Why dont we hear/see individual neural firing events??

RAdams2000 radams2000 at aol.com
Fri Sep 6 20:51:13 EST 1996


Here is a basic question from someone who knows a lot
about signal processing but only a little about the human
sensory organs. Given that there are about 4000 nerve fibers that
connect the basilar membrane in the ear to the barin, and that
each fiber only fires at a 500 Hz or so rate, why dont we
hear the collection of firing events as noise?? The standard argument
seems to be that if you average (filter) some number of these fibers,
the "noise" would be eleiminated, but a few basic calculations show
that even a few thousand fibers averaged with a time constant on the
order of a millisecond would only have a signal-to-noise ratio of
40 dB or so; not exactly hi-fi! And the signal-to-noise ratio only
increases as the square root of the number of fibers, so you dont
win very fast by increasing the number of fibers included in the average.
The same question applies to the eye, why dont we see snow??.
You can argue that the brain does all sorts of eleborate processing,
but noise is noise; its not predictable and even the most advanced 
signal processing could not eliminate it after the fact.

Bob



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