Re: Effect of duration on pitch perception

[Erik Larsen <elarsen@xxxxxxx>]

Martin,

I don't agree with your reasoning. You say that the pitch of a complex
tone with F0 100 Hz is perceived faster than the pitch of a pure tone
with F0 100 Hz, and explain it by a smaller cochlear latency for the
higher harmonics of the complex tone. Then you go on to say that this
disproves place and pattern theories of pitch, because these would imply
slower pitch perception for complex tone vs pure tones, due to
additional processing.

First: Place/pattern mechanisms of pitch coding are not necessarily more
complex than temporal mechanisms, in fact, I would say they may be
simpler. It doesn't take much processing to detect neural activity at a
set of harmonically related frequencies. It doesn't matter that more
neurons activated because the processing can be done in parallel.

Second: According to your argument about latencies, the pitch of a pure
tone of F0 500 Hz should be perceived earlier than the pitch of a
complex tone of F0 100 Hz with 4 harmonics (including F0). Is there any
evidence for this? I would expect the contrary (see my third point
below). Also, there should be a rather large difference in the latency
of pitch perception between pure tones of F0 100 Hz vs 1 kHz, due to the
difference in traveling wave delay. Is there any evidence for this?

Third: A (more?) probable reason for the stated difference in latency of
pitch perception between complex tones and pure tones is due to the fact
that a complex tone provides much more pitch information than a pure
tone (because of the additional harmonics). Whether pitch coding is
based on a place/pattern or temporal representation, it is a fairly
simple matter to go through the math (which we won't do here) and show
that the estimate of F0, from a noisy peripheral representation of
harmonic frequencies, increases in accuracy as the number of harmonics
increases. Because we can also assume internal noise (in the neural
processing), the time window that is required to estimate F0 to within
that internal noise limit, from the noisy peripheral representation,
will be lower for a complex tone than a pure tone.

My conclusion is that a latency difference between pitch perception of
pure tones vs complex tones probably says nothing about the mechanism of
pitch coding, and the effect of traveling wave delays is probably small.

Erik

--
Erik Larsen
Speech and Hearing Bioscience and Technology
Harvard-MIT Division of Health Sciences and Technology
Cambridge MA


> There is a big difference between pure and complex tones, here. Pitch of
> the
> latter is discriminated much faster. For example, a pitch of a complex tone
> with a fundamental f0 = 100 Hz is perceived more than four times as fast as
> the pitch of a pure-tone of 100 Hz (Patterson et al., 1983). The probable
> reason is that cochlear and neural latencies decrease with frequency, which
> means that harmonics provide earlier periodicity information for the pitch
> detector than the fundamental.
>
> [By the way, these results should have been the ultimate death for all
> place
> and pattern theories of pitch, because these theories necessarily imply
> that
> f0 pitch should be discriminated slower than pure-tone pitch, due to the
> additional neural processing. Well, it's just one of the many examples in
> hearing research, where progress has been impeded for decades by massive
> self-amputation.]
>
> Patterson, R.D., Peters, R.W., Milroy, R., 1983. Threshold duration for
> melodic pitch. In: R. Klinke, W. Hartmann (Eds.), Hearing - Physiological
> bases and Psychophysics, Springer-Verlag, Berlin, pp. 321-25.
>
> Martin
>
> ----------------------------
>
> Martin Braun
> Neuroscience of Music
> S-671 95 Klässbol
> Sweden
> web site: http://w1.570.telia.com/~u57011259/index.htm