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.
..this is interesting, but is he really SEING anything?..nope, not really, no.
Sense or see
by anonymous poster
[Comment posted 2008-12-23 15:38:09]
I agree with Phil. The term "sense" is better than the word "see" to describe this situation.
We know that blind patients sense things better than "normal" people. Your sensors are better when you close your eyes.
Non-visual sensing
by Phil Ticehurst
[Comment posted 2008-12-22 18:59:00]
My understanding is that this person is totally blind in that he cannot see anything (His internal video screen is blank). He is sensing people's faces, and the obstacles, through his eyes but the information is not being presented to his conscious mind in a visual form. My hypothesis is testable in that, I predict, he would not be able to sense these things if he was blindfolded (if he could still do these things with his eyes shut then it would have to be by heat sensing or echo sensing or ESP!)
Another Possibility
by Charles Wehner
[Comment posted 2008-12-22 13:40:28]
Or is it possible he is sensing the other mans movement behind him?
Can or can't he see, sensing with eye or else, can he draw what he sensed?
by anonymous poster
[Comment posted 2008-12-22 12:38:46]
Very interesting, but:
Can or can't he see?
Sensing with eye or else?
Can he draw what he senses?
superior colliculus function
by anonymous poster
[Comment posted 2008-12-22 12:33:34]
I thought that blindsight was evidence of the role of the superior colliculus in mapmaking functions.
Definitions?
by anonymous poster
[Comment posted 2008-12-22 12:12:50]
While this is a very interesting article, it leaves two areas unclear (which may be clarified in the published article):
- While there is bilateral brain damage, how is some activity on either side ruled out?
- The ability to sense faces and objects doesn't square with "blind in every sense of the word" to me. If the eyes were actually non-functional, that would be different than the concept of having processing occur in another portion of the brain.