Subject: Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave From: Andrew Bell <andrew.bell@xxxxxxxx> Date: Thu, 4 Oct 2007 14:44:21 +1000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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@xxxxxxxx ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -----Original Message----- From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx On Behalf Of Richard F. Lyon Sent: Thursday, 4 October 2007 12:35 PM To: AUDITORY@xxxxxxxx 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 > > > ----- Original Message ----- From: "A.J. Aranyosi" <aja@xxxxxxxx> To: <AUDITORY@xxxxxxxx> 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.