Humans Can Learn to "See" With Sound, Study Says

Kate Ravilious
for National Geographic News
July 6, 2009
With just a click of the tongue, anyone can learn to "see" with their ears, according to a new study of human echolocation.

Several animals, such as bats, dolphins, whales, and some shrews, are known to use echolocation—sound waves bounced off nearby objects—to sense what's around them.

Inspired by a blind man who also navigates using sound, a team of Spanish scientists has found evidence that suggests most humans can learn to echolocate.

The team also confirmed that the so-called palate click—a sharp click made by depressing the tip of the tongue against the roof of the mouth—is the most effective noise for people to use.

Sound Training

Daniel Kish, executive director of World Access for the Blind in Huntington Beach, California, was born blind. He taught himself to "see" using palate clicks when he was a small child.

Kish is able to mountain bike, hike in the wilderness, and play ball games without traditional aids.

(Related: "Mystery of 'Blindsight' Lets Some Blind People 'See.'")

To better understand Kish's skill, Juan Antonio Martínez and his colleagues at the University of Alcalá in Madrid trained ten sighted students to echolocate.

"It was very difficult to persuade some people to take part in the experiments, because most [of our] colleagues though that our idea was absurd," Martínez said.

The students were asked to close their eyes and make sounds until they could tell whether any objects were nearby.

After just a few days of training, the students had all acquired basic echolocation skills, the scientists report in the March/April 2009 issue of the journal Acta Acustica.

The team then recorded the students making three different noises: a 'ch' noise made with the tongue, a 'ch' made with the lips, and the palate click.

After studying the shape of the sound wave that each noise produced, Martínez and his colleagues found that the palate click gives the most detailed feedback about a person's surroundings.

Visual Bias

In animals that echolocate, the skill is often key to survival, and the animals have specially adapted organs for the task, Martínez noted.

Dolphins, for example, have special structures in their noses that can produce 200 clicks a second. Humans can manage just three or four clicks a second.

"It seems reasonably tough, perhaps tougher for those who can see, because we are very visual animals and don't tend to use that ability at all, so there is a 'visual bias' to overcome," said Peter Scheifele, a bioacoustician at the University of Connecticut who wasn't involved in the study.

The average person can develop good echolocation skills in about a month if he or she trains for one to two hours a day. Blind people are likely to pick up the skill more quickly, Martínez said.

In addition to aiding the blind, echolocation could help rescue teams locate people in foggy conditions or help firefighters quickly find exit points in smoky buildings.

The researchers add that artificial echolocation devices, such as wristbands that beep, can't yet outperform the simple tongue click.

"Such devices are worse than natural echolocation at present, because they don't reproduce the complete haptic [touch] perception of the echoes," Martínez said.

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