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

Lee Kent Hempfling lkh at mail.cei.net
Mon Sep 23 03:44:03 EST 1996


radams2000 at aol.com (RAdams2000) enunciated:

>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

Bob;

It is a very common misconception that neurons only fire. What neurons
do is accept a charge value, hold it until they accept a second charge
and the result of the calculation is discharged from the neuron. It is
this discharge that is observed as firing.  There is no noise in that
process. If there was, we would all be dealing with incorrect sensory
perception. It is not a binary function.

lkh




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