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More Praise for

the invisible gorilla

“Should be required reading by every judge and jury member in our crimi- nal justice system, along with every battlefi eld commander, corporate CEO, member of Congress, and, well, you and me . . . because the mental illusions so wonderfully explicated in this book can fool every one of us.”

—Michael Shermer, publisher of Skeptic magazine, monthly columnist for

Scientifi c American, and author of Why People Believe Weird Things

“A breathtaking and insightful journey through the illusions that infl u- ence every moment of our lives.”

—Richard Wiseman, author of Quirkology:

How We Discover the Big Truths in Small Things

“Not just witty and engaging but also insightful. . . . Reading this book won’t cure you of all these limitations, but it will at least help you recognize and compensate for them.”

—Thomas W. Malone, author of The Future of Work and

founder of the MIT Center for Collective Intelligence

“Everyday illusions trick us into thinking that we see—and know—more than we really do, and that we can predict the future when we can’t. The Invisible Gorilla teaches us exactly why, and it does so in an incredibly engaging way. Chabris and Simons provide terrifi c tips on how to cast off our illusions and get things right. Whether you’re a driver wanting to steer clear of on- coming motorcycles, a radiologist hoping to spot every tumor, or just an aver- age person curious about how your mind really works, this is a must-read.”

—Elizabeth Loftus, PhD, Distinguished Professor, University of

California–Irvine, and author of Memory and Eyewitness Testimony

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“An eye-opening book. After reading The Invisible Gorilla you will look at yourself and the world around you differently. Like its authors, the book is both funny and smart, fi lled with insights into the everyday illusions that we all walk around with. No matter what your job is or what you do in life, you will learn something from this book.”

—Joseph T. Hallinan, Pulitzer Prize–winning

author of Why We Make Mistakes

“Cognitive scientists Chris Chabris and Dan Simons deliver an entertaining tour of the many ways our brains mislead us every day. The Invisible Gorilla is engaging, accurate, and packed with real-world examples—some of which made me laugh out loud. Read it to fi nd out why weathermen might make good money managers, and what Homer Simpson can teach you about thinking clearly.”

—Sandra Aamodt, PhD, coauthor of Welcome to Your Brain

and former editor, Nature Neuroscience

“Wonderfully refreshing . . . The Invisible Gorilla makes us smarter by reminding us how little we know. Through a lively tour of the brain’s blind spots, this book will change the way you drive your car, hire your employees, and invest your money.”

—Amanda Ripley, senior writer, Time magazine,

and author of The Unthinkable

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the invisible gorilla

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Chab_9780307459657_5p_00_r1.indd ivChab_9780307459657_5p_00_r1.indd iv 3/17/10 11:39 AM3/17/10 11:39 AM

Christopher Chabris

and Daniel Simons

c r o w n New York

the invisible gorilla And Other Ways Our Intuitions Deceive Us

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Copyright © 2010 by Christopher F. Chabris and Daniel J. Simons

All rights reserved. Published in the United States by Crown Publishers, an imprint of the Crown Publishing Group, a division of Random House, Inc., New York. www .crownpublishing .com

CROWN and the Crown colophon are registered trademarks of Random House, Inc.

Library of Congress Cataloging- in- Publication Data

Chabris, Christopher F. The invisible gorilla : and other ways our intuitions deceive us / Christopher F. Chabris and Daniel J. Simons. p. cm. Includes bibliographical references and index. 1. Perception. 2. Memory. 3. Thought and thinking. I. Simons, Daniel J. II. Title.

BF321.C43 2010 153.7'4—dc22

2009045325

ISBN 978- 0- 307- 45965- 7

Printed in the United States of America

Design by Ralph Fowler / rlf design

10 9 8 7 6 5 4 3 2 1

First Edition

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C O N T E N T S

Introduction: Everyday Illusions ix

1. “I Think I Would Have Seen That” 1

2. The Coach Who Choked 43

3. What Smart Chess Players and Stupid Criminals Have in Common 80

4. Should You Be More Like a Weather Forecaster or a Hedge Fund Manager? 116

5. Jumping to Conclusions 150

6. Get Smart Quick! 185

Conclusion: The Myth of Intuition 224

Ac know ledg ments 243

Notes 247

Index 291

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I N T R O D U C T I O N

everyday illusions

“There are three things extremely hard: steel,

a diamond, and to know one’s self.”

—Benjamin Franklin, Poor Richard’s Almanack (1750)

About twelve years ago, we conducted a simple experiment with the students in a psychology course we were teaching at Harvard University. To our surprise, it has become one of the best- known experiments in psychology. It appears in textbooks and is taught in introductory psychology courses throughout the world. It has been featured in magazines such as Newsweek and The New Yorker and on tele vi sion programs, including Dateline NBC. It has even been exhib- ited in the Exploratorium in San Francisco and in other museums. The experiment is pop u lar because it reveals, in a humorous way, something unexpected and deep about how we see our world— and about what we don’t see.

You’ll read about our experiment in the fi rst chapter of this book. As we’ve thought about it over the years, we’ve realized that it illustrates a broader principle about how the mind works. We all believe that we are

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x INTRODUCTION

capable of seeing what’s in front of us, of accurately remembering im- portant events from our past, of understanding the limits of our knowl- edge, of properly determining cause and effect. But these intuitive beliefs are often mistaken ones that mask critically important limita- tions on our cognitive abilities.

We must be reminded not to judge a book by its cover because we take outward appearances to be accurate advertisements of inner, un- seen qualities. We need to be told that a penny saved is a penny earned because we think about cash coming in differently from money we al- ready have. Aphorisms like these exist largely to help us avoid the mis- takes that intuition can cause. Likewise, Benjamin Franklin’s observation about extremely hard things suggests that we should question the intui- tive belief that we understand ourselves well. As we go through life, we act as though we know how our minds work and why we behave the way we do. It is surprising how often we really have no clue.

The Invisible Gorilla is a book about six everyday illusions that pro- foundly infl uence our lives: the illusions of attention, memory, confi - dence, knowledge, cause, and potential. These are distorted beliefs we hold about our minds that are not just wrong, but wrong in dangerous ways. We will explore when and why these illusions affect us, the conse- quences they have for human affairs, and how we can overcome or min- imize their impact.

We use the word “illusions” as a deliberate analogy to visual illusions like M. C. Escher’s famous never- ending staircase: Even after you realize that something about the picture as a whole is not right, you still can’t stop yourself from seeing each individual segment as a proper staircase. Everyday illusions are similarly per sis tent: Even after we know how our beliefs and intuitions are fl awed, they remain stubbornly resistant to change. We call them everyday illusions because they affect our behav- ior literally every day. Every time we talk on a cell phone while driving, believing we’re still paying enough attention to the road, we’ve been af- fected by one of these illusions. Every time we assume that someone who misremembers their past must be lying, we’ve succumbed to an illusion. Every time we pick a leader for a team because that person expresses the

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INTRODUCTION xi

most confi dence, we’ve been infl uenced by an illusion. Every time we start a new project convinced that we know how long it will take to com- plete, we are under an illusion. Indeed, virtually no realm of human be- havior is untouched by everyday illusions.

As professors who design and run psychology experiments for a living, we’ve found that the more we study the nature of the mind, the more we see the impact of these illusions in our own lives. You can develop the same sort of x-ray vision into the workings of your own mind. When you fi nish this book, you will be able to glimpse the man behind the curtain and some of the tiny gears and pulleys that govern your thoughts and be- liefs. Once you know about everyday illusions, you will view the world differently and think about it more clearly. You will see how illusions affect your own thoughts and actions, as well as the behavior of every- one around you. And you will recognize when journalists, managers, advertisers, and politicians— intentionally or accidentally— take advan- tage of illusions in an attempt to obfuscate or persuade. Understanding everyday illusions will lead you to recalibrate the way you approach your life to account for the limitations— and the true strengths— of your mind. You might even come up with ways to exploit these insights for fun and profi t. Ultimately, seeing through the veils that distort how we perceive ourselves and the world will connect you— for perhaps the fi rst time— with reality.

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the invisible gorilla

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1C H A P T E R “ i think i would have

seen that”

Around two o’clock on the cold, overcast morning of January 25, 1995, a group of four black men left the scene of a shooting at a hamburger restaurant in the Grove Hall section of Boston.1 As they drove away in a gold Lexus, the police radio erroneously announced that the victim was a cop, leading offi cers from several districts to join in a ten- mile high- speed chase. In the fi fteen to twenty minutes of mayhem that ensued, one police car veered off the road and crashed into a parked van. Eventually the Lexus skidded to a stop in a cul- de- sac on Wood- ruff Way in the Mattapan neighborhood. The suspects fl ed the car and ran in different directions.

One suspect, Robert “Smut” Brown III, age twenty- four, wearing a dark leather jacket, exited the back passenger side of the car and sprinted toward a chain- link fence on the side of the cul- de- sac. The fi rst car in pursuit, an unmarked police vehicle, stopped to the left of the Lexus. Michael Cox, a decorated offi cer from the police antigang unit who’d grown up in the nearby Roxbury area, got out of the passenger seat and took off after Brown. Cox, who also is black, was in plainclothes that night; he wore jeans, a black hoodie, and a parka.2

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2 THE INVISIBLE GORILLA

Cox got to the fence just after Smut Brown. As Brown scrambled over the top, his jacket got stuck on the metal. Cox reached for Brown and tried to pull him back, but Brown managed to fall to the other side. Cox prepared to scale the fence in pursuit, but just as he was starting to climb, his head was struck from behind by a blunt object, perhaps a baton or a fl ashlight. He fell to the ground. Another police offi cer had mistaken him for a suspect, and several offi cers then beat up Cox, kick- ing him in the head, back, face, and mouth. After a few moments, some- one yelled, “Stop, stop, he’s a cop, he’s a cop.” At that point, the offi cers fl ed, leaving Cox lying unconscious on the ground with facial wounds, a concussion, and kidney damage.3

Meanwhile, the pursuit of the suspects continued as more cops ar- rived. Early on the scene was Kenny Conley, a large, athletic man from South Boston who had joined the police force four years earlier, not long after graduating from high school. Conley’s cruiser came to a stop about forty feet away from the gold Lexus. Conley saw Smut Brown scale the fence, drop to the other side, and run. Conley followed Brown over the fence, chased him on foot for about a mile, and eventually captured him at gunpoint and handcuffed him in a parking lot on River Street. Conley wasn’t involved in the assault on Offi cer Cox, but he began his pursuit of Brown right as Cox was being pulled from the fence, and he scaled the fence right next to where the beating was happening.

Although the other murder suspects were caught and that case was considered solved, the assault on Offi cer Cox remained wide open. For the next two years, internal police investigators and a grand jury sought answers about what happened at the cul- de- sac. Which cops beat Cox? Why did they beat him? Did they simply mistake their black colleague for one of the black suspects? If so, why did they fl ee rather than seek medical help? Little headway was made, and in 1997, the local prose- cutors handed the matter over to federal authorities so they could investigate possible civil rights violations.

Cox named three offi cers whom he said had attacked him that night, but all of them denied knowing anything about the assault. Initial po- lice reports said that Cox sustained his injuries when he slipped on a

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“I THINK I WOULD HAVE SEEN THAT” 3

patch of ice and fell against the back of one of the police cars. Although many of the nearly sixty cops who were on the scene must have known what happened to Cox, none admitted knowing anything about the beating. Here, for example, is what Kenny Conley, who apprehended Smut Brown, said under oath:

Q: So your testimony is that you went over the fence within seconds of seeing him go over the fence?

A: Yeah.

Q: And in that time, you did not see any black plainclothes police offi cer chasing him?

A: No, I did not.

Q: In fact, no black plainclothes offi cer was chasing him, accord- ing to your testimony?

A: I did not see any black plainclothes offi cer chasing him.

Q: And if he was chasing him, you would have seen it?

A: I should have.

Q: And if he was holding the suspect as the suspect was at the top of the fence, he was lunging at him, you would have seen that, too?

A: I should have.

When asked directly if he would have seen Cox trying to pull Smut Brown from the fence, he responded, “I think I would have seen that.” Conley’s terse replies suggested a reluctant witness who had been advised by lawyers to stick to yes or no answers and not volunteer information. Since he was the cop who had taken up the chase, he was in an ideal posi- tion to know what happened. His per sis tent refusal to admit to having seen Cox effectively blocked the federal prosecutors’ attempt to indict the offi - cers involved in the attack, and no one was ever charged with the assault.

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4 THE INVISIBLE GORILLA

The only person ever charged with a crime in the case was Kenny Conley himself. He was indicted in 1997 for perjury and obstruction of justice. The prosecutors were convinced that Conley was “testilying”— outlandishly claiming, under oath, not to have seen what was going on right before his eyes. According to this theory, just like the offi cers who fi led reports denying any knowledge of the beating, Conley wouldn’t rat out his fellow cops. Indeed, shortly after Conley’s indictment, prom- inent Boston- area investigative journalist Dick Lehr wrote that “the Cox scandal shows a Boston police code of silence . . . a tight inner circle of offi cers protecting themselves with false stories.”4

Kenny Conley stuck with his story, and his case went to trial. Smut Brown testifi ed that Conley was the cop who arrested him. He also said that after he dropped over the fence, he looked back and saw a tall white cop standing near the beating. Another police offi cer also testifi ed that Conley was there. The jurors were incredulous at the notion that Conley could have run to the fence in pursuit of Brown without noticing the beating, or even seeing Offi cer Cox. After the trial, one juror explained, “It was hard for me to believe that, even with all the chaos, he didn’t see something.” Juror Burgess Nichols said that another juror had told him that his father and uncle had been police offi cers, and offi cers are taught “to observe everything” because they are “trained professionals.”5

Unable to reconcile their own expectations—and Conley’s—with Conley’s testimony that he didn’t see Cox, the jury convicted him. Kenny Conley was found guilty of one count each of perjury and ob- struction of justice, and he was sentenced to thirty- four months in jail.6 In 2000, after the U.S. Supreme Court declined to hear his case, he was fi red from the Boston police force. While his lawyers kept him out of jail with new appeals, Conley took up a new career as a carpenter.7

Dick Lehr, the journalist who reported on the Cox case and the “blue wall of silence,” never actually met with Kenny Conley until the summer of 2001. After this interview, Lehr began to wonder whether Conley might actually be telling the truth about what he saw and expe- rienced during his pursuit of Smut Brown. That’s when Lehr brought the former cop to visit Dan’s laboratory at Harvard.

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“I THINK I WOULD HAVE SEEN THAT” 5

Gorillas in Our Midst

The two of us met over a de cade ago when Chris was a graduate student in the Harvard University psychology department and Dan had just arrived as a new assistant professor. Chris’s offi ce was down the hall from Dan’s lab, and we soon discovered our mutual interest in how we perceive, remember, and think about our visual world. The Kenny Conley case was in full swing when Dan taught an undergraduate course in research methods with Chris as his teaching assistant. As part of their classwork, the students assisted us in conducting some experi- ments, one of which has become famous. It was based on an ingenious series of studies of visual attention and awareness conducted by the pio- neering cognitive psychologist Ulric Neisser in the 1970s. Neisser had moved to Cornell University when Dan was in his fi nal year of graduate school there, and their many conversations inspired Dan to build on Neisser’s earlier, groundbreaking research.

With our students as actors and a temporarily vacant fl oor of the psy- chology building as a set, we made a short fi lm of two teams of people moving around and passing basketballs. One team wore white shirts and the other wore black. Dan manned the camera and directed. Chris co- ordinated the action and kept track of which scenes we needed to shoot. We then digitally edited the fi lm and copied it to videotapes, and our students fanned out across the Harvard campus to run the experiment.8

They asked volunteers to silently count the number of passes made by the players wearing white while ignoring any passes by the players wearing black. The video lasted less than a minute. If you want to try the task yourself, stop reading now and go to the website for our book, www . theinvisiblegorilla .com, where we provide links to many of the experi- ments we discuss, including a short version of the basketball-passing video. Watch the video carefully, and be sure to include both aerial passes and bounce passes in your count.

Immediately after the video ended, our students asked the subjects to report how many passes they’d counted. In the full-length version, the correct answer was thirty- four—or maybe thirty- fi ve. To be honest, it

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6 THE INVISIBLE GORILLA

doesn’t matter. The pass- counting task was intended to keep people en- gaged in doing something that demanded attention to the action on the screen, but we weren’t really interested in pass- counting ability. We were actually testing something else: Halfway through the video, a female stu- dent wearing a full- body gorilla suit walked into the scene, stopped in the middle of the players, faced the camera, thumped her chest, and then walked off, spending about nine seconds onscreen. After asking subjects about the passes, we asked the more important questions:

Q: Did you notice anything unusual while you were doing the counting task?

A: No.

Q: Did you notice anything other than the players?

A: Well, there were some elevators, and S’s painted on the wall. I don’t know what the S’s were there for.

Q: Did you notice anyone other than the players?

A: No.

Q: Did you notice a gorilla?

A: A what?!?

Amazingly, roughly half of the subjects in our study did not notice the gorilla! Since then the experiment has been repeated many times, under different conditions, with diverse audiences, and in multiple countries, but the results are always the same: About half the people fail to see the gorilla. How could people not see a gorilla walk directly in front of them, turn to face them, beat its chest, and walk away? What made the gorilla invisible? This error of perception results from a lack of attention to an unexpected object, so it goes by the scientifi c name “inattentional blind- ness.” This name distinguishes it from forms of blindness resulting from a damaged visual system; here, people don’t see the gorilla, but not be- cause of a problem with their eyes. When people devote their attention to

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“I THINK I WOULD HAVE SEEN THAT” 7

a par tic u lar area or aspect of their visual world, they tend not to notice unexpected objects, even when those unexpected objects are salient, po- tentially important, and appear right where they are looking.9 In other words, the subjects were concentrating so hard on counting the passes that they were “blind” to the gorilla right in front of their eyes.

What prompted us to write this book, however, was not inattentional blindness in general or the gorilla study in par tic u lar. The fact that people miss things is important, but what impressed us even more was the sur- prise people showed when they realized what they had missed. When they watched the video again, this time without counting passes, they all saw the gorilla easily, and they were shocked. Some spontaneously said, “I missed that?!” or “No way!” A man who was tested later by the producers of Dateline NBC for their report on this research said, “I know that gorilla didn’t come through there the fi rst time.” Other subjects accused us of switching the tape while they weren’t looking.

The gorilla study illustrates, perhaps more dramatically than any other, the powerful and pervasive infl uence of the illusion of attention: We experience far less of our visual world than we think we do. If we were fully aware of the limits to attention, the illusion would vanish. While writing this book we hired the polling fi rm SurveyUSA to contact a representative sample of American adults and ask them a series of questions about how they think the mind works. We found that more than 75 percent of people agreed that they would notice such unexpected events, even when they were focused on something else.10 (We’ll talk about other fi ndings of this survey throughout the book.)

It’s true that we vividly experience some aspects of our world, par- ticularly those that are the focus of our attention. But this rich experi- ence inevitably leads to the erroneous belief that we pro cess all of the detailed information around us. In essence, we know how vividly we see some aspects of our world, but we are completely unaware of those aspects of our world that fall outside of that current focus of attention. Our vivid visual experience masks a striking mental blindness— we as- sume that visually distinctive or unusual objects will draw our atten- tion, but in reality they often go completely unnoticed.11

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8 THE INVISIBLE GORILLA

Since our experiment was published in the journal Perception in 1999, under the title “Gorillas in Our Midst,”12 it has become one of the most widely demonstrated and discussed studies in all of psychology. It earned us an Ig Nobel Prize in 2004 (awarded for “achievements that fi rst make people laugh, and then make them think”) and was even discussed by characters in an episode of the television drama CSI.13 And we’ve lost count of the number of times people have asked us whether we have seen the video with the basketball players and the gorilla.

Kenny Conley’s Invisible Gorilla

Dick Lehr brought Kenny Conley to Dan’s laboratory because he had heard about our gorilla experiment, and he wanted to see how Conley would do in it. Conley was physically imposing, but stoic and taciturn; Lehr did most of the talking that day. Dan led them to a small, window- less room in his laboratory and showed Conley the gorilla video, asking him to count the passes by the players wearing white. In advance, there was no way to know whether or not Conley would notice the unex- pected gorilla— about half of the people who watch the video see the gorilla. Moreover, Conley’s success or failure in noticing the gorilla would not tell us whether or not he saw Michael Cox being beaten on Woodruff Way six years earlier. (These are both important points, and we will return to them shortly.) But Dan was still curious about how Conley would react when he heard about the science.

Conley counted the passes accurately and saw the gorilla. As is usual for people who do see the gorilla, he seemed genuinely surprised that anyone else could possibly miss it. Even when Dan explained that people often miss unexpected events when their attention is otherwise en- gaged, Conley still had trouble accepting that anyone else could miss what seemed so obvious to him.

The illusion of attention is so ingrained and pervasive that everyone involved in the case of Kenny Conley was operating under a false no- tion of how the mind works: the mistaken belief that we pay attention to— and therefore should notice and remember— much more of the

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“I THINK I WOULD HAVE SEEN THAT” 9

world around us than we actually do. Conley himself testifi ed that he should have seen the brutal beating of Michael Cox had he actually run right past it. In their appeal of his conviction, Conley’s lawyers tried to show that he hadn’t run past the beating, that the testimony about his presence near the beating was wrong, and that descriptions of the inci- dent from other police offi cers were inaccurate. All of these arguments were founded on the assumption that Conley could only be telling the truth if he didn’t have the opportunity to see the beating. But what if, instead, in the cul- de- sac on Woodruff Way, Conley found himself in a real- life version of our gorilla experiment? He could have been right next to the beating of Cox, and even focused his eyes on it, without ever actually seeing it.

Conley was worried about Smut Brown scaling the fence and escap- ing, and he pursued his suspect with a single- minded focus that he de- scribed as “tunnel vision.” Conley’s prosecutor ridiculed this idea, saying that what prevented Conley from seeing the beating was not tunnel vision but video editing—“a deliberate cropping of Cox out of the picture.”14

But if Conley was suffi ciently focused on Brown, in the way our sub- jects were focused on counting the basketball passes, it is entirely possible that he ran right past the assault and still failed to see it. If so, the only inaccurate part of Conley’s testimony was his stated belief that he should have seen Cox. What is most striking about this case is that Conley’s own testimony was the primary evidence that put him near the beating, and that evidence, combined with a misunderstanding of how the mind works, and the blue wall of silence erected by the other cops, led prosecutors to charge him with perjury and obstruction of justice. They, and the jury that convicted him, assumed that he too was protecting his comrades.