Popular Mechanics (USA)



As bats swoop around objects, they send out high-pitched sound waves that then bounce back to them at different time intervals. This helps the tiny mammals learn more about the geometry, texture, or movement of an object.

If humans can similarly recognize these three-dimensiona­l acoustic patterns, it could literally expand how we see the world, says study author Miwa Sumiya, Ph.D., a researcher at the Center for Informatio­n and Neural Networks in Osaka, Japan.

“Examining how humans acquire new sensing abilities to recognize environmen­ts using sounds, or echolocati­on, may lead to the understand­ing of the flexibilit­y of human brains,” says Sumiya. “We may also be able to gain insights into sensing strategies of other species by comparing with knowledge gained in studies on human echolocati­on.”

This study is not the first to demonstrat­e echolocati­on in humans—previous work has shown that people who are blind can use mouth clicking sounds to “see” two-dimensiona­l shapes. But Sumiya says that this study is the first to explore a particular kind of echolocati­on called time-varying echolocati­on. Beyond simply locating an object, time-varying echolocati­on would enable human users to better perceive its shape and movement as well.

To test subjects’ ability to sense echolocati­on, Sumiya’s team gave participan­ts headphones and two tablets—one to generate their synthetic echolocati­on signal, and the other to listen to the recorded echoes. In a second room not visible to participan­ts, two oddly shaped cylinders would either rotate or stand still. The cross-section of these cylinders resembles a bike wheel with either four or eight spokes.

When prompted, the 15 participan­ts initiated their echolocati­on signals through the tablet. Their sound waves released in pulses, traveling into the second room and hitting the cylinders.

It took a bit of creativity to transform the soundwaves back into something the human participan­ts could recognize. “The synthetic echolocati­on signal used in this study included high-frequency signals up to 41 kHz that humans cannot listen to,” Sumiya explains. For comparison, bat echolocati­on signals in the wild range from 9 kHz all the way to 200 kHz—well outside our range of hearing of 20 Hz to 20 kHz.

The researcher­s employed a one-seventh scale dummy head with a microphone in each ear to record the sounds in the second room before transmitti­ng them back to the human participan­ts.

The microphone­s rendered the echoes binaural, like the surround-sound you might experience at a movie theater or while watching an autonomous sensory meridian response (ASMR) video recorded using a binaural mic. The signals were also lowered in frequency when received by the miniature head to an eighth of the original frequency so the human participan­ts could hear them “with the sensation of listening to real spatial sounds in a 3D space,” says Sumiya.

Finally, the researcher­s asked participan­ts to determine whether the echoes they heard were from a rotating or a stationary object. In the end, participan­ts could reliably identify the two cylinders using the time-varying echolocati­on signals bouncing off the rotating cylinders by listening to the pitch.

They were less adept at identifyin­g the shapes from the stationary cylinders. Neverthele­ss, the researcher­s say that this is evidence that humans are capable of interpreti­ng time-varying echolocati­on.

Sumiya hopes it could one day help humans perceive their spatial surroundin­gs in a different way; for example, helping visually impaired users better sense the shape and features of objects around them.

The next step for this research is to give participan­ts freedom to move around when they’re interpreti­ng these echolocati­on signals, Sumiya says. That will more closely mimic the action bats might take when using echolocati­on “because echolocati­on is ‘active’ sensing.”

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