Seeing with Your Ears
Sighted people often use a simple form of echolocation, too, perhaps without even realizing it. When you’re hanging a picture on a wall, one way to locate a stud within it is to knock around and listen for changes in pitch. But when you tap on a hollow space in the wall, you usually don’t hear an actual echo — yet you can tell somehow that the space sounds hollow.
Research shows we can perceive these types of stimuli subconsciously. When we do hear echoes, it’s from sound bouncing back off distant objects. When you click your tongue or whistle toward a nearby object, though, the echo returns so fast that it overlaps the original sounds, making it hard to hear an echo. But the brain unconsciously interprets the combination of the sound thrown in one direction and the returning sound as an alteration in pitch. What makes Ben and Kish so remarkable is that they can use what everyone’s brain unconsciously detects in an active way to navigate the world. And although Ben and Kish may seem superhuman because of their perceptual abilities, research confirms that sighted humans can acquire echolocation, too. After all, the visual cortex does process some sounds, particularly when the brain seeks to match auditory and visual sensory inputs.
American psychologist Winthrop Niles Kellogg began his human-echolocation research program around the time of the Cuban Missile Crisis. His research showed that both blind and sighted subjects wearing blindfolds could learn to detect objects in the environment through sound, and a study by another researcher showed that, with some training, both blind and sighted individuals can precisely determine certain properties of objects, such as distance, size, shape, substance and relative motion from sound alone. While sighted individuals show some ability to echolocate, Kellogg showed that blind echolocators seem to operate a bit differently when collecting sensory data. They move their heads in different directions when spatially mapping an environment, while sighted subjects don’t move their heads when given the same types of tasks.
Interestingly, when sighted individuals are deprived of visual sensory information for an extended period of time, they naturally start echolocating, possibly after only a few hours of being blindfolded. What’s more, with their newfound echolocation skills comes some visual imagery. After a week of being blindfolded, the imagery becomes more vivid. One of Kellogg’s research participants said he experienced “ornate buildings of whitish green marble and cartoon-like figures.”
Is sound alone responsible for echolocators’ ability to navigate the environment? Researchers wonder whether touch cues, such as the way air moves around objects, can offer information about the surroundings. Philip Worchel and Karl Dallenbach from the University of Texas at Austin sought to answer these questions in the 1940s. Their experiments involved asking both blind and blindfolded sighted participants to walk toward a board placed at varying distances. Participants were rewarded for learning to detect the board by not walking into it face-first. After multiple trials, both the blindfolded and blind subjects became better able to detect the obstacle. After about 30 trials, blindfolded subjects were as successful at stopping in front of the boards as blind subjects when they were wearing hard-soled shoes. But this ability disappeared when subjects performed the same experiments on carpet or while wearing socks, which muffled the sound their footsteps created. The researchers concluded that the subjects relied on sound emanating from their shoes, implying sound is responsible for navigational ability.
The increased ability to navigate via sound appears to be the result of sound processing in the brain, not merely increased acuity of hearing. One study showed that the blind and the sighted scored similarly on normal hearing tests. But when a recording had echoes, parts of the brain associated with visual perception in sighted people activated in echolocators but not in sighted people. These results showed how echolocators extracted information from sound that wasn’t available to the sighted controls.
Some reports seem to indicate that humans can’t perceive objects that are very close — within 2 meters of them — through echolocation. But a 1962 study by Kellogg at Florida State University showed that blind people can detect obstacles at much shorter distances — 30 to 120 centimeters. Some participants were accurate even within 10 centimeters, suggesting that although subjects aren’t consciously aware of the echo, they still can respond appropriately to echo stimuli.
The above cases show that our perceptual experiences involve a lot more than just what we’re consciously aware of. Our brain is primed to accomplish the seemingly superhuman, even at the basic level of perception. It’s an extraordinary organ that creates our rich experiences by turning waves that merely strike the eardrum into complicated, phenomenal representations of our surroundings.