Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!well!nagle
From: nagle@well.sf.ca.us (John Nagle)
Newsgroups: comp.ai.philosophy
Subject: Re: Reasoning Paradigms
Message-ID: <21128@well.sf.ca.us>
Date: 11 Oct 90 02:45:15 GMT
References: <3586@media-lab.MEDIA.MIT.EDU> <69347@lll-winken.LLNL.GOV> <3593@media-lab.MEDIA.MIT.EDU> <69377@lll-winken.LLNL.GOV> <11@tdatirv.UUCP> <3642@media-lab.MEDIA.MIT.EDU>
Lines: 45

minsky@media-lab.MEDIA.MIT.EDU (Marvin Minsky) writes:

>In article <11@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes:

>>..... And since the human brain is,
>>by definition, an NN this consititutes an existance proof for a way of
>>solving this problem in NN's. 

>This is a dangerous rhetorical trick.  Because in the usual context of
>discussion, a "neural network" or NN is considered to be a relatively
>homogeneous, uniform structure equipped with a relatively systematic
>learning procedure.  The brain is at least 400 different architectures
>interconnected in accord with genetic specifications that appear to
>involve the order of at least 30,000 genes.   

     Yes.  See section 6.3 of "The Metaphorical Brain 2" (Arbib, M., 1989,
Wiley, ISBN 0-471-09853-1), where some wiring diagrams for parts of the
nervous system are given.  Some hard data in this area is starting to 
come in.  The parts of the nervous system we understand consist of
functional units that do special-purpose processing, interconnected
in generally plausible ways from a control-theory perspective.  There
is clear higher-level hard-wired structure in the nervous system.  This
is not speculation; the experimental results are in.

     It's also worth bearing in mind that nothing like the backward-
propagation learning of the NN world has yet been discovered in biology.
The mechanism found so far look much more like collections of
adaptive controllers operating control loops.  However, it should
be noted that most of the neural structures actually understood are
either in very simple animals (like slugs) or very close to sensors
and actuators (as in tactile control), where one would expect
structures that work like adaptive feedback control systems.
The more abstract levels of brain processing are still weakly
understood.  

     Personally, I favor the hypothesis that the higher levels of processing
are built out of roughly the same components as the lower levels.
In the absence of experimental data to the contrary, this is a
plausible assumption.  This leads one to consider some rather
different lines of approach than the more popular ones.  The various
artificial insect groups are proceeding in directions consistent
with this assumption.  How far it can be pushed remains to be seen.


					John Nagle