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How does a hearing aid help?

Stephen Black sblack at HERA.UBISHOPS.CA
Fri May 9 14:00:33 EST 1997


I wonder if anyone would care to take a shot at this one:

There are two kinds of deafness--nerve deafness and conductive deafness.
In nerve deafness, the problem is damage within the cochlea, the auditory
nerve or at some higher level. Conductive deafness is due to impairment
before this point, usually in the middle ear. The nerve transmission part
remains ok. 

So it would seem that a hearing aid would be useful for conductive
deafness but not nerve deafness, and this is what most elementary
textbooks say. One curious exception is the text I use (Kalat, 1995, p. 
240) in which Kalat mentions hearing aids only in reference to nerve
deafness and says that they "can compensate for the loss". 

Nevertheless, some knowledgeable sources do say that hearing aids may also
be of value in nerve deafness. For example, Moore (1982) says that "the
condition [of nerve deafness] is usually not completely alleviated by a
hearing aid", which implies that it does help. Of all the sources I've
looked at (physiological psychology textbooks, specialized texts in
hearing), the most detailed statement I've found is in Matlin and Foley
(1992, p. 267-68). 

They say "A hearing aid would be useful for people with moderate levels 
of conduction deafness" [no problem there]. Then they say "A simple 
hearing aid would not help someone with complete nerve deafness, just as 
a pair of glasses would not help someone who has a detached retina [my 
understanding, also].

But then they say "Furthermore, if some hair cells are intact, a standard 
hearing aid can be modified so that it differentially amplifes the 
different frequencies" and go on to say "Thus, the design of a hearing 
aid for a nerve-deaf person must take care of two problems..."

So it looks as though hearing aids can be of some benefit even in nerve 
deafness. My question: I don't understand how. If anyone one knows, and 
particularly if they can supply a good source, I'd be interested to hear 
about it.

i can anticipate and reject one possible explanation that may be 
advanced. This is that if there is only partial damage to the hair cells, 
hearing function can be enhanced by more intense stimulation of those 
remaining through hearing aid amplification. But hair cells are tuned to 
different frequencies, so no matter how strongly those remaining are 
stimulated, they still cannot bring back perception of the missing 
frequencies. Is there another explanation?

-Stephen

References

Matlin, M. & Foley, H. (1992). Sensation and Perception, 3rd ed. Allyn
  and Bacon.

Moore, B. (1982). An Introduction to the Psychology of Hearing, 2nd ed.
  London: Academic.

Kalat, J. (1995). Biological Psychology, 5th ed. Brooks/Cole.

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Stephen Black, Ph.D.                      tel: (819) 822-9600 ext 2470
Department of Psychology                  fax: (819) 822-9661
Bishop's University                    e-mail: sblack at ubishops.ca
Lennoxville, Quebec               
J1M 1Z7                    Bishop's Department of Psychology web page at:                                                      
Canada                        http://www.ubishops.ca/ccc/div/soc/psy

                        "I'm a scientist. Certainty is a big word for me."
                                 -from the movie "Volcano"                
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