Subject: purely spectral pitch From: John Culling <jfc(at)BRENTWOOD.PSYC.CF.AC.UK> Date: Wed, 25 Oct 2000 18:37:58 +0100
I wrote... >> 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. Peter wrote... > But the output of the coincidence detectors also has time structure that > is related > to the pitch. If one runs these kinds of stimuli through a filterbank > and through > a binaural coincidence net (e.g. Huggins pitch, Bilsen multiple phase > delay pitch, other interaurally decorrelated signals, I did this several > years ago), > and one looks at the summary autocorrelation of the output of the > binaural temporal cross-correlator, > one finds that there are dips in the interval distribution at the pitch > period and > its multiples. There are two lines of evidence that suggest that the auditory system does not process such time structure. Krumbholz and Patterson (1999, 2000) showed that the lowest discernible pitch for complex dichotic pitches and for complex tones unmasked by the binuaral system is about an octave higher than the lowest pitch of stimuli that also provide temporal cues. This increase in the lower limit of pitch is to be expected from a mechanism that relies on spectral decomposition by the cochlea, because the ERB never gets below about 30 Hz and components less that 60 Hz or so apart cannot be resolved at any frequency. Krumbholz and Patterson (2000) and Culling and Colburn (2000) have found that binaural sluggishness applies to detection of temporal modulation of signals unmasked by the binaural system. In other words, it detects only the grossest of temporal structures. John.