Blind people who can echolocate actually process the sounds in the visual centers of their brains, according to an article published in the May issue of PLos ONE.
Bats and certain marine mammals including dolphins use echolocation to navigate. This study was the first to investigate the neural underpinnings of human echolocation, used by some blind people to do things thought to be impossible without vision, such as riding a bicycle.
“The enormous potential of this ‘natural’ echolocation ability is realized in a segment of the blind population that has learned to sense silent objects in the environment simply by generating clicks with their tongues and mouths and then listening to the returning echoes,” the article states.
Canadian researchers placed tiny microphones in the ears of two blind individuals who practice echolocation and recorded their clicks and returning echoes as they tried to identify objects in the environment. The recordings were played back to the subjects and their brain activity was studied with functional magnetic resonance imaging (fMRI).
The team found that the blind echolocators could sense objects based on the recorded echoes, identifying “the shape, motion and location of objects with great accuracy,” according to the paper.
Interestingly, the fMRI scanner showed activity in an area of the brain known as the calcarine cortex, which usually processes visual information in sighted people. Moreover, the areas of the brain that usually process auditory information showed no more activity when the echolocators listened to recordings of outdoor environments with echoes than to recordings of the same scene without echoes.
“This suggests that visual brain areas play an important role for echolocation in blind people,” says lead author Lore Thaler, a postdoctoral fellow at the University of Western Ontario, in a press release.
In contrast, sighted control subjects who do not echolocate could not detect objects based on the echo recordings, and their brain scans did not show activity related to the echoes.However, “there is the possibility that even in sighted people who learn to echolocate, visual brain areas might be recruited,” adds co-author Stephen Arnott, researcher at the Rotman Research Institute, in the release
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