ABR Evaluations

Jeffrey Sirianni audioman at HCTC.NET
Tue Nov 12 23:38:53 EST 1996


In reply to:

>From: Kate Johnston <Kate at ricochet.net>

>Jeffrey Sirianni wrote:
>> 
>> {Joel R. Bealer writes:}
>> 
>> >Does anyone else see the problem here? Since when do we qualify
>> >normal hearing with a threshold ABR? I am about 6 months removed from
>> >clinical settings (now working in occupational audiology) however, as
>> >I recall, all ABR recordings are repeated for the basic reason of
>> >validity.
>> 
>> I guess it depends on patient history (re: possible psuedohypocusis), but
>> I agree that ABR results cannot be used to prove normal hearing, just as
>> normal OAE results cannot prove normal hearing.
>> 
>
>I have a question here. I am NOT an audiologist. I have had a severe 
>hearing loss since birth however, AND I am the mother of an autistic 
>son.
>
>When you say ABR results cannot be used to prove normal hearing, what 
>exactly are you saying? And what exactly is a 'threshold ABR'?

Many people consider "hearing" as a behavioral perception in that it will
elicit a cognitive or behavioral response.  It is the act of hearing that we
measure using audiometrics, although a failure to respond audiometrically
does not necessarily mean that one is not able to hear, only that the
testing did not elicit a behavioral or cognitive response.  Using an
example, an autistic child may not respond during audiometric testing
although the hearing mechanisms are still intact and functioning.

Turn the coin over and look at ABR testing.  The recording of the ABR is
somewhat complicated, but it involves measuring brainwaves that arise when
the auditory system is stimulated.  A positve ABR result (recordable
brainwaves in response to sound) only implies that the auditory mechanisms
are intact (even if behavorial responses during audiometric testing is
absent).  Now spin the around and consider the implications of a negative
ABR (no recordable brainwaves in response to sound).  The implications are
two-fold being (1) the auditory mechanism is not functional (hearing loss)
or (2) the auditory mechanism is functional, but there is no synchronization
of the waves, so that the peaks in the waveform are not seen (flat or
negative ABR).

If one looks at audition in this fashion, the ABR cannot prove or disprove
normal hearing sensitivity or hearing loss, it only tells us about the
auditory mechanism itself.

Back to your question, threshold ABR measures tell the examiner how soft the
stimulus can be presented whereby recordable brainwaves can be detected.  It
gives information on predicting behavioral auditory thresholds, when
reliable behavioral responses cannot be obtained.

>Before my son was diagnosed as autistic, we thought he might have a 
>slight hearing loss. Myself being hearing impaired since birth, I had 
>observed him carefully, and was convinced he was not deaf, but he 
>*could* be hard of hearing, like his mother.
>
>He was given a hearing test in a soundproof booth, sitting on my lap, 
>while playing with a toy. When sounds were piped into the soundproof 
>booth, he was supposed to respond by looking up, and would be 'rewarded' 
>by seeing a teddy bear in the corner light up. There were sounds that 
>made *me* jump with pain that he had no response to whatsoever.
>
>We were told our son was deaf, and when we questioned the results, the 
>test was repeated, under the same conditions, with the same results. 
>Because we still questioned the results, we were sent to Stanford for an 
>ABR.
>
>Getting my son medicated for the ABR was traumatic for all of us, and I 
>wouldn't want to wish that experience on anyone. However, he finally 
>did fall asleep, and the test was begun. He woke up before the test was 
>fully completed, but the technician said she had enough data to verify 
>that he had normal hearing in both ears.

Or in other terms "His hearing mechanism is functioning at a level that
suggests normal sensitivity, although he does not respond to the stimuli as
expected due to his autism".

>Is this different from what you are saying? Recognizing, of course, 
>that autism is different from hearing loss. My own audiologist was 
>shocked when I told her about the autism diagnosis: from her own casual 
>observations of my son, she was sure he was deaf.

It is IMPORTANT that clinicians report all of the implications when giving
test results.  A non-responsive child to audiometric testing is not
necessarily deaf, only that he or she did not respond to the stimuli.
Possible causes for this: deafness, autism, or behavioral responses not able
to be elicited.  The same goes for ABR testing:  A positive ABR implies only
that the auditory mechanism is functioning, and that auditory information is
being processed in the brainstem neural centers responsible to processing
and relaying auditory information.  A negative ABR implies that the a
synchronized neural signal could not be detected during the testing for
reasons listed above.

>She did tell me, however, that the ABR doesn't test for all ranges of 
>sound -- I think she said it tests for only the high-frequency sounds? 
>She suggested that since my son had such a high-pitched voice, that 
>maybe he wasn't hearing those sounds? Or something like that. This was 
>almost a year ago, so I can't remember exactly.

The ABR is dependent on the high frequency auditory mechaismand tells us
little about low frequency functioning.

>My concern now is that my son is starting to say a lot of words, very 
>few of them are clear, especially frustrating to me with my own hearing 
>impairment. He seems to be able to say 'b' words very well: button, 
>balloon, bagel (which to me sounds like 'bago'), etc.

If you ae concerned, ask your child's audiologist to make a speech and
lanuage referral so that a speech patholgist can determine whther his speech
and language is age-appropriate or delayed.

Jeff

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* Jeff Sirianni, M.A., CCC-A           *
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