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Re: BM motion

Yes, it is also possible to model the effect (low and high side 2TS) using passive models.

David Mountain wrote: 
Conventional traveling-wave theory does account for high-side suppression.
In an active cochlea, as the traveling wave approaches its best location,
it is amplified over a region basal to the peak. If the suppression tone
excites this basal region, it will interfere with the amplification
process.

For more information on the spatial extent of high-side suppression, see:

Javel E, Geisler CD, Ravindran A.
Two-tone suppression in auditory nerve of the cat: rate-intensity and
temporal analyses  J Acoust Soc Am. 1978 Apr;63(4):1093-104.

--------------------------------------------------------------------

David C. Mountain, Ph.D.
Professor of Biomedical Engineering

Boston University
44 Cummington St.
Boston, MA 02215

Email:   dcm@xxxxxx
Website: http://www.bu.edu/dbin/bme/faculty/?prof=dcm
Phone:   (617) 353-4343
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Office:  ERB 413
On Wed, 14 Nov 2007, Matt Flax wrote:

Hi list and Richard,

Travelling waves have no mechanism for high side suppression...
it is simply not possible.

Clearly in the literature [1] last paragraph for example ... here
is an excerpt :
... neither models nor experiments have yet answered what
is perhaps the central question of mammalian cochlear
physiology, namely, the origin of the CF specificity of
two-tone suppression and other mechanical nonlinearities.

I have other references.

[1]
@ARTICLE{Ruggero:1992,
  author = {Ruggero, M.A. and Robles, L. and Rich, N.C.},
  title = {Two-tone suppression in the basilar membrane of the cochlea:
mechanical
	basis of auditory-nerve rate suppression},
  journal = {Journal of Neurophysiology},
  year = {1992},
  volume = {68},
  pages = {1087-1099},
  number = {4},
  month = {October}
}


On Tue, Nov 13, 2007 at 08:22:06PM -0800, Richard F. Lyon wrote: 
No matter how the nonlinearity affects the tone amplitudes, the sum of two
sinusoids of different frequencies is easily distinguishable from a larger
single sinusoid, through the temporal pattern, which will be appararent in
the auditory nerve firing-time patterns, even when both frequencies are
higher than can be coded by synchrony.

As to the nonlinearity, it shows up clearly in the mechanics, when the OHCs
are functioning, and it's not hard to see how OHCs in one region can change
the response to other tones that travel through that region to be localized
further on; that is, how high-f can suppress low-f if not too much lower.
The other direction works slightly differently, but the key is that
different frequencies share the same traveling wave medium that amplifies
them, so you get suppression.  There may yet be mysteries in the
micromechanical details, but not in the overall functional effect.

Matt, is the "'frequency specificity' mystery" something that you find in
the literature?  Or do you just mean you haven't found a clear enough
explanation?

Dick 
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