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Echolocation acts as supplemental sense for the blind

When estimating a weight, blind people using echolocation fall prey to the same size-weight illusion that stumps those who can see.

By Brooks Hays

EDINBURGH, Scotland, Dec. 23 (UPI) -- Echolocation is most famously employed by bats and toothed whales like dolphins and porpoises. But new research suggests the technique can offer a substitute vision-like sense to blind people.

"Some blind people use echolocation to assess their environment and find their way around," Gavin Buckingham, a psychological scientist at Scotland's Heriot-Watt University, said in a recent press release. "They will either snap their fingers or click their tongue to bounce sound waves off objects, a skill often associated with bats, which use echolocation when flying."

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Ironically, scientists were able to confirm the value of echolocation to vision-impaired humans by proving blind study participants were susceptible to the "size-weight illusion," also known as the Charpentier illusion. The size-weight illusion is the name given to the phenomenon whereby people underestimate the weight of the larger of two boxes with the same mass.

The basic explanation for the illusion is that people lift the larger object with expectation of increased weight. For a reasons that are still not entirely understood, when that expectation is undermined the brain is tricked into perceiving the object's weight to be less than it is.

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In the new study, researchers showed that blind people using echolocation fell prey to the size-weight illusion -- just as sighted participants did. Blind people who didn't employ echolocation were not tricked.

"We were interested to discover that echolocators, who only experienced the size of the box through echolocation, also experienced this illusion," Buckingham said. "This showed that echolocation was able to influence their sense of how heavy something felt. This resembles how visual assessment influenced how heavy the boxes felt in the sighted group."

The new study, which included assistance from researchers at the Brain and Mind Institute at Canada's Western University, was published this week in the journal Psychological Science.

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