Echolocation allows blind to 'see' using sound
CTV.ca News Staff
Published Wednesday, May 25, 2011 6:15PM EDT
Dolphins, bats and other creatures use echolocation to find their way through dark waters or dark skies. And it seems humans can as well, to see through the darkness of blindness.
Daniel Kish lost his sight to retinal cancer as a baby, but uses tongue "clicks" to help him "see" objects. He makes the sounds as he moves about and listens for the echoes as they bounce back.
Just by listening to echoes, Kish can tell how far away an object is, how large it is and how "dense" or deep it is. He can tell the difference between a wall in front of him, and a bush or pole beside him.
Kish has refined the technique so well over a lifetime that he can even ride a bike without bumping into anything.
When Melvyn A. Goodale at the University of Western Ontario's Centre for Brain and Mind heard about Kish, he was intrigued.
"What went through our minds was, ‘My goodness, how is his brain allowing him to do this?' We assume it's a case of some sort of neuroplasticity, something in his brain changed as a consequence of learning how to echolocate," Goodale tells CTV News.
Goodale was able to convince Kish, along with another blind man who learned the technique as an adult, to conduct a couple of experiments with them.
Through brain scans, the researchers discovered that the two men use what is normally the "visual" part of their brain to process the clicks and echoes, to envision the hazards around them.
While it's long been known that unused brain areas can get "recruited" to do other functions, the researchers say this study is the first to show that the visual brain areas in blind people can still play an important role.
This study appears this month in the scientific journal, PLoS ONE.
To study how Kish's brain had re-wired itself, Goodale's team recorded Kish and the other blind man as they made clicks in front of a number of objects outdoors. They also recorded the echoes that came back.
Goodale said he was amazed at what Kish could do.
"If you put a pole in front of him and then moved it only three degrees to the side, by using clicks and echoes, he can tell that you've moved it. He can tell that it's changed. So his accuracy is amazing," Goodale told CTV.
After making their recordings, researchers then placed the men in a functional MRI machine (magnetic resonance imaging) and played the recording of their clicks and resulting echoes. They found that the men could identify the objects just by listening to the recordings.
What's more, the brain scans revealed that the two men were processing the clicks in the visual cortex of their brains.
"What this tells us is that the visual cortex can be exploited by the auditory system. We can use parts of the brain that are normally devoted for vision to process auditory information when visual information is removed," Goodale said.
The researchers then conducted the same experiments in two people who weren't blind. Not only could these individuals not perceive objects through echolocation, their brains didn't show any activity in the visual areas when they listened to the recordings.
Interestingly, the brain region that normally processes sound was not differently active between any of the study participants.
Goodale said it's clear that echolocation enables blind people to do things that are otherwise thought to be impossible without vision.
"Clearly, echolocation is quite liberating for someone who can do it," he said.
Kish now regularly trains other blind people on his echolocation technique, which he calls FlashSonar. Through his non-profit organization, World Access for the Blind, he has taught hundreds of people how to "see" with their ears.
With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip