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What is an auditory illusion?
Dear List,
Given the last email, it might be worthwhile agreeing on an acceptable
operational definition of what constitutes an auditory illusion. We might
then be able to decide if "The Case of the Missing Fundamental" is indeed
an illusion or a natural and predictable consequence of auditory (pitch)
processing; or indeed whether tinnitus is an auditory illusion or perhaps
even an auditory hallucination?
An often-used (circular) definition is simply that an auditory illusion is
the aural equivalent of an optical illusion, and though non-informative, it
at least has the advantage of using a reference that is well known to most
and reasonably well understood: we all know when we see a visual illusion
(?), and there seems to be no getting away from the fact that any
discussion/description of auditory illusions seems to always refer back to
optical illusions.
A (slightly) better definition, which at least attempts to set out the
essential attributes of the thing being defined, might be that an auditory
illusion corresponds to a listener hearing: (1) sound(s) that are not
present in the physical stimulus; or (2) so-called "impossible sounds". The
former definition is not overly helpful, as clearly the auditory system is
capable of generating (sometimes audible) distortion products in response
to an input sound, although it would work well enough for explaining the
"continuity effect"; and the latter definition needs further definition:
what constitutes "impossible"? Something that cannot exist in the real
world? But we don't perceive the real world; only the 'story' or narrative
our brain makes up from the (selected) sensory information available to it.
I would argue that for something to be called an auditory illusion, it must
include those general assumptions, based on organisational principles, that
the brain makes during perception/cognition. Accordingly, we hear an
auditory illusion when we misinterpret auditory sensory information. In
other words, auditory illusions tell us more about auditory cognition than
they do about auditory sensory processing: it is our assumptions (about the
real world) that lead us astray when we think we perceive an auditory
illusion. Any auditory effect (e.g., the missing fundamental) that can be
reasonably well understood as a consequence of what we know about
peripheral auditory processing is, I would suggest, not an auditory
illusion. The sensory information is not being 'distorted' or
misinterpreted in any way in these cases; our brainstems and brains are
only trying to give the best answer to sometimes conflicting or missing
information.
No doubt some people may not agree with me; however, in the absence of a
good working definition, any discussion of auditory illusions will be
severely limited.
Cheers,
Jose
On Aug 2 2011, Ranjit Randhawa wrote:
Dear Nedra,
In my opinion the most enduring (over 200 years) of all auditory
"illusions" is what has been called the "missing fundamental". The fact
that this has not been satisfactorily resolved by the tortured use of
existing signal processing techniques leads some, including yours truly,
to believe that the auditory system has figured out a unique way to do
frequency analysis and to meet the dictum in biology that "form follows
function". Taking into account where we are and the discussions that
take place, e.g. this forum, it is interesting that there has been no
discussion as to why the cochlear has the shape it does. Therefore some
experimental phenomenon that we may call as an illusion, could have a
very natural consequence of how frequency analysis is done. One is lead
to believe that we are truly very far from understanding how the
auditory system works and therefore hearing aid designs are a bit of a
hoax foisted on the "proletariat". Sorry if I sound a bit harsh, but I
think it is time people recognized that the emperor has not clothes.
Regards,
Randy Randhawa
On 7/30/2011 3:16 AM, Nedra Floyd-Pautler, LLC wrote:
My apologies for an over-active spell checker that changed "people" to
"proletariat" in my recent posting. Below is the message I intended to
send:
I'm a science writer/audiologist researching an article on auditory
illusions. What value do they have "on the ground" for people with
hearing deficits? Do what they tells us about the brain and hearing
have application to hearing aid design?
Thank you,
Nedra Floyd-Pautler
www.thenedra.com <http://www.thenedra.com>
--
José Ignacio Alcántara, PhD
University Lecturer
Department of Experimental Psychology
University of Cambridge
Downing Street
Cambridge CB2 3EB
UK
Tel: +44 (0)1223 764412
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Tel: +44 (0)1223 472126