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Re: granular synthesis and auditory segmentation
I'd like to thank you all for the lively discussion that
followed my somewhat provocative reply to Richard Fabbri:
> I don't know about your neurons, but mine completely fail
> to replenish their synapses above about 1 or 2 kHz even
> after plenty of coffee. Of course there is a role for
> non-Fourier type processing too, but no simple scheme
> covers the entire audible [20 Hz, 20 kHz] range.
After sending this note, I realized that reactions would
probably follow about the 4-5 kHz correlations in nerve
fibers, and I appreciated Peter Cariani's clear account
of the "volley principle" that easily explains how, e.g.,
1 kHz neurons can lead to higher frequency periodicities
in (stochastic) nerve activity. Also, I'd like to stress
that I do not favour either a place or temporal theory
of hearing, but I do expect (any) temporal processing to
occur mainly via the various auditory channels that first
result after mechanical (place-type) filtering has taken,
umm, place. Again in line with what Didier Depireux said:
> The half-wave rectification occurs _after_ the frequency
> decomposition performed on the basilar membrane, i.e.
> after you have decomposed the signal into frequency
Temporal information is still available in these channels,
so both "theories" can therefore be complementary, and
there are many indications that they *are* complementary,
with significant temporal processing at lower frequencies,
under 1 or 2 kHz.
I'd like now to present my simplified view of the world,
and would appreciate hearing from the auditory experts
how wrong my view is (totally wrong, or just inaccurate):
1. Human auditory neurons fail to replenish their synapses
above 1 or 2 kHz. (Just like I had already stated.)
2. The "volley principle" leads to higher frequency
periodicities in neural activity of the auditory
nerve, say up to 4 or 5 kHz. This is confirmed by
neurophysiological measurements (mainly in cats).
3. [My hypothesis]
The *higher* frequencies (say 3 - 5 kHz) that arise due to
the "volley principle" do *not* lead to *psychophysically*
observable effects, in spite of the fact that the higher
frequencies are measured *neurophysiologically* (invasively)
within the auditory nerve.
Reasoning behind my hypothesis:
- Psychophysical effects involve auditory processing
through much more wetware than only the auditory
nerve, and the initial phase locking *could* easily
be lost "along the road".
- Binaural masking level differences (MLD's) are
significant only up to 1 or 2 kHz (e.g., 1500 Hz
mentioned in Brian Moore's Psychology of Hearing).
My own informal auditory display experiments have
confirmed these values.
- Significant evolutionary pressure would be expected
to try and raise the above MLD transition frequency
to improve sound localization accuracy and cocktail
party type filtering, so if it still didn't get us
beyond 2 kHz there, why would it occur in any other
psychophysically observable auditory effect?
- Binaural phase detection also fails above ~1500 Hz.
Note that I am not an auditory perception expert, and I am
only trying to increase my understanding of the subject through
(my) conjectures and (your) falsification. I'd love to hear
about *psychophysical* auditory perception experiments that
unambiguously demonstrate temporal processing in humans in
the 3 to 5 kHz range! My expectation is that such results
have not been found...
Soundscapes from The vOICe - Seeing with your Ears!
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