Mechanisms of hearing question

kkollins at pop3.concentric.net kkollins at pop3.concentric.net
Mon Dec 14 20:58:03 EST 1998


If you're so inclined, Didier, I "cast my vote" in favor of your
continuing. In my work, I've focussed upon Vision, and would be Happy to
Learn what someone Knowledgeable in Audition has to say.

[I've a personal interest, too. Although my elderly father has two
expensive hearing aids, he's beginning to have trouble separating out
conversation from background. I'm hoping to find "noise-canceling", or
better, hearing aids for him. (He was a carreer Soldier. His ears were
damaged during his days in an Artillery Company... ear protection wasn't
"respected" back then, and he just stood there getting "hammered"...]
ken collins

Didier A. Depireux wrote:
> 
> TONYJEFFS (tonyjeffs at aol.com) wrote:
> : >
> : > but why do you invoke higher centers in this "tuning"?
> : Because the common theory is that the Inner hair cells only send messages   to
> : the brain, while the OHCs mostly (90%) receive messages from the brain, and I
> 
> If you really want to know all the details, they can be found in one of the
> 7 "Green Books", edited by Art Popper and published by Springer-Verlag. One
> of the green books (vol 8, I think) is entitled 'The cochlea'.
> 
> There is a big difference between the retina and the cochlea, in that the
> local inhibitory circuit that's found in the retina itself doesn't appear
> in the auditory pathway until the cochlear nucleus. In the auditory nerve,
> about 5 % of the auditory nerve fibers course from the CNS to the cochlea,
> whereas the rest goes the other way. The descending fibers all target outer
> hair cells (and nothing else), whereas the ascending fibers connect only to
> inner hair cells. In other words, the only possible lateral inhibition
> would be from descending fibers, although I should point out that if this
> were the mechanism for lateral inhibition, anatomy tells us it would have
> to be through the superior olivary complex.
> 
> The truth is that no one knows what the descending pathway does, really.
> Cats can detect sounds at a -15 dB level (re SPL), at which power level the
> sound vibrations in the cochlea are about 1/10th of the average brownian
> motion. What this means in all likelihood is that OHCs are very unstable
> oscillators, that amplify very weak vibrations. Look at Bialek's article in
> Physics Letters A (1987 or so) to see an interesting analysis of the fact
> that a passive cochlea cannot account for our perception.
> 
> I should probably stop here! I don't want to go on and on...
> 
>                                         Didier
> 
> --
> Didier A Depireux                              didier at isr.umd.edu
> Neural Systems Lab                 http://www.isr.umd.edu/~didier
> Institute for Systems Research          Phone: 301-405-6557 (off)
> University of Maryland                                -6596 (lab)
> College Park MD 20742 USA                     Fax: 1-301-314-9920



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