Re: Cochlea Amplifier models : a new list

[Gestur Björn Christianson <g.christianson@xxxxxxxxx>]

On 12 Oct 2007, at 11:05, Martin Braun wrote:

> Caution is good, but there is also something like reasonable  
> treatment of data. Both you and Erik have not mentioned the fact  
> that the peak split at 100 dB showed up in two separate experiments  
> in the same animal (Figs. 7A and 7B). Further both of you have  
> disregarded the finding that in both experiments (Fig. 7A and 7B)  
> there are two (Fig. 7A) and three (Figs. 7B) lower rate level  
> points between the two peaks, not one. Thus it is simply not  
> possible to attribute the findings of these authors to stochastic  
> fluctuation.

My point is that in the absence of variability data, it is impossible  
to say whether any of those points are lower than the others.  Your  
claim of the last sentence requires data the paper does not present.

> Further, the fiber responses in Figs. 7A and 7B show no sign of  
> saturation at all. This is seen in Fig. 7D only (different animal).

This depends on the variability in response.

> Most importantly, none of your or Erik's concerns question the  
> finding that the first fiber neural data do NOT mirror the half- 
> octave shift seen in basilar membrane (BM) behavior.

This is an unrelated point.  Based on principles and data that no one  
has yet questioned (that the auditory nerve fibres are connected to  
hair cells which in turn are driven by a limited region of the  
basilar membrane), there is no way that auditory nerve fibres could  
display a half-octave shift in tuning over short time scales; the  
maximum range of frequencies which can conceivably drive them is on  
the order of an octave or so.

I do not trust the maximum intensity curves in the Geisler et al  
data, primarily because of the methodological issues I mentioned.   
The lower intensity curves are consistent with a shift in preferred  
frequency with changing intensity.  The magnitude of this change at a  
single-fibre level, however, is not consistent with the magnitude of  
the effects you have described in the BM.

Bjorn