Re: candidates for the cochlear amplifier (Eckard Blumschein )

Subject: Re: candidates for the cochlear amplifier
From:    Eckard Blumschein  <Eckard.Blumschein@xxxxxxxx>
Date:    Mon, 22 Oct 2007 19:20:50 +0200

Hello Matt, At the first glimpse I misunderstood the word list and thought why not using Jont's list for the nittygritty? I feel a bit guilty. A while ago Lionel Naftalin and Azzo Azzi sent to me their papers because they were not taken seriously elsewhere. Perhaps, they are wrong. I am unable to judge which suggested mechanism fits best. Being an electrical engineer, I wonder if the role of electrical phenomena is already clarified sufficiently. Azzi points to the cochlear microphonic. Is there anybody to whom I could redirect my Azzi papers? Is there new work by Fettiplace? The CRC-book 'Active Filters, Theory and Design' by Pactitis will perhaps not answer all our questions. I object to the attitude by Reinhard Frosch, Richard Lyon and others in so far as the word traveling wave should not be misused just because there is a common desire to defend an established erroneous concept. > After our discussion last week, I have made a new list of possible > physiological Cochlea Amplifiers (some of these are weakly > physiologically based). I currently count seven. > Can anyone think of other physiologically based CAs to add to the list ? > If so then please add them and change the subject line. > a] Oscillators : Van Der Pol type oscillators, which I believe began > with Johannesma [1] Explains high amplification. Weakness: No particular physical mechanism, does not explain propagation. > b] Squirting wave : Andrew Bell's Organ of Corti squirting amplifier [2] Technically inspired. Advantage: Focus on radial direction. Role of some mechanical resonance parameters neglected. > c] Dual resonance : Martin Braun's dual resonance model [3] If mechanics of BM would only protect hair cells, then one could not understand why mammals reach much higher frequencies. > d] Feedback amp. : Zwicker's feedback amplifier [4] No specified physiolgical mechanism. > e] Hopf amplifier : Hopf bifurcation augmenting the travelling wave [5,6] PRL prints any defense of TW. > f] Active TW : Active travelling wave amplifiers - of which I > believe there are many, I reference only one [7] Tautology in combination with defense of an obviously wrong concept. I would agree if we clarify that a bank of cochlear amplifiers amplifies the local mechanical mainly up and down as well as radial back and forth directed motion in a manner that looks like a wave that propagates longitudinally. > g] Active CW : Active compression wave amplifier. Of which I have > seen no complete models - as of yet. Cochlear activity indeed causes measurable OAEs, which are, however, most likely not yet the whole story. Compression waves would not act like tuned filters. In all: Neither of the candidates is already my only favorite. As long as there is no more detailed understanding, we have to ask what practical application a model might have. Models that predict reflected waves are presumably not appropriate. Non-linearity resides in the unidirectionality of hair cells. While at the time of Lighthill, unapt mechanical models were overly tweaked in order to by force fit psychoacoustic measurements, I recommend to conclude from directly measured data to what extent phenomena like tuning curve can be ascribed just to basilar membrane. Eckard Blumschein

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