Canadian researchers have discovered just how some blind people are able to navigate accurately using the same echolocation technique as bats and dolphins.
A nunber of people have been able to develop the ability, with some so efficient at it that they can ride bikes or play basketball. They do it by making clicks with their mouths, and listening for the echoes that return from the surrounding objects.
"It is clear echolocation enables blind people to do things otherwise thought to be impossible without vision and can provide blind and visually-impaired people with a high degree of independence," says
senior author Mel Goodale of the University of Western Ontario's Centre for Brain and Mind.
What hasn't been properly understood is quite how the human brain achieves this feat. But by using functional magnetic resonance imaging (fMRI), the researchers say they've shown that blind echolocators use what is normally the 'visual' part of their brain to process the clicks and echoes.
Goodale and his team first made recordings of the clicks and their very faint echoes using tiny microphones in the ears of the blind echolocators as they stood outside and tried to identify different objects such as a car, a flag pole, and a tree.
The researchers then played the recorded sounds back to the echolocators while their brain activity was being measured in Western's fMRI) brain scanner.
When the echolocation recordings were played back to the subjects, they were able to perceive the objects based on the echoes.
However - and very surprisingly - the brain areas that process auditory information were no more activated by sound recordings of outdoor scenes containing echoes than they were by sound recordings of outdoor scenes with the echoes removed.
Instead, the subjects' brains showed activity in those areas of the brain that process visual information in sighted people.
When the same experiment was carried out with sighted people who did not echolocate, their brains showed no echo-related activity.