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Mind

What You See Is What You Don't

By Susan KruglinskiFebruary 20, 2006 6:00 AM

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Some people who have lost their sight retain a peculiar relic of vision: They can "guess" the movement, color, and shape of objects around them and get the answers right most of the time. Neuroscientist Tony Ro at Rice University in Houston has now induced this spooky sense in people with sight and suggests that it may be an important part of how we perceive the world.

Short-circuiting the visual cortex with an electromagnetic zap, Ro induced momentary blindness in 10 test subjects with normal vision. During that split second, a computer flashed a picture of colored disks or of horizontal or vertical bars. Although the participants were not aware that they had seen anything, they could describe the color or orientation of the images correctly 75 to 80 percent of the time, well above the results of chance.

This phenomenon—sensing visual information without actually "seeing" it—is called blindsight. Ro speculates that blindsight happens when our eyes take in images that bypass the primary visual cortex, the brain's main vision center. We are not aware that we are seeing such images, but other parts of the brain may process the information nonetheless. Previous research on monkeys whose visual cortex had been removed supports Ro's theory.

Blindsight might be the brain's way of avoiding sensory overload. "Typically, when we're looking at the world, there's far more information than we can process at any one moment, but it is very important to be able to process much of that information for means of survival," Ro says. The unconscious flow of information, he believes, allows us to change our behavior and make decisions without ever quite knowing why we did.

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