Please, no more "2-point descrimination": it is "discrimination",
"temporal" discrimination, and entirely different from two-point
discrimination!!
At least find time to read Tallal. Temporal resolution on the order
important for auditorally-based language appears to be at the thalamic
level, and the distinction between parvocellular and magnocellular
regions of the medial geniculate, if I recall correctly.
The order of magnitude which is important for speech seems to be
resolution of rapid formant changes across a span of 40ms: they carry
the information necessary for discrimination of stop consonants.
It may be that relevant refractory periods are such that those
intervening small blips are simply masked or over-ridden by activity
coding the longer ones; but your question does raise an interesting
conjecture--analogous to active inhibition of weakly stimulated cells
by a strongly stimulated cell surrounded by them, perhaps there is some
similar "sharpening" of the image in the auditory domain.
Don't know if it is relevant to this, but there is the well known
phenomenon of "categorical perception". For example: the difference
between the phonemes represented by "t" and "d" is a difference in
voice-onset time (VOT): the "stop" ends sooner and "voice" begins
sooner for "d" than for "t"; if one starts with a very brief VOT and
gradually lenghtens it listeners may continue to hear "d" long after
the VOT is longer than usual for a "d", but suddenly they will begin to
hear "t" instead--and vice versa, for long VOTs gradually shortened.
That is, sounds are categorized as either "d" or "t" rather than heard
as a contimuum of intermediate sounds. (Haskins Labs did most of the
research underlying this info about VOT, formant transitions, etc.).
(Haskins researchers and also Paula Tallal have been speakers at some
of our NYNG meetings)
F. Frank LeFever, Ph.D.
New York Neuropsychology Group
In <35FBA407.F3A20130 at writeme.com> Zoro <Duy at writeme.com> writes:
>>Thankyou for the detailed help. Unfortunately due to time restraints I
>won't be able to follow up on all your suggested reading (but as many
as
>possible :).
>>If possible, I would like your opinion on theories I have come up
with,
>with regards to auditory 2-point descrimination:
>(Forgive the 2nd year level niavity)
>>Looking at the auditory pathway, I first proposed that it may be the
>tympanic membrane and/or hair cells which is the limiting factor in
the
>ability to descriminate 2 sounds. Unfortunately, texts reveal that
hair
>cells are capable of handling up to 1Megahertz of vibration (our
results
>show fusion begins around 17 millissec), and is clearly not. Next I
began
>to look at the afferent fibers which connect to the hair cells, my
group
>advises me that they have an absolute refractory period of 1ms, still
not a
>limiting factor. From this I concluded (?) that it must be higher
brain
>functions that are the cause of the perception of fusion. My theory is
that
>since the noise in the middle is so small, the brain descriminates
against
>it, casting it aside as unimportant background noise. Perhaps like the
>blind spot in the eye?
>>~~~~ ~ ~~~~
>~ = noise
>>What do you think?
>>Regards,
>>Duy
>