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

Subject: Re: Wasn't v. Helmholtz right?
From:    Eckard Blumschein  <Eckard.Blumschein(at)E-TECHNIK.UNI-MAGDEBURG.DE>
Date:    Wed, 24 May 2000 10:27:24 +0200

Dear Richard Pastore, Thank you very much for your message! You are quite right, and bony conduction could indeed tempt the writers of textbooks to use it for a nice example illustrating the fact that the epi-phenomen traveling wave is independent of transmission through the oval window. Warren did not so. He wrote: "Even when the compression wave is made to travel in an antidromic direction from apex to base, the traveling wave still originates at the base and travels in the usual fashion toward the apex." Because, there is no obvious reason why the sound pressure due to bony conduction might be different in scala vestibuli and scala tympani, excitation must be mediated via vibration of the whole bony structure. Anyway, I pointed to a different question. When you correctly concluded that vibration of basilar membrane does not necessarily start at the oval window, you tacitly referred to location of input. When Warren also correctly wrote, it always originates there, he meant the location of the beginning. That is the point which I consider to be the source of rather common confusion. We have to clarify whether mechanics of basilar membrane must be thought and modeled as a genuine wave transmitting energy from base to stapes and possibly being reflected, or the organ of Corti rather acts on the basis of local mechanical response as suggested by v. Helmholtz. In order to avoid further confusion and finally decide the question, I recommend to at first separate the issues of mechanics (as reliably investigated by Mario Ruggero and Peter Dallos) and function (as for instance suggested by Braun) of the organ of Corti. Motility of the outer hair cells does not matter in that respect. Only if one trusts in local resonance, then the temporal structure of mechanical response to any stimulus can be easily calculated. Otherwise, one has to tinker with the buttons of a more or less flexible mathematical solution of the wave equation or with arbitrary elements of a corresponding transmission line model. I am not aware of any justification for that. In particular, the model of local resonance (as suggested by v. Helmholtz) is consistent with net delay of cochlea for condensation clicks as well as rarefaction clicks measured by Kiang et al (1965). BTW, I am aware that I share this opinion, at least in part, with people who are pondering about its publication. I would only approve such undertaking on condition of careful discussion within and eventual support by this group. What about bony conduction, the very little I am aware of can be summarized as follows: Sound is transmitted by fat in animals which are adapted to living in water. When sound in air impinges directly upon a liquid, a loss of about 30 dB takes place. That is why we need the middle ear at least up to 12 kHz. Cats' frequency response of stapes velocity drops sharply above 20 kHz. Bony conduction seems to be important for airborne input in excess of that value, application of a tuning fork to the skull, and perception of the own voice. Yours sincerely, Eckard Blumschein At 17:10 23.05.00 -0400, you wrote: >Dear Eckard: > A few decades ago, when I was a post-doc, I shared an office with >another post-doc who was developing multiple site recordings along the >cochlea. One of our discussions was about the traveling wave that von >Bekesy had observed, and that was evident in the multiple electrode >recordings along the cochlea. When I asked about the traveling wave, I was >reminded that, with bone conduction, sound reaches the cochlea through the >skull bone rather than the middle ear. Therefore, with bone conduction, >sound vibration reaches the basilar membrane through the bony structure of >the cochlea, rather then through the oval window. In other words, the >pattern of vibration within the cochlea does not require that the vibration >start at the oval window. I believe that this observation stems from the >work of von Bekesy. > I am not sure how directly this addresses your concerns. > Dick Pastore >---------------------------------------------------------------------------- >---- >Richard E. Pastore >Director, Center for Cognitive and Psycholinguistic Sciences >Professor of Psychology and Linguistics >Binghamton University (SUNY University Center) >Binghamton, NY 13902-6000 > > > >

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