Re: Cochlea Amplifier models : a new list

[Martin Braun <nombraun@xxxxxxxxx>]

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.

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).

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.

Martin



----- Original Message ----- 
From: "Gestur Björn Christianson" <g.christianson@xxxxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Friday, October 12, 2007 9:32 AM
Subject: Re: Cochlea Amplifier models : a new list


> On 11 Oct 2007, at 9:55, Martin Braun wrote:
> > A "stochastic model of the fiber response" is not needed. The rate  count 
> > figures are so high that their significance need not be  tested by 
> > further mathematics.
>
> This is a claim that requires justification, I think.  As a rule, 
> variability of response increases proportionally to the mean rate of 
> discharge.  While the proportionality is normally less than that seen  in 
> cortical areas, it is still significant.  In this case, as Erik  pointed 
> out, it is very important to demonstrate that the response at  5.5 kHz is 
> significantly lower that the response to the surrounding  frequencies, as 
> in the absence of that single point all that is  evident is that the 
> discharge rate saturates at 100 dB.
>
> In the context of this discussion, there is also a significant 
> methodological confound in this study.  Geisler et al. did not use 
> pseudo-random stimulus delivery.  Instead, they presented a single 
> frequency repeatedly, stepping up the intensity from the minimum to  the 
> maximum.  This raises concerns about habituation.  Note that at  both 5.5 
> and 5.75 kHz, you can see an increase in discharge rate with  increasing 
> intensity until the peak discharge rate of slightly more  than 250 
> spikes/sec is achieved, at which case response begins to  drop off. 
> Because of their methodology, this is a progression in  time, and 
> consistent with known spike-rate adaptation effects; thus,  even if the 
> response to 5.5 kHz at 100 dB is significantly lower than  the response to 
> surrounding frequencies, it potentially reflects  spiking mechanics and 
> not contributions from the cochlea (or  otherwise).  I'd suggest that 
> caution should be taken when trying to  interpret the highest stimulus 
> intensity plots in their data.
>
> Bjorn