Blind people can learn to navigate like bats by “seeing” objects from sounds reflected off them, a study has shown.
They make clicking noises with their mouths and listen to the returning echoes to make sense of their environment.
A few are so adept at the skill that they use it to go mountain biking, play ball games, or explore unknown places.
Surprisingly, the echoes are processed using the visual part of the brain – not the auditory region that receives sound signals from the ears, scientists have discovered.
Researchers in Canada carried out functional magnetic resonance imaging scans to study the brain activity of two blind “echolocators”.
Tiny microphones were placed in the volunteers’ ears to record the clicks they made and pick up their very faint echoes.
Both male participants, one aged 43 and the other 27, were left completely blind due to conditions suffered in childhood.
Each was asked to stand outside and try to perceive different objects such as a car, a flag pole and a tree.
The scientists later played back the recorded sounds while the men’s brains were scanned.
During the play back, not only could the two individuals identify the shape and movement of objects from their echoes, but they focused the associated brain activity in regions that normally process visual information.
No echo-related activity was seen in the auditory brain areas, which would be expected to process sound.
The best performer was the 43-year-old man who lost his vision earliest. He had his eyes removed at 13 months of age due to retinoblastoma, a rare blinding cancer.
Sighted people who could not echolocate were unable to copy the blind men’s ability in follow-up experiments. Nor did listening to echoes trigger activity in their visual brain regions.
Senior scientist Mel Goodale, from the University of Western Ontario, said: “It is clear that echolocation enables blind people to do things that are otherwise thought to be impossible without vision, and in this way it can provide blind and vision-impaired people with a high degree of independence in their daily lives.”
The findings were published in the online journal Public Library of Science One.
It may be possible for anyone to learn to echolocate like a bat, according to the researchers.
Co-author Stephen Anott, from the Rotman Research Institute in Toronto, said: “There is the possibility that even in sighted people who learn to echolocate, visual brain areas might be recruited.”