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Scientific American

None So Blind

published March 2004 | comments (1)
Perceptual-blindness experiments challenge the validity of eyewitness testimony and the metaphor of memory as a video recording
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Picture yourself watching a one-minute video of two teams of three players each. One team wears white shirts and the other black shirts, and the members move around one another in a small room tossing two basketballs. Your task is to count the number of passes made by the white team — not easy given the weaving movement of the players. Unexpectedly, after 35 seconds a gorilla enters the room, walks directly through the farrago of bodies, thumps his chest and, nine seconds later, exits. Would you see the gorilla?

Most of us believe we would. In fact, 50 percent of subjects in this remarkable experiment by Daniel J. Simons of the University of Illinois and Christopher F. Chabris of Harvard University did not see the gorilla, even when asked if they noticed anything unusual (see their paper “Gorillas in Our Midst”). The effect is called inattentional blindness. When attending to one task — say, talking on a cell phone while driving — many of us become blind to dynamic events, such as a gorilla in the crosswalk.

I’ve incorporated the gorilla video into my lecture on science and skepticism given at universities around the country. I always ask for a show of hands of those who did not see the gorilla during the first viewing. About half of the more than 10,000 students I encountered last year confessed their perceptual blindness. Many were stunned, accusing me of showing two different clips. Simons had the same experience: “We actually rewound the videotape to make sure subjects knew we were showing them the same clip.”

These experiments reveal our perceptual vainglory, as well as a fundamental misunderstanding of how the brain works. We think of our eyes as video cameras and our brains as blank tapes to be filled with sensory inputs. Memory, in this model, is simply rewinding the tape and playing it back in the theater of the mind, in which some cortical commander watches the show and reports to a higher homunculus what it saw.

This is not the case. The perceptual system and the brain that analyzes its data are far more complex. As a consequence, much of what passes before our eyes may be invisible to a brain that is focused on something else. “The mistaken belief that important events will automatically draw attention is exactly why these findings are surprising; it is also what gives them some practical implications,” Simons told me. “By taking for granted that unexpected events will be seen, people often are not as vigilant as they could be in actively anticipating such events.” Driving is an example. “Many accident reports include claims like, ‘I looked right there and never saw them,’ ” Simons notes. “Motorcyclists and bicyclists are often the victims in such cases. One explanation is that car drivers expect other cars but not bikes, so even if they look right at the bike, they sometimes might not see it.” Simons recounts a study by NASA research scientist Richard F. Haines of pilots who were attempting to land a plane in a simulator with the critical flight information superimposed on the windshield. “Under these conditions, some pilots failed to notice that a plane on the ground was blocking their path.”

Over the years in this column I have pounded paranormalists pretty hard, so they may rightly point to these studies and accuse me of inattentional blindness when it comes to ESP and other perceptual ephemera. Perhaps my attention to what is known in science blinds me to the unknown.

Maybe. But the power of science lies in open publication, which, with the rise of the Internet, is no longer constrained by the price of paper. I may be perceptually blind, but not all scientists will be, and out of this fact arises the possibility of new percepts and paradigms. There may be none so blind as those who will not see, but in science there are always those whose vision is not so constrained. But first they must convince the skeptics, and we are trained to look for gorillas in our midst.

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One Comment to “None So Blind”

  1. Roger Says:

    Similar to the Boston experiment where a hopelessly blurred slide is sharpened incrementally but persons who witnessed from the beginning held on to preconcieved ideas of what they were looking at long after it became apparant to someone walking into the room.

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