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The stunning acoustic power of human echolocators

Illustration of an echolocation click's sound waves. (Thaler et al.)

Human echolocation might sound like the stuff of comic book heroes. But navigating by sound is a matter of acoustics, not marvels. For the first time, researchers describe these echolocation clicks in detail. The clicks are fast, focused and energetic.

Lore Thaler, a psychology professor at Durham University in Britain, said that echolocation has captured scientific interest since the 1940s and ’50s. “At first they thought this was some mystical skill that people are born with,” she said. “They didn't think this was something you could explain based on physics.”

Physics, of course, won out. “Echolocation, on a very basic level, is quite a simple process,” Thaler said. “You rely on the reverberation of sound or sound echoes.” We all do it to some extent, she said, when, for instance, we walk across a floor and can hear that we're in a school gymnasium or in a small furnished office.

Thaler began investigating echolocation sounds in 2009, after watching a video of a man named Daniel Kish. Kish, perhaps the most famous echolocator, is blind. Retinal cancer took his eyes when he was 13 months old. As a child he taught himself to find his way though the world by clicking the roof of his mouth with his tongue.

The clicks “are flashes of sound that go out and reflect from surfaces all around me, just like a bat's sonar,” Kish said during a March 2015 TED talk, “and return to me with patterns, with pieces of information, much as light does for you.”

Kish can hear the separate parts of a tree. Bark echoes differently than leaves, he wrote in the Guardian. Wanting to bike to school like his friends, he trained along a wall, clicking as he went to maintain a straight line. Practice paid off. YouTube videos, like the one Thaler saw, show Kish years later, riding his bike while avoiding traffic.

In the new report published Thursday in the journal PLOS Computational Biology, Thaler and her colleagues recorded the clicks from three men, all blind, who had used echolocation since early childhood or their teens. The scientists found that the average click was 3 milliseconds long. That's three times faster than coarser estimates had suggested. (When speaking, by contrast, it takes a human brain about 600 milliseconds to retrieve a word and pass it to the mouth.) The analysis also revealed that echolocators emit clicks in much tighter beams, in 60-degree cones of sound, than spoken words.

“It's more directional than speech. It gives you a bit more focus. When you move your head you direct this,” Thaler said, likening the ability to an acoustic flashlight.

Echolocation experts not involved with the study praised this work for the level of detail it offered. “Absolutely, a great job for this research group to have persuaded people to pay for it,” said Daniel Rowan, an audiologist at the University of Southampton in Britain. And “to get the expert echolocators to the lab. They would have clicked a hell of a lot.”

There were a few limits to what the researchers can conclude based on the new work. Thaler and her colleagues acknowledge that simply because the expert echolocators use clicks of the same average duration and frequency doesn't mean these are the optimal sounds. They also did not analyze the time between clicks, said Juan Antonio Martínez Rojas, a researcher at the University of Alcalá in Spain.

“Unfortunately, three subjects is a very small sample and conclusions cannot be generalized,” he said. “However, this is not a criticism of this excellent paper, because longtime expert echolocation users are only a few in the world.”

The study has the potential to forward the field of echolocation research, Rowan said. “From a science point of view, the authors have not just given us some data — they’ve given us some tools to proactively make our science better.” Given this information, what he called a “crazy-stupid” idea occurred to him: “Knowing these characteristics, we could build an iPad app” that gave feedback on people's clicks, Rowan said, perhaps in a manner similar to foreign-language programs like Duolingo. 

Thaler's team also developed software to simulate echolocators in a virtual environment. She said she hopes to use these clicking avatars to answer some of the many questions about echolocation. “We know that human echolocations can determine the shape of object using clicks,” she said. “What we don’t know at present is how.”

Thaler said that many echolocators live rich and independent lives. But it is not a replacement for sight. Despite echolocation's sensitivity, almost all blind echolocators also use tools like long canes or guide dogs.

Rojas, who said he could sustain continuous echolocation for about two hours, called it an “extremely demanding task” both physically and psychologically. Though sighted people are fascinated by echolocation, he said, it's still a rare practice in the blind community.

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