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Re: New Scientist question and Pitch and pressure effects
Interestingly, I am just writing up a research project that has
specifically looked at the issue of pitch shifts with changes in ear
A study by Fritze (1995) in Acta Otolaryngol. [Stockh] measured
interaural pitch matching and varied the ear canal pressure in a single
ear using a tympanometer (0 vs +/- 4kPa). He reports an upward pitch
shift of around 0.7% using a 1kHz 60dB(A) pure-tone as the standard (in
the ear that the prerssure was varied) with +/- pressure.
SOAE frequency is also dependent on ear canal pressure and there is a
school of thought that the mechanical properties of the oval window,
which are dependent on tran-tympanic pressure, help determine the
frequency of SOAE, maybe by via an effect on the BM (?) (maybe some of
you OAE modellers can help on this one).
Anyway, I have done an experiemt looking at the influence of ear canal
pressure on 0.5kHz and 4kHz pure tones, also using interaural pitch
matching. No pitch shift at 4kHz although there was an effect on
thresholds (thus presumably the middle ear). At 0.5kHz one or two
subjects had a downward shift in pitch by approx 0.3%. Hopefully full
details of experiment will be published in due course.
Myself and my colleagues here have tried the jaw clenching thing.
Haven't observed anything. I think there is something in pitch shifts
due to direct middle ear influences on cochlea mechanics, although I'm
not convinced we are looking at an effect the size described by Corey
(as much as a semi-tone). If we limit ourselves to two options, either
the frequency of the tone changes on route to the cochlea (not likely)
or the coding of frequency is influenced. I am convinced that the
pitch-intensity effect was well controlled in my study. So, if it is an
influence on frequency coding is it place or periodicity? I can see no
reason to suspect periodicity. So then perhaps these middle ear
influences do affect place coding. If so, given that most of the
evidence is from pitch shifts at low frequencies, maybe this also
indicates that place coding is important below 2kHz after all? More
questions than answers unfortunately. This area certainly needs more
systematic research. If anyone else is working on this area or has got
any theoretical comments, please get in touch!!!
Institute of Sound and Vibration Research
University of Southampton