From: erich@dehn.mth.pdx.edu (Erich Boleyn)
Newsgroups: sci.nanotech
Subject: Re: Multiple Experiences
Date: 19 Aug 92 02:10:01 GMT


I've missed parts of the discussion, but I'm a glutton for punishment...

sinster@cse.ucsc.edu (Darren Senn) writes:

>In article <Aug.9.20.33.10.1992.15549@planchet.rutgers.edu>
>	hsr4@vax.oxford.ac.uk (Auld Sprurklie) writes:
>>
>>Although my knowledge of NNs is small (possibly even trivial, although it is
>>growing), from what I've learned so far it would appear that all memories are
>>interdependent to an extent, in that the addition of a new memory (by
>>learning) results perhaps in a change to weights, thresholds, maybe even to
>>transfer functions until the entire net stabilises again.

   Although there is a certain resemblance between mathematical neural nets
and "real" neurons in mammalian nervous systems, there are also a lot of
differences.  Living neural systems are different from research systems
in a few important ways, two which leap to mind are:

	1) artificial neural systems rarely have any kind of functional
	specialization.  Layering could be treated as an example, but at
	best it is primitive.

	2) living neural systems are completely dynamic.  Artificial
	neural systems are (as a rule) static.

>[...]
>output to leave whatever tolerance I choose.  The smaller the network or
>tighter my tolerance, the smaller the number of weights I can change.
>It's important to remember that any particular memory stored in a neural
>network is distributed through _all_ of the neurons.  Some play a larger
                                ^^^^^
>role than others, to be sure, but the distribution is still complete.

   Whoa!  For some artificial systems, this is the case.  This is,
however, an ideal situation.  I can't see how this would be the case unless
the artificial neural net in question is fairly homogenous.  Layered
systems (and more arbitrarily structured ones as well) don't quite exhibit
this quality.

   If one is to take evidence gathered from study of the human brain, it
appears that this is definitely not the case for real biological systems.
Functional specialization appears to take place where the hyppocampus and
temporal lobes are the two important locations for long term memory (for
those who don't know, the hippocampus is basically in the center of the brain,
branching out to connect in some way with most of the other parts, and the
temporal lobes are on the sides just about (I think) the level of the ears
stretching back nearly to the back of the skull).  In those regions, a kind
of distributed machanism takes place...  but it is not known exactly what
the temporal lobes store (the hippocampus is important in establishing long-
term memory, the temporal lobes apparently are the keying mechanism for
retrieval).  It could be just a kind of "key/content" pointer index to
the rest of the neocortex for all we know.

   Erich

--
             "I haven't lost my mind; I know exactly where it is."
    / --  Erich Stefan Boleyn  -- \       --=> *Mad Genius wanna-be* <=--
   { Honorary Grad. Student (Math) } Internet E-mail: <erich@dehn.mth.pdx.edu>
    \  Portland State University  /      WARNING: INTERESTED AND EXCITABLE