Subject: Re: Bite-induced pitch shift? From: Andrew Bell <andrew.bell(at)ANU.EDU.AU> Date: Fri, 20 Jun 2003 11:32:27 +1000Bekesy 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(at)anu.edu.au phone +61 2 6125 9634 fax +61 2 6125 3808 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~