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Re: Is there considerable phase locking up to 6 kHz?

Now that I've read Eckard Blumschein's note about how maybe "Pitch
apparently relates to a kind of autocorrelation that is not based on
phase locking," I think I need to clarify Jan Schnupp's answer in
relation to Hi Cheng-Gia's question.

It is fair to say that "most auditory physiologists would be very
surprised if any mammal was found to phase lock appreciably to
frequencies above 4 kHz."  But this should NOT be interpreted to mean
that auditory neurons with a CF above 4 kHz will not show accurate
synchrony to high-frequency complexes with a lower pitch.  No phase
locking to frequencies above 4 kHz should be re-phrased as no phase
locking to sine waves above 4 kHz.

The original question noted that autocorrelation type mechanisms
could work for the "complex tones with unresolved odd-numbered
harmonics", "...if temporal cues for pitch extraction were assumed to
be maintained in the range of 4 - 6 kHz."  It should be noted that
even were the components resolved, there would be regions of the
cochlea responding with strong modulation to the beat envelopes, and
a pitch near the difference frequency would be expencted.
Furthermore, it doesn't take much synchrony to the fine-scale
structure of the 4-6 kHz components to induce autocorrelation peaks
shifted slightly from the envelope frequency.  Do we have good
experimental data on the degree of synchrony to such complexes?
Probably so, but it's been a long time since I looked.

Similar questions come up in binaural laterization by
cross-correlation.  It is impossible to localize sinusoids around 4
to 6 kHz, but if I recall correctly, complexes with enough temporal
structure in that frequency band can be localized quite well,
corresponding to time errors well under a cycle.  It seems to me that
if we can localize such sounds, then there must be enough synchrony
there to use for pitch extraction as well.


At 11:34 AM +0000 03/16/2004, jan schnupp wrote:
chen-gia tsai wrote:

Dear all,

I am working on the pitch perception of music sounds with dominant
upper odd-numbered harmonics.

... snip...

This finding prompts the question: is there considerable phase
locking up to 6 kHz?

Hi Cheng-Gia,
to the best of my knowledge, the answer to your prompted question is
that, unless you are a barn owl (who may phase lock up to 9 kHz),
the answer is almost certainly no. Auditory nerve recordings in cat
and guinea pig have shown rather similar roll-offs in phase locking,
starting at about 2 kHz or so (the curve rolls off earlier in guinea
pigs) and by 4kHz there is practically no phase locking left. I
don't know of any data from human auditory nerve fibres (for obvious
reasons, such data would be hard to come by) but I think most
auditory physiologists would be very surprised if any mammal was
found to phase lock appreciably to frequencies above 4 kHz.
Non-mammals typically do much worse than mammals. In this respect
(as in many others) barn owls seem to be extremely unusual, and they
should perhaps be reclassified as aliens from outer space.
When you mention that your stimuli lead to a perception of a rising
"melody", you may have to tread a little carefully. When you say,
"the musical pitch is ambiguous", some might argue that "ambiguous"
means there no longer is "pitch" in the strict sense, and hence
there is no longer "true melody". This isn't really my field of
expertise, but I believe that frequency discrimination limens get
much larger for frequencies above 4 kHz. If listeners can no longer
easily discriminate a semitone, are we still looking at pitch



Dr. Jan Schnupp
University Laboratory of Physiology             St Peter's College
Oxford University                               New Inn Hall Street
Parks Road, Oxford OX1 3PT, UK                  Oxford OX1 2PL
Tel (01865) 272513                              Tel (01865) 278889
Fax (01865) 272469