Re: Pitch orientation-discriminating feature detectors? (Daniel Pressnitzer )

Subject: Re: Pitch orientation-discriminating feature detectors?
From:    Daniel Pressnitzer  <Daniel.Pressnitzer(at)IRCAM.FR>
Date:    Wed, 25 Sep 2002 18:24:29 +0200

Thanks for these sweeping comments... I'll try to provide a couple of precisions where I can. Al's comment: > On what scale were the frequency excursions? If it was a > log-frequency scale, A justification for the scale, as Laurent pointed out, would be that you cover approximately the same distance on the basilar membrane with a log scale. EEG studies I've seen nevertheless used a linear scale and they still found different responses to upward and downward glides. Pierre's comment: > Question re/ your new fMRI experiments on frequency change: What > cortical structures are you looking at? We are doing MEG at the moment and we only tried a 2 dipole model --you make the simplifying hypothesis that the magnetic field observed comes from 2 focal sources. The sources were where you would expect Heschl's gyrus, but we'll need the anatomical MRI for each subject to say something more interesting about the structures involved. About the relatively obscure reference, the work by Ruhm has actually been repeated and expanded by others. For instance, see: (at)Article{kohn78, author = {Kohn, M. and Lifshitz, K. and Litchfield, D.}, title = {Averaged evoked potentials and frequency modulation}, journal = {Electroenceph. clin. Neurophysiol.}, year = 1978, volume = 45, pages = {236-243} } Eckard's comment: I'd be more than happy with a peripheral explanation for the phenomenon, but I still don't feel there is a satisfactory one around. It cannot be masking by basilar membrane spread of excitation, because it would go in the wrong direction: you would expect more masking for peaks than for troughs. The travelling wave delay is rather small in comparison to the rate of FM over which the perceptual asymmetry can be observed. I'm still not sure how neurotransmitter release might do the trick. Martin's comment: In another unprobable reference, Horii (1989) observed that singers usually start their vibrato with an upward and not a downward glide. Possibly this has to do with muscular tension. (at)Article{horii89, author = {Horii, Y.}, title = {Frequency modulation characteristics of sustained /a/ sung in vocal vibrato}, journal = {Journal of Speech and Hearing Research}, year = 1989, volume = 32, pages = {829-836} } Wolfgang's comments: Thanks for pointing out this paper. If I'm not mistaken, the effect you found was only present for small frequency deviations. In contrast, the peak/trough asymmetry can be seen for deviations larger than one octave. This does not mean that the kind of across-channel combination of information that you put forward cannot occur in such a case (I believe it can) but this still needs to be formalised. Cheers, Daniel

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Electrical Engineering Dept., Columbia University