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purely spectral low-frequency pitch
It depends a little on your theoretical position about what auditory
processing gives rise to dichotic pitches, but, if you believe that they
are produced by a mechanism that detects interaural decorrelation (or
more precisely "incoherence"), then they are purely spectral pitches.
They only occur below about 1500 Hz, because (in part) the process of
analysing the correlation is dependent upon phase locking. The result
of this analysis, however, is a channel-by-channel coherence measurement.
So, a "purely spectral" pitch may be achieved by, for instance, replacing
one sub-band of a diotic noise at one ear with an independently generated
band of noise. The result is a noise which is diotic at most frequencies,
but uncorrelated in one sub-band. The stimulus at each ear is (and sounds
like) white noise. When both earphones are used, however, a distinct
whistling sound is heard above this noise. The pitch of this whistling
sound corresponds with the centre-frequency of the manipulated band.
Anyone fancy looking for it in A1?
See Culling et al (1998) JASA v103, 3509. and Krumbholz and Patterson
(2000) Br. J. Audiol. v34, 99. for arguments supporting the channel-by-
channel coherence-measurement mechanism, which is ultimately based on
Durlach's E-C theory.
Dr. John Culling,
Sch. of Psychology,
P.O. Box 901
Tel. +44 029 20874523
FAX +44 029 20874858