Subject: Re: Autocorrelation From: Christian Kaernbach <chris(at)PSYCHOLOGIE.UNI-LEIPZIG.DE> Date: Wed, 19 Jul 2000 07:19:03 +0200Dear Peter, > > Please forgive me that I will not enter into this discussion in this > > detail. ... > I would not want to waste any more (than 10 minutes) of your time > regarding these broader issues, I did not mean to discourage the discussion of broader issues. > In any case, we don't throw out the Copernican model because we > observe that the orbits are ellipses not circles, and that the sun is > not exactly at the center of the solar system. One doesn't go back to > epicycles (or to spectral pattern mechanisms) because of such > observations; one refines the models. Once we knew it's ellipses we would no longer state it's circles. Rejecting autocorrelation models would not mean "to go back to spectral pattern mechanisms". I think we are in want of a temporal model that shows an asymmetry between first- and second-order regularities. I guess that such a model will not be realizable with any sort of (neural) autocorrelation. Sure, such a model should ... > involve the neural substrates of auditory percepts that encompass > phenomena other than the masking of these click trains ...but it should also encompass those little click train observations. I really don't want to overemphasize the importance of the findings of K&D, but when I am called to the defence of our paper, I defend it. > The tails of tuning curves come into the present discussion partly > because K & D used low-pass noise, and this low-pass noise also has > the effect of masking the pitch produced by higher partials, thereby > lowering its salience and making the task more like a pitch detection > near threshold rather than the masking of a more salient pitch well > above threshold The use of low-pass noise is indispensable. A major argument to assume that there is a second mechanism involved in pitch perception working on unresolved harmonics (let's call it "mechanism B") is the increase of the JND once resolvable harmonics are excluded. Exclusion means: down-filtering _and_ masking. As long as harmonics well below 15 Fo (say at 10 Fo) are either present or not masked, the improvement in JND by a factor of at leat five indicates that we have not yet isolated "mechanism B". This is nicely illustrated in our paper under revision (Bering & Kaernbach). For the same reason, Houtsma & Smurzynski used pink noise that was not even low-pass filtered. Anyway, as we employed high-pass filtered click trains there should be regions where the signal is relatively undisturbed by the low-pass filtered noise. And the use of low-pass noise does not offer a plausible explanation of why first- and second-order regularities should be treated differently. - Christian Kaernbach