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Re: granular synthesis and auditory segmentation

R. Fabbri wrote:
> >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...

Few psychophysical experiments unambiguously demonstrate that
a particular neural mechanism is used, because there are
many possible neural mechanisms that can carry out the
same function. What they sometimes do, however, is show
that sole reliance on a given kind of neural information is not
sufficient to account for perceptual capability (which rules
out that coding scheme) or that psychophysical judgements
covary with the availability of  particular kinds of
neural information (which suggests but does not prove that
that particular information is used).

>From 3kHz to 5 kHz the quality of timing information as
well as tonality and frequency discrimination decline
precipitously. At 3kHz there is considerable phase-locking;
at 5 kHz it is much much weaker.

1. Phase locking and musical tonality covary.
 -- one can still make good octave
judgments if the upper tone is at 3 kHz, but this
becomes guesswork by the time one gets up to 5 kHz. When I made
a melody of pure tones whose upper tones descended systematically
from 10 kHz downwards, for me the melody became easily recognizable
only when the upper tone had a frequency  below 4 kHz.

2. Phase locking and frequency discriminations covary.
Models of frequency discrimination (Goldstein & Srulowicz
first-order interval model) that use phase-locked
information predict relative frequency jnd's as a function
of frequency in the 3-5 kHz range. If one extrapolates the
decline of phase-locking out to 10 kHz, these models predict well
the relative frequency jnd's out to 10 kHz. There are
caveats and complexities in the interpretation, but in general
human and cat jnd's decline with frequency in a
manner that is generally consistent with the decline of
phase locking, whereas rate place information shows the
opposite trend, getting relatively better as frequency increases.

But why should the burden of proof be placed on just one
putative coding scheme? What in your opinion is the
unambiguous evidence in favor of some other (name your
favorite) coding scheme in the 3-5 kHz range?

Peter Cariani

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