Wasn't v. Helmholtz right? (Eckard Blumschein )

Subject: Wasn't v. Helmholtz right?
From:    Eckard Blumschein  <Eckard.Blumschein(at)E-TECHNIK.UNI-MAGDEBURG.DE>
Date:    Wed, 5 Jul 2000 10:43:02 +0200

Dear all who replied, I greatly appreciate all your valuable contributions. Unfortunately, I was not yet able to carefully respond to any of them. Nonetheless, the list might benefit from the most important hints I got privately. Jont Allen sent me a paper (1) entitled "Cochlear Signal Processing" to appear in a book to be published in a few month. I am not aware of any better review of history of one-dimensional cochlear transmission line models. Jan van Dijk pointed me to a paper (2) in TINS Vol. 21, No. 4, 1998, 159-167 by Nobili et al. The telltale title "How well do we understand the cochlea?" reminds me to the very insightful Peter Dallos who frankly admitted he was examining his students every year with the same questions. No problem, as long as the correct answers were different each time. Notwithstanding, the paper (2) nicely explains the formation of traveling waves in a manner that has been accepted for years. It also adds some interesting statements. For instance, hypothetical 250 kW/kg of OHCs outperform any technical engine. Now I am able to draw conclusions with respect to my questions (#134 of the archive): Wasn't v. Helmholtz right? ----Yes, in the sense, the dominant principle seems to be pretty local resonance. "Pretty" includes some details of interaction with the neighborhood like local stimulation by outer hair cells with non-linear responsiveness, and strong hydrodynamic coupling being presumably ten times stronger in radial (r) than in longitudinal (x) direction. Electrical memorizing effects are not excluded. Just a part of these details has been included in the term micromechanics. Is the traveling wave the result of energy transmission from base to apex inside basilar membrane or might it rather be an epiphenomenon, i.e. an attendant symptom of local resonance? ----No, the amount of energy that travels within the traveling wave from base to apex inside basilar membrane is definitely not appreciable. Zwislocki (1946 and 1948) was wrong. The 1D long wave theory is not appropriate. Present modeling of cochlear mechanics does not rely on that energy transfer. Instead, they assume vectors of individual pressure input p(x, t) and undamping (i.e. OHC) input u(y(x), t). With such inputs, even the 1D active model (see Boston-Univ.) could be reasonable. I understand and I respect Antony Locke who expresses the feelings of many people who possibly depend on outdated textbooks. On the other hand, I do not consider it justified to take obviously wrong views as a gospel. For instance, Ohm was wrong in his dispute with Seebeck. Fletcher (1924) was wrong when the tried to defend Ohm's position, etc. Having roughly outlined my position with respect to the basic question, I feel obliged to briefly acknowledge the forward-looking contributions to the subject by A. Bell, M. Braun, A. Dancer, A. Hudspeth, N. Todd, and R. Warren. Meanwhile, some doctrines have been put into question, and focus has shifted on tectorial membrane. I recommend for laymen www.iurc.montp.inserm.fr/cric/audition. and www.bcm.tmc.edu/oto/research/cochlea/Volta. Thanks to Stefan Uppenkamp, I understood that the claimed compensation of cochlear delay obviously happens within the auditory pathway, not within cochlea itself. What about the dispute between Dancer and Ruggero, I realized very good agreement between measurements by Dancer et al.(1997) and the prediction by Nobili et al. (1993). So I just quote Dancer: "It is now possible to re-examine the interpretation of some cochlear physiological phenomena: i.e., the latency of neural response, of the evoked oto-acoustic emissions and distortion products..., according to the actual hydromechanical behaviour of the cochlea." I quote from (2): "For oscillatory motion, at the characteristic frequency, the coherence length (that is, the distance over which a transversal section of the tectorial membrane will appear to move as a single structure) is about 120 micrometer at the base and 1.2 millimeter at the apex of the cochlea. Both these figures are in excess of the corresponding tectorial membrane thickness, implying that it oscillates like a solid mass attached to the top of the OHC stereocilia bundles." I further quote from (2) concerning auditory nerve pattern in cats listening to the vowel a (Secker-Walker and Searle 1990): "The patterning suggests that groups of fibres respond similarly, even though their characteristic frequencies might differ by nearly an octave. " I largely share a comment by Vercoe (in Perception and Cognition of Music) on this important effect but I suspect that the pattern resulted from some repetitions. If so, my conclusions were slightly different. May I ask for hints to some more of such measurements? I merely know Shamma (JASA 1985). Thank you very much, Eckard Blumschein

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