Re: Cochlea Amplifier models : a new list

[Erik Larsen <elarsen@xxxxxxx>]

The data in that figure (nerve response as a function of stimulus level, 
Fig. 7B) can be taken to suggest any number of things. Your 
interpretation is one possibility, but I could give you several others. 
For example, as sound level goes up, the fiber's response area broadens, 
especially towards lower frequencies. This would be entirely consistent 
with the BM tuning dependence on level, combined with a saturating 
response of the fiber. The fact that at 100 dB only (not 90 dB) there 
appear to be two best frequencies could be attributed entirely to the 
stochastic nature of the fiber response, i.e. at 5.5 kHz the response 
just happens to be a bit low (only 10% below maximum). There are no 
error bars so it is not clear whether this is a real dip in the response 
or not. My interpretation isn't any better or worse than yours if 
neither of us can offer a stochastic model of the fiber response that 
explains this data. Its all to easy to find features you are looking 
for, otherwise.

Another problem is that this data is from the 6 kHz CF place - I assume 
this is not in the basal turn for squirrel monkey so we really do not 
know the BM mechanics at that point.

Your conclusion (point 4) based on the paper you quote is therefore 
neither perfect nor obvious.

I'm sure the data is real, but it is incomplete, and explaining it not 
straightforward

Erik
> For an example, take Fig. 7B in this paper:
>
> http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=4215872&ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum 
>
>
> Here we see that at one single auditory nerve fiber recording site the
> firing rate was strongest at the lowest sound levels of 40 and 50 dB, 
> when
> the probe tones had a frequency 6 kHz. At a sound level of 100 dB the 
> firing
> rate was *again* strongest, when the probe tones had a frequency 6 
> kHz. Most
> interestingly, the data for the 100 dB probe tones show a second peak 
> at 5.2
> kHz. So, the neural data mainly reflect the OHC tuning, and 
> secondarily also
> reflect the passive BM tuning. At following stages of neural processing
> these secondary peaks are then filtered out by lateral inhibition.