Audiogram defects (was Re: Cochlea -- quality of filtering)

susan moreland smorelan at MAGNUS.ACS.OHIO-STATE.EDU
Sun Sep 24 09:26:44 EST 1995

>All the discussion about "critical bands" is great, but let's not forget
>it is only a theory -  a model of the auditory system.  

to clarify, it's a model of the *peripheral* auditory system only.  

It is a good way
>to describe many characteristics of auditory processing but it is in no
>way complete.  The work by Kolarauch (' 90s) in off-frequency hearing is a
>perfect example of where critical band theory fails.  

actually, that's not quite true.  one of the beauties of the critical band
theory is that it *does* address the shape and size of the filters.
fletcher, in his original theory, assumed they were symmetrical, but did not
know for sure.  when patterson and moore created psychophysical tuning
curves they were asymmetrical, so patterson controlled for off-freq
listening by using notched noise.  when he did that, it forced the subjects
to listen to the filter centered on fs and the bands were shown to be

There is also a
>great article by Hall and Grose (JSHR, late 80's) showing the way we have
>measured frequency selectivity effects our estimates.  Also, if you
>include binaural processing there are many other factors to consider. 

sure there are.  the critical band theory just addresses the peripheral
auditory system -- specifically, what happens on the basilar membrane alone.
of course when you add in binaural factors everything gets infinitely more
complicated.  but that doesn't invalidate the critical band theory.  it's
good at describing what it intends to describe.

>study by Parker (1991) and another by Parker and Small (submitted JSHR)
>show that, in the older population, although word recognition may be
>decreased, binaural frequency selectivity stays equal to that of young
>listeners (hearing level was a controled factor). 

right.  i don't think anyone would disagree with you on that. critical bands
widen with hearing loss, not age.  antoher study by stover and norton (1993)
showed the same thing.
>I think it was a great question posed to the group - and a good follow-up
>question. Current data suggests the auditory system is capable of high
>tuning or frequency selectivity - what we need to answer now is which
>mechanisims are essential for that tuning and what role does the central
>system play?!?!?  
ahhh, *that's* the $64,000 question!  

>Just dropping in my 2 cents ...

we stroll together silently,
just the two of us -- my wolf and me...

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