Echolocation: humans are able to "see" with sound

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

For some it may seem very, very strange, but echolocation is not only in bats and dolphins (and some other animals), but also in humans. And we do not mean here special devices, but a person's own ability to navigate in space, capturing the reflected echo.

There is a number of evidences that blind people use echolocation to find something or not bump into some kind of obstacle on their way - like whales, they click their tongues hard to echo through the echo that there is a chair in the room, and do not you need to bend down slightly so as not to hit from a too low doorway.

On the one hand, something like this could be expected: the brain is trying to compensate for the lack of visual information, sharpening hearing as much as possible. Of course, a person is still far from bats, but those who have severe vision problems, the ability to echolocate significantly increases. Nevertheless, echolocation abilities in humans have hardly been studied in detail, and it was not very clear to what extent they could be developed.

Researchers from the University of Durham, along with colleagues from the Technical University of Eindhoven and the University of Birmingham, decided to find out how echolocation abilities allow blind people to "see" objects around them. The experiment involved eight people who have long lost their sight and managed to achieve impressive success in echolocation.

They were led into a room where there was nothing but a disc 17.5 cm in diameter sitting on a pole, and it was just the location of this disc that had to be guessed. Microphones were attached to the volunteers in order to know exactly what sounds they make themselves and what sounds come back to them; the room itself was completely soundproof, that is, nothing outside could interfere with the experiment. The blind stood motionless, but the location of the disc changed: it was in relation to them at one, then at another angle.

An article in the Proceedings of the Royal Society B says that the participants in the experiment clicked their tongues in different ways - trying to determine the location of the object, they changed the volume and frequency of sounds.

It turned out that the object was best "visible" to them when it was directly in front of them. They also heard it well if it was at an angle of 45 ° or even 90 ° (that is, quite from the side). But even when the object was behind the back, the volunteers could still determine its location using echolocation, albeit with less accuracy. For example, if the angle was 135 ° - that is, the disc was placed behind and on the side - then the probability that a person would accurately determine its location was 80%. Finally, when the disc was placed directly behind the back, the likelihood of being accurately probed by echolocation dropped to 50%.

On the other hand, it is still surprising that a blind person can know with such accuracy that he has something behind him, just listening to the echo from his own clicks of the tongue. The most curious thing was that the volunteers heard such a faint echo, which, it is believed, the human ear can no longer hear. And this once again demonstrates how flexible our brain is and how much it is able to adapt to such conditions, to which, it would seem, it is simply impossible to adapt.

In a new article published in Proceedings of the Royal Society B, Tayler and her colleague Liam J. Norman write about how the brain of blind people who are adept at echolocation perceives the world around them.

There are special areas of the cortex in the brain for signals from the senses.

For example, information from the eyes primarily arrives at the primary visual cortex in the back of the brain. It is known that something like a map of the area appears in the primary visual cortex, that is, when we see two closely spaced objects, then the areas located next to each other will react to these two objects on the retina - and when the signal from the retina goes to the brain, then two adjacent zones are also activated in the visual cortex.

It turned out that in people with an echo sounder, the visual cortex reacts in the same way, but to sounds. The authors of the work set up an experiment with sighted people, with the blind who did not use their own echo sounder, and with the blind, who already knew how to navigate by the reflected sounds very well. They were allowed to listen to sounds that emanated from different places in the room and at the same time monitored their brain activity using magnetic resonance imaging.

For those who were pros in echolocation, sounds activated the visual cortex, and so that a map of the area appeared in the cortex - as if the visual cortex actually saw the surrounding space. But for the sighted and those blind who did not use echolocation, no sound card appeared in the visual cortex.