Mechanisms of hearing question

gene johnson gjohnson at rlc.net
Wed Dec 16 10:08:06 EST 1998


"Didier A. Depireux" wrote:

> First, I apologize for saying "The 7 green books"... 7 was the original
> plan, but by now they are at volume 11... Anyway, these books, in the
> Springer Handbook of Auditory Research series, are the state of the art in
> hearing (and of course many are already outdated!).
>
> F. Frank LeFever (flefever at ix.netcom.com) wrote:
> : find the time to look systematically at the distinctionns between
> : retina and cochlea that Didier describes, but a nagging question about
>
> Now, there are differences between the cochlea and the retina, but they may
> not be relevant. As a matter of fact, you can go a long way thinking of the
> cochlea as a one-dimensional retina that looks at the time-windowed Fourier
> transform of the acoustic waveform along a log-frequency axis.  That's the
> point of view of our lab, doing recordings in inferior colliculus and
> auditory cortex. I.e., the idea is that once you have gone beyond the
> sensory epithelium, hearing and vision use similar principles to decompose
> and analyze perception (for instance, we use auditory gratings to study
> single units in auditory cortex). The big difference btw cochlea and retina
> is the local iris provided by the outer hair cells, and the timescales
> involved (auditory nerve fibers lock to a stimulus up to 2 kHz, and have
> steady firing rates of up to 200 Hz).
>
> : to the idea that neural noise enhances detection of extremely
> : weak signals: is this relevant to the point Dider makes about cats
> : detecting signals below the level of Brownian movement?  Would this
> : make a sufficiently "non-passive" cochlea?
>
> I can only say this with certainty: stochastic firing enhancing signal
> detection has only been shown in batracians, where you have the advantage
> that you can change the noise level (by changing the temperature of the
> animal, therefor changing the thermal noise) and therefore study
> transmission as a function of the noise. I don't think (but I don't know
> for sure) that it's been shown in mammals. It could be used.
>
> However, the point about the OHC is that if you measure the pressure in the
> cochlea at a given frequency (at rest, with no stimulation), you find a
> gaussian type of noise. Nothing exciting there. But once in a while, we
> (mammals) all have these high pitch sounds in one ear, that last about 10
> seconds to a minutes, and that sound like a TV is being turned on. These
> otoacoustic emissions occur all the time, and we don't hear most of them.
> But if you record the pressure at the frequency of one otoacoustic
> emission, you will find a U-shaped distribution of the amplitudes, just as
> you would get from a sinusoidal oscillation. We know that these emissions
> are from the OHC... Draw your conclusions!
>
>

The subject emissions may be an active reference signal for an
interferometry-based control
system for spatial location.  Haven't been able to find out much about it, but
Holophonic
Sound,  an ultra-high fidelity 3-D sound imaging and recording technique,
includes a pair of reference signals at the ear locations on a human head model
used in recording.
Vestigial Bat Men, perhaps.  The nervous system is certainly  piggy-backed.
Looking for
citations.  The Holophonic secrets seem to be closely guarded, so maybe not
much is in the
open literature.

GJ


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