with therapy and training). Many people believe that e a c h half, or hemisphere, of your brain may actually be a completely separate mental system with its own individual abilities for learning, remembering, perceiving the world, and feeling emotions. T h e c o n c e p t s underlying this view of the brain rest on early scientific research on the effects of splitting the brain into two separate hemispheres. T h a t research was pioneered by R o g e r W. Sperry ( 1 9 1 3 - 1 9 9 4 ) , beginning about 15 years prior to the article e x a m i n e d in this chapter. In his early work with animal subjects, Sperry m a d e many remarkable discoveries. F o r example, in o n e series of studies, cats' brains were surgically altered to sever the connection between the two halves of the brain and to alter the optic nerves so that the left eye transmitted information only to the left hemisphere and the right eye only to the right hemisphere. Following surgery, the cats appeared to behave normally and exhibited virtually no ill effects. T h e n , with the right eye covered, the cats learned a new behavior, such as walking through a short maze to find food. After the cats b e c a m e skilled at maneuvering through the maze, the eye cover was shifted to the cats' left eyes. Now, when the cats were placed back in the maze, their right brains had no idea where to turn and the animals had to relearn the entire maze from the beginning. Sperry c o n d u c t e d many related studies over the n e x t 30 years, and in 1 9 8 1 he received the Nobel Prize for his work on the specialized abilities of the two hemispheres of the brain. W h e n his research endeavors t u r n e d to h u m a n participants in the early 1960s, he was j o i n e d in his work at the California Institute of Technology (Caltech) by Michael Gazzaniga. Although Sperry is considered to be the founder of split-brain research, Gazzaniga's article has b e e n chosen h e r e because it is a clear, concise s u m m a r y of their early collaborative work with h u m a n participants and it, along with o t h e r related research by Gazzaniga, is cited often in psychology texts. Its selection is in no way intended to overlook or overshadow either Sperry's leadership in this field or his great contributions. Gazzaniga, in large part, owes his early research, and his discoveries in the a r e a of hemispheric specialization, to R o g e r W. Sperry (see Sperry, 1 9 6 8 ; Puente, 1 9 9 5 ) . To understand split-brain research, some knowledge of human physiology is required. T h e two hemispheres of your brain are in constant communication with o n e a n o t h e r via the corpus callosum, a structure m a d e up of about 2 0 0 million nerve fibers (Figure 1-1). If your corpus callosum is cut, this major line of communication is disrupted, and the two halves of your brain must then function independently. If we want to study each half of your brain separately, all we need to do is surgically sever your corpus callosum.

Reading 1

One Brain or Two?

Corpus Callosum

FIGURE

1-1

The

Corpus

Callosum. (Getty Images, Inc.)

But c a n scientists surgically divide the brains of h u m a n s for research purposes? T h a t sounds m o r e like a Frankenstein movie than real science! Obviously, research ethics would never allow such drastic m e t h o d s simply for the purpose of studying the specialized abilities of the brain's two hemispheres. However, in the late 1950s, the field of medicine provided psychologists with a golden opportunity. In some people with very r a r e a n d very e x t r e m e cases of uncontrollable epilepsy, seizures could be greatly r e d u c e d or virtually eliminated by surgically severing the corpus callosum. This operation was (and is) successful, as a last resort, for those patients who c a n n o t be helped by any o t h e r means. W h e n this article was written in 1 9 6 6 , 10 such operations h a d been undertaken, and four of the patients consented to participate in examination and testing by Sperry a n d Gazzaniga to d e t e r m i n e how their p e r c e p tual and intellectual skills were affected by this surgical treatment.

THEORETICAL PROPOSITIONS T h e researchers wanted to e x p l o r e the e x t e n t to which the two halves of the h u m a n brain are able to function independently, as well as whether they have separate and unique abilities. If the information traveling between the two

4

Chapter I

Biology and Human Behavior

halves of your brain is i n t e r r u p t e d , would the right side of your body suddenly be unable to c o o r d i n a t e with the left? If language is controlled by the left side of the brain, how would your ability to speak a n d understand words be affected by this surgery? Would thinking a n d reasoning processes exist in both halves separately? If the brain is really two separate brains, would a person be capable of functioning normally when these two brains a r e no longer able to c o m m u n i c a t e ? Considering that we receive sensory input from both the right a n d the left brains, how would the senses of vision, hearing, and touch be affected? Sperry a n d Gazzaniga a t t e m p t e d to answer these a n d many o t h e r questions in their studies of split-brain individuals.

METHOD T h e r e s e a r c h e r s developed t h r e e types of tests to e x p l o r e a wide r a n g e of mental a n d p e r c e p t u a l capabilities of the patients. O n e was designed to e x a m i n e visual abilities. T h e y devised a technique that allowed a picture of an object, a word, or parts of words to be transmitted only to the visual a r e a (called a field) in either the right or left brain h e m i s p h e r e , but not to both. Normally, both of your eyes send information to both sides of your brain. However, with e x a c t p l a c e m e n t of items or words in front of you, a n d with your eyes fixed on a specific point, images c a n be fed to the right or the left visual field of your brain independently. A n o t h e r testing situation was designed for tactile ( t o u c h ) stimulation. Participants could feel, but n o t see, an object, a block letter, or even a word in c u t o u t block letters. T h e apparatus consisted of a screen with a space u n d e r it for the participant to r e a c h t h r o u g h a n d t o u c h the items without being able to see them. T h e visual a n d the tactile devices could be used simultaneously so that, for e x a m p l e , a picture of a pen could be p r o j e c t e d to o n e side of the brain a n d t h e same object could be s e a r c h e d for by either h a n d a m o n g various objects b e h i n d t h e screen (see F i g u r e 1-2).

FIGURE 1-2

A typical visual testing device for split-brain participants.

Reading 1

One Brain or Two?

5

Testing auditory abilities was somewhat trickier. W h e n sound enters either of your ears, sensations a r e sent to both sides of your brain. T h e r e f o r e , it is not possible to limit auditory input to only o n e side of the brain even in split-brain patients. However, it is possible to limit the response to such input to o n e brain hemisphere. H e r e is how this was done: Imagine that several c o m m o n objects (a spoon, a pen, a m a r b l e ) are placed into a cloth bag a n d you a r e then asked, verbally, to find certain items by touch. You would probably have no trouble doing so. If you place your left h a n d in the bag, it is being controlled by the right side of your brain, a n d vice versa. Do you think either side of your brain could do this task alone? As you will see in a m o m e n t , both halves of the brain are not equally capable of responding to this auditory task. W h a t if you a r e not asked for specific objects but a r e asked simply to r e a c h into the bag and identify objects by touch? Again, this would not be difficult for you, but it would be quite difficult for a split-brain patient. Gazzaniga c o m b i n e d all these testing techniques to reveal s o m e fascinating findings about how the brain functions.

RESULTS First, you should know that following this radical brain surgery, the patients' intelligence level, personality, typical emotional reactions, a n d so on were relatively u n c h a n g e d . They were very happy a n d relieved that they were now free of seizures. Gazzaniga r e p o r t e d that o n e patient, while still groggy from surgery, j o k e d that he had "a splitting h e a d a c h e . " W h e n testing began, however, these participants demonstrated many unusual mental abilities. Visual Abilities O n e of the first tests involved a b o a r d with a horizontal row of lights. W h e n a patient sat in front of this b o a r d a n d stared at a point in the middle of t h e lights, the bulbs would flash across both the right a n d left visual fields. However, when the patients were asked to explain what they saw, they said that only the lights on the right side of the b o a r d h a d flashed. N e x t when t h e res e a r c h e r s flashed only the lights on the left side of the visual field, the patients claimed to have seen nothing. A logical conclusion from these findings was that the right side of t h e brain was blind. T h e n an amazing thing h a p p e n e d . T h e lights were flashed again, only this time t h e patients were asked to point to the lights that h a d flashed. A l t h o u g h they h a d said they only saw the lights on the right, they pointed to all the lights in both visual fields. Using this m e t h o d of pointing, it was found that both halves of the brain had seen the lights a n d were equally skilled in visual p e r c e p t i o n . T h e i m p o r t a n t point h e r e is that when t h e patients failed to say that they h a d seen all the lights, it was n o t b e c a u s e they didn't see t h e m but b e c a u s e the c e n t e r for speech is located in t h e brain's left h e m i s p h e r e . In o t h e r words, for you to say you saw something, the object has to have b e e n seen by the left side of your brain.

6

Chapter I

Biology and Human Behavior

Tactile Abilities You c a n try this test yourself. Put your hands behind your back. T h e n have s o m e o n e place familiar objects (a spoon, a pen, a book, a watch) in either your right or your left h a n d a n d see if you c a n identify the object. You would n o t find this task to be very difficult, would you? This is basically what Sperry a n d Gazzaniga did with the split-brain patients. W h e n an object was placed in the right h a n d in such a way that the patient could n o t see or h e a r it, messages about the object would travel to the left h e m i s p h e r e and the patient was able to n a m e the object a n d describe it and its uses. However, when the same obj e c t s were placed in the left h a n d ( c o n n e c t e d to the right h e m i s p h e r e ) , the patients could n o t n a m e t h e m or describe t h e m in any way. But did the patients know in their right brain what the object was? To find out, the researchers asked the participants to m a t c h the object in their left hand (without seeing it, r e m e m b e r ) to a g r o u p of various objects presented to them. This they could do as easily as you or I could. Again, this places verbal ability in the left hemisphere of the brain. Keep in mind that the reason you are able to n a m e unseen objects in your left h a n d is that the information from the right side of your brain is transmitted via the c o r p u s callosum to the left side, where your c e n t e r for language says, "That's a spoon!"

Visual Plus Tactile Tests Combining these two types of tests provided support for the preceding findings a n d also offered additional interesting results. If participants were shown a picture of an object to the right h e m i s p h e r e only, they were unable to n a m e it or describe it. In fact, they might display no verbal response at all or even deny that anything had been presented. However, if the patients were allowed to r e a c h u n d e r the screen with their left h a n d (still using only the right hemis p h e r e ) a n d t o u c h a selection of objects, they were always able to find the o n e that h a d b e e n presented visually. T h e right h e m i s p h e r e c a n think a b o u t and analyze objects as well. Gazzaniga r e p o r t e d that when the right h e m i s p h e r e was shown a picture of an item such as a cigarette, the participants could t o u c h 10 objects behind the screen, all of which did n o t include a cigarette, a n d select an object that was most closely related to the item pictured—in this case, an ashtray. He went on to explain: Oddly enough, however, even after their correct response, and while they were holding the ashtray in their left hand, they were unable to name or describe the object or the picture of the cigarette. Evidently, the left hemisphere was completely divorced, in perception and knowledge, from the right, (p. 26) O t h e r tests were c o n d u c t e d to shed additional light on the language-processing abilities of the right h e m i s p h e r e . O n e very famous, ingenious, and revealing use of the visual apparatus c a m e when the word HEART was projected to the patients so that HE was sent to the right visual field a n d ART was sent to the left. Now, keeping in mind (your c o n n e c t e d m i n d ) the functions of the two

Reading 1

One Brain or Two?

7

hemispheres, what do you think the patients verbally r e p o r t e d seeing? If you said ART, you were c o r r e c t . However, a n d h e r e is the revealing part, when the participants were presented with two cards with the words HE a n d ART printed on them and asked to point with the left h a n d to the word they h a d seen, they all pointed to HE! This demonstrated that the right hemisphere is able to c o m p r e h e n d language, although it does so in a different way from the left: in a nonverbal way. T h e auditory tests c o n d u c t e d with the patients p r o d u c e d similar results. W h e n patients were asked to r e a c h with their left h a n d into a grab bag hidden from view and pull out certain specific objects (a watch, a marble, a c o m b , a c o i n ) , they had no trouble. This demonstrated that the right hemisphere was c o m p r e h e n d i n g language. It was even possible to describe a related aspect of an item with the same a c c u r a t e results. An e x a m p l e given by Gazzaniga was when the patients were asked to find in a grab bag full of plastic fruit "the fruit monkeys like best," they retrieved a banana. Or when told "Sunkist sells a lot of them," they pulled out an o r a n g e . However, if these same pieces of fruit were placed out of view in the patients' left hand, they were unable to say what they were. In o t h e r words, when a verbal response was required, the right hemisphere was unable to speak. O n e last e x a m p l e of this amazing difference between the two hemispheres involved plastic block letters on the table behind the screen. W h e n patients were asked to spell various words by feel with the left h a n d , they h a d an easy time doing so. Even if three or four letters that spelled specific words were placed behind the screen, they were able, left-handed, to a r r a n g e them correctly into words. However, immediately after completing this task, the participants could not n a m e the word they had just spelled. Clearly, the left hemisphere of the brain is superior to the right for speech (in some left-handed people, this is reversed). But in what skills, if any, does the right hemisphere excel? Sperry and Gazzaniga found in this early work that visual tasks involving spatial relationships and shapes were p e r f o r m e d with g r e a t e r proficiency by the left h a n d (even though these patients were all right-handed). As can be seen in Figure 1-3, participants who copies three-dimensional drawings (using the pencil behind the screen) were m u c h m o r e successful when using the left hand. T h e researchers wanted to e x p l o r e emotional reactions of split-brain patients. While performing visual experiments, Sperry a n d Gazzaniga suddenly flashed a picture of a nude woman to either the left or right hemisphere. In o n e instance, when this picture was shown to the left hemisphere of a female patient: She laughed and verbally identified the picture of a nude. When it was later presented to the right hemisphere, she said . . . she saw nothing, but almost immediately a sly smile spread over her face and she began to chuckle. Asked what she was laughing at, she said: "I don't know . . . nothing . . . oh—that funny machine." Although the right hemisphere could not describe what it had seen, the sight nevertheless elicited an emotional response like the one evoked in the left hemisphere, (p. 29)

8

Chapter I

Biology and Human Behavior

EXAMPLE

FIGURE 1-3

LEFT HAND

RIGHT HAND

Drawings made by split-brain patients. (Adapted

from p. 27, "The Split Brain in Man," by Michael S. Gazzaniga.)

DISCUSSION T h e overall conclusion drawn from the research r e p o r t e d in this article was that two different brains exist within e a c h person's c r a n i u m , e a c h with complex abilities. Gazzaniga notes the possibility that if o u r brain is really two brains, then p e r h a p s we have the potential to process twice as m u c h information if the two halves a r e divided. Indeed, s o m e research evidence suggests that split-brain patients have the ability to p e r f o r m two cognitive tasks as fast as a n o r m a l person c a n c a r r y out o n e .

SIGNIFICANCE OF FINDINGS These findings and subsequent research c a r r i e d out by Sperry, Gazzaniga, and others were extremely significant a n d far-reaching. T h e y demonstrated that the two halves of your brain have many specialized skills and functions. Your left brain is "better" at speaking, writing, mathematical calculation, and reading, and it is the primary c e n t e r for language. Your right hemisphere, however, possesses superior capabilities for recognizing faces, solving problems involving spatial relationships, symbolic reasoning, and artistic activities. In the years

Reading 1

One Brain or Two ?

9

since Sperry and Gazzaniga's "split-brain" discoveries, psychobiological researchers have continued to uncover the amazing complexities of the h u m a n brain. O u r brains a r e far m o r e divided and compartmentalized than merely two hemispheres. We now know that a multitude of specific structures within the brain serve very specialized cognitive a n d behavioral functions. O u r increased knowledge of the specialized functioning of the brain allows us to treat victims of stroke or head injury m o r e effectively. By knowing the location of the d a m a g e , we can predict what deficits a r e likely to exist as a patient recovers. T h r o u g h this knowledge, therapists can employ appropriate relearning a n d rehabilitation strategies to help patients recover as fully a n d quickly as possible. Gazzaniga and Sperry, after years of continuous work in this area, suggested that each hemisphere of your brain really is a mind of its own. In a later study, split-brain patients were tested on m u c h m o r e c o m p l e x problems than have been discussed here. O n e question asked was "What profession would you choose?" A male patient verbally (left hemisphere) responded that he would choose to be a draftsman, but his left hand (right hemisphere) spelled, by touch in block letters, automobile racer (Gazzaniga & LeDoux, 1 9 7 8 ) . Gazzaniga has taken this theory a step further. He has proposed that even in people whose brains are normal and intact, the two hemispheres may not be in complete c o m munication (Gazzaniga, 1 9 8 5 ) . F o r example, if certain bits of information, such as those forming an emotion, are not stored in a linguistic format, the left hemisphere may not have access to it. T h e result of this is that you may feel sad and not be able to say why. As this is an uncomfortable cognitive dilemma, the left hemisphere may try to find a verbal reason to explain the sadness (after all, language is its main j o b ) . However, because your left hemisphere does not have all the necessary data, its explanation may actually be wrong! CRITICISMS T h e findings from the split-brain studies carried out over the years by Sperry, Gazzaniga, and others have rarely been disputed. T h e main body of criticism about this research has focused instead on the way the idea of right- a n d leftbrain specialization has filtered down to popular culture a n d the media. A widely believed myth states that s o m e people a r e m o r e right-brained or m o r e left-brained, or that o n e side of your brain needs to be developed in o r d e r for you to improve certain skills. J e r r e Levy, a psychobiologist at the University of Chicago, has been in the forefront of scientists trying to dispel the notion that we have two separately functioning brains. She claims that it is precisely because each hemisphere has separate functions that they must integrate their abilities instead of separating them, as is c o m m o n l y believed. T h r o u g h such integration, your brain is able to p e r f o r m in ways that are g r e a t e r than and different from the abilities of either side alone. W h e n you read a story, for e x a m p l e , your right hemisphere is specializing in emotional c o n t e n t (humor, p a t h o s ) , picturing visual descriptions, keeping track of the story structure as a whole, and appreciating artistic writing

10

Chapter I

Biology and Human Behavior

style (such as the use of m e t a p h o r s ) . While all this is happening, your left h e m i s p h e r e is understanding the written words, deriving meaning from the c o m p l e x relationships a m o n g words a n d sentences, and translating words into their p h o n e t i c sounds so that they can be understood as language. T h e reason you a r e able to read, understand, a n d appreciate a story is that your brain functions as a single, integrated structure (Levy, 1 9 8 5 ) . In fact, Levy explains that no h u m a n activity uses only o n e side of the brain. T h e popular myths a r e interpretations a n d wishes, not the observations of scientists. N o r m a l people have n o t half a brain, n o r two brains, but o n e gloriously differentiated brain, with e a c h hemisphere contributing its specialized abilities" (Levy, 1 9 8 5 , p. 4 4 ) . RECENT APPLICATIONS T h e continuing influence of the split-brain research by Sperry and Gazzaniga echoes the quote from Levy. A review of r e c e n t medical and psychological lite r a t u r e reveals n u m e r o u s articles in various fields referring to the early work and methodology of R o g e r Sperry, as well as to m o r e r e c e n t findings by Gazzaniga a n d his associates. F o r example, a study from 1 9 9 8 conducted in F r a n c e ( H o m m e t & Biliard, 1 9 9 8 ) has questioned the very foundations of the Sperry a n d Gazzaniga studies—namely, that severing the corpus callosum actually divides the hemispheres of the brain. T h e F r e n c h study found that children who were b o r n without a corpus callosum (a r a r e brain malformation) demonstrated that information was being transmitted between their brain hemispheres. T h e researchers concluded that significant connections o t h e r than the corpus callosum must exist in these children. W h e t h e r such subcortical connections a r e indeed present in split-brain individuals remains unclear. L a t e r that same year, a study was published by a team of neuropsychologists, including Gazzaniga, from several prestigious research institutions in the United States (University of Texas, Stanford, Yale, and D a r t m o u t h ) . T h e study demonstrated that split-brain patients may routinely perceive the world differently from the rest of us (Parsons, Gabrieli, Phelps, & Gazzaniga, 1 9 9 8 ) . T h e researchers found that when participants were asked to identify whether drawings presented to only o n e brain hemisphere were drawn by right- or left-handed people, the split-brain patients were able to do so correctly only when the handedness of the artist was the opposite oi the hemisphere to which the picture was projected. Normal control subjects were c o r r e c t regardless of which hemisphere "saw" the drawings. This implies that communication between your brain hemispheres is necessary for imagining or simulating in your mind the movements of others— that is, "putting yourself in their place" to perceive their actions correctly. Researchers continue to explore the idea that o u r two brain hemispheres have separate, yet distinct, functions a n d influences. O n e such study (Morton, 2 0 0 3 ) demonstrated how your d o m i n a n t hemisphere may lead you toward specific interests a n d professions. Morton's research m a d e two discoveries in this regard. Using a special written test called T h e Best H a n d Test," which measures hemispheriáty (whether a person is right- or left-brain o r i e n t e d ) , Morton found that a m o n g 4 0 0 students enrolled in first-year, general college courses,

Reading 2

More Experience = Bigger Brain

11

5 6 % were left-brain oriented. However, when the same methods were applied to 180 students in various, specialized upper-level courses, the range of left brain students ranged from 3 8 % to 6 5 % . This difference indicated that something about a person's brain hemispheres was associated with spreading students out over a variety of college degrees and interests. Second, and m o r e revealing, Morton employed the same method in determining the hemispheric orientation of members of various professions in university settings. T h e findings indicated that hemispheric specialization appears to be predictive of professional choices. F o r example, a m o n g biochemists Morton found that 8 3 % were left-brain oriented, while a m o n g astronomers only 2 9 % showed a left-brain preference (p. 3 1 9 ) . You can see how this would make sense in relation to Sperry and Gazzaniga's work. Biology and chemistry rely m o r e heavily on linguistic abilities, whereas astronomers must have greater abilities in spatial relationships ( n o pun intended).

CONCLUSION Some have carried this, seperate-brain idea a step further and applied it to some psychological disorders, such as dissociative, multiple personality disorder (e.g., Schiffer, 1 9 9 6 ) . T h e idea behind this notion is that in some people with intact, "nonsplit" brains, the right hemisphere may be able to function at a greater-thannormal level of independence from the left, and it may even take control of a person's consciousness for periods of time. Is it possible that multiple personality disorder might be the expression of hidden personalities contained in o u r right hemispheres? It's something to think a b o u t . . . with both of your hemispheres. Gazzaniga, M. S. (1985). The sodal brain. New York: Basic Books. Gazzaniga, M. S., & Ledoux.J. E. (1978). The integrated mind. New York: Plenum Press. Hommet, C, & Biliard, C. (1998). Corpus callosum syndrome in children. Neurochirurgie, 44(1), 110-112. Levy,J. (1985, May). Right brain, left brain: Fact and fiction. Psychology Today, 42-44. Morton, B. E. (2003). Line bisection-based hernisphericity estimates of university students and professionals: Evidence of sorting during higher education and career selection. Brain and Cognition, 52(3), 319-325. Parsons, L., Gabrieli.J., Phelps, E., & Gazzaniga, M. (1998). Cerebrally lateralized mental representations of hand shape and movement. Neuroscience, 18(16), 6539—6548. Puente, A. E. (1995). Roger Wolcott Sperry ( 1 9 1 3 - 1 9 9 4 ) . American Psychologist, 5 0 ( 1 1 ) , 9 4 0 - 9 4 1 . Schiffer, F. (1996). Cognitive ability of the right-hemisphere: Possible contributions to psychological function. Harvard Review of Psychiatry, 4 ( 3 ) , 126-138. Sperry, R. W. (1968). Hemisphere disconnection and unity in conscious awareness. American Psychologist, 23, 723-733.

Reading 2: MORE EXPERIENCE = BIGGER BRAIN Rosenzweig, M. R., Bennett, E. L, & Diamond, M. C. (1972). Brain changes in response to experience. Scientific American, 226(2), 22-29.

If you were to e n t e r the baby's r o o m in a typical A m e r i c a n middle-class h o m e today, you would probably see a crib full of stuffed animals a n d various colorful toys dangling directly over or within r e a c h of the infant. S o m e of these toys

12

Chapter I

Biology and Human Behavior

may light up, move, play music, or do all three. W h a t do you suppose is the parents' reasoning behind providing infants with so m u c h to see and do? Aside from the fact that babies seem to enjoy and respond positively to these toys, most parents' believe, whether they verbalize it or not, that children n e e d a stimulating environment for optimal intellectual development and brain growth. T h e question of whether certain experiences p r o d u c e physical changes in the brain has been a topic of c o n j e c t u r e a n d research a m o n g philosophers a n d scientists for centuries. In 1 7 8 5 , Vincenzo Malacarne, an Italian anatomist, studied pairs of dogs from the same litter a n d pairs of birds from the same batches of eggs. F o r e a c h pair, he would train o n e participant extensively over a long period of time while the o t h e r would be equally well cared for but untrained. He discovered later, in autopsies of the animals, that the brains of the trained animals a p p e a r e d m o r e c o m p l e x , with a greater n u m b e r of folds a n d fissures. However, this line of research was, for unknown reasons, discontinued. In the late 19th century, attempts were m a d e to relate the circ u m f e r e n c e of the h u m a n h e a d with the a m o u n t of learning a person had experienced. Although s o m e early findings claimed such a relationship, later research d e t e r m i n e d that this was n o t a valid m e a s u r e of brain development. By the 1960s, new technologies had been developed that gave scientists the ability to m e a s u r e brain c h a n g e s with precision using high-magnification techniques a n d assessment of levels of various brain enzymes a n d neurotransmitter chemicals. Mark Rosenzweig a n d his colleagues Edward Bennett and Marian Diamond, at the University of California at Berkeley, incorporated those technologies in an ambitious series of 16 experiments over a period of 10 years to try to address the issue of the effect of e x p e r i e n c e on the brain. T h e i r findings were r e p o r t e d in the article discussed in this chapter. F o r reasons that will b e c o m e obvious, they did not use h u m a n s in their studies, but rather, as in m a n y classic psychological experiments, their subjects were rats.

THEORETICAL PROPOSITIONS Because psychologists a r e ultimately interested in humans, not rats, the validity of using n o n h u m a n subjects must be demonstrated. In these studies, the authors explained that, for several reasons, using rodents r a t h e r than higher m a m m a l s such as primates was scientifically sound as well as m o r e convenient. T h e p a r t of the brain that is the main focus of this research is smooth in the rat, not folded a n d c o m p l e x as it is in higher animals. T h e r e f o r e , it can be exa m i n e d a n d m e a s u r e d m o r e easily. In addition, rats a r e small a n d inexpensive, which is an i m p o r t a n t consideration in the world of research laboratories (usually underfunded a n d lacking in s p a c e ) . Rats bear large litters, and this allows for m e m b e r s from the same litters to be assigned to different experimental conditions. T h e authors point out that various strains of inbred rats have been p r o d u c e d , a n d this allows researchers to include the effects of genetics in their studies if desired.

Reading 2

More Experience = Bigger Brain

13

Implicit in Rosenzweig's research was the belief that animals raised in highly stimulating environments will d e m o n s t r a t e differences in brain growth and chemistry when c o m p a r e d with animals r e a r e d in plain or dull circumstances. In each of the experiments r e p o r t e d in this article, 12 sets of 3 male rats, each set from the same litter, were studied.

METHOD T h r e e male rats were chosen from each litter. They were then randomly assigned to o n e of three conditions. O n e rat r e m a i n e d in the laboratory c a g e with the rest of the colony; a n o t h e r was assigned to what Rosenzweig t e r m e d the "enriched" environment cage; and the third was assigned to the "impoverished" cage. Remember, 12 rats were placed in each of these conditions for each of the 16 experiments. T h e three different environments (Figure 2-1) were described as follows: 1. T h e standard laboratory colony c a g e contained several rats in an adequate space with food a n d water always available. 2. T h e impoverished environment was a slighdy smaller cage isolated in a separate r o o m in which the rat was placed alone with adequate food and water.

FIGURE 2-1

Rosenzweig's three cage environments.

14

Chapter I

Biology and Human Behavior

3. T h e e n r i c h e d environment was virtually a rat's Disneyland ( n o offense intended to Mickey!). Six to eight rats lived in a "large cage furnished with a variety of objects with which they could play. A new set of playthings, drawn out of a pool of 25 objects, was placed in the cage every day" (p. 2 2 ) . T h e rats were allowed to live in these different environments for various periods of time, ranging from 4 to 10 weeks. Following this differential treatm e n t period, the experimental rodents were e x a m i n e d to d e t e r m i n e if any differences h a d developed in brain development. To be sure that no experim e n t e r bias would occur, the examinations were d o n e in r a n d o m o r d e r by c o d e n u m b e r so that the person doing the autopsy would not know in which condition the rat was raised. T h e rats' brains were then m e a s u r e d , weighed, a n d analyzed to determ i n e the a m o u n t of cell growth a n d levels of n e u r o t r a n s m i t t e r activity. In this latter m e a s u r e m e n t , o n e brain enzyme was of particular interest: acetylcholinesterase. This chemical is i m p o r t a n t because it allows for faster and m o r e efficient transmission of impulses a m o n g brain cells. Did Rosenzweig a n d his associates find differences in the brains of rats raised in e n r i c h e d versus impoverished environments? T h e following are their results.

RESULTS Results indicated that the brains of the e n r i c h e d rats were indeed different from those of the impoverished rats in many ways. T h e cerebral cortex (the part of the brain that responds to e x p e r i e n c e and is responsible for movement, memory, learning, a n d sensory input: vision, hearing, touch, taste, smell) of the e n r i c h e d rats was significantly heavier a n d thicker. Also, g r e a t e r activity of the nervous system enzyme acetylcholinesterase, m e n t i o n e d previously, was found in the brain tissue of the rats with the e n r i c h e d e x p e r i e n c e . Although no significant differences were found between the two groups of rats in the n u m b e r of brain cells (neurons), the e n r i c h e d environment prod u c e d larger neurons. Related to this was the finding that the ratio of RNA to DNA, the two most i m p o r t a n t brain chemicals for cell growth, was g r e a t e r for the e n r i c h e d rats. This implied that a higher level of chemical activity had taken place in the e n r i c h e d rats' brains. Rosenzweig a n d his colleagues stated that "although the brain differences induced by environment a r e not large, we a r e confident that they a r e genuine. W h e n the e x p e r i m e n t s a r e replicated, the same pattern of differences i s found repeatedly . . . . T h e most consistent effect o f e x p e r i e n c e o n the brain that we found was the ratio of the weight of the c o r t e x to the weight of the rest of the brain: the sub-cortex. It appears that the c o r t e x increases in weight quite readily in response to e x p e r i e n c e , whereas the rest of the brain changes little" (p. 2 5 ) . This m e a s u r e m e n t of the ratio of the c o r t e x to the rest of the brain was the most a c c u r a t e m e a s u r e m e n t of brain changes because the

Reading 2

FIGURE 2-2

More Experience = Bigger Brain

15

Ratio of cortex to the rest of the brain: en-

riched compared with impoverished environment. (Results in experiments 2 through 16 were statistically significant.) (Adapted from Rosenzweig, Bennett, & Diamond, p. 26.)

overall weight of the brain may vary with the overall weight of each animal. By considering this ratio, such individual differences are c a n c e l e d out. Figure 2-2 illustrates this finding for all 16 studies. As you can see, in only o n e experim e n t was the difference not statistically significant. T h e researchers r e p o r t e d a finding relating to the two r a t groups' brain synapses (the points at which two n e u r o n s m e e t ) . Most brain activity o c c u r s at the synapse, where a nerve impulse is either passed from o n e n e u r o n to the next so that it continues on, or it is inhibited and stopped. U n d e r g r e a t magnification using the electron m i c r o s c o p e , the researchers found that the synapses of the enriched rats' brains were 5 0 % larger than those of the impoverished rats, potentially allowing for increased brain activity.

DISCUSSION AND CRITICISMS After nearly 10 years of research, Rosenzweig, Bennett, and Diamond were willing to state with confidence, "There can now be no doubt that many aspects of brain anatomy and brain chemistry are changed by experience" (p. 2 7 ) . However, they were also quick to acknowledge that, when they first reported their findings, many other scientists were skeptical because such effects had not been so clearly demonstrated in past research. Some criticism contended that perhaps it was not the enriched environment that produced the brain changes but rather other differences in the treatment of the rats, such as m e r e handling or stress.

16

Chapter I

Biology and Human Behavior

T h e criticism of differential handling was a valid o n e in that the enriched rats were handled twice each day when they were removed from the cage as the toys were being c h a n g e d , but the impoverished rats were not handled. It was possible, therefore, that the handling alone might have caused the results and n o t the enriched environment. To respond to this potentially confounding factor, the researchers handled o n e g r o u p of rats every day and did not handle a n o t h e r g r o u p of their litter mates (all were raised in the same environment) . Rosenzweig and his associates found no differences in the brains of these two groups. In addition, in their later studies, both the enriched and impoverished rats were handled equally and, still, the same pattern of results was found. As for the criticisms relating to stress, the a r g u m e n t was that the isolation e x p e r i e n c e d by the impoverished rats was stressful, and this was the reason for their less-developed brains. Rosenzweig et al. cited other research that h a d exposed rats to a daily routine of stress (cage rotation or mild electric shock) a n d had found no evidence of changes in brain development due to stress alone. O n e of the problems of any research carried out in a laboratory is that it is nearly always an artificial environment. Rosenzweig and his colleagues were curious about how various levels of stimulation might affect the brain develo p m e n t of animals in their natural environments. They pointed out that laboratory rats and m i c e often have been raised in artificial environments for as many as a h u n d r e d generations and bear little genetic resemblance to rats in the wild. To e x p l o r e this intriguing possibility, they began studying wild d e e r mice. After the mice were trapped, they were randomly placed in either natural o u t d o o r conditions or the enriched laboratory cages. After 4 weeks, the o u t d o o r mice showed g r e a t e r brain development than did those in the enriched laboratory environment. 'This indicates that even the enriched laboratory environment is indeed impoverished in comparison with a natural environment" (p. 2 7 ) . T h e most important criticism of any research involving animal subjects is the question of its application, if any, to humans. Without a doubt, this line of research could never be p e r f o r m e d on humans, but it is nevertheless the responsibility of the researchers to address this issue, and these scientists did so. T h e authors explained that it is difficult to generalize from the findings of o n e set of rats to a n o t h e r set of rats, and consequently it is m u c h m o r e difficult to try to apply rat findings to monkeys or humans. And, although they r e p o r t similar findings with several species of rodents, they admit that m o r e research would be necessary before any assumptions could be m a d e responsibly about the effects of e x p e r i e n c e on the h u m a n brain. They proposed, however, that the value of this kind of research on animals is that "it allows us to test concepts and techniques, s o m e of which may later prove useful in research with h u m a n subjects" (p. 2 7 ) . Several potential benefits of this research were suggested by the authors. O n e possible application pertained to the study of memory. Changes in the

Reading 2

More Experience = Bigger Brain

17

brain due to e x p e r i e n c e might lead to a better understanding of how m e m o ries are stored in the brain. This could, in turn, lead to new techniques for improving m e m o r y a n d preventing m e m o r y loss due to aging. A n o t h e r a r e a in which this research might prove helpful was in explaining the relationship between malnutrition a n d intelligence. T h e c o n c e p t p r o p o s e d by the a u t h o r s in this r e g a r d was that malnutrition may be a person's responsiveness to the stimulation available in the environment a n d consequently may limit brain development. T h e authors also noted that o t h e r studies suggested that the effects of malnutrition on brain growth may be either r e d u c e d by environmental enrichment or increased by deprivation.

RELATED R E S E A R C H AND RECENT APPLICATIONS This work by Rosenzweig, Bennett, and D i a m o n d has served as a catalyst for continued research in this developmental a r e a that continues today. Over the decades since the publication of their article, these scientists and many others have continued to confirm, refine, a n d e x p a n d their findings. F o r e x a m p l e , research has d e m o n s t r a t e d that learning itself is e n h a n c e d by e n r i c h e d envir o n m e n t a l e x p e r i e n c e s and that even the brains of adult animals raised in impoverished

conditions

can

be

improved

when

placed

in

an

enriched

environment (see Bennett, 1 9 7 6 , for a c o m p l e t e review). Some evidence exists to indicate that e x p e r i e n c e does indeed alter brain development in humans. T h r o u g h careful autopsies of h u m a n s who have died naturally, it appears that as a person develops a g r e a t e r n u m b e r of skills a n d abilities, the brain actually b e c o m e s m o r e c o m p l e x and heavier. O t h e r findings have c o m e from examinations during autopsies of the brains of people who were unable to have certain experiences. F o r example, in a blind person's brain, the portion of the c o r t e x used for vision is significantly less developed, less convoluted, and thinner than in the brain of a person with n o r m a l sight. Marian Diamond, o n e of the authors of this original article, has applied the results of work in this a r e a to the process of h u m a n intellectual developm e n t t h r o u g h o u t life. She says, "For people's lives, I think we can take a m o r e optimistic view o f the aging brain . . . . T h e main factor i s stimulation. T h e nerve cells a r e designed for stimulation. A n d I think curiosity is a key factor. If o n e maintains curiosity for a lifetime, that will surely stimulate neural tissue a n d the c o r t e x may i n turn respond . . . . I looked for people who were extremely active after 88 years of age. I found that the people who use their brains don't lose them. It was that simple" (in Hopson, 1 9 8 4 , p. 7 0 ) . Two r e c e n t studies have e l a b o r a t e d on Rosenzweig, D i a m o n d , a n d Bennett's notions of environmental influences on brain development in very diverse applications. Weiss and Bellinger ( 2 0 0 6 ) e x p a n d e d on the r e s e a r c h by suggesting that studies of the effects of environmental toxins on early brain development in h u m a n s must encompass n o t only the toxicity of the chemical but also should consider all the factors present within the individual's overall life c o n t e x t , including g e n e t i c t e n d e n c i e s a n d e n r i c h e d o r impoverished

18

Chapter I

Biology and Human Behavior

environments. T h e authors p r o p o s e d that, in h u m a n s , the effects of exposure to toxic substances tends to be direcdy related to growing up in an e n r i c h e d versus an impoverished environment. In o t h e r words, when children are raised in poverty, not only is their developmental environment likely to be impoverished, but they may also be at a g r e a t e r risk of e x p o s u r e to n e u r o t o x i c chemicals. Moreover, the environmental factors that are present can affect the o u t c o m e of the toxic e x p o s u r e on brain development. Weiss and Bellinger asserted that when r e s e a r c h e r s have studied environmental toxins, the tendency has b e e n to focus on the toxic substance itself a n d to minimize the a c c o m p a nying situational variables. As the authors stated: We argue that the outcomes of exposure to neurotoxic chemicals early in life are shaped by the nature of a child's social environment, including that prevailing before birth . . . . We contend that a true evaluation of toxic potential and its neurobehavioral consequences is inseparable from the ecologic setting [such as environmental richness] in which they act and which creates unique, enduring individual vulnerabilities." (p. 1497) Another article cites Rosenzweig's 1 9 7 2 study in critiquing some recent attempts to oversimplify e n r i c h m e n t strategies in attempts to enhance children's brain development (Jones & Zigler, 2 0 0 2 ) . As you can imagine, when the public learns about research such as Rosenzweig's, a popular movement may be born that sounds attractive but has little basis in scientific fact. O n e of these from the 1990s, which you may have h e a r d about, has b e c o m e known as the "Mozart Effect" This fad began with some preliminary research showing that when children listen to Mozart (but not o t h e r classical composers) they b e c o m e better learners. This idea has grown to the point that entire Web sites are devoted to the benefits of the "Mozart Effect" for children and adults alike, involving claims that certain music c a n e n h a n c e overall health, improve memory, treat attention deficit disorder, r e d u c e depression, and speed healing from physical injuries. CONCLUSION J o n e s a n d Zigler ( 2 0 0 2 ) maintain that such popular applications of the research a r e ineffective a n d even dangerous. T h e y c o n t e n d , "Brain research is being misappropriated to the service of misguided 'quick fix' solutions to m o r e complicated, systemic issues" (p. 3 5 5 ) . T h e y further suggest that when scientific brain a n d learning r e s e a r c h is applied carefully a n d correctly, it can make a "substantive contribution of high quality, intensive, multidomain interventions to early cognitive a n d social development" (p. 3 5 5 ) . Bennett, E. L. (1976). Cerebral effects of differential experience and training. In M. R. Rosenzweig & E. L. Bennett (Eds.), Neural mechanisms of learning and memory. Cambridge, MA: MIT Press. Hopson, J. (1984). A love affair with the brain: A PT conversation with Marian Diamond. Psychology Today, 11, 62-75. Jones, S., & Zigler, E. (2002). The Mozart Effect: Not learning from history. Journal of Applied Developmental Psychology, 23, 355-372. Weiss, B., & Bellinger, D. C. (2006). Social ecology of children's vulnerability to environmental pollutants. (Commentary). Environmental Health Perspectives, 114, 1479-1485.

Reading3

Are You a "Natural?"

19

Reading 3: ARE YOU A "NATURAL?" Bouchard, T., Lykken, D., McGue, M., Segal, N., &Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250, 2 2 3 - 2 2 9 . This study represents a relatively r e c e n t and ongoing fundamental c h a n g e in the way many psychologists view h u m a n n a t u r e in its broadest sense. You can relate to this c h a n g e in a personal way by first taking a m o m e n t to answer in your mind the following question: "Who a r e you?" Think for a m o m e n t about some of your individual characteristics: your "personality traits." Are you high strung or laid-back? Are you shy or outgoing? Are you adventurous, or do you seek out comfort and safety? Are you easy to get along with, or do you tend toward the disagreeable? Are you usually optimistic or m o r e pessimistic about the o u t c o m e of future events? Think about yourself in terms of these or any o t h e r questions you feel a r e relevant. Take your time . . . . Finished? Now, answer this next, and, fór this reading, m o r e i m p o r t a n t question: "Why are you who you are?" In o t h e r words, what factors contributed to "creating" this person you are today? If you are like most people, you will point to the child-rearing practices of your parents and the values, goals, and priorities they instilled in you. You might also credit the influences of brothers, sisters, grandparents, aunts, uncles, peers, teachers, and o t h e r m e n t o r s who played key roles in molding you. Still others of you will focus on key life-changing events, such as an illness, the loss of a loved o n e , or the decision to attend a specific college, choose a major, or take a particular life course that seemed to lead you toward b e c o m i n g your c u r r e n t self. All these influences share o n e characteristic: they a r e all environmental p h e n o m e n a . Hardly anyone ever replies to the question "Why are you who you are?" with "I was b o r n to be who I am; it's all in my genes." Everyone acknowledges that physical attributes, such as height, hair color, eye color, and body type, are genetic. M o r e and m o r e people a r e realizing that tendencies toward many illnesses, such as cancer, h e a r t disease, and high blood pressure, have significant genetic c o m p o n e n t s . However, almost no o n e thinks of genes as the main force behind who they a r e psychologically. This may strike you as odd when you stop to think about it, but in reality very understandable reasons explain o u r "environmental bias." First of all, psychology during the second half of the 2 0 t h century was dominated by the behaviorism theory of h u m a n nature. Basically, that theory states that all h u m a n behavior is controlled by environmental factors, including the stimuli that provoke behaviors and the consequences that follow response choices. Strict behaviorists believed that the internal psychological workings of the h u m a n mind were n o t only impossible to study scientifically but, also, that such study was unnecessary and irrelevant to a c o m p l e t e explanation for h u m a n behavior. W h e t h e r the wider culture a c c e p t e d or even understood formal theories of behaviorism is not as important as the reality of

20

Chapter I

Biology and Human Behavior

their influence on today's firmly e n t r e n c h e d popular belief that experience is the primary or exclusive architect of h u m a n nature. A n o t h e r understandable reason for the pervasive a c c e p t a n c e of envir o n m e n t a l explanations of behavior is that genetic and biological factors do not provide visible evidence of their influence. It's easy for s o m e o n e to say "I b e c a m e a writer because I was deeply inspired and e n c o u r a g e d by my seventhg r a d e composition teacher." You r e m e m b e r those sorts of influences; you see them; they a r e p a r t of your past a n d present conscious experiences. You would find it m u c h m o r e difficult to recognize biological influences and say "I b e c a m e a writer because my DNA contains a g e n e that has been expressed in me that predisposes me to write well." You can't see, touch, or r e m e m b e r the influence of your genes, a n d you don't even know where in your body they might be located! In addition, many people a r e uncomfortable with the idea that they might be the p r o d u c t of their genes r a t h e r than the choices they have m a d e in their lives. Such ideas smack of determinism and a lack of free will. Most people have a strong dislike for any t h e o r y that might in some way limit their conscious ability to d e t e r m i n e the o u t c o m e s in their lives. Consequently, genetic causes of behavior a n d personality tend to be avoided or rejected. In reality, genetic influences interact with e x p e r i e n c e to mold a complete h u m a n , and the only question is this: W h i c h is m o r e dominant? Or, to phrase the question as it frequenüy appears in the media, "Is it nature or nurture?" T h e article by T h o m a s B o u c h a r d , David Lykken, and their associates at the University of Minnesota in Minneapolis that is referenced in this c h a p t e r is a review of research that began in 1 9 7 9 to e x a m i n e the question of how m u c h influence your genes have in determining your personal psychological qualities. This research grew out of a need for a scientific m e t h o d to separate genetic influences ( n a t u r e ) from environmental forces ( n u r t u r e ) on people's behavior a n d personality. This is no simple task when you consider that nearly every o n e of you, assuming you were n o t adopted, grew and developed u n d e r the direct environmental influence of your genetic d o n o r s (your p a r e n t s ) . You might, for e x a m p l e , have the same sense of h u m o r as your father ( n o offense!) because you l e a r n e d it from him ( n u r t u r e ) or because you inherited his "sense-of-humor" g e n e ( n a t u r e ) . No systematic a p p r o a c h can tease those two influences apart, right? Well, B o u c h a r d a n d Lykken would say "wrong." T h e y have found a way to d e t e r m i n e with a reasonable d e g r e e of confidence which psychological characteristics a p p e a r to be d e t e r m i n e d primarily by genetic factors and which a r e molded m o r e by your environment. THEORETICAL

PROPOSITIONS

It's simple, really. All you have to do is take two humans who have exacdy the same genes, separate t h e m at birth, a n d raise them in significandy different environments. T h e n you can assume that those behavioral a n d personality characteristics they have in c o m m o n as adults must be genetic. B u t how on

Reading3

Are You a "Natural?"

21

earth can researchers possibly find pairs of identical people (don't say "cloning"; we're not t h e r e yet!)? And even if they could, it would be unethical to force them into diverse environments, wouldn't it? As you've already guessed, the researchers didn't have to do that. Society had already d o n e it for them. Identical twins have virtually the same genetic structure. T h e y a r e called monozygotic twins because they start as o n e fertilized egg, called a zygote, and then split into two identical embryos. Fraternal twins a r e the result of two separate eggs fertilized by two separate sperm cells a n d a r e referred to as dizygotic twins. Fraternal twins a r e only as genetically similar as any two nontwin siblings. As unfortunate as it sounds, twin infants are sometimes given up for adoption and placed in separate homes. Adoption agencies will try to keep siblings, especially twins, together, but the m o r e i m p o r t a n t goal is to find good homes for them even if it means separation. Over time, thousands of identical and fraternal twins have been adopted into separate h o m e s and raised, frequently without the knowledge that they were a twin, in different and often contrasting environmental settings. In 1 9 8 3 B o u c h a r d and Lykken began to identify, locate, a n d bring together pairs of these twins. This 1 9 9 0 article reports on results from 56 pairs of monozygotic reared-apart (MZA) twins from the United States and seven o t h e r countries who agreed to participate in weeklong sessions of intensive psychological and physiological tests and m e a s u r e m e n t s (that this research is located in Minneapolis, o n e half of "the Twin Cities" is an irony that has not, by any means, g o n e u n n o t i c e d ) . T h e s e twins were c o m p a r e d with monozygotic twins reared together ( M Z T ) . T h e surprising findings continue to reverberate throughout the biological and behavioral sciences.

METHOD Participants T h e first challenge for this project was to find sets of monozygotic twins who were separated early in life, r e a r e d apart for all of most of their lives, a n d reunited as adults. Most of the participants were found through word of m o u t h as news of the study began to spread. T h e twins themselves or their friends or family members would c o n t a c t the research institute, the Minnesota C e n t e r for Twin and Adoption Research ( M I C T A R ) , various social-services professionals in the adoption a r e n a would serve as contacts, or, in some cases o n e m e m b e r of a twin-pair would c o n t a c t the c e n t e r for assistance in locating a n d reuniting with his or h e r sibling. All twins were tested to ensure that they were indeed monozygotic before beginning their participation in the study. Procedure T h e researchers wanted to be sure they obtained as m u c h data as possible during the twins' one-week visit. E a c h twin c o m p l e t e d approximately 50 hours of testing on nearly every h u m a n dimension you might imagine. They c o m pleted four personality trait scales, three aptitude a n d occupational interest

22

Chapter I

Biology and Human Behavior

inventories, a n d two intelligence tests. In addition, the participants filled in checklists of household belongings (such as power tools, telescope, original artwork, unabridged dictionary), to assess the similarity of their family resources, a n d a family e n v i r o n m e n t scale that m e a s u r e d how they felt about the parenting they received from their adoptive parents. They were also administered a life history interview, a psychiatric interview, and a sexual history interview. All these assessments were c a r r i e d out individually so that it was not possible for o n e twin to inadvertently influence the answers and responses of the other. As you might imagine, the hours of testing c r e a t e d a huge database of information. T h e most i m p o r t a n t a n d surprising results are discussed here.

RESULTS Table 3-1 summarizes the similarities for s o m e of the characteristics measured in the monozygotic twins r e a r e d apart (MZA) a n d includes the same data for monozygotic twins r e a r e d t o g e t h e r ( M Z T ) . T h e d e g r e e of similarity is expressed in the table as correlations or rvalues. T h e larger the correlation, the g r e a t e r the similarity. T h e logic h e r e is that if environment is responsible for individual differences, the MZT twins who shared the same environment as they grew up should be significantly m o r e similar than the MZA twins. As you c a n see, this is not what the r e s e a r c h e r s found.

'Adapted from Table 4, p. 226. **1.00 would imply that MZA twin pairs were found to be exactly as similar as MZT twin pairs.

Reading3

Are You a "Natural?"

23

T h e last column in Table 3-1 expresses the difference in similarity by dividing the MZA c o r r e l a t i o n on e a c h characteristic by the M Z T correlation. If both correlations were the same, the result would be 1.00; if they were entirely dissimilar, the result could be as low as 0 . 0 0 . E x a m i n i n g c o l u m n 4 in the table carefully, you'll find that the correlations for characteristics were remarkably similar—that is, close to 1.00 a n d no lower than . 7 0 0 for MZA a n d MZT twin pairs.

DISCUSSION AND IMPLICATIONS OF FINDINGS These findings indicate that genetic factors ( o r the genome) a p p e a r to a c c o u n t for most of the variations in a remarkable variety of h u m a n characteristics. This finding was demonstrated by the data in two i m p o r t a n t ways. O n e is that genetically identical h u m a n s (monozygotic twins), who were raised in separate and often very different settings, grew into adults who were extraordinarily similar, not only in a p p e a r a n c e but also in basic psychology a n d personality. T h e second demonstration in this study of the d o m i n a n c e of genes is the fact that there a p p e a r e d to be little effect of the environment on identical twins who were raised in the same setting. Here's B o u c h a r d and Lykken's take on these discoveries: For almost every behavioral trait so far investigated, from reaction time to religiosity, an important fraction of the variation among people turns out to be associated with genetic variation. This fact need no longer be subject to debate; rather, it is time to consider its implications. Of course, some will a r g u e with B o u c h a r d a n d Lykken's notion that the time to debate these issues is over. S o m e varying views a r e discussed in the n e x t section. However, a discussion of the implications of this a n d o t h e r similar studies by these same researchers is clearly warranted. In what ways do the genetic findings r e p o r t e d in this study c h a n g e psychologists' and, for that matter, all of o u r views of h u m a n nature? As m e n t i o n e d previously, psychology a n d Western culture have been dominated for over 50 years by environmental thinking. Many of o u r basic beliefs about parenting, education, c r i m e a n d punishment, psychotherapy, skills a n d abilities, interests, occupational goals, and social behavior, just to n a m e a few, have been interpreted from the perspective that people's e x p e r i e n c e molds their personalities, n o t their genes. Very few of us look at someone's behavior and think, T h a t person was born to behave like that!" We want to believe that people learned their behavior patterns because that allows us to feel some measure of confidence that parenting makes a difference, that positive life experiences can win out over negative ones, and that unhealthy, ineffective behaviors can be unlearned. T h e notion that personality is a d o n e deal the m o m e n t we a r e born leaves us with the temptation to say "Why bother?" Why b o t h e r working h a r d to be g o o d parents? Why b o t h e r trying to help those who a r e down a n d out? Why b o t h e r trying to offer quality education? And so on. B o u c h a r d a n d Lykken would want to be the first to disagree with such an interpretation of their findings. In

24

Chapter I

Biology and Human Behavior

this article, they offer three of their own implications of their provocative conclusions: 1. Clearly, intelligence is primarily d e t e r m i n e d by genetic factors ( 7 0 % of the variation in intelligence appears to be due to genetic influence). However, as the authors state very clearly, [T]hese findings do not imply that traits like IQ cannot be enhanced . . . . A survey covering 14 countries has shown that the average IQ test score has increased in recent years. The present findings, therefore, do not define or limit what might be conceivably achieved in an optimal environment, (p. 227) Basically, what the authors a r e saying is that although 7 0 % of the variation in IQ is d u e to naturally o c c u r r i n g genetic variation, 3 0 % of the variation r e m a i n s subject to increases or decreases due to environmental influences. T h e s e influences include many that a r e well known, such as e d u c a t i o n , family setting, toxic substances, a n d s o c i o e c o n o m i c status. 2. T h e basic underlying assumption in B o u c h a r d and Lykken's research is that h u m a n characteristics are d e t e r m i n e d by some combination of genetic a n d environmental influences. W h e n the environment exerts less influence, differences must be attributed m o r e to genes. T h e converse is also true: as environmental forces create a stronger influence on differences in a particular characteristic, genetic influences will be weaker. F o r e x a m p l e , most children in the United States have the opportunity to learn to ride a bicycle. This implies that the environment's effect on bicycle riding is somewhat similar for all children, so differences in riding ability will be m o r e affected by genetic forces. On the other hand, variation in, say, food preferences in the United States are m o r e likely to be explained by environmental factors because food and taste experiences in childhood and throughout life are very diverse and will, therefore, leave less r o o m for genetic forces to function. Here's the interesting part of the researchers' point: they maintain that personality is m o r e like bicycle riding than food preferences. T h e authors a r e saying, in essence, that family environments e x e r t less influence over who the kids grow up to be than do the genes they inherit from birth. Understandably, most parents do not want to h e a r or believe this. They a r e working hard to be g o o d parents and to raise their children to be happy individuals a n d g o o d citizens. T h e only parents who might take some c o m f o r t from these findings a r e those who a r e nearing their wits' e n d with out-of-control or incorrigible sons or daughters a n d would appreciate being able to take less of the blame! However, B o u c h a r d a n d Lykken a r e quick to point out that genes a r e not necessarily destiny a n d that devoted parents can still influence their children in positive ways, even if they a r e only working on a small p e r c e n t a g e of the total variation.

Reading3

Are You a "Natural?"

25

3. T h e most intriguing implication that B o u c h a r d a n d Lykken suggest is that it's not the environment influencing people's characteristics, but vice versa. T h a t is, people's genetic tendencies actually mold their environments! T h e following is an e x a m p l e of the idea behind this theory. T h e fact that some people are m o r e affectionate than others is usually seen as evidence that some parents were m o r e affectionate with their children than were o t h e r parents. In o t h e r words, affectionate kids c o m e from affectionate environments. W h e n this kind of assumption has been studied, it is usually found to be true. Affectionate people have, indeed, received m o r e affection from their parents. B o u c h a r d a n d Lykken are proposing, however, that variation in "affectionateness" may be, in reality, genetically d e t e r m i n e d so that some children a r e just b o r n m o r e affectionate than others. T h e i r inborn tendency toward affectionate behavior causes them to respond to affection from their parents in ways that reinforce the parents' behavior m u c h m o r e than genetically nonaffectionate children. This, in turn produces the affectionate behavior in the parents, not the o t h e r way around. T h e researchers c o n t e n d that genes function in this way for many, if not most, h u m a n characteristics. They state it this way: The proximal [most immediate] cause of most psychological variance probably involves learning through experience, just as radical environmentalists have always believed. The effective experiences, however, to an important extent are self-selected, and that selection is guided by the steady pressure of the genome, (p. 228)

CRITICISMS A N D RELATED R E S E A R C H As you might imagine, a great many related studies have been carried out using the database of twins developed by B o u c h a r d a n d Lykken. In general, the findings continue to indicate that many h u m a n personality characteristics and behaviors are strongly influenced by genes. Many attributes that have been seen as stemming largely or completely from environmental sources a r e being reevaluated as twin studies reveal that heredity contributes either the majority of the variation or a significantly larger proportion than was previously contemplated. F o r e x a m p l e , studies from the University of Minnesota team found n o t only that the vocation you c h o o s e is largely d e t e r m i n e d by your genes but also that about 3 0 % of the variation in your overall j o b satisfaction a n d work ethic appears d u e to genetic factors (Arvey et al., 1 9 8 9 ; Arvey et al., 1 9 9 4 ) even when the physical requirements of various professions were held constant. O t h e r studies c o m p a r i n g identical (monozygotic) twins with fraternal (dizygotic) twins, both r e a r e d t o g e t h e r a n d r e a r e d apart, have focused m o r e directly on specific personality traits that a r e t h o u g h t to be influential a n d stable in h u m a n s ( B o u c h a r d , 1 9 9 4 ; Loehlin, 1 9 9 2 ) . T h e s e and o t h e r studies' findings d e t e r m i n e d that the people's variation on the characteristics of extraversion-introversion (outgoing versus shy), neuroticism (tendency to

26

Chapter I

Biology and Human Behavior

suffer from high anxiety a n d e x t r e m e emotional reactions), and conscientiousness (degree to which a person is competent, responsible, and t h o r o u g h ) is explained m o r e ( 6 5 % ) by genetic differences than by environmental factors. Of course, not everyone in the scientific community is willing to accept these findings at face value. T h e criticisms of B o u c h a r d and Lykken's work take several directions (see Billings et al., 1 9 9 2 ) . S o m e studies claim that the researchers a r e not publishing their data as fully and completely as they should, and, therefore, their findings c a n n o t be independendy evaluated. T h e s e same critics also claim that many articles a r e reporting on case studies demonstrating strong environmental influences on twins that B o u c h a r d and Lykken fail to consider. In addition, some researchers have voiced a major criticism of o n e aspect of twin research in general, referred to as the "equal environment assumption" (e.g., J o s e p h , 2 0 0 2 ) . This a r g u m e n t maintains that many of the conclusions drawn by B o u c h a r d a n d Lykken about genetic influence assume that monozygotic a n d dizygotic twins raised together develop in identical environments. T h e s e critics maintain that such an assumption is not valid a n d that fraternal twins a r e treated far m o r e differendy than a r e identical twins. This, they c o n t e n d , draws the entire m e t h o d of twin research as a determinant of genetic influences into question. However, several o t h e r articles have refuted this criticism a n d supported the "equal environment assumption" (e.g., Kendler et al., 1 9 9 3 ) .

RECENT APPLICATIONS In 1 9 9 9 , B o u c h a r d reviewed the n a t u r e - n u r t u r e evidence from the Minnesota twin registries ( B o u c h a r d , 1 9 9 9 ) . He c o n c l u d e d that, overall, 4 0 % of the variability in personality a n d 5 0 % of the variability in intelligence appears to be genetically based. He also reiterated his position, discussed previously, that your genes drive your selection of environments and your selection or avoida n c e of specific personality-molding environments a n d behaviors. Research at the Minnesota C e n t e r for Twin and Adoption Research continues to be very active. S o m e fascinating research has e x a m i n e d very c o m plex h u m a n characteristics a n d behaviors that few would have even guessed to be genetically driven, such as love, divorce, and even death (see Minnesota Twin Family Study, 2 0 0 7 ) . They have studied people's selection of a mate to see if "falling in love" with Mr. or Ms. Right is genetically predisposed. It turns out that it is not. However, the researchers have found a genetic link to the likelihood of divorce, eating disorders, a n d age at the time of death. B o u c h a r d a n d Lykken's research has been applied to the larger philosophical discussion of h u m a n cloning (see Agar, 2 0 0 3 ) . If a h u m a n being is ever successfully cloned, the question is, as you a r e probably thinking, to what e x t e n t will a person's essence, an individual's personality, be transferred to his or h e r clone? T h e fear that h u m a n identity might be c h a n g e d , degraded, or lost has been a c o m m o n a r g u m e n t of those opposed to cloning. On the o t h e r

Reading 4

Watch out for the Visual Cliff!

27

hand, results of twin studies, such as those of B o u c h a r d a n d Lykken suggest that "the cloned person may, u n d e r certain circumstances, be seen as surviving, to some d e g r e e , in the c l o n e . . . . However... r a t h e r than warranting c o n c e r n , the potential for survival by cloning o u g h t to help p r o t e c t against the misuse of the technology" (Agar, 2 0 0 3 , p. 9 ) . In a separate study e x a m i n i n g the issue of identical twins and cloning (Prainsack & Spector, 2 0 0 6 ) , researchers found that identical twins rarely consider the genetic aspects of their real-life e x p e r i e n c e of being identical twins. In addition, from a personal perspective, they did n o t view the idea of h u m a n cloning as u n n a t u r a l or immoral but were m o r e c o n c e r n e d a b o u t the ethics underlying the reasons for h u m a n cloning. Of c o u r s e , this is philosophical discussion so far, but as the prospect of h u m a n cloning looms ever closer, it b e c o m e s increasingly important and interesting food for thought. Agar, N. (2003). Cloning and identity. Journal of Medicine and Philosophy, 28, 9 - 2 6 . Arvey, R., Bouchard, T., Segal, N., & Abraham, L. (1989). J o b satisfaction: Environmental and genetic components. Journal of Applied Psychology, 74(2), 187-195. Arvey, R., McCall, B., Bouchard, T., & Taubman, P. (1994). Genetic influences on job satisfaction and work value. Personality and Individual Differences, 17(1), 2 1 - 3 3 . Billings, P., Beckwith, J . , & Alper, J. (1992). The genetic analysis of human behavior: A new era? Social Science and Medicine, 35(3), 227-238. Bouchard, T. (1994). Genes, environment, and personality. Science, 264(5166), 1700-1702. Bouchard, T. (1999). Genes, environment, and personality. In S. Ceci, et al. (Eds.), The naturenurture debate: The essential readings, pp. 9 7 - 1 0 3 . Maiden, MA: Blackwell. Joseph.J. (2002). Twin studies in psychiatry and psychology: Science or pseudoscience? Psychiatric Quarterly, 73, 71-82. Kendler K., Neale M., Kessler R., Heath A., & Eaves L. ( 1 9 9 3 ) . A test of the equal environment assumption in twin studies of psychiatric illness. Behavioral Genetics, 23, 21-27. Loehlin,J. (1992). Genes and environment in personality development. Newbury Park, CA: Sage Publications. Minnesota Twin Family Study (2007). What's spcial about twins to science? Retrieved March 10, 2007 from http://www.psych.umn.edu/psylabs/mtfs/special.htm. Prainsack, B., & Spector, T. D. (2006). Twins: a cloning experience. Social Science & Medicine, 63(10), 2739-2752.

Reading 4: WATCH OUT FOR THE VISUAL CLIFF! Gibson, E. J . , & Walk, R. D. (1960). The "visual cliff." Scientific American, 202(A), 67-71.

O n e of the most often told anecdotes in psychology c o n c e r n s a m a n called S. B. (initials used to p r o t e c t his privacy). S. B. had been blind his entire life until the age of 5 2 , when he u n d e r w e n t a newly developed operation (the nowc o m m o n c o r n e a l transplant) and his sight was restored. However, S. B.'s new ability to see did n o t m e a n that he automatically perceived what he saw the way the rest of us do. O n e i m p o r t a n t e x a m p l e of this b e c a m e evident soon after the operation, before his vision had cleared completely. S. B. looked out his hospital window and was curious about the small objects he could see moving on the g r o u n d below. He began to crawl out on his window ledge, thinking he would

28

Chapter I

Biology and Human Behavior

lower himself down by his hands and have a look. Fortunately, the hospital staff prevented him from trying this. He was on the fourth floor, and those small moving things were cars! Even though S. B. could now see, he was not able to perceive depth. O u r visual ability to sense a n d interpret the world a r o u n d us is an a r e a of interest to experimental psychologists because, obviously, it affects o u r behavior in important ways. In addition, within this ability lies the central question of whether o u r sensory processes a r e inborn or learned: the n a t u r e - n u r t u r e issue o n c e again. Many psychologists believe that o u r most important visual skill is depth perception. You can imagine how difficult, and probably impossible, survival of the h u m a n species would have been if we could not perceive depth. We might have run headlong into things, been unable to j u d g e how far away a p r e d a t o r was, or stepped right off eliffs. T h e r e f o r e , it might be logical to assume that depth perception is an inborn survival mechanism that does n o t require e x p e r i e n c e to develop. However, as E l e a n o r Gibson a n d Richard Walk point o u t in their article: Human infants at the creeping and toddling stage are notoriously prone to falls from more or less high places. They must be kept from going over the brink by side panels on their cribs, gates on stairways, and the vigilance of adults. As their muscular coordination matures, they begin to avoid such accidents on their own. Common sense might suggest that the child learns to recognize falling-off places by experience—that is, by falling and hurting himself" (p. 6 4 ) . T h e s e researchers wanted to study this visual ability of depth perception scientifically in the laboratory. To do this, they conceived of and developed a remarkable research tool they called the visual cliff.

THEORETICAL PROPOSITIONS If you wanted to find out at what point in the early developmental process animals or people a r e able to perceive depth, o n e way to do this would be to put t h e m on the edge of a cliff and see if they are able to avoid falling off. This is a ridiculous suggestion because of the ethical considerations of the potential injury to participants who were unable to perceive depth (or, m o r e specifically, h e i g h t ) . T h e visual cliff avoids this problem because it presents the participant with what appears to be a drop-off, when no drop-off actually exists. Exactly how this is d o n e will be explained shordy, but it is i m p o r t a n t first to recognize that the i m p o r t a n c e of this apparatus lies in the fact that h u m a n or animal infants c a n be placed on the visual cliff to see if they a r e able to perceive the drop-off a n d avoid it. If they a r e unable to do this a n d step off the "cliff," there is no d a n g e r of falling. Gibson and Walk took a "nativist" position on this topic: they believed that depth perception and the avoidance of a drop-off appear automatically as part of our original biological equipment and are not, therefore, products of experience. T h e opposing view, held by empiricists, contends that such abilities are learned. Gibson and Walk's visual cliff allowed them to ask these questions: At

Reading 4 Watch out for the Visual Cliff!

29

what stage in development can a person or animal respond effectively to the stimuli of depth and height? Do these responses appear at different times with animals of different species and habitats? Are these responses p r e p r o g r a m m e d at birth or do they develop as a result of e x p e r i e n c e and learning?

METHOD T h e visual cliff is c o m p r i s e d of a table about 4 feet high with a top m a d e from a piece of thick, clear glass (Figures 4-1 a n d 4 - 2 ) . Direcdy u n d e r half of the glass on the table (the shallow side) is a solid surface with a red-and-white c h e c k e r e d pattern. U n d e r the o t h e r half is the same p a t t e r n , but it is down at the level of the floor u n d e r n e a t h the table (the d e e p side). At the edge of the shallow side, then, is the a p p e a r a n c e of a sudden drop-off to the floor, although, in reality, the glass extends all the way across. Between the shallow a n d the deep sides is a c e n t e r b o a r d about a foot wide. T h e process of testing infants using this device was extremely simple. T h e participants for this study were 36 infants between the ages of 6 m o n t h s and 14 months. T h e m o t h e r s of the infants also participated. E a c h infant was placed on the c e n t e r b o a r d of the visual cliff a n d was then called by the mother, first from the d e e p side a n d then from the shallow side. To c o m p a r e the development of depth p e r c e p t i o n in h u m a n s with that in o t h e r baby animals, the visual cliff allowed for similar tests with o t h e r

Glass over patterned surface

Deep side

FIGURE 4-1

Shallow side

Gibson and Walk's visual cliff. From Introduction to Child Devel-

opment (5th ed.), by J. Dworetzky (c) 1993. Reprinted with permission of Wadsworth, an imprint of the Wadsworth Group, a division of Thomson Learning.

30

Chapter I

Biology and Human Behavior

FIGURE 4-2

The visual cliff in a testing situation. (Mark

Richards/PhotoEdit/Courtesy of Joe Campos & Rosanne Kermoian.)

species (without a m o t h e r ' s beckoning, however). T h e baby animals were placed on the c e n t e r b o a r d and observed to see if they could discriminate between the shallow and d e e p sides a n d avoid stepping off "the cliff." You c a n imagine the r a t h e r unique situation in the psychology labs at Cornell University when the various baby animals were brought in for testing. They included chicks, turtles, rats, lambs, kids (baby goats, that is), pigs, kittens, a n d puppies. O n e has to wonder if they were all tested on the same day! R e m e m b e r that the goal of this r e s e a r c h was to e x a m i n e whether depth perception is l e a r n e d or innate. W h a t makes this m e t h o d so ingenious is that it allowed that question to at least begin to be answered. Infants, whether h u m a n or animal, c a n n o t be asked if they perceive depth, and, as mentioned, h u m a n infants c a n n o t be tested on real cliffs. In psychology, answers to perplexing questions are often found t h r o u g h the development of new m e t h o d s for studying the questions. T h e results of Gibson and Walk's early study provide an excellent e x a m p l e of this.

RESULTS A N D D I S C U S S I O N Nine children in the study refused to move at all off the c e n t e r board. This was not explained by the researchers, but perhaps it was just infant stubbornness. W h e n the m o t h e r s of the o t h e r 27 called to t h e m from the shallow side, all the infants crawled off the b o a r d and crossed the glass. Only t h r e e of them, however, crept, with g r e a t hesitation, off the brink of the visual cliff when called by their m o t h e r s from the d e e p side. W h e n called from the "cliff side, most of the children either crawled away from the m o t h e r on the shallow side

Reading 4 Watch out for the Visual Cliff!

31

or cried in frustration at being unable to r e a c h the m o t h e r without moving over the "cliff." T h e r e was litde question that the children were perceiving the depth of the "cliff." "Often they would p e e r down t h r o u g h the glass of the d e e p side a n d then back away. O t h e r s would pat the glass with their hands, yet despite this tactile assurance of solidity would refuse to cross" (p. 6 4 ) . Do these results prove that humans' ability to perceive depth is innate r a t h e r than learned? It does not, because all the children in this study h a d at least 6 months of life e x p e r i e n c e in which to learn about depth through trial a n d error. However, h u m a n infants c a n n o t be tested in this way prior to 6 months of age because they do not have adequate l o c o m o t o r abilities. It was for this reason that Gibson and Walk decided to test various o t h e r animals as a comparison. As you know, most n o n h u m a n animals gain the ability to move about m u c h sooner than humans. T h e results of the animal tests were extremely interesting, in that the ability of the various animals to perceive depth developed in relation to when the species n e e d e d such a skill for survival. F o r example, baby chickens must begin to scratch for their own food soon after hatching. W h e n they were tested on the visual cliff at less than 24 hours of age, they never m a d e the mistake of stepping off o n t o the d e e p side. Kids a n d lambs are able to stand a n d walk very soon after birth. F r o m the m o m e n t they first stood up, their response on the visual cliff was as accurate and predictable as that of the chicks. N o t o n e e r r o r was m a d e . W h e n o n e of the researchers placed a one-day-old baby goat on the d e e p side of the glass, the goat b e c a m e frightened and froze in a defensive posture. If it was then pushed over the shallow side, it would relax a n d j u m p forward o n t o the seemingly solid surface. This indicated that the visual sense was in c o m p l e t e control and that the animals' ability to feel the solidity of the glass on the d e e p side had no effect on the response. F o r the rats, it was a different story. They did n o t a p p e a r to show any significant preference for the shallow side of the table. Why do you suppose this difference was found? Before you c o n c l u d e that rats a r e just stupid, consider Gibson and Walk's m u c h m o r e likely explanation: a rat does n o t d e p e n d very m u c h on vision to survive. Because it is nocturnal, a rat locates food by smell and moves a r o u n d in the dark using cues from the stiff whiskers on its nose. So when a rat was placed on the c e n t e r board, it was not fooled by the visual cliff because it was not using vision to decide which way to go. To the rat's whiskers, the glass on the d e e p side felt the same as the glass on the shallow side and, thus, the rat was just as likely to move off the c e n t e r b o a r d to the deep side as to the shallow side. You might e x p e c t the same results from kittens. They are basically n o c turnal and have sensitive whiskers. However, cats a r e predators, not scavengers like rats. T h e r e f o r e , they depend m o r e on vision. And, accordingly, kittens were found to have excellent depth perception as soon as they were able to move on their own: at about 4 weeks. Although at times this research article, a n d this discussion, risk sounding like a children's animal story, it has to be r e p o r t e d that the species with

32

Chapter I

Biology and Human Behavior

t h e worst p e r f o r m a n c e on the visual cliff was the turtle. T h e baby turtles c h o sen to be tested were of the aquatic variety because the researchers e x p e c t e d that they might prefer the d e e p side of the "cliff because their natural envir o n m e n t is water. However, it a p p e a r e d that the turtles were "smart" e n o u g h to know that they were n o t in water: 7 6 % of t h e m crawled off o n t o the shallow side, while 2 4 % went "over the edge." ' T h e relatively large minority that c h o s e the d e e p side suggests either that this turtle has p o o r e r depth perception than o t h e r animals, or its natural habitat gives it less occasion to 'fear' a fall" (p. 6 7 ) . Clearly, if you live your life in water, the survival value of depth perception, in terms of avoiding falls, would be diminished. Gibson a n d Walk pointed out that all of their observations were consistent with evolutionary theory. T h a t is, all species of animals, if they are to survive, n e e d to develop the ability to perceive depth by the time they achieve i n d e p e n d e n t m o v e m e n t . F o r h u m a n s , this does not o c c u r until a r o u n d 6 m o n t h s of age; but for chickens and goats it is nearly immediate (by 1 day o l d ) ; a n d for rats, cats, a n d dogs, it is about 4 weeks of age. T h e authors conclude, therefore, that this capacity is inborn because to learn it through trial a n d e r r o r would cause too many potentially fatal accidents. If we a r e so well p r e p a r e d biologically, why do children take so many falls? Gibson a n d Walk explained that the h u m a n infants' perception of depth h a d m a t u r e d s o o n e r than had their skill in movement. During testing, many of the infants supported themselves on the d e e p side of the glass as they t u r n e d on the c e n t e r b o a r d , a n d s o m e even backed up o n t o the d e e p side as they began to crawl toward the m o t h e r across the shallow side. If the glass had n o t b e e n t h e r e , s o m e of the children would have fallen off the "clifF! CRITICISMS AND SUBSEQUENT RESEARCH T h e most c o m m o n criticism of the researchers' conclusions revolves around the question of whether they really proved that depth perception is innate in humans. As mentioned, by the time infants were tested on the visual cliff, they had already learned to avoid such situations. A later study placed younger infants, ages 2 to 5 months, on the glass over the deep side of the visual cliff. W h e n this happened, all the babies showed a decrease in heart rate. Such a decrease is thought to be a sign of interest, not fear, which is accompanied by heart rate increases (Campos et al., 1 9 7 8 ) . This indicates that these younger infants had not yet learned to fear the drop-off and would learn the avoidance behavior somewhat later. These findings argued against Gibson and Walk's position. It is important to notice, however, that although there was and still is controversy over just when we are able to perceive depth (the nativists vs. the empiricists) , m u c h of the research that is d o n e to find the answer incorporates the visual cliff apparatus developed by Gibson and Walk. In addition, o t h e r related research using the visual cliff has t u r n e d up some fascinating findings. O n e e x a m p l e is the work of S o r c e et al. ( 1 9 8 5 ) , who put 1-year-old infants on a visual cliff for which the drop-off was neither shallow n o r d e e p but in between (about 30 inches). As a baby crawled toward the "cliff," it would

Reading 4 Watch out for the Visual Cliff! 33 stop a n d look down. On the o t h e r side, as in the Gibson a n d Walk study, the m o t h e r was waiting. Sometimes the m o t h e r had been instructed to maintain an expression of fear on h e r face, while o t h e r times the m o t h e r looked happy a n d interested. W h e n infants saw the expression of fear, they refused to crawl any farther. However, most of the infants who saw their m o t h e r looking happy checked the "cliff again and crawled across. W h e n the drop-off was m a d e flat, the infants did not check with the m o t h e r before crawling across. This m e t h o d of nonverbal c o m m u n i c a t i o n used by infants in determining their behavior is called social referencing.

RECENT APPLICATIONS Gibson and Walk's groundbreaking invention of the visual cliff still exerts a major influence on c u r r e n t studies of h u m a n development, perception, e m o tion, a n d even mental health. Following is a brief sample. A study by B e r g e r and Adolph ( 2 0 0 3 ) cited Gibson and Walk's early study in their research on how toddlers analyze the characteristics of tasks involving heights, specifically crossing over a bridge. T h e researchers c o a x e d very young toddlers ( 1 6 months) to cross bridges of various widths, some with handrails, some without. They found that the children were significandy m o r e likely to cross wider bridges than narrower ones (pretty smart for 16 m o n t h s ! ) . M o r e interesting, however, was the finding that the toddlers were m o r e likely to attempt the narrow bridge if it had handrails. "Infants who explored the bridge and handrail before stepping onto the bridge and devised alternative bridgecrossing strategies were m o r e likely to cross successfully. [These] results challenge traditional conceptualizations of tools: babies used the handrail as a means for augmenting balance and for carrying out an otherwise impossible goal-directed task" (p. 5 9 4 ) . A n o t h e r practical application of the visual cliff study looked at the possibilities for using virtual reality to help developmentally disabled children learn to deal safely with the physical environment a r o u n d them. Strickland ( 1 9 9 6 ) developed a system that incorporates virtual reality to help autistic children safely explore a n d interact with the world a r o u n d them. Often these children pose a d a n g e r to themselves because their perceptions a r e either distorted or not fully developed. F o r e x a m p l e , an autistic child might not perceive d r o p o f f s such as those represented by the visual cliff a n d would, therefore, be p r o n e to dangerous falls. According to Strickland, however, virtual reality allows us to design custom p r o g r a m s so e a c h individual child may gain valuable m o t o r e x p e r i e n c e without d a n g e r of physical injury.

CONCLUSION T h r o u g h the inventiveness of Gibson a n d Walk, behavioral scientists have been able to study depth perception in a clear and systematic way. Behavioral scientists continue to debate the question of whether this a n d o t h e r p e r c e p tual abilities a r e innate or learned. T h e truth may lie in a c o m p r o m i s e that

34

Chapter I

Biology and Human Behavior

p r o p o s e s an i n t e r a c t i o n between n a t u r e a n d n u r t u r e . Perhaps, as various studies have indicated, d e p t h p e r c e p t i o n is present at birth, but fear of falling a n d a v o i d a n c e o f d a n g e r a r e l e a r n e d t h r o u g h e x p e r i e n c e , after t h e infant is old e n o u g h to crawl a r o u n d e n o u g h to "get into trouble." B u t whatever the questions a r e , e l e g a n t m e t h o d o l o g i c a l advances such as the visual cliff allow us to c o n t i n u e to s e a r c h for answers. Berger, S., & Adolph, K. ( 2 0 0 3 ) . Infants use handrails as tools in a locomotor task. Developmental Psychology, 39, 5 9 4 - 6 0 5 . Campos,!., Hiatt, S., Ramsay, D., Henderson, C, & Svejda, M. (1978). The emergence of fear on the visual cliff. In M. Lewis & L. A. Rosenblum (Eds.), The development of affect. New York: Plenum Press. Sorce, J . , Emde, R., Campos, J . , & Klinnert, M. ( 1 9 8 5 ) . Maternal emotion signaling: Its effect on the visual cliff behavior of 1-year-olds. Developmental Psychology, 21, 195-200. Strickland, D. ( 1 9 9 6 ) . A virtual-reality application with autistic children. Presence: Teleoperators and Virtual Environments, 5(3), 3 1 9 - 3 2 9 .

PERCEPTION AND CONSCIOUSNESS Reading 5 TAKE A L O N G L O O K Reading 6 T O SLEEP, N O D O U B T T O D R E A M Reading 7 U N R O M A N C I N G T H E D R E A M Reading 8 A C T I N G A S I F Y O U A R E H Y P N O T I Z E D

T h e study of perception a n d consciousness is of g r e a t interest to psychologists because these activities define and reveal m u c h of your psychological interaction with your environment. Think for a m o m e n t about how your senses are b o m b a r d e d constandy by millions of pieces of information from the c o m bined stimuli that s u r r o u n d you at any given m o m e n t . It is impossible for your brain to process all of it, so your brain organizes this b a r r a g e of sensory data into sets of information that yield form a n d meaning. That's what psychologists refer to as perception. Clearly, your level of consciousness, also c o m m o n l y r e f e r r e d to as your state of awareness, governs to a large e x t e n t what you perceive and how your brain organizes it. As you go through your day, night, week, year, and life, you e x p e r i e n c e many and varied states of awareness: you c o n c e n t r a t e (or n o t ) , daydream, fantasize, sleep, dream; maybe you've been hypnotized at some point or used psychoactive drugs (even caffeine a n d nicotine a r e psychoactive drugs!). These varying mental conditions a r e all altered states of consciousness that p r o d u c e changes in your perceptions of the world that, in turn, influence your behavior. Within the research areas of perception a n d consciousness, some of the most influential and interesting studies have focused on perceptual abilities in early childhood, sleep, dreams, a n d hypnosis. This section begins with a famous a n d influential study that contributed a brilliant a n d remarkable m e t h o d that allows researchers to study the thinking processes, the perceptions, of preverbal infants as young as a few days old. This m e t h o d , called preference looking, provides insights into the functioning of infants' brains a n d how they conceptualize the world. T h e second reading contains two articles that changed psychology because they ( 1 ) discovered rapid eye m o v e m e n t ( R E M ) sleep and ( 2 ) revealed the relationship between R E M a n d dreaming. T h i r d is an influential and controversial study proposing that d r e a m s are n o t mysterious messages from your unconscious, as F r e u d a n d others suggested (and as you probably believe), but r a t h e r that d r e a m s a r e the result of purely r a n d o m , 35

36

Chapter II

Perception and Consciousness

electrochemical impulses firing off in your brain while you sleep. F o u r t h is o n e of many studies that have influenced traditional psychological thinking by making a case against the widespread belief that hypnosis is a unique a n d powerful altered state of consciousness. This last study offers evidence suggesting that hypnotized people a r e no different from normally awake people—they a r e just a bit m o r e motivated to behave in certain ways.

Reading 5: TAKE A LONG LOOK Fantz, R. L. (1961). The origin of form perception. Scientific American, 204(May), 61-72.

If you want to know about o t h e r people's perceptions of the world a r o u n d them, an easy way to find o u t is to ask them. Depending, of course, on exacdy what you ask, they will often tell you. But have you ever tried to ask this of an infant? As m u c h as infants may seem, at times, to be trying to tell you what they are thinking a n d perceiving, they cannot; they can't talk; they probably could not tell you very m u c h if they could; and, most likely, they couldn't even understand your question! If you have h a d the opportunity to spend time a r o u n d infants (and you all likely have to varying d e g r e e s ) , you may have often thought to yourself, "I wonder what this baby is thinking!" or "If only this baby could talk . . . ." Unfortunately, that's n o t going to happen (John Travolta's series of Look Who's Talking movies aside). But psychologists' interest in studying a n d understanding infants has been a top priority throughout psychology's history (this book contains seven studies that have focused on infants). However, in R o b e r t Fantz's discoveries that we will discuss in this chapter, the questions that plagued the researchers were "How can we study an infant's cognitive processes?" "How can we catch a real glimpse inside very young babies' brains to see what might be going on, what they are perceiving, a n d how m u c h they really understand?" In the 1950s, R o b e r t L. Fantz, a psychologist at Western Reserve University in Cleveland (now, Case Western Reserve University), noticed something very interesting about infants; however, these were not h u m a n infants but newly h a t c h e d chicks—that's right: chickens. Fantz r e p o r t e d that almost immediately upon breaking out of their shell, chicks perceive their environment well e n o u g h to begin searching a n d pecking for food. (See "Watch O u t for the Visual Cliff!" in the previous g r o u p of readings for m o r e about the perceptual talents of chicks.) This suggested to Fantz that chicks, in some ways, actually have superior perceptual abilities than h u m a n infants, making the chicks ideal subjects for research in this area. T h a t said, it is important to note that when psychologists study n o n h u m a n animals, their ultimate goal is to apply what they learn to o u r understanding of human behavior, but we will further discuss that issue later.

Reading 5

Take a Long Look .

37

THEORETICAL PROPOSITIONS Prior to Fantz's studies, research had clearly demonstrated that h u m a n infants are able to perceive the world a r o u n d them in some r u d i m e n t a r y ways, such as the ability to see light, discriminate basic colors, and detect movement. However, as Fantz pointed out, "It has often been argued that they c a n n o t respond to such stimuli as shape, pattern, size, or solidity; in short, they c a n n o t perceive form" (p. 6 6 ) . But Fantz was skeptical of this a r g u m e n t , so in the late 1950s and early 1960s he set about developing a new research technique that would allow researchers to study in g r e a t e r detail what infants can perceive; to pinpoint when perceptual skills develop; a n d to d e t e r m i n e the degree of c o m plexity of their perceptual skills. He proposed that h u m a n infants, from the m o m e n t of birth, not entirely unlike newly h a t c h e d chicks, a r e actually able to perceive various forms, and this can be demonstrated by observing how babies "analyze" their world—that is, what they look at and for how long they look at it. This m e t h o d of studying infants' mental abilities, called preferential looking, swept through the psychology world a n d began a revolution, that continues today, into understanding the minds of infants.

METHOD It wasn't difficult for Fantz to demonstrate some of what newly h a t c h e d chicks could and could not perceive. Fantz simply presented the chicks, before they had any e x p e r i e n c e pecking for real food, with objects of different shapes a n d sizes and r e c o r d e d how often they pecked at each o n e . T h e y pecked significantly m o r e often at r o u n d shapes versus pyramid shapes; circles m o r e than triangles; spheres m o r e than flat disks; and when shapes of various sizes of circles were presented, they preferred those that were about -g- inch in d i a m e t e r over larger or smaller sizes. Without any previous learning, chicks were able to perceive form, a n d they clearly preferred shapes most like potential food: seeds or grain. Fantz expressed in his article what you are probably thinking right now: "Of course, what holds true for birds does not necessarily apply to h u m a n beings" (p. 6 7 ) . He considered the possibility that this innate ability in birds to perceive form (and this is true of many bird species) may not have developed during the evolution of primates (including h u m a n s ) , or that perhaps primates acquire such abilities only after a period of development or learning following birth. So, when Fantz turned his attention to primate infants, he needed a new research m e t h o d because, obviously, primate infants do not peck at anything, a n d they don't have the m o t o r development to do so even if they are so inclined (which they aren't because infants a r e n o t terribly fond of grain and seeds). Infants do engage in o n e behavior, however, that might allow them to be tested in a similar way to the chicks: they stare at things. If Fantz could figure out a way to see if they stare at some forms predictably m o r e often or longer than others, the only explanation would be that they could tell the difference,

38

Chapter II

Perception and Consciousness

that they could perceive form. Working at first with infant chimpanzees, the primate genetically most closely related to humans, Fantz and his associates developed what he called a "looking chamber," which was basically a padded, comfortable bassinette inside of a large, plain box. In the top panel of the b o x were two openings for presenting objects to the infants and peepholes allowing the researchers to observe the looking behavior of the infants. W h e n the researchers ascertained that infant chimps a p p e a r e d to show a systematic prefere n c e for certain objects over others ( d e t e r m i n e d by duration of staring), they applied the same basic techniques to studying h u m a n babies. T h e r e s e a r c h e r s did nothing to interfere with the babies' usual schedule or activities but simply placed the infants into the comfortable, p a d d e d viewing b o x a n d presented various pairs of object for them to look at. T h e infants r a n g e d in age from 1 to 15 weeks of age. T h e stimuli presented to the babies included solid a n d t e x t u r e d disks; spheres; an oval with a h u m a n face; an oval with the features of a h u m a n face j u m b l e d up; a n d shapes a n d patterns of varying complexity (see Figure 5 - 1 ) . T h e researchers revealed the objects in various paired combinations a n d observed the total a m o u n t of time during e a c h 1-minute trial the infants spent staring at the different pairs of objects, as well as which object within e a c h pair they "preferred" (stared at l o n g e r ) . T h e i r findings provided powerful evidence that babies of all ages possess the ability to perceive a n d discriminate a m o n g diverse forms.

0

5 Average

10 Seconds

of

15 Fixation

FIGURE 5-1 Infants' interest in form pairs as a function of average looking time for 220 tests. (Source: Fantz,

20 in

1-Minute

Test

1961, p. 70.)

Reading 5

Take a Long Look . . .

39

RESULTS F o r their first r o u n d of testing, the babies saw pairs of various black-and-white test patterns, including a square with horizontal stripes a n d a square with a bull's-eye; a c h e c k e r b o a r d and a plain, no-pattern square; a wide plus-sign a n d a circle; and a pair of identical triangles as c o n t r o l stimuli. T h e results a r e graphically illustrated in Figure 5-1. Clearly the infants "preferred" the forms with the greatest complexity (the bull's-eye, stripes, a n d c h e c k e r b o a r d ) . This degree of preference was the same, regardless of the infant's age, which indicates that the ability to discriminate a m o n g these forms is innate, present at birth. Beginning at approximately 8 weeks of age, the infants preferred the bull's-eye to the stripes and the c h e c k e r b o a r d to the plain square. This time delay implies that either some learning has o c c u r r e d in those 2 m o n t h s or that maturation of the brain a n d / o r visual system a c c o u n t e d for the c h a n g e . As interesting as these findings were, an i m p o r t a n t link between the infants' abilities and the earlier studies of the chicks was still missing. If h u m a n infants are b o r n with an unlearned, natural ability to discriminate form, we must ask why. F o r chicks, the answer appears r a t h e r straightforward: they perceive the forms that allow t h e m to find n o u r i s h m e n t a n d to survive. How could such an innate ability to perceive specific forms have survival value for h u m a n infants? Maybe it is for a similar reason. Fantz wrote: In the world of the infant, people have an importance that is perhaps comparable to the importance of grain in the chick's world. Facial pattern is the most distinctive aspect of a person . . . for distinguishing a human being from other objects and identifying him. So, a facelike pattern might be expected to bring out selective perception in an infant if anything could (p. 7 0 ) . In o t h e r words, h u m a n infants do not d e p e n d u p o n f o r m perception for nourishment and survival; they d e p e n d on o t h e r people to c a r e for them. J u s t as chicks can perceive specific shapes best, it would make sense that infants' perceptual tendencies should favor the h u m a n face. And it does. Fantz's team presented 49 infants between 4 days a n d 6 m o n t h s old with three identically sized oval disks. O n e was painted with the features of a h u m a n face, a n o t h e r with those same features scrambled, a n d the third, the control disk, an oval with just a p a t c h of black at o n e e n d equal to the total area of the facial features on the o t h e r two disks (see Figure 5 - 2 ) . T h e infants

a

b

c

FIGURE 5-2 Fantz's Facial Figure Test. Infants preferred A over B, and strongly preferred A and B over C. (Source: Fantz, 1961, p. 7 2 )

40

Chapter II

Perception and Consciousness

50 Percent of Total Fixation Time

FIGURE 5-3 Infants' looking time for patterns and colors (black bars = 8-12 months; grey bars = over 12 months of age). (Source: Fantz, 1961, p. 72.)

clearly showed g r e a t e r interest in the ovals with the facial features and stared at t h e m intendy while virtually ignoring the control oval. Moreover, this prefe r e n c e was approximately the same strength for all infants regardless of age, demonstrating again that basic form perception is present at birth and ruling o u t a learning or developmental factor. In the final study r e p o r t e d in this article, the researchers tested the h u m a n infants again for their ability to recognize facial forms. T h e infants were presented with six flat disks, e a c h 6 inches in diameter with the following designs: ( 1 ) a h u m a n face; ( 2 ) a bull's-eye; ( 3 ) a r a n d o m fragment of a printed page (such as a newspaper or t e x t b o o k ) ; ( 4 ) entirely red; ( 5 ) entirely fluorescent yellow; and ( 6 ) plain white. T h e time of the infants' first look at e a c h disk was r e c o r d e d . W h i c h o n e do you think they looked at the most? If you said "the face," you a r e c o r r e c t ; they gazed at the h u m a n face disk far m o r e than any o t h e r f o r m o r c o l o r (see Figure 5 - 3 ) . SUBSEQUENT RESEARCH AND RECENT APPLICATIONS This study, like so m a n y in this book, significandy c h a n g e d psychology for two reasons: the groundbreaking discoveries and the m e t h o d the r e s e a r c h e r developed to make those discoveries possible. Until the middle of the 2 0 t h century, many behavioral a n d biomedical researchers assumed that babies were b o r n with few if any perceptual or sensory abilities and that they developed or l e a r n e d most, if n o t all, of these skills as they interacted with their environm e n t over time. This idea of the psychologically "empty" newborn was rela-

Reading 5

Take a Long Look . . .

41

tively easy to accept because we did not, at the time, possess the necessary research methodologies to reveal very young infants' t r u e capabilities. Fantz gave us preferential-looking methods that, quite literally, o p e n e d the doors to the mind of the infant. This m e t h o d is used so c o m m o n l y today that it is to psychology what a microscope is to biology: o n e of the first tools researchers turn to when they want to study how babies think. Of course, the discovery that infants c o m e into the world with various perceptual skills does not r e d u c e the i m p o r t a n c e of learning and development. But the inborn skills researchers have discovered using Fantz's methods a p p e a r to set the stage for an infant's future survival and growth. As Fantz points out: Innate knowledge of the environment is demonstrated by the preference of newly hatched chicks for forms likely to be edible and by the interest of young infants in kinds of forms that will later aid in object recognition, social responsiveness, and spatial orientation. This primitive knowledge provides a foundation for the vast accumulation of knowledge through experience, (p. 72) Fantz's discoveries ignited a research revolution into the perceptual abilities of infants. You can see the influence of Fantz's methodological ingenuity throughout the fields of developmental and cognitive psychology. F o r e x a m ple, some of the leading researchers in the world in the a r e a of infant cognition, such as R e n e e Baillargeon at the University of Illinois's Infant Cognition L a b and Elizabeth Spelke at Harvard's L a b o r a t o r y for Developmental Studies, have m a d e extensive use of Fantz's preference-looking research strategies in many studies (see Talbot, 2 0 0 6 , for a review of this work). In addition, Fantz's work helped clarify when and how well babies can perceive depth a n d dropoffs as studied in g r e a t e r detail by Gibson a n d Walk in their classic research incorporating the visual cliff (see C h a p t e r I ) . Probably the most important extension of Fantz's work is credited to Frances Horowitz at the University of Kansas, who discovered that in addition to preferential looking, babies also b e c o m e bored seeing the same stimulus over and over (Horowitz, & Paden et al., 1 9 7 2 ) . W h e n you show infants a novel visual pattern (such as those used in Fantz's studies), they gaze at it for a given a m o u n t of time, but as you repeatedly present the same stimulus, the a m o u n t of time they look predictably decreases. This is called habituation. If you then change or alter the pattern, their interest appears to revive and they look at it longer, a response known as dishabituation. By combining preferential looking, habituation, and dishabituation methodologies, researchers can now learn a great deal about what very young infants, even newborns, "know" about their world. F o r example, in a recent study, researchers wanted to see when humans acquire the ability to distinguish between "possible" objects and "impossible" objects (Shuwarai, Albert, & Johnson, 2 0 0 7 ) . You undoubtedly have seen so