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Re: comparison of vision and auditory system

Richard, right!

as Lloyd Jeffress used to point out, if (1) it takes a millisecond or so
to cross a synapse, (2) there is some reasonably proportional variance in
that crossing time, and (3) there are several synapses between cochlea and
cortex....then you'd darned well better extract any microsec-level
temporal information early on in the system, because it won't be in very
good shape further on...if it can be found at all.  (Lloyd probably said
it more simply)  That was the point in putting his "coincidence detector"
in the medial geniculate, and then later moving it down to the superior


On Fri, 30 May 1997, Richard Lyon wrote:

> >Jont Allen <jba@RESEARCH.ATT.COM> wrote:
> >> ... The frequency JND is very small, but the acuity of temporal events
> >> is suprisingly bad.
> I find this point cited often, but the notion of temporal events is not
> usually clearly pinned down in the discussion.
> For low-level temporal events, such as waveform peaks as resolved by the
> cochlear filtering, the auditory system has an amazingly precise ability
> to represent time.  Binaural comparison of event times has JND around
> 10 to 20 MICROseconds.  Monaural detection of displaced pulses in regular
> click trains is not much worse.  Generally, the time JND for low-level
> events is much better than the reciprocal of the frequency JND for
> sine waves--as opposed to "suprisingly bad."
> For higher-level events, such as separately perceived sounds, or gaps
> in speech, the time JND is indeed much larger.  But I don't see why that
> is surprising, as there's no reason to expect these higher-level processes
> to response on the same scale as the low-level sound detection levels
> of the auditory nervous system.  They respond on a scale appropriate to
> the kinds of events that they extract.
> Dick