The findings are published this week in the journal Psychological Science.
“Some blind people use echolocation to assess their environment and find their way around. 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. But we don’t yet understand how much echolocation in humans has in common with how a sighted individual would use their vision,” says Gavin Buckingham, a former postdoctoral fellow at Western and now a researcher at Heriot-Watt University in Scotland.
“Ironically, the proof for the vision-like qualities of echolocation came from blind echolocators wrongly judging how heavy objects of different sizes felt,” explains Melvyn Goodale, Director of the Brain and Mind Institute.
The experiment conducted by Goodale and his collaborators demonstrated that echolocators experience a ‘size-weight illusion’ when they use their echolocation to get a sense of how big objects are, in just the same way as sighted people do when using their normal vision. (The size-weight illusion is what you experience when a small box containing a kilogram of lead feels like it weighs more than a big box containing a kilogram of feathers.)
Three groups participated in the experiment: blind echolocators, blind non-echolocators, and control subjects with no visual impairment. All three groups were asked to judge the weight of three cubes which were identical in weight but differed in size. Study participants never touched the boxes directly but lifted each of them by pulling on a string that was attached to the top of the box.
The blind group, who did not echolocate, experienced no illusion, correctly judging the boxes as weighing the same amount as one another because they had no indication of how big each box was before they lifted it with the attached string.
The sighted group, where each person was able to see how big each box was, overwhelmingly succumbed to the ‘size-weight illusion’ and experienced the smaller box as feeling a lot heavier than the largest one when they lifted each box by pulling on the string.
Remarkably, the blind echolocators, who detected the size of the box only through echolocation, also experienced the illusion. This shows that using echolocation to figure out the size of each box influenced their sense of how heavy something felt – just like the sighted observers.
Goodale explained that the findings are consistent with the team’s earlier findings showing that blind echolocators use ‘visual’ regions of their brain when listening to their own echoes.
“This new study shows that echolocation is not just a functional tool to help visually-impaired individuals navigate their environment, but actually has the potential to be a complete sensory replacement for vision,” says Goodale.
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