Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave

["Richard F. Lyon" <DickLyon@xxxxxxx>]

At 8:01 PM +0200 10/4/07, Eckard.Blumschein@xxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
> Look at what I am offering, the purely mathematical cosine 
> spectrogram. It can be imagined like an ideal so called filter bank, 
> a continuum of local resonators, and surprizingly, it shows in 
> response to a click epiphenomenal traveling waves, a propagating one 
> and stationary ones rolling on the spot at the harmonics, and phase 
> accumulation.

Eckard, this is true, and a point I've often made myself.  You can't 
really distinguish a filterbank model (causal filters like your 
cosine spectrogram) from a traveling-wave model, if they both have 
similar magnitude and phase transfer functions that model the cochlea.

However, I can't interpret that as you do, as surprising, or as 
evidence against the traveling wave.  Rather, I take it as an 
opportunity to make a simplified model, a model that describes the 
response at each location as the output of a linear parallel 
filterbank with common input from the stapes.  The next step is then 
to incorporate nonlinearities in a way that describes the real 
nonlinear behavior of the cochlea; it's here that the physics of the 
traveling-wave system can lead to cascade-filter models that 
incorporate nonlinearities in a natural way to give good fits to a 
wider range of data and phenomena.

Perhaps I'm too closed-minded about this stuff that I thought was 
settled a decade or two ago.  Maybe some day I'll have to do the work 
to do detailed comparisons of a good nonlinear cascade model against 
all the latest data of various sorts.  Or maybe some grad student 
wants to do that and I can help and advise...

Dick