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Re: mechanical cochlear model

Hello !

I, too, would be glad if the cochlear-mechanics discussion on the Auditory 
List could continue. If possible, the postings should be kept short.

Today I would like to continue my point-by-point comments
on the posting of March 7 by Andrew Bell:

>In addition to Martin's 2 pieces of evidence against the traveling wave
>model, we can add:
>2. The variation in stiffness is inadequate to tune the cochlea from 20 to
>20000 Hz. Three decades of frequency calls for a million times variation in
>stiffness (more than between foam rubber and tungsten), and this is in
>contrast to measurements of 2 or 3 orders at most. See Naidu & Mountain
>1998, Hear Res 124, 124. Bekesy found the value to be about a hundred-fold
>(p. 476 of Exp in Hearing). 

The human BM resonance frequency, f_BMR = (1 / 2pi) * sqrt(S / M) at
the base appears to be about 20 kHz. At the apex, however, that
resonance frequency may well be considerably greater than 20 Hz.

Both in post-mortem and healthy cochleae, the travelling wave does
not reach the BM resonance place. At given frequency >1 kHz the 
passive (active) response peak is basal of the BM resonance place
by about 1.0 (0.5) octave distance. In homo, that distance is ~5mm. 


Reinhart Frosch,
Dr. phil. nat.,
r. PSI and ETH Zurich,
Sommerhaldenstr. 5B,
CH-5200 Brugg.
Phone: 0041 56 441 77 72.
Mobile: 0041 79 754 30 32.
E-mail: reinifrosch@xxxxxxxxxx .