Re: Bite-induced pitch shift?

[David Mountain <dcm@xxxxxx>]

The von Bekesy result (compression of veins causing a 2% reduction in
pitch) was most evident for low tones of moderate intensity. The
perceptual phenomenon of pitch apprears to depend on both the spectral and
temporal properties of the stimulus.  Therefore, the pitch shift observed
by von Bekesy could be the result in a change in some aspect of temporal
processing rather than a change in cochlear mechanics.  If the effect is,
in fact due to a change in temporal processing, then you would not expect
t observe it for frequencies above the auditory nerve phase-locking limit
(~2 kHz). If the pitch-shift effect is due to pressure changes altering
cochlear mechanics, then perhaps the pitch effect is related to the
fluctuating low-frequency hearing loss that is commonly associated with
Menieres syndrome.  This hearing loss is commonly thought to be due to a
static displacement of the basilar membrane caused by increased
endolymphatic pressure (endolymphatic hydrops).

Small static displacements of the basilar membrane would not cause a
significant change in stiffness (see Olson and Mountain, 1991, J Acoust
Soc Am. 89:1262-75 as well as our other basilar membrane stiffness papers
for examples of stiffness-deflection curves).  Static deflections
would, however, be expected to alter the operating point of the outer hair
cells since the sensitive region of the hair cell transducer
characteristic spans only a fraction of a micron (Russell et al., 1986,
Hear Res. 22:199-216).

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David C. Mountain, Ph.D.
Professor of Biomedical Engineering
Boston University
44 Cummington St.
Boston, MA 02215

Email:   dcm@bu.edu
Website: http://earlab.bu.edu/dcm/
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