Super hearing in flies may improve hearing aid ...( a sound source. Our results demonstrat...)

a sound source. "Our results demonstrate that in terms of directional hearing, the flies are as good as any system known," says Mason, who carried out the experiments while working as a postdoctoral fellow at Cornell. "These flies possess one of the most accurate and efficient auditory systems in the animal kingdom which is critical to their survival."

To measure Ormia's ability to pinpoint a sound source, Mason and his colleagues tethered flies on a spherical treadmill made from a ping-pong ball. The ball was floated on an air-stream to reduce friction so that the flies' walking movements were translated into rotations of the ball. When the researchers played artificial cricket sounds from various locations using a movable speaker, the flies walked towards the sound and the computer recorded their walking path. They found that the flies could detect changes in sound-source location smaller than two degrees. "Even humans trying to detect who is speaking in a crowded room can't do better than that," notes Mason. See www.scar.utoronto.ca/~amason/movie/flyball2.mpg for a demonstration.

The flies have only about 100 nerve cells in each ear, compared with thousands in the human ear. Other experiments by Mason, Oshinsky and Hoy used electrodes to demonstrate how the simpler nervous system of the fly can process sound information so accurately. "Beyond the mechanical processes of the ear drum movement, we now know how the nervous system converts movement of the eardrums into information on sound direction," says Mason.

The fly's ears act essentially as an extremely small, simple and sensitive directional microphone. Hearing aids that incorporate directional microphones would help the hearing impaired filter out background noise and tune in to one sound - a task that would enable them to better decipher what one person is saying in a crowd of people. "Hearing aids
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Contact: Sue Toye
sue.toye@utoronto.ca
416-978-0260
University of Toronto
4-Apr-2001

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