Re: Temporal encoding of pitch from resolved harmonics (Peter Cariani )

Subject: Re: Temporal encoding of pitch from resolved harmonics
From:    Peter Cariani  <peter(at)>
Date:    Tue, 17 Oct 2000 19:55:30 -0400

Hi Chris, Annemarie, Various groups of people use the terms spectral information and spectral cues in different ways. It helps to be clear about whether one is talking about 1) frequency-related structure in the power spectrum of the stimulus, (acoustical sense) or 2) frequency-based neural representations of the stimulus, (neurophysiological sense) or 3) the ability of listeners to discriminate different acoustic spectra (psychophysical sense). I know that it is an unwritten assumption amongst many psychophysicists that psychophysically-resolvable harmonics imply some kind of frequency-based neural representation (usually some variant of a rate-place representation, often sharpened up by using neural synchrony and/or lateral inhibition). That harmonics are resolved psychophysically does not necessarily imply that rate-place profiles in neural frequency maps (however one wants to construe these) will contain the information necessary to distinguish individual partials and to accurately estimate their frequencies (as one might do in a partial-matching task). There are alternative possible neural correlates of resolvability in neural interspike interval distributions which involve the ability of (putative) central interval analyzers to distinguish and recognize multiple interval patterns in a composite whole. For example, make a series of harmonic complexes of F0=100, in the series of 4, 4+5, 4+5+6+7,... or in the descending series 5, 5+4, 5+4+3, etc., and compute the autocorrelation functions of the individual partials (the autocorrelation of a sinusoid is a cosine at the same frequency). (For these kinds of low frequency stimuli and rough demonstrations of principle, the autocorrelation is not a terrible zeroeth-order surrogate for an ANF population-interval distribution). If one looks at the correlations between the autocorrelation of the complex and the autocorrelation of the harmonic of interest (say the 4th), the correlation drops greatly with the addition of extra harmonics, especially after 3 are added. Visually, the pattern related to the harmonic of interest becomes harder and harder to discern, and the auditory counterpart would be that it is increasingly harder to hear it out. It would be interesting to determine whether resolvability (and the effects of harmonic mistunings on fusion) can be accounted for in terms of correlations between interval distributions. Peter Cariani Peter Cariani, Ph.D. Eaton Peabody Laboratory of Auditory Physiology Massachusetts Eye & Ear Infirmary 243 Charles St., Boston, MA 02114 USA tel(at)EPL (617) 573-4243 tel(at)MGH (617) 726-5419 FAX (617) 720-4408 Email peter(at) Web: Chris Plack wrote: > > Hi Annemarie, > > > > >are there any studies reporting pitch extraction from low, resolved > >harmonics that can only be attributed to temporal phase locking but not > >to spectral encoding? > > Sounds like an impossible experiment! > > The very fact that the harmonics are resolved implies that there must be > spectral information. You might be able to argue about whether the results > are more consistent with a spectral or a temporal explanation (as many > have), but I don't think you'd be able to rule out spectral cues entirely. > At least not for a common-or-garden complex tone. > > I suppose you could construct the harmonics using bandpass AM noise at > different rates or something, but that would be cheating! > > Cheers, Chris > > ************************************* > Chris Plack - psychoacoustician, pop star > Department of Psychology, University of Essex, > Wivenhoe Park, Colchester, CO4 3SQ, UK. > Tel: (01206) 873493 > Fax: (01206) 873590 > > *************************************

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