Re: Physiological models of cochlea activity - alternatives to the travelling wave

[Matt Flax <flatmax@xxxxxxxx>]

Hi Richard and the list,

The active travelling wave has some issues ... for example :
a] The delay associated with the active response is more then ten cycles [1]
   according to electrical measurements the delay should be very small [2].
b] Travelling wave activity is too localised ... basally located 
   activity is required whilst the localisation has no mechanism of 
   communicating this across the BM to the basal location. [No reference 
   - common knowledge that basal activity is required]
c] Active phenomena exist in animals which have no Basilar Membrane ! 
   For example DPOAEs. Shera's current model of DPOAE generation [1] is 
   heavily dependent on the BM and other reflection points ... which 
   requires a distributed active region ... see point 'b]' again.

So for these reasons, travelling wave activity is still questionable ... 
I have other reasons, but these I save for my thesis.

Hopf models are mathematical augmentations to travelling wave models of 
activity ... so your statements on Hopf models are going to cut at the 
foundation of localised travelling wave activity...

I do not wish to discredit people who have localised second filter 
models ... I see them as having affect. I do believe however that the 
second filter models don't model activity as well as other methods - 
which we are still searching for...

Matt

[1] @ARTICLE{shera:2005,
  author = {Shera, C.A. and Tubis, A. and Talmadge, C.L.},
  title = {{Coherent reflection in a two-dimensional cochlea: Short-wave 
versus
	long-wave scattering in the generation of reflection-source 
otoacoustic
	emissions}},
  journal = {The Journal of the Acoustical Society of America},
  year = {2005},
  volume = {118},
  pages = {287},
  publisher = {ASA}
}

[2] @ARTICLE{Wilson:1980,
  author = {Wilson, J.P.},
  title = {Evidence for a cochlear origin for acoustic re-emissions, 
threshold
	fine-structure and tonal tinnitus},
  journal = {Hearing Research},
  year = {1980},
  volume = {2},
  pages = {233-252},
  number = {3-4},
  month = {June}
}


On Wed, Oct 03, 2007 at 12:26:10AM -0700, Richard F. Lyon wrote:
> At 12:57 PM +1000 10/2/07, Matt Flax wrote:
>> Current physiologically based models incorporate feedback. Alas a
>> majority of them are dependent on the traditional travelling wave
>> process. This is not a problem however, I can use the travelling wave as
>> a passive mode of input if the research community suggests it is the way
>
> Why would you consider a passive travelling wave, when an active one is 
> much better, more plausible, and not hard to model?
>
>> Perhaps the biggest problem with feedback models is that they don't
>> specify the physiological correlation between the feedback and the hair
>> cell, Organ of Corti nor Cochlea.
>
> You mean there's not a well established micro-mechanical mechanism for how 
> the OHCs push back on the BM with an appropriate phase? Maybe so, but 
> functionally it's pretty clear what has to be modeled. Chuck Steele at 
> Stanford has some credible-looking micro-mechanical simulations, as well.
>
>> Here are some feedback models with no physiological basis for the
>> feedback :
>> a] Zwicker's fantastic model - which begins with the travelling wave [1]
>> b] Hopf bifurcation models - which augment the travelling wave. [2] for
>>    example.
>
> The Hopf thing (Thomas Duke & Frank Julicher paper) seems to lead to a 
> way-too-sharp filter when the gain is high.  With feedback that is not 
> highly tuned, not near local oscillation, but with distributed 
> amplifiication of the traveling wave, you can get much more realistic, not 
> too narrow, filters.  The system can still have oscillations, or near 
> oscillations, if points of damage cause reflections.
>
> Dick

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