Blind man aces obstacle course
[Entry posted at 22nd December 2008 05:01 PM GMT]

How much can you see with non-functioning visual cortex? A clinically blind man, with lesions on both sides of his visual cortex, was able to flawlessly navigate an obstacle course, a paper to be published tomorrow in Current Biology reports.

The patient, called only TN in the paper, is a former doctor, who had suffered two strokes that damaged both sides of his striate cortex, the brain region dedicated to processing vision. The findings reinforce previous observations that other routes in the brain besides the visual cortex can process visual information, the study's authors say.

"I don't think there's ever been a bilateral blindsight patient that's been studied in any depth whatsoever, that's why it's interesting," Robert Kentridge, from the University of Durham, who was not involved in the study, told The Scientist.

TN has a condition known as blindsight. He is blind in every sense of the word: He walks with a sensing stick and needs guidance by another person. However, he is able to sense facial expressions, indicated by activity in brain regions that respond to facial expressions such as fear or anger.

To test TN's ability for locomotion, the researchers, led by Beatrice de Gelder, from Tilburg University in the Netherlands, set up a crude obstacle course in a narrow hallway. To the researchers' shock TN walked flawlessly through the course, sidestepping boxes and chairs without the help of a guide. (Click on the movie below to watch TN navigate the obstacle course)

For decades, patients with damage to one side of their visual cortex have demonstrated the ability to recognize objects and facial expressions. In experiments dating from the 1980s of patients with lesions in one side of their visual cortex that leave them blind in one direction of sight, they can still identify the orientation of objects -- either horizontal or vertical, for example -- presented in their blind field, without being aware of seeing anything. It is not fully understood how this is possible. One theory is that the brain, being a flexible organ, is receiving information from the intact region of the cortex.

"This is the only patient known in the literature that has this kind of brain damage" on both sides of the visual cortex, de Gelder told The Scientist. "It means there's no possibility that he is compensating for the lesion on one side with intact brain on other side."

While it is known that alternate routes in the brain process what is perceived by the eye, these findings support their ability to bypass the visual cortex and process information, Kentridge said.

Related stories:
  • Facelessness, faced
    [November 2007]
  • Visual system surprise
    [7 July 2008]
  • An eye on history
    [29 August 2008]

























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