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Re: candidates for the cochlear amplifier

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