Auditory Illusions and Cognitive Impenetrability

From: Walker, Guy (
Date: Fri Feb 21 1997 - 11:52:46 GMT

With regard to the course text, imparticular chapter three which
outlines "perceptual processes and computational reflexes," we had many
popular examples of visual "illusions" and so forth, but I believe a
good opportunity was missed out on when it was mentioned (only in
passing) that there is a lot less work on auditory "illusions." I think
that the text is incorrect in saying this because there is, in fact, a
whole branch of psychology dedicated to auditory phenomena, namelly
"Psychoacoustics." What makes this area of enquiry rather more
different is that auditory illusions are fully exploited commercially,
and in fact, I can give you some examples that (if I am correct) serve
to illustrate computational reflexes. Hey kids!, you can even try these
in the safety of your own home!

When you listen to your stereo, speak to someone on the phone, see a
film at the cinema, and if you are rich, listen to music on a Sony
Minidisc player, your "computational reflexes" are being exploited to
the full. Let me explain.

When you listen to your "stereo," the stereo effect is an auditory
illusion. The outputs of the two speakers are slightly different, but
nevertheless, it is the brain which creates the effect of, for example,
a singers" voice "appearing" between the two speakers. If you were a
physician, there is nothing particularly special about stereo sound,
the thing is, that it means something to the human auditory system -
perceptual modules, or whatever, are sensitive to the components of
stereo, and create the 3D sound illusion, and without you having any
real conscious control either.

A telephone, and a Sony Minidisc player exploit more or less the same
auditory phenomena. In order to cram thousands of telephone
conversations down a phone line, or to cram the contents of a 5" CD
onto a 3" Mini Disc you have to reduce the amount of data - but -
taking advantage of computational reflexes you can still recognise and
understand your friends voice down the phone, and the music still
sounds great on a Mini Disc even though there is half the amount of
data, plus all sorts of noise and trash with it.

The auditory system (particularly the perceptual decoding elements - in
this case referred to as computational reflexes), is actually very good
at filling in gaps (extrapolating) and hearing what it wants, or
expects to hear.

The crux of the matter is (and, sorry to bore you all with this one),
that now you are consciously aware of these auditory phenomena, next
time you see a film at the cinema, it won't sound ANY different even
though you now KNOW that ALL, (and more) of the above phenomena are
being used. Therefore serving to further illustrate cognitive
impenetrability, or the fact that your knowledge is not going to tell
your ears!

All this without recourse to the same old boring Muller-Lyer

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