Cochlea -- quality of filtering

Didier A. Depireux didier at eng.umd.edu
Wed Sep 20 08:20:28 EST 1995


erc at cinenet.net (Eric Smith) writes:
>
>How well does the cochlea divide sound into its frequency components?
>
Very poorly! The early experiments of von Bekesy used cochleae from 
fresh human cadavers and at least showed that the passive mechanics of the 
cochlea are such that the traveling wave that propagates down the basilar
membrane (the membrane where the hair cells that measure vibrations are 
located) excites very large regions of the membrane for any pure tone presented
to the ear. When the cochlea is 'alive' (inside a living organism), the 
frequency selectivity is a lot better, thanks for the outer hair cells. 
Anyway, you probably don't want this to be too technical, so I would advise you
to look at
http://www.boystown.org/cel/cochmech.html
if you are really interested. The traveling wave portion of that page, 
http://www.boystown.org/cel/waves.html
contains some mpegs showing you the basilar membrane displacements for a 
series of pure tones and clicks, and will leave you wondering how we can 
have such a good frequency selectivity... Check it out! The rest of the page (the
first address I gave) is also important to understand how the ear works, esp the
part about outer hair cell motility. 
If you want to learn more about the inner ear anatomy, you should check out
another really great page, 
http://lab9924.wustl.edu/Intro1.htm
from the cochlear fluid lab at Washington University. It talks about how some
disease of the inner ear damage your hearing...


						Didier
						didier at src.umd.edu



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