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Re: Cariani's question:"What is the visual analogue of pitch?"

Dear Eliot,

> I've come to find that a useful approach is one that
>analogizes from computer vision -- ie, hierarchically builds up larger
>entities -- "objects" -- from low level features --
>ie, things like orientational trends -- in a way that seems highly
>evocative of the patterns of computation

  Exactly the approach I believe in. I'm developing a model based on that idea. A hierarchical approach may explain auditory functions that are currently in a state of ambiguity.
  Implementing this idea requires identifying elementary objects that can function as the bricks and mortar for constructing the hierarchical structure. Photons are the elements of vision. What similar elementary object is there in sound? Finding that object could be the key to understanding the auditory process. (Epicurus around 300BC had a similar perspective.) In my approach I use zero crossings to define an elementary unit of sound. This method seems to work. Are there others?

>It would be useful to know, in this regard, whether we possess
>orientation-selective cells -- which doesn't seem implausible. If these existed, then almost certainly some sort of hierarchic computations would take advantage of these.  I haven't seen any research that directly supports
>this, though.

 With an elementary acoustic object it may be possible to describe the functions of your proposed orientation-selective cells that could populate the cochlea, and so on up the auditory pathway.

>pitch::space = audition:vision strikes me as much too simple. If I'm
>right in thinking that music is a kind of
>auditory system analogue to vision, then there are very mny more factors
>that need to be accomodated. The
>most important of these, I think, are "parallelisms" -- ie, repetitions
>(in structure, for instance, and potentially

   I agree that there are parallels between the basic functions of perceiving sight and sound. Time between events in sound is analogous to distance between objects in space. Conjectures in an elementary context could get somewhere in explaining how we hear. However, as seems to be the case now, focusing on an assumption of regularity between acoustic events (pitch) seems too confining to produce a general model of hearing. There's much more in the auditory scene than vowels and tones. Concentrating research on  pitch detection  isn't likely to lead to a credible auditory model but a credible auditory model should yield an excellent pitch detector.

-- John Bates

Time/Space Systems
Pleasantville, NY