Mechanisms of hearing (followup)

F. Frank LeFever flefever at ix.netcom.com
Sun Dec 13 20:30:56 EST 1998


Agreed. I think he is referring to frequency "sharpening", analoguous
to retinal lateral inhibition "sharpening" the fuzzy image which would
result without it (adjacent receptors getting a gradient of stimulation
from a punctate primary focus on one receptor).

Temporal resolution on the order of 30-40 msec is critical for
perception of stop-consonants, and impaired resolution at this level
(possibly via thalamic or even cortical abnormalities in the left
hemisphere) may underly at least some development language disorders
and dyslexias (I am fresh from my umpteenth lecture by Paula
Tallal--have followed her work for c. 2 decades--at NYU Ctr for Neural
Science, last week).

(see also my earlier reply to this query)

F. Frank LeFever, Ph.D.
New York Neuropsychology Group


In <750kgh$htv$1 at mserv2.dl.ac.uk> Eugene Leitl
<root at lrz.uni-muenchen.de> writes: 
>
>On 13 Dec 1998, TONYJEFFS wrote:
>
>The latency has got little to do with temporal resolution. It might
well
>be that the enhanced resolution is unavailable for short sound bursts.
For
>this experimental evidence should be obtainable.
>
>Regards,
>Eugene Leitl
>
>> My understanding is that the 'dead' cochlea has a frequency
resolution of
>> around 1/2 an octave, and in vivo it is the 'lateral inhibition'
provided by
>> the motile outer hair cells (OHCs) that refines this frequency
resolution.
>> 
>> Now consider the following: 
>> IHCs initially detect a sound pressure wave and send the information
to the
>> brain. The brain processes this data, and send instructions back to
the
>> appropriate OHCs.  The OHCs do their 'fine tuning' work, enabling
the
>> appropriate IHCs to accurately identify the frequency of the
incoming sound.
>> 
>> If that is approximately correct, I see a  problem:-:
>> There would be a delay of the order of milliseconds while (1) the
initial
>> information is relayed to appropriate brain nuclei, (2) The
information is
>> processed, (3) instructions are sent to the OHCs.
>> 
>> Several milliseconds delay seems rather a long time, particularly as
I think
>> (?) we can hear sounds of a shorter duration than this.
>> 
>> Is my description along the right lines? I suspect I'm missing
something!
>> Could  there really such a delay?
>> 
>> Thanks
>> Tony
>> 
>> 
>> 
>




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