Mystery of "Blindsight" Lets Some Blind People "See," Study Shows

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However this is never "clean" or specific damage—other parts of the brain are also impaired. Studies with these patients are therefore difficult, he said.

To study blindsight directly, researchers often purposefully and permanently disrupt the primary visual cortex in monkeys and other mammals, a method that would be unethical to use on humans, Mole said.

"What [Ro's team] has done is cleverly manage to interfere with the brain in a totally temporary way … It doesn't have any long-term lasting effects at all," he said.

The technique devised by the Rice researchers induced blindness for a fraction of a second in people who ordinarily have good vision.

During the state of temporary blindness, an object was flashed on a screen in front of the test subjects' eyes.

In one experiment the object was either a vertical or horizontal bar, and the subjects were asked to guess the bar's orientation. In the second experiment the researchers flashed a colored disc, and subjects were asked to guess the color.

In both experiments the blinded volunteers correctly guessed the characteristics of the objects at much higher levels than chance alone.

This fits the definition of blindsight and raises the question of how it is possible.

"What we believe is happening is people are able to discriminate orientation and color—as our experiments showed—by processing routes into the brain that aren't consciously accessible," Ro said.

"We believe there are pathways that go from the eyes into the brain that bypass the normal routes tied to conscious processing of information."

Ro added that the study supports the theory that these pathways go to a visual center in the brain that is more sophisticated than the visual centers common to all mammals. This suggests the pathways may be unique to higher-order species.

The test results also show that volunteers were more accurate when they were more confident in their guesses.

"It's unclear what that reflects, but what we think it reflects is that this unconscious processing system can contribute to feelings of certainty," Ro said.

In follow-up experiments the team will test why people feel varying levels of confidence in their guesses. Perhaps the unconscious processing routes are stronger in some people than others, Ro said.

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