Thanks to David Buck for the link.
http://www.eurekalert.org/pub_releases/2009-06/f-sf-ssd063009.php

A team of researchers from the University of Alcalá de Henares (UAH) has shown scientifically that human beings can develop echolocation, the system of acoustic signals used by dolphins and bats to explore their surroundings. Producing certain kinds of tongue clicks helps people to identify objects around them without needing to see them, something which would be especially useful for the blind.

"In certain circumstances, we humans could rival bats in our echolocation or biosonar capacity", Juan Antonio Martínez, lead author of the study and a researcher at the Superior Polytechnic School of the UAH, tells SINC. The team led by this scientist has started a series of tests, the first of their kind in the world, to make use of human beings' under-exploited echolocation skills.

In the first study, published in the journal Acta Acustica united with Acustica, the team analyses the physical properties of various sounds, and proposes the most effective of these for use in echolocation. "The almost ideal sound is the 'palate click, a click made by placing the tip of the tongue on the palate, just behind the teeth, and moving it quickly backwards, although it is often done downwards, which is wrong", Martínez explains.

The researcher says that palate clicks "are very similar to the sounds made by dolphins, although on a different scale, as these animals have specially-adapted organs and can produce 200 clicks per second, while we can only produce three or four". By using echolocation, "which is three-dimensional, and makes it possible to 'see' through materials that are opaque to visible radiation" it is possible to measure the distance of an object based on the time that elapses between the emission of a sound wave and an echo being received of this wave as it is reflected from the object.

In order to learn how to emit, receive and interpret sounds, the scientists are developing a method that uses a series of protocols. This first step is for the individual to know how to make and identify his or her own sounds (they are different for each person), and later to know how to use them to distinguish between objects according to their geometrical properties "as is done by ships' sonar".

Some blind people had previously taught themselves how to use echolocation "by trial and error". The best-known cases of these are the Americans Daniel Kish, the only blind person to have been awarded a certificate to act as a guide for other blind people, and Ben Underwood, who was considered to be the world's best "echolocator" until he died at the start of 2009.
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http://www.eurekalert.org/pub_releases/2009-06/f-sf-ssd063009.php