It's well-known that bats use a biological version of sonar, called echolocation, to find their way around at night. That blind humans could do it too was suspected but not known.

Now, Canadian researchers have proved that they can.

Intriguingly, they did so by using a part of the brain normally involved in processing visual images. They discovered this by carrying out brain scans on two male volunteers, aged 43 and 27, who had both been blind since childhood.

Each was asked to stand outside and try to perceive different objects such as a car, a flag pole and a tree by making clicking noises and then picking up their very faint echoes. Tiny microphones were placed in the volunteers' ears to record the outgoing and incoming sounds.

The men later had these sounds played back to them, while their brain activity was monitored using functional magnetic resonance imaging (fMRI) scans. During playback, they were able to identify which object was which from the echoes.

The fMRI scans showed that these echoes were being processed by brain regions normally used to process visual information; no echo-related activity was seen in the auditory brain areas, which would be expected to process sound, 'The Daily Telegraph' reported.

The 43-year-old, whose lost his sight earlier, performed better. His eyes were removed at 13 months due to a rare cancer called retinoblastoma. The same test on sighted people showed no ability to echolocate, and no echo-related activity in their visual brain regions.

Dr Mel Goodale from the University of Western Ontario, led the study, 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 study has been published in the 'Public Library of Science One' journal.