Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!rice!uw-beaver!ssc-vax!bcsaic!ray
From: ray@bcsaic.UUCP (Ray Allis)
Newsgroups: comp.ai
Subject: Re: "Boss, look: da brain, da Brain!"
Keywords: symbols representations neural
Message-ID: <10982@bcsaic.UUCP>
Date: 28 Mar 89 06:53:09 GMT
Organization: Boeing Computer Services-Commercial Airplane Support
Lines: 65


> From: throopw@agarn.dg.com (Wayne A. Throop)
> 
> > harnad@elbereth.rutgers.edu (Stevan Harnad)
> > If you examine the brain with a view to slicing off its "transducers"
> > and "effectors," you come up against a problem, because even if you
> > yank off the sensory surfaces, what is actually left over is repeated
> > analog transforms of the sensory surfaces as you go deeper and deeper
> > into the brain.
> 
> An interesting assertion.  It seems incorrect on two counts.  First is
> the trivial one, that the chemical reactions in the brain are, at
> base, representable as discrete and symbolizable. 

Perhaps, but can they be *replaced* by symbols?  I think not.

>                                                     That is, there is a
> limit to the "analogness" of the brain's representation of the world
> around it.
> 
> Second, no case has been made for how much of the "analogness" of the
> signal that makes its way to the brain is significant.  

I assert that the "analogness" is absolutely critical.  My case is based on
the fundamental difference between _representations_ and _symbols_.  (i.e. 
the voltages, frequencies, chemical concentrations and so on are
_representations_ of "external reality" rather than symbols.  Symbols appear
at a much "higher" level of cognition, where _representations_ can be
associated with each other.

>                                                          There is some
> evidence that the "analogness" is, in fact, filtered out quite
> quickly, and what is left are symbolic representations of
> relationships among various input stimuli. 

What evidence?  Is there neurological evidence?  The neurological research
I've seen does seem to point to a series of analog transforms.  Do you have
some references, please?

>                                             In fact, it would be very,
> VERY surprising if the analogness mattered, because the analogness
> that exists in human neural systems is not accurate. 

What value "accuracy"?  True, analog computers fell out of favor because they
didn't perform numerical computation to the same "accuracy" as digital
computers.  But we sometimes tend to gloss over the truth that any
computation is only as good as its input measurements, assumptions and
premises.  A digital computer is the archetypical physical symbol system; it
manipulates symbols according to specified relationships among them, with
absolute disregard for whatever they symbolize.  In contrast, your nervous
system's state at, say, the visual cortex, *represents* the effect your
environment is having on your sensory equipment, with nary a symbol to be
found.

>                                                        It seems
> plausible (and even likely) that the "analogness" of signals within
> the brain are not representations of analog quantities in the "real
> world".
> 

I'm sorry, but I don't understand what you mean by this.  

> Wayne Throop      <the-known-world>!mcnc!rti!xyzzy!throopw

Ray Allis  ray@atc.boeing.com   bcsaic!ray