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

[Andrew Bell <andrew.bell@xxxxxxxxxx>]

Dick:

The point is that we are talking about the input signal to the cochlear
amplifier. There has to be a passive signal (the effective stimulus) on
which the positive feedback process can work. The BM displacement that is
measured in a normal cochlea is _after_ amplification has occurred (remember
that AJ's original figure of 1 pm was derived from Ruggero et al. 1997 by
looking at their post-mortem data). 

So the fundamental question is, how can a normal cochlea detect 1 pm and
amplify it a thousand-fold (60 dB) so that we see a 1 nm displacement? I
agree with Martin that it can't, and there has to be some other, larger,
effective stimulus.


Andrew.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Andrew Bell
Research School of Biological Sciences
The Australian National University
Canberra, ACT 0200, Australia
T: +61 2 6125 5145
F: +61 2 6125 3808
andrew.bell@xxxxxxxxxx
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



-----Original Message-----
From: AUDITORY - Research in Auditory Perception
[mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Richard F. Lyon
Sent: Thursday, 4 October 2007 12:35 PM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: [AUDITORY] HC selectivity ... was Re: Physiological models of
cochlea activity - alternatives to the travelling wave


At 10:01 AM +1000 10/4/07, Andrew Bell wrote:
>Martin makes a telling point about the impossibly small magnitudes (1 
>pm) associated with a hydrodynamic traveling wave

The motion might be that small in a severely hearing-impaired 
cochlea, but in a normal cochlea it's probably about 60 dB bigger, or 
1 nm.  So I don't understand this strange straw-man.

Dick


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>
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----- Original Message ----- 
From: "A.J. Aranyosi" <aja@xxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Tuesday, October 02, 2007 8:59 PM
Subject: Re: HC selectivity ... was Re: Physiological models of cochlea 
activity - alternatives to the travelling wave


Dear Martin,

If we take Ruggero's [post-mortem] measurements (Ruggero et al 1997, figure
16) and extrapolate back to 0 dB SPL, the resulting BM displacement is about
0.15-0.5 picometers peak, or about 0.3-1 pm peak-to-peak.  [...clip...]  And
as the input of a feedback system with a gain of 60 dB...

Of course, this argument assumes a perfect, noiseless system.  With only
50-100 transduction channels per cell, and with each of them flipping
randomly between open and closed states, the transduction current will have
some "noise" associated with it.  Is this noise large enough to mask small
changes in the open probability?  I don't know.  Perhaps someone with more
knowledge in this area could comment.

-A.J.