Klarinet Archive - Posting 001191.txt from 2004/03

From: Tony Pay <tony.p@-----.org>
Subj: [kl] Musical Hyperspace, et al (was, pitch perception)
Date: Sat, 20 Mar 2004 12:53:18 -0500

In message <005901c40c41$393727a0$220018ac@wakeling>
"Joseph Wakeling" <joseph.wakeling@-----.net> wrote:

> What I was getting at is that perceived pitch is a very different thing
> from the waveform of the sound you are hearing. The waveform gets filtered
> through neural mechanisms which evolved to solve very different problems,
> so what we perceive is often rather different from what is "actually out
> there".

It's worth looking at what Joe is saying here from a more general point of
view. (I know he made an earlier, more general post himself, but his
emphasis there was slightly different.) There are two rather nice examples
of this point of view that I'll outline below.

> It emerges from the combination of the waveform with a "random noise"
> process that is a much older and more fundamental part of brain activity
> than the auditory system.

I think it's more helpful to regard the 'random noise' bit, which is a new
idea due to Joe's friend Dante Chialvo, as a neural trick that is one way of
extracting useful information -- 'useful' in the sense that it has survival
value -- from incoming data. The trick may well be used in the visual as
well as the auditory domain, as Joe points out elsewhere.

But brilliant as it undoubtedly is, that's a detail of a low level
description of how human and animal systems may do the job. Looked at on the
next level up, the fundamental underlying fact which has been known for some
time is that our perceptual systems are tuned by evolution to be more
responsive to some things than to others.

That's so simply because creatures that weren't sufficiently sensitive to
something that might be (1) a meal, (2) a mate, or (3) a predator, didn't do
so well as those that were more sensitive to that something.

Pretty clearly, selective systems -- ones that are more sensitive to some
things than they are to others, which they may well even ignore -- don't
represent accurately 'what is out there'. And as Joe says, that means that
things like drawing and music are inextricably human, because at least a part
of what they use for their effect is bound up with the selectiveness of the
systems we came to depend on for our survival.

How might that affect music? Well, our auditory systems are sensitive to
sounds that are harmonic because 'auditory scene analysis', which is to do
with the identifying of sound sources (animal cries in particular) requires
that sensitivity. So the harmonic series is inevitably involved in our
development of music.

This argument is particularly powerfully developed in an essay called,
'A journey into musical hyperspace', on the web as a pdf file at:

http://www.atm.damtp.cam.ac.uk/people/mem/papers/LHCE/lucidity-note-58.pdf

As Mike McIntyre, the author of that essay points out elsewhere, it might be
said that the harmonic series is to our auditory systems what straight lines
are to our visual systems. He gives a striking visual example of how our
internal models are tuned to 'straight line' aspects of reality that have
biological importance here:

http://www.atm.damtp.cam.ac.uk/people/mem/papers/LHCE/lucidity-preface.html

The description he appends to the 'walking lights' demo is pretty
unequivocal. But just think again of the degree of interpretation required
for us to see what we see. We have to impose the constraint that the
apparently moving collection of dots in two dimensions represents the
piecewise rigid motion of the ends of a collection of rods/limbs in *three*
dimensions.

And we don't do that just by recognising that 'it's a person'. We do the
same thing, for example, with just two dots moving diametrically opposite
each other round an ellipse -- which creates the illusion of a rigid rod
rotating about its centre in three dimensions; and with just two dots moving
diametrically opposite each other round a rectangle -- which creates the
illusion of a rigid rod rotating and twisting in a complicated
three-dimensional motion.

By the way, Mike is interested to know whether the 'hyperspace' article would
be at all useful to young composers starting to develop a technique. Has
anybody any assessment of that possibility?

Tony
--
_________ Tony Pay
|ony:-) 79 Southmoor Rd tony.p@-----.org
| |ay Oxford OX2 6RE http://classicalplus.gmn.com/artists
tel/fax 01865 553339

... Mary had a little lamb. The doctor was surprised.

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