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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.


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.
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
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