Reported May 2009

HUMAN HEARING: Our ears detect sound as vibrations in the air. Sound waves cause the eardrum to vibrate, which sends waves through a fluid inside the cochlea. This in turn causes tiny hairs -- each tuned to the different pitches of the sound -- to vibrate as well, stimulating nerves which send electrical signals to the brain for processing. Having two ears makes it possible to determine from where a sound is coming. Time lag and differences in volume provide useful clues. For instance, sound coming from one direction will reach the ear furthest away about 1/500 second later than the closer ear, and the brain can detect this time lag. A difference in volume between the two ears depends on the frequency of the sounds. It is easier for us to tell the direction of high frequency sounds better than low frequency sounds, because the higher frequencies are more easily blocked by the head and therefore may not reach the far ear.

ABOUT HEARING LOSS: Loud sounds stress and potentially damage the delicate hair cells within the inner ear that convert mechanical vibrations (sound) into the electrical signals that the brain interprets as sound. Over time, the hair cells can become permanently damaged and stop working, producing hearing loss. Noise-induced hearing loss can be caused by two types of noise: sudden bursts, such as firearms or fireworks, or continuous exposure to loud noise, such as motorized recreational vehicles, loud sporting events, power tools, farming equipment or amplified music. For the latter, the damage depends on the level and duration of the noise exposure. Repeated exposures over many years can cause a gradual onset of hearing loss in both children and adults.

The Acoustical Society of America contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

George M. Strain
(225) 578-9758
strain@lsu.edu

Acoustical Society of America
Melville, NY 11747-4502
(516) 576-2360
http://asa.aip.org
asa@aip.org

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