Re: Cochlea Amplifier models : a new list ("reinifrosch@xxxxxxxx" )


Subject: Re: Cochlea Amplifier models : a new list
From:    "reinifrosch@xxxxxxxx"  <reinifrosch@xxxxxxxx>
Date:    Thu, 18 Oct 2007 14:49:40 +0000
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Hello Dick Lyon and List, The main point of my long note of Oct. 17 is that the present state of cochlear mechanics is, in my opinion, not badly confused, in spite of the impression generated (on me, at least) be the posting of Matt Flax of Oct. 9 ("Cochlea Amplifier models: a new list") and the many reactions to it. Of the list (a, b, ... , f) presented in Matt's Oct.-9 posting, the last item ("active travelling wave amplifiers") appears to me to be significantly more plausible than the others. One can start with the Neely-Kim (1983) model, but one should replace the "TM (tectorial membrane) suspended on two springs" by a different second degree of freedom, namely by the "Hensen cell" resonator (spring = OHC's and maybe other nearby structures; mass = Hensen cells and other nearby structure; angle formed by RL and BM varies in its vibration). Fig. 1b of Mammano and Ashmore (1993) [see point 3 of my Oct.-17 posting] yields that this resonator has the required resonance frequency about one octave below the resonance frequency of the BM-resonator at the same place. The model builders should use the many admirable physiological experiments which have been done on the function of the inner-ear organs. I have not studied in detail the complicated mathematics of the models involving Andronov-Hopf bifurcations, but I fear that they tend to disregard at least a part of the detailed information supplied by those experiments, and I tend to agree with the conclusions reached by G. Zweig (2003) in his paper "Cellular Cooperation in Cochlear Mechanics" in the proceedings book "Biophysics of the Cochlea", A. W. Gummer, ed., World Scientific, New Jersey, etc., 315-330: "[...] the responses of these two systems [saccular bullfrog hair cells, BM of the cochlea] have little in common, even qualitatively. Nonlinear aspects of [mammal] hearing do not arise from a cochlea poised near a Hopf bifurcation. [...]" The passive peak and the active peak: One should always state (I think) whether one uses the panoramic view (fixed sine-tone frequency and sine-tone level at the stapes, variable distance x_b from the base on the BM) or the frequency domain (fixed x_b and stapes level, variable sine-tone frequency). In the panoramic view, the function of local BM vibration level (or "response", in dB) versus x_b of the wave generated by a soft or medium-loud sine-tone indeed shows a continuum (i.e., a profile) containing a broad passive peak (which stays there if the OHC's die) and, at a location x_b about 1.4 mm further apex-ward (for guinea pigs), an active peak. At 15 kHz and 55 dB, for instance, the active peak is (according to the mentioned data of Russell and Nilsen) higher than the passive peak by a BM-displacement factor of 10, i.e., by 20 dB. I shall reply separately to the points raised by Matt Flax. Reinhart Frosch. P.S.: One more correction, to my note "Correction ..." sent two hours ago: In line 9, replace "abscissa" by "ordinate". 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@xxxxxxxx . ----Ursprüngliche Nachricht---- Von: DickLyon@xxxxxxxx Datum: 18.10.2007 02:38 An: <reinifrosch@xxxxxxxx>, <AUDITORY@xxxxxxxx> Betreff: Re: AW: Cochlea Amplifier models : a new list Reinhart, I remain unclear on the point of your long note, interesting though it was. Are you saying that the passive peak and the active peak that are a half octave apart in cochlear mechanics are distinct things, or are you saying that they are two ends of a level-dependent continuum? I tend to believe the latter; do the data you describe tend to push the interpretation one way or the other? Dick


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Electrical Engineering Dept., Columbia University