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Thursday, July 14, 2011

Echolocating humans

Although common in bats and dolphins, echolocation is exceedingly rare in humans. The surprising thing is that it’s not nonexistent. There actually are individuals who have learned to echolocate. Melvyn Goodale and Lore Thaler of the University of Western Ontario and Stephen Arnott of the Rotman Research Institute put a couple of blind echolocators in an fMRI to see how they do it.

Natural echolocators, like the two subjects used in the study, often use palatal clicks to produce their echoes. Because the inside of an fMRI scanner offers little opportunity for navigation, the researchers recorded both those clicks and the resulting echoes as they would sound from within the subjects’ own ears. In this way, they could simulate the effect of being in front of various objects. The volunteers would hear the clicks and the echoes as if they were in an open space, rather than in a claustrophobic tube. Two sighted controls were treated in the same manner.

All the participants had normal hearing. However, unlike the sighted people who only used the auditory parts of their brains to process the signals, the blind participants employed their calcarine cortexes (a part of the brain devoted to vision) to make sense of the clicks. In other words, they were literally creating pictures from sounds. Those pictures included details like size, distance, even texture.

Of the two subjects in the study, one has been blind virtually since birth but the other didn’t lose his eyesight until his teens. The fact that both have been able to learn this technique indicates that it could be within the power of most blind people.

For more information, check out Ed Yong’s Not Exactly Rocket Science blog.