"Some blind people have learned to echolocate by making clicking noises and listening to the returning echoes.

A study of two such people, published in PLoS ONE , showed a part of the brain usually associated with sight was activated when listening to echoes.

Action for Blind People said further research could improve the way the technique is taught.

Bats and dolphins bounce sound waves off their surroundings and by listening to the echoes can "see" the world around them.

Some blind humans have also trained themselves to do this, allowing them to explore cities, cycle and play sports.

Brain scan

Researchers looked at two patients who use echolocation every day. EB, aged 43, was blinded at age 13 months. LB, 27, had been blind since age 14.

They were recorded echolocating, while microphones were attached to their ears.

The recordings were then played while their brain activity was being recorded in an fMRI machine.

Increased activity in the calcarine cortex was discovered.

Dr Lore Thaler, from University of Western Ontario, said: "This suggests that visual brain areas play an important role for echolocation in blind people."

The study looked at only two people so cannot say for certain what happens in the brains of all people who learn the technique, but the study concludes: "EB and LB use echolocation in a way that seems uncannily similar to vision."

Susie Roberts, rehabilitation officer at Action for Blind People, said: "This research into brain activity and echolocation is very interesting and improves our understanding of how some visually impaired people may be processing information to help them navigate safely.

"Further investigation may help to improve the way the technique is taught to people in the future, potentially improving their mobility and independence.""

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