[Comp-neuro] Noise, redundancy and biophysics]

David Tam dtam at unt.edu
Fri Jul 25 08:01:40 CEST 2008


Noise is merely in the eyes of the beholder.  What is noise to one, is
signal to another.  (E.g., Is spam noise?)  If you use it, it is signal.  If
you don't use it (or throw it out), it is noise.  That is the classical
definition of noise in communication theory.  It all depends on the encoder
and the decoder.  So if the CNS uses it, it is signal, not noise, even if it
is stochastic.

So some may define noise based on determinism vs. stochasticity rather than
the usual definition of noise in engineering that is based on signal
content.

But determinism and stochasticity is merely in the eyes of the beholder also
-- nothing more than the duality of nature, depending on your perspective.
If you are god, everything is deterministic.  If you are human, everything
is stochastic.  Just because the system is probabilistic, it doesn't mean it
is noisy.  Is Brownian motion noisy?  It all depends on what you want to get
out of those Brownian motions that makes it noisy or not noisy.  So noise is
really a moot point.

To put it more philosophically, noise is what you "don't care" to have.
"Don't care" is not necessary a bad philosophical perspective.  There are
too many examples of "don't care" terms in math logic truth table or
computer science that serve real (and convenient) purposes.  The stochastic
view of the world is a good example of how we only care about the
probability but don't care about the determinism.  As such, the stochastic
view of the universe (or the brain) is not noisy whatsoever, but rather very
predictable based on probability.

So do neurons (or the brain) use noise in its computation?  If the neurons
care about those signals, it is not noise.  If they don't care, yes, then it
is noise.

So the question we should be asking is: Are we assigning functions to those
poor neurons irrespective of what they are actually doing?  Do they really
care, literally?  :)

David Tam, Ph.D.
Associate Professor
Dept. of Biological Sciences
University of North Texas
Denton, TX 76203
940-565-3261




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