Echolocation — sending out a sound wave, hearing how it bounces back at you, and using that information to navigate your environment — is a technique generally associated with animals like bats and dolphins, not people. And yet some visually impaired folks learn to use finger snaps or tongue clicks to help them get around.
In a study published in Psychological Science, a team led by Gavin Buckingham of Heriot-Watt University in Scotland tried to learn about how this skill works. To do so, they used a well-known quirk of human perception called the size-weight illusion: If you ask someone to pick up two objects of the same weight but different sizes, the smaller one will feel heavier.
The study asked three small groups — blind echolocators, a control group of blind non-echolocators, and a control group of sighted people (also non-echolators) — to pick up one cube five times to gauge its weight. Then they looked or clicked at a second, differently sized cube of the same weight for as long as they wanted, after which they lifted up that second cube with a pulley (past research has shown that the size-weight illusion holds even when subjects use a pulley). They were then asked to estimate the weight of that second one relative to the first, allowing researchers to identify or measure the presence of size-weight illusion.
The blind non-echolators didn’t experience any such illusion, which makes sense since they had no visual cues to go on. Interestingly, the blind echolocators did experience a size-weight illusion, albeit a smaller one than the sighted individuals. The researchers report that this is the first time echolocation has been tied to this perceptual illusion. It’s fascinating to think that echolocation could share perceptual aspects with “regular” sight, and it’s a striking example of just how flexible and creative humans can be when it comes to their need to navigate the world.