The Invisible Gorilla: And Other Ways Our Intuitions Deceive Us

by Christopher Chabris

  Similarly, we expect lifeguards at swimming pools to notice anyone in danger of drowning, but this is a false sense of safety brought on by the illusion of attention. Lifeguards have the nearly impossible task of scanning a large expanse of water and detecting the rare event of someone drowning.52 The difficulty of their task is exacerbated because swimmers regularly do things that look like drowning but aren’t, such as swimming under water, lying on the bottom of the pool, splashing frantically, and so on. Lifeguards take regular breaks, change their viewing stations repeatedly during shifts, and take many other steps to maintain their vigilance, but vigilance, besides being subject to its own limitations, cannot eliminate inattentional blindness. The lifeguards simply cannot see everything, but the illusion of attention makes us believe they will.

  Only becoming aware of the illusion of attention can help us to take steps to avoid missing what we need to see. In some cases, like lifeguarding, technological innovations such as automated scanning could help. Without awareness of our limitations, though, technological intervention can hurt. Head-up displays might improve our ability to navigate and to keep our eyes on the road, but they might impair our ability to detect unexpected events. Similarly, in-car GPS navigation systems might help us find our way, but when trusted implicitly, they can lead us to drive without noticing where we are going.53 A driver in Germany followed his navigation instructions despite several “closed for construction” signs and barricades, eventually barreling his Mercedes into a pile of sand. Twice in 2008, drivers in New York State blindly followed their GPS instructions and turned onto a set of train tracks in front of an oncoming train (neither was injured, fortunately). A driver in Britain caused a train crash after unwittingly driving onto the Newcastle-Carlisle rail line tracks.

  A more common problem in Britain occurs when truck drivers follow their GPS commands onto streets that are too small for their trucks. In one case, a driver wedged his truck so firmly into a country lane that he couldn’t move backward, move forward, or even open his door. He had to sleep in his cab for three days before being towed out by a tractor. The problem, of course, is that the navigation system doesn’t know or take account of the size of the vehicle—and some of us don’t know that it doesn’t know. Our favorite example of GPS-induced blindness comes from the British town of Luckington. In April 2006, rising waters made a ford through the start of the Avon River temporarily impassable, so it was closed and markers were put on both sides. Every day during the two weeks following the closure, one or two cars drove right past the warning signs and into the river. These drivers apparently were so focused on their navigation displays that they didn’t see what was right in front of them.

  Technology can help us to overcome the limits on our abilities, but only if we recognize that any technological aid will have limits too. If we misunderstand the limits of the technology, these aids can actually make us less likely to notice what is around us. In a sense, we tend to generalize our illusion of attention to the aids we use to overcome the limits on our attention. In the next chapter, we will consider this question: If we successfully pay attention to something and notice it, will it then be remembered? Most people think yes, but we will argue that this too is an illusion—the illusion of memory.

  the coach who choked

  BEFORE RETIRING FROM COACHING COLLEGE basketball in 2008, Bobby Knight led his teams to victory in more than nine hundred college games, more than any other Division I coach. He was a four-time national coach of the year, led the 1984 Olympic gold medal basketball team that featured future NBA stars Michael Jordan and Patrick Ewing, and won three national collegiate titles as the coach of the Indiana University Hoosiers. He was famous for running a “clean” basketball operation: His organizations were never accused of the sorts of recruiting violations that plague many top-tier basketball programs, and the majority of his players completed their college degrees. He was a coaching innovator whom many of his former players credit for their personal and professional successes. Despite this unparalleled record of achievement, Bobby Knight was fired from Indiana University in September 2000 after an undergraduate yelled “Hey, Knight, what’s up?” and Knight responded by grabbing the student’s arm and lecturing him on being respectful.

  That Knight’s dismissal was triggered by a lecture on respect is ironic. Throughout his coaching career, Knight had a national reputation for a volatile temper, crass behavior, and a disdainful attitude toward the press and others. He regularly berated referees and journalists, and on occasion, he even threw chairs onto the court. He was the subject of a Saturday Night Live parody in which Jim Belushi played a high school chess coach who knocked over an opponent’s pieces and yelled at his own player, “Move it! Move it! Move the bishop!” Compared with other events in his career, the “what’s up” incident was actually small beer. It was considered a firing offense only because of a report published earlier that year that had led the university to adopt a zero-tolerance policy for his future indiscretions.

  In March 2000, CNN and Sports Illustrated ran a story about why several top recruits had left the Indiana program. It focused on an incident described by Neil Reed, one of Knight’s former players. Reed was a star recruit, a high school All-American who scored an average of about ten points per game during his three years at Indiana. During a practice in 1997, Knight confronted Reed for failing to call out a teammate’s name when making a pass, but Reed stood his ground against Knight, claiming he had in fact yelled the name. According to Reed, Knight then physically attacked him:

  At that point coach thrust right at me, just came right at me, wasn’t far away enough to where I couldn’t see it coming, was close enough to come at me and reach and put his hand around my throat. He came at me with two hands but grabbed me with one hand. People came in and separated us like we were in a school yard to fight…. He had me by the throat for I would probably say that little situation lasted about 5 seconds. I grabbed his wrist and started walking back and by this time people, coaches Dan Dakich, Felling grabbed coach Knight and pulled him away.

  The national reporting of this incident caused a sensation and led Indiana officials to shorten their coach’s leash. Reed’s account vividly confirmed Knight’s stormy reputation and put it in an even darker light. But shortly after the Sports Illustrated report, other people present at the time told a different story. Knight’s former assistant Dan Dakich said, “His allegation that I had to separate him from coach Knight is totally false.” Another player who had been on the team at the time said, “The statement that he was choked by coach Knight is totally ridiculous.” Christopher Simpson, a vice president of the university who attended many practices, was quoted as saying about Reed’s statements, “… I question anything Neil Reed says.” The team’s trainer at the time, Tim Garl, stated baldly, “The choking thing never happened … give me a lie detector.” Bobby Knight himself said, “I might have grabbed him by the back of the neck. I might have grabbed the guy and moved him over. I mean, if you choke a guy, I would think he would need hospitalization.” Everyone involved believed that their memories had accurately recorded what had happened, but their recollections were contradictory.1

  How We Think About Memory

  This chapter is about this illusion of memory: the disconnect between how we think memory works and how it actually works. But how, exactly, do we think it works? Before answering this question, we’d like you to try a brief memory test. Read through the following list of words: bed, rest, awake, tired, dream, wake, snooze, blanket, doze, slumber, snore, nap, peace, yawn, drowsy. We’ll get back to them in a few paragraphs.

  Most of us cannot remember a fifteen-digit number, and we know that we cannot, so we do not even try. We all sometimes forget where we put our car keys (or our car), we fail to recall a friend’s name, or we neglect to pick up the dry cleaning on the way home from work. And we know that we often make these mistakes—our intuitive beliefs about such everyday memory failures are reasonably accurate. Our intu
itions about the persistence and detail of memory are a different story.

  In the national survey of fifteen hundred people we commissioned in 2009, we included several questions designed to probe how people think memory works. Nearly half (47%) of the respondents believed that “once you have experienced an event and formed a memory of it, that memory doesn’t change.” An even greater percentage (63%) believed that “human memory works like a video camera, accurately recording the events we see and hear so that we can review and inspect them later.” People who agreed with both statements apparently think that memories of all our experiences are stored permanently in our brains in an immutable form, even if we can’t access them. It is impossible to disprove this belief—the memories could in principle be stored somewhere—but most experts on human memory find it implausible that the brain would devote energy and space to storing every detail of our lives (especially if that information could never be accessed).2

  Just as the illusion of attention leads us to think that important and distinctive events capture our attention when they don’t, the illusion of memory reflects a basic contrast between what we think we remember and what we actually remember. Why do people easily grasp the limitations of short-term memory, but misunderstand the nature of long-term memory? This chapter is about how our memories can mislead us and how our beliefs about the workings of memory are mistaken. The illusion of attention happens when what we notice is different from what we think we notice. The illusion of memory happens when what we remember is different from what we think we remember.

  Now we’d like you to try to recall all of the words from the list you read. Do your best to recall as many as you can. Write them down on a piece of paper before you continue reading.

  What could be simpler than recalling a list of words that you read only moments ago? Not much, but even a task as simple as this reveals systematic distortions in memory. Look at the list you wrote down. How do you think you did? Most likely, you didn’t recall all fifteen words. When we use this task as a classroom demonstration, most students recall a few words from the beginning of the list and a few from the end of the list.3 They often recall fewer than half of the words from the middle of the list, though, and on average, they tend to recall only about seven or eight of the fifteen words correctly. Stop to think about this for a moment. Those words were all utterly common and familiar, you were not under any special stress (we hope) when you read them, and there was no time pressure when you had to recall them. Computers built in the 1950s were able to perfectly store fifteen words in memory, but despite our magnificent cognitive abilities, we cannot remember with precision what we read just minutes ago.

  If you ask a small child to remember a short list of words for a few minutes, you will notice that as late as age four kids still don’t appear to realize that they need to exert special effort to keep the words in memory. As adults, though, we have learned that there are limits to how much we can maintain in memory for a short time. When we have to remember a phone number long enough to dial it, we repeat it to ourselves, either silently or out loud, as long as necessary. Once an arbitrary list is longer than the “magic number” of about seven items, most people have trouble holding it in their short-term memories.4 That is why license plates have only about seven letters and numbers and why phone numbers historically only required seven numbers (and why the three-digit prefix often began with the first two letters of the town or neighborhood’s name; where Chris grew up, in Armonk, New York, some old signs and advertisements still listed the numbers of local businesses as starting with AR-3 instead of 273). When we have to remember anything more than this, we use memory crutches (notepads, voice recorders, and so on) to help.

  The reason your difficulty recalling all fifteen words in our list illustrates the illusion of memory is not that it reveals limits on how much we can remember. People generally understand those limits. It reflects the illusion of memory because it highlights how we remember what we do. Take a look at the list of words you recalled. Does it contain the word “sleep”? About 40 percent of the people reading this book will recall having seen the word “sleep.” If you are one of those people, you are probably as confident about having seen “sleep” as you are about any of the other words you remembered. You might even have a distinct recollection of seeing it on the list—but it wasn’t there. You fabricated it.

  Memory depends both on what actually happened and on how we made sense of what happened. The list you read was designed to produce just this type of false memory. All of the words are closely associated with the missing word “sleep.” As you read the words on the list, your mind made sense of them, automatically processing the connections among them. At some level, you knew that they were all related to sleep, but you didn’t take special note of the fact that “sleep” was not on the list. Then, when you recalled the words, your mind reconstructed the list as best it could, based on both your specific memory for the words you saw and on your knowledge of how the words were generally related.

  When we perceive something, we extract the meaning from what we see (or hear, or smell …) rather than encode everything in perfect detail. It would be an uncharacteristic waste of energy and other resources for evolution to have designed a brain that took in every possible stimulus with equal fidelity when there is little for an organism to gain from such a strategy. Likewise, memory doesn’t store everything we perceive, but instead takes what we have seen or heard and associates it with what we already know. These associations help us to discern what is important and to recall details about what we’ve seen. They provide “retrieval cues” that make our memories more fluent. In most cases, such cues are helpful. But these associations can also lead us astray, precisely because they lead to an inflated sense of the precision of memory. We cannot easily distinguish between what we recall verbatim and what we construct based on associations and knowledge. The word-list example, originally devised in the 1950s by psychologist James Deese and then studied extensively by Henry Roediger and Kathleen McDermott in the 1990s,5 is a simple way to demonstrate this principle, but memory distortions and the illusion of memory extend well beyond arbitrary lists of words.

  Just as the gorilla experiment showed that people see what they expect to see, people often remember what they expect to remember. They make sense of a scene, and that interpretation colors—or even determines—what they remember about it. In a dramatic demonstration of this principle, psychologists William Brewer and James Treyens conducted a clever experiment using a simple ruse.6 Subjects in their study were led to a graduate student office and asked to wait there for a minute while the experimenter made sure the previous subject was finished. About thirty seconds later, the experimenter returned and led the subjects to another room, where they unexpectedly were asked to write down a list of everything that they had seen in the waiting room. In most respects, the waiting room was a typical graduate student office, with a desk, chairs, shelves, and so on. Almost all of the subjects recalled such common objects. Thirty percent of them also recalled seeing books, and 10 percent recalled seeing a file cabinet. But this office was unusual—it contained no books or file cabinets.

  In the same way that people tended to recall having seen the word “sleep” when remembering a list of words associated with sleep, their memory reconstructed the contents of the room based both on what actually was there and on what should have been there. (If you look at a picture of the office, it will probably seem perfectly normal until someone points out what’s missing, and then it will suddenly start to look strange.) What is stored in memory is not an exact replica of reality, but a re-creation of it. We cannot play back our memories like a DVD—each time we recall a memory, we integrate whatever details we do remember with our expectations for what we should remember.

  Memories in Conflict

  Neil Reed recalled Coach Knight choking him during a practice. He remembered Assistant Coach Dan Dakich having to pull Knight off him, but Dakich claimed it never happe
ned. One of them had a distorted memory for the event, but which one? In most cases of disputed memory like this, there’s no definitive way to determine who was right and who was wrong. What makes this example particularly interesting is that well after Reed, Dakich, and others went public with their accusations and memories, a videotape of the practice surfaced. It showed Knight approach Reed, grab him by the front of the neck with one hand for several seconds, and push him backward. Other coaches and players stopped what they were doing and watched. Nobody came to rescue Reed. No assistant coaches separated them. Reed correctly recalled that Knight had grabbed him by the throat, at least momentarily, but over time, in his mind, the memory was elaborated and distorted. It was made consistent with what plausibly might have happened rather than what did happen. And, to Reed, his totally false memory of being forcibly separated from Coach Knight was just as real as his more accurate memory of being choked. After viewing the video for a follow-up CNN/Sports Illustrated report, Reed said:

  I know what happened and that [tape] proves what happened. I think the moment after something like that, especially a 20-year-old kid being in that situation, I don’t think you can find fault in a little bit of … I mean … I’m not lying. That’s how I remember the thing happening and [former assistant coach Ron] Felling’s five feet from me. As far as people coming in between, I remember people coming between us.7

  Why did Reed remember an embellished event while Knight remembered nothing at all? Before the tape surfaced, Knight told HBO’s Frank Deford that he didn’t remember choking Reed, and added, “There isn’t anything that I have done with one kid that I haven’t done with a lot of other kids.”8 For Knight, this was an unremarkable event—it was business as usual. His memory for the event was distorted to become consistent with his broader beliefs and expectations for what happens at practices: Coaches grab kids and move them around, showing them where to stand and what to do. Physical contact, for Knight, is a regular part of coaching. He misremembered the event as being less consequential than it was, distorting it to be more consistent with his own beliefs about typical coaching situations. For Reed, this event likely was far more consequential. As he noted, he was a “twenty-year-old kid” at the time and he probably hadn’t been grabbed by the neck often in practice. To him, it was a jarring and unusual event, one that he stored in his memory as “coach choked me.” He remembered the event based on the ways that it was salient to him, and as a result, it was distorted in the opposite direction from Knight’s version, becoming traumatic rather than trivial. For Knight, the incident was just like another arbitrary word in a list. For Reed, the incident had a powerful meaning, and the details were filled in accordingly.