Subject: purely spectral low-frequency pitch From: John Culling <jfc(at)BRENTWOOD.PSYC.CF.AC.UK> Date: Fri, 20 Oct 2000 09:32:56 +0100It 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. John. Dr. John Culling, Sch. of Psychology, Cardiff University, P.O. Box 901 Cardiff CF10 3YG Tel. +44 029 20874523 FAX +44 029 20874858 http://www.cf.ac.uk/uwcc/psych/CullingJ/