Читать книгу The Invisible Gorilla: And Other Ways Our Intuition Deceives Us - Christopher Chabris - Страница 22

Professor Ulric Neisser, whose research inspired our gorilla experiment, watched the change blindness demonstration in which an actor changed into another person while answering a phone, and he pointed out a possible limitation of all of these studies: They all used videos. He commented that watching video is an inherently passive activity: The action unfolds in front of us, but we do not actively engage with it the way we do when we interact socially with other people. Neisser argued that change blindness might not occur if a person were changed in the middle of a real-world encounter rather than across a cut in a passively viewed motion picture. The two Dans thought Neisser probably was right, that people would notice such a change in the real world, but they decided to run an experiment to test Neisser’s prediction anyway.

Imagine you are strolling across a college campus and up ahead of you, you see a man holding a map and looking lost. The man approaches you and asks directions to the library. You start giving him directions, and as you’re pointing to the map, a couple of people behind you abruptly say “Excuse me, coming through,” and they rudely carry a big wooden door right between you and the lost pedestrian. Once they pass, you finish giving directions. Would you notice if the original lost pedestrian were replaced by a different person as the workers carried the door through? What if the two people wore different clothes, differed in height by about three inches, had different builds, and had noticeably different voices? You would have to be pretty oblivious to miss the change. After all, you were in the middle of a conversation with the man, and you had plenty of time to look at him. That’s certainly what the two Dans and Ulric Neisser thought.

That’s also what more than 95 percent of undergraduates thought when asked whether they would notice.²³ And they were all wrong. All of us, undergraduates as well as scientists familiar with all of the research leading up to these experiments, fell prey to the illusion of memory. All were convinced that only the rare, unusually oblivious person could possibly miss the change. Yet nearly 50 percent of the people in the original experiment did not notice that they were talking to different people before and after the interruption!²⁴

Serendipitously, one day several years later when we were conducting a followup experiment at Harvard, many of the undergraduate psychology students were attending a lecture in the basement of the building. During the lecture, Professor Stephen Kosslyn (Chris’s graduate school mentor and longtime collaborator) happened to describe the “door” study in detail as an example of research being conducted by other faculty members in the department. When they left the lecture, several students were overheard making comments like, “There’s no way I would have missed that change.” Our recruiter asked them if they would like to be in an experiment and sent them to the eighth floor. As they stood at a counter after filling out a form, the experimenter who had been talking to them ducked down behind the counter—ostensibly to file away some papers—and a different person stood up. All of the students missed the change!²⁵

Change blindness is a surprisingly pervasive phenomenon considering that it has only been studied intensely since the 1990s. It occurs for simple shapes on a computer display, for photographs of scenes, and for people in the middle of a real-world interaction.²⁶ And the illusion of memory leads people to believe that they’re great at change detection even though they’re lousy. This illusion is so powerful that even change blindness researchers regularly experience it. We only came to recognize the limits of our intuitions about memories when our own data repeatedly showed us how wrong we could be. Similarly, filmmakers learn about the illusion of memory the hard way, by seeing evidence of their own mistakes on the big screen. Trudy Ramirez, the Hollywood script supervisor, has experienced this many times: “The way you remember something, how your memory shapes what you think you saw, as sure as you think you are…often it’s different if you can actually look back at it. There were times when I would have staked my life on something and later on realized I was wrong.”

There are limits to change blindness, of course. When we spoke publicly about the early person-change studies, we were often asked whether people would notice if a man changed into a woman. “Of course they would,” we thought, but of course our certainty was another reflection of the illusion of memory. The only way to find out was to try it. Later experiments in Dan’s lab showed that people do in fact notice when you change a man into a woman or when you change the race of an actor in a movie. And people are more likely to notice a change to the identity of a person who is a member of their own social group.²⁷ But most other changes often go undetected.

Even when subjects notice the person swap in these real-world experiments, they’re far from perfect in picking the original experimenter from a photographic lineup. And people who miss the change do no better with the lineup than they would have done by just guessing randomly.²⁸ In a brief encounter, we appear to store so little information about another person that we not only fail to see changes, but we also can’t even identify the person we saw just minutes earlier. When you interact briefly with a stranger, there are only a few pieces of general information you can be certain of retaining: sex, race, and social group (student, bluecollar worker, businessperson, and so on). Most of the rest of what you perceive about the person probably won’t make it into memory at all.

Recall Leslie Meltzer and Tyce Palmaffy, who witnessed a knife attack from their car but recalled it differently just moments later. In light of the evidence that people sometimes fail to notice that a person has almost instantaneously been replaced by someone completely different, Leslie and Tyce’s discrepant eyewitness memories are unsurprising. After all, they were just observing the person from a distance, not standing face-to-face with him and giving him directions.