Re: candidates for the cochlear amplifier

[Eckard Blumschein <Eckard.Blumschein@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

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