Researchers say finding suggests alternate vision routes in the brain
MONDAY, Dec. 22 (HealthDay News) -- Call it a case of second sight: Scientists report that a blind man in Switzerland was able to make his way through a maze, even though he has no conscious sensation of seeing the world around him.
This phenomenon is an indication that the human brain has ways of processing vision beyond those that are currently understood, the scientists said.
Visual skills include mechanisms "for orienting and doing in the world rather than for understanding," study lead author Beatrice de Gelder, a researcher at Tilburg University in the Netherlands and Harvard Medical School, said in a news release.
Scientists were already aware of a phenomenon called "blindsight," in which the sightless show the ability to sense things around them. In the case of the man profiled in the new study, for example, he can sense facial expressions, and his brain shows signs of reacting to the emotions shown on the faces of others.
But the study authors said the man also has a skill not seen before in the blind -- the ability to navigate a maze, in this case a series of boxes and chairs placed in his way.
The man, whose age and name were not disclosed, suffered two strokes that damaged the visual centers of his brain. He can't see, and brain scans show no signs of activity in the visual centers, the study authors said.
The researchers wrote that the man walks like a blind man and only gets around with the assistance of another person or a cane.
Still, as the study authors reported in the Dec. 23 issue of the journal Current Biology, the man was able to navigate the maze without any problem and didn't require the help of an assistant who stood by in case he stumbled.
The researchers said it's possible, though unlikely, that the man used sound waves to detect the location of the obstacles.
Colin Ellard, associate chair of the department of psychology at the University of Waterloo in Canada, said the study findings reflect previous research that suggests the comprehension of vision isn't limited to one part of the brain.
The study "is useful in the sense that it adds to a larger story about how vision is organized in the brain," Ellard said. "The take-home message would be that our ability to 'see' consists of a constellation of different types of abilities. Some can help us to understand, think and talk about what is in the external world, but others act to help us organize movements such as reaching or walking to targets. This study highlights the fact that these different abilities depend on different parts of our brain."
Learn more about blindsight from Bryn Mawr University.
SOURCES: Colin Ellard, Ph.D., associate chair, department of psychology, University of Waterloo, Ontario, Canada; Dec. 23, 2008, Current Biology
All rights reserved