Re: Bite-induced pitch shift?

[Andrew Bell <andrew.bell@xxxxxxxxxx>]

Bekesy noticed something similar. If the veins of the neck are compressed,
the pitch of a tone can diminish by 2 per cent. [Physik Zeitschr. 30 (1929),
p.738; also reported in 'Hearing' by Stevens and Davis (1938), p.278].

I think this, and the bite-induced effect, can be explained as an effect of
pressure on the micromechanics of the cochlea rather than as a neural
effect.

My explanation is that manipulating blood pressure changes the pressure of
the cochlear fluids (because the fluids are in continuous hydraulic
connection with cerebrospinal fluid in the skull), and this has a direct
influence on outer hair cells, which are the basis of the cochlear
amplifier. We already know that changes in blood pressure, and resulting
intracochlear pressure, alter the frequency of spontaneous otoacoustic
emissions (see Bell, 1992, Hearing Research 58, 91-100).

As you indicate, conventional traveling wave theory has a problem seeing
how static pressure in the cochlea can have a frequency-shifting effect. One
proffered explanation is that the mass of the basilar membrane is changed
(via its vessels) when blood pressure alters. See Long and Talmadge, 1997,
JASA 102, 2831-2848. The alternative, that OHCs directly sense a.c. pressure
(and incidentally d.c. pressure), gives a more immediate explanation.
However, in this case the traveling wave theory is put aside and replaced by
a resonance theory of hearing, which I am currently developing. The resonant
elements here are speculated to be reverberating waves between neighbouring
rows of OHCs.

Andrew.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Andrew Bell
Research School of Biological Sciences
Institute of Advanced Studies
Australian National University
Canberra, ACT 0200, Australia
andrew.bell@anu.edu.au
phone +61 2 6125 9634
fax +61 2 6125 3808
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