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New Scientist question and Pitch and pressure effects
Daniel Rowan wrote:
> 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?
This was my first thought too. It would be really nice to have such a
simple and non-invasive (as long as pressure is good controlled;) way to
influence place codes, and then see how it influences pitch of various
sounds. Temporal code should not be affected at all.
There are several issues that need to be addressed. The pitch shift
phenomenon should be investigated such that other possibilites
(pitch-intensity confusion, pitch-intensity interaction) are excluded.
It should be established (perhaps not "beyond doubt" but at least to a
high plausibility) that this shift is due to changes of inner ear
Then one would need to find subjects that show this effect to a certain
degree and (most importantly) over a fair range of frequencies. If this
effect is, for instance, restricted to low frequencies only, it would be
nearly impossible to run purely temporal stimuli as controls: They
should cover the same basilar membrane region, but to a fundamental
which is 15 times lower so that after filtering and masking of
distortion products one would have a purely temporal signal. A
reasonable frequency would be 1 kHz, with f0=66Hz. A purely spatial
stimulus could be the Zwicker aftertone.
It seems to be a fairly interesting field, but I fear it will take more
than just a couple of experiments to get convincing conclusions.
- Christian Kaernbach