Echo-location is not something you would associate with human hearing, but the idea is not as daft as it may at first seem.
Everyone has experienced the feeling of emptiness in a room devoid of soft furnishings, carpets and curtains. Much of that feeling is due to the difference in the returning echoes coming from the empty walls, windows and floors compared with the echoes in a room full of sound-absorbing furnishings.
People who have been blind since birth, or from an early age, are known to become extremely sensitive to sounds and so it should come as little surprise that some of them have become adept at using echoes to form uncanny mental images of their surroundings. It is but a small step for them to actively produce their own sounds or clicks and listen to the quality and timbre of the reflected echo.
Daniel Kish has evidently perfected the technique to a remarkable extent, and studies have indicated that he is exploiting the under-utilised visual cortex of his brain, which in humans is considerably larger than the region devoted to processing auditory impulses. However, it would be an exaggeration to suggest that he is able to echo-locate his way around like a bat or a dolphin – echo-location in these animals is in quite a different league.
The most obvious difference is the rate of clicking. Bats produce anywhere between 10 and 200 clicks a second, depending on whether they are doing general sweeps of the environment or homing in on a flying insect. Dolphins produce up to 600 clicks a second, focused in a narrow echo-locating beam ahead of them.
Bats also vary the frequency of their clicks, which are of such a short wavelength that they are beyond human hearing. Combined with the high pulse rate, this provides far more information than the relatively simple vocal clicks made by Mr Kish.
Nevertheless, the apparent use of a simple form of echo-location in blind people is testament to the incredible adaptability of the human brain.Reuse content