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
>
>http://psychology.binghamton.edu/faculty/pastore.htm
>
>