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From: dredick@bbn.com (Barry Kort)
Newsgroups: comp.ai
Subject: Re: Hayes vs. Searle
Summary: The Limitation of Harnad's Model
Keywords: Symbols
Message-ID: <58446@bbn.BBN.COM>
Date: 25 Jul 90 20:05:13 GMT
References: <129.26a5feab@csc.fi> <14385@venera.isi.edu> <58376@bbn.BBN.COM> <14417@venera.isi.edu>
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Reply-To: bkort@BBN.COM (Barry Kort)
Organization: BBN Labs (Cambridge, MA)
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In article <14385@venera.isi.edu> smoliar@vaxa.isi.edu (Stephen Smoliar)
wrote:

 > > > This argument assumes that the human brain HAS symbols (or, at least,
 > > > that is implied through the use of the possessive "its").  There is
 > > > no evidence that this is the case.  I think it would be fair to say
 > > > that the point is still up for debate, just like the premise that the
 > > > human brain "has" mental images.

In article <58376@bbn.BBN.COM> bkort@BBN.COM I interrupted:

 > > I don't understand this, Steve.  Spoken and written language symbolize
 > > the elements of our world.  And these word-symbols are stored and
 > > processed in the brain.  (At least that's where *I* store them!)  So
 > > while the point may be worthy of debate, how can you argue that there
 > > is no evidence?

In article <14417@venera.isi.edu> smoliar@vaxa.isi.edu (Stephen Smoliar)
responds:

 > I guess we are in a position of mutual conflict, here, Barry.  How can
 > you argue that there IS evidence?  Your introspection is your personal
 > abstraction of what you think is going on.  There is nothing wrong with
 > that, as long as you don't fall into the trap of confusing the abstraction
 > with the reality. 

OK, but isn't my introspection at least weak evidence that something going
on in my brain looks suspiciously like symbols rattling around?

 > Look, let's try to establish a level playing field.  In his "Symbol
 > Grounding Problem" paper, Stevan Harnad defines a symbol system to
 > be "(1) a set of arbitrary 'PHYSICAL TOKENS' (scratches on paper,
 > holes on a tape, events in a digital computer, etc.) that are (2)
 > manipulated on the basis of 'EXPLICIT RULES' that are (3) likewise
 > physical tokens and STRINGS of tokens.  The rule-governed symbol-token
 > manipulation is based (4) purely on the SHAPE of the symbol tokens
 > (not their 'meaning'), i.e., it is purely SYNTACTIC, and consists of
 > (5) 'RULEFULLY COMBINING' and recombining symbol tokens.  There are
 > (6) primitive ATOMIC symbol tokens and (7) COMPOSITE symbol-token strings.
 > The entire system and all its parts -- then atomic tokens, the composite
 > tokens, then syntactic manipulation (both actual and possible) and the
 > rules -- are all (8) 'SEMANTICALLY INTERPRETABLE:'  The syntax can be
 > SYSTEMATICALLY assigned a meaning (e.g., as standing for objects, as
 > describing states of affairs)."  Given the constraints of such a
 > definition, I think that the level of debate may descend to the point
 > of arguing whether or not the sorts of events which take place at the
 > neuronal level constitute the sorts of physical tokens which form the
 > core of Harnad's definition.  In other words we can, indeed, argue
 > over whether or not there is any evidence! 

Oh.  Gee, Steve, I don't think I store or process symbols like that
at all.  First of all, I don't rely exclusively on rules to drive
my thinking.  I do a lot of model-based reasoning, along with
visual reasoning and lots of generate-and-test.  As far as I can
tell by introspection, I don't use explicit rules for these forms
of information processing.  I tend to use rules when I am doing
formal analysys, like parsing sentences or solving equations.

But if you let me include my keyboard and monitor as extensions of
my symbol-processing system, then it is true that much of my thinking
takes place with formal symbols and strings of symbols.  For some
strange reason, thinking and writing have become so mutually intertwined
for me, that I can't think without writing.  And I can't write very much
without using a full screen word-processor.

Still, I find Stevan Harnad's definition uncomfortably confining, and
based on those ground rules, I agree that the point is quite debatable.

Barry Kort                       bkort@bbn.com
Visiting Scientist
BBN Labs