[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Autocorrelation

Dear 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