Re: Autocorrelation-like representations and mechanisms (Christian Kaernbach )

Subject: Re: Autocorrelation-like representations and mechanisms
From:    Christian Kaernbach  <chris(at)PSYCHOLOGIE.UNI-LEIPZIG.DE>
Date:    Wed, 5 Mar 2003 08:22:25 +0100

Peter Cariani wrote: > most pitch phenomena do behave in a manner that is consistent with > an autocorrelation-like representation ... > discard all-order interspike interval representations on the basis > of very limited evidence that is interpreted in the most shallow way. ... Peter, You can imagine that I am once more disappointed to see how evidence against AC models is discarded as limited, and its interpretation as shallow. You name quite a number of phenomena that are accounted for by AC models. But science is not democracy: Evidence against a mechanism can not be counter-balanced by any number of studies where AC models do well. Here is a short summary of the evidence that is not compatible with AC models (for references see below): Carlyon (1996) demonstrates that mixtures of unresolved harmonics do not elicit two pitches, not even one, but just a crackle percept. AC models would predict that both pitches would be audible. Kaernbach & Demany (1998) show that second-order intervals are much less detectable than first-order intervals. AC models would not predict such a difference. Kaernbach & Bering (2001) replicate that finding with much lower cut frequencies, avoiding the criticism that this might concern only loci on the basilar membrane where temporal processing might be less important. It has often been said that our data disprove waveform AC, but not realistic auditory nerve fiber AC. But why then don't AC modelers test their models with second-order click trains and prove that they are compatible with the above data data? Pressnitzer et al. (2002) compared all-order interval (AOI) and first-order interval (FOI) statistics for the stimuli of the K&D study. Their figure 5 shows clearly that there is a big difference for ABX and X stimuli in both AOI and FOI statistics. So neither FOI nor AOI of auditory nerve data explain the low detectability of ABX stimuli. My guess is that if one takes into account the volley principle of temporal coding, by implementing a coincidence stage after the hair cell model, one would be back close to the waveform AC, with FOI showing no difference between ABX and XXX. This is not to say that AC models don't serve well for anything. They may be regarded a convenient short-cut to describe temporal processing, and as long as we don't have a detailed account compatible with all evidence (including the one you dismiss) it might be considered the best model we have. But we would have to keep in mind: It is a model, it is not the truth. There is evidence that it can not be the truth. Best regards, Christian REFERENCES ========== Carlyon, R. P. (1996). Encoding the fundamental frequency of a complex tone in the presence of a spectrally overlapping masker, J. Acoust. Soc. Am. 99, 517–524. Kaernbach, C., Bering, C. (2001). Exploring the temporal mechanism involved in the pitch of unresolved harmonics, Journal of the Acoustical Society of America 110, 1039-1048. Kaernbach, C., Demany, L. (1998). Psychophysical evidence against the autocorrelation theory of auditory temporal processing, Journal of the Acoustical Society of America 104, 2298-2306. Pressnitzer, D., de Cheveigné, A. Winter, I.M. (2002). Perceptual pitch shift for sounds with similar waveform autocorrelation. Acoustics Research Letters Online 3, 1-6.

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