Subject: Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave From: Eckard Blumschein <Eckard.Blumschein@xxxxxxxx> Date: Thu, 4 Oct 2007 20:01:27 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Quoting "Richard F. Lyon" <DickLyon@xxxxxxxx>: > At 2:44 PM +1000 10/4/07, Andrew Bell wrote: >> 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. > > Yes, that is the fundamental question, sort of. It's not like there's > some element that detects an "input" of 1 pm and amplifies to an > "output" of 1 nm; rather, there's a distributed amplifier that > multiplies up the power of traveling waves. At the low end of the > range, everything behaves linearly. As long as the noises of the many > hair cells are reasonably uncorrelated, the system will be able to work > to orders of magnitude below the level that would cause a "noticeable" > effect in a single hair cell. Ultimately, the shot noise of ion > channels, averaged over many OHCs, is what will set the sensitivity > limits; there's no "threshold" below which amplification stops working, > the signal just gets down below the noise. Signals below the noise are audible. In order to try an answer to John Bates, I would like to specify one of the decisive selection criteria in technical terms: denoising, more specifically: denoising at frequencies where hearing is most sensitive, i.e. about 1 kHz, sine. Of course, there are almost no pure tones of relevance in natural environment. However, high sensitivity is the basis for pattern recognition and localisation by ear. Comparison between a signal and its somewhat delayed copy is perhaps a most effective method of natural denoising. I looked at the structure of the organ of Corti and found several strange peculiarities: There are e.g. so far mechanically interpreted filaments joining the nth OHC with the n+1 th. In case of the mole rat, the nth joins the n+4th. Why? Why is there an angle of about 20° of the V-shaped bundles of hair cells relative to the radial direction? Why are afferent fibers projecting to more basal OHCs? I envision such details canditates for a more realistic while perhaps not necessary model of what seems to be evident: a pretty local resonance with predominantly radial motion of liquid back and forth. I do not understand: Why is someone like you who is a renowned expert for years not ready to clearly confess that the idea of a genuine mechanical traveling wave was proven wrong already by Thomas Gold? I don't exactly recall when he did so, maybe it was as early as in 1947. Kemp, Fettyplace, Geoffrey Manley, Steven Greenberg, and many others including Andrew, Martin, and Matt provided further mountig evidence. When I discussed with Mario Ruggero, he called phase accumulation the decisive argument, allegedly furnishing evidence for a genuine traveling wave driven by enery propagating from base to apex as calculated by Lighthill. Look at what I am offering, the purely mathematical cosine spectrogram. It can be imagined like an ideal so called filter bank, a continuum of local resonators, and surprizingly, it shows in response to a click epiphenomenal traveling waves, a propagating one and stationary ones rolling on the spot at the harmonics, and phase accumulation. So there is not a single argument against my judgement that the traveling wave is just a phenomen of local resonance. I cannot decide whether Andrem, Martin, or someone else already has a correct solution to the question how do the cochlear amplifier and the CB work in detail. I merely found out for sure that the idea of a genuine mechanical traveling wave is definitely at odds with reality. Let's be honest. Even if v. Békésy was correct with his guess that chochlea works like a mechanical traveling wave, having read this speech, I would argue that just he did not deserve the Nobel price. Lighthill for all that made a sound while inapt theory. Ruggero deserved the price for his intriguing measurements. However, my cosine spectrogram independently shows: The traveling wave is only an epiphenomenon. So the wild guess by v. Békésy was not only unfounded but wrong. One just needs courage to admit such obvious mistake. Helmholtz did not find local resonators. History of explanation how audition works has a record for wrong conclusions from seemingly missing physiological evidence. AJA of MIT claimed predicting power of the mechanical models. I rather doubt that it makes any sense to endless modify and tweak models that are based on tools, which are just available by chance but inapppropriate. The first one who insisted that the ear has to obey theory was Ohm. Peter Dallos was more prudent when he frankly admitted to examine his students every year with the same questions. No problem, the correct answers to give were always new ones. Regards, Eckard Blumschein