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Reduced Speech Discrimination Despite "Normal Hearing after Surge

Paul D Dybala dybala at utdallas.edu
Thu Oct 2 10:53:37 EST 1997


Jesudas J. Dayalan (DSJESUDA at BCSC02.GOV.BC.CA) wrote:
> To: AUDIOLOG--INTERNET audiolog at net.bio.n


> Hello Susan, Michael, Kimberly and others:

> What was reported is an interesting fact. I am sure all of us are aware of
> reduced speech discrimination in subjects with sensorineural hearing loss. I
> would urge you to read Journal of American Audiology Volume 4, Number 5. This
> was a special issue on Auditory deprivation.In case if you have not read it.

> Just like the sensorineural ears, ears with conductive hearing loss can also
> show auditory deprivation. I believe who ever posted that note has opened an
> interesting discussion. I have a child here who has unilateral congenital
> conductive hearing loss. Over the years her conductive hearing loss has
> increased in it's air bone gap and at the same time her/his speech
> discrimination has gradually become worse. We have fit this child with hearing
> aid and we are observing some improvement in her word recognition.

There has been a lot of talk about how a peripheral hearing loss
causes central plasticity changes in the auditory system.

I recently got runner up in a student writing contest when I wrote
a paper on this topic.  The compete paper is on my website
http://www.utdallas.edu/~dybala
and a condensed version was in last month's Hearing Journal
September 1997.

Some of the articles that I talk about are from the Ear and Hearing
Supplement that came out on auditory deprivation June 1996.

In some of the articles that I summarize they had induced cochlear
losses (and I think some conductive losses) in animals and saw dramatic
changes in the tuning of the Inferior Colliculus and Aud Cortex.

A hot theory in what causes tinnitus is that there is something
that happens in the peripheral or lower centers of the auditory
system (eg cochlear hearing loss) which causes a reduction or abnormal
impulses to be sent up to the brain.  The brain tries to figure
out what is this new signal, focuses on it (turns up the neural gain of
the signal) and perceives it as
tinnitus.  Currently, a professor here at Callier is performing
electrophysiological experiments to see if he can find evidence of this.

Dr. Pawel Jastreboff in Maryland has been on of the leading researchers
in this area and has developed a treatment plan where by low level
broadband maskers are worn to increase the overal level of neural
noise in the system so that the tinnitus "noise" is not as noticeable
and can be ignored and forgotten.

This is a radical difference from using a masker to cover up
the tinnitus, in that with the low level maskers you still
hear the tinnitus.  Over time though (12-18 months) the central
system "recalibrates" so that the tinnitus signals are forgotten or
ignored.  

This has been effective in about 80% of cases.

But I digress!

In the case of auditory deprivation in the  long standing
unilateral conductive loss that was repaired to 15 dB HL.

Stuart Gatehouse has theorized that auditory deprivation
is an effect of listening level as opposed to deprivation.

Example:

Traditionally auditory deprivation occurs when you have hearing loss
in both ears and good discrim.

If you aid only one ear and not the other, the discrimination score
for the aided ear will be good, but over time the unaided discrimination
score with diminish.

The use it or lose it effect aka auditory deprivation.
(as a side note we have all of our patients who decide
to be fit with monaural aids sign a diclaimer that they
have been advised about the benefits of binaural amplification
but that they have decided to be fit monaurally).

Gatehouse has hypothesized that what is actually happening is that
the aided ear is used to listening to sounds at a louder level than
the unaided ear so it will so better at suprathreshold tasks.


In the example of the conductive loss (for a long time) that 
was finally repaired. Even though it was a peripheral
problem,  there were certian to be central plasticity effects
due to the conductive loss that may take a long time to reverse or may
never reverse.

What I would recommend for this gentleman is
going over some communication strategies
and extra counseling on what to expect from this ear

-- 
Thank you for your support, 
Paul Dybala 
dybala at utdallas.edu
http://www.utdallas.edu/~dybala




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