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

November 1, 2005

An innovative research technique is providing insight into why some blind people are able to sense and describe objects they cannot see.

The phenomenon of "blindsight" occurs in some people who suffer injuries to the primary visual cortex, the region of the brain considered essential for sight.

Blindsight allows people to use visual information they get through their eyes even though they have no consciousness of the visual experience, said Christopher Mole, a postdoctoral fellow in philosophy at Washington University in St. Louis, Missouri.

"But that of course is quite hard to show in the lab," he said.

A team of psychologists at Rice University in Houston, Texas, may have found a way to directly study blindsight in the lab.

They are using electromagnetic stimulation on the brains of people who can see to render them partially and temporarily blind.

"The way it works is an electric current inducts into the brain via a magnetic pulse, and that causes a disruption of underlying neurons in the brain," said Tony Ro, a member of the Rice team.

"What this technique allows us to do essentially is in a safe and noninvasive way shut down a portion of the brain temporarily," he added.

Ro and colleagues report their technique and findings in the current issue of the journal Proceedings of the National Academy of Sciences.

Mole said the Rice team reports "compelling proof" for blindsight.

Unconscious Pathway

Blindsight is most prevalent among people who suffer damage to the primary visual cortex, such as in some stroke victims, Mole explained.

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