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From: harnad@mind.UUCP (Stevan Harnad)
Newsgroups: comp.cog-eng,comp.ai
Subject: Re: The symbol grounding problem: 3 routes to grounding needed?
Message-ID: <975@mind.UUCP>
Date: Sun, 5-Jul-87 01:05:53 EDT
Article-I.D.: mind.975
Posted: Sun Jul  5 01:05:53 1987
Date-Received: Sun, 5-Jul-87 05:37:17 EDT
References: <.... <6174@diamond.BBN.COM> <917@mind.UUCP> <8404@ut-sally.UUCP>
Organization: Cognitive Science, Princeton University
Lines: 104
Summary: On probabilistic features, indeterminacy and underdetermination
Xref: mnetor comp.cog-eng:187 comp.ai:623



In Article 181 of comp.cog-eng berleant@ut-sally.UUCP (Dan Berleant)
of U. Texas CS Dept., Austin, Texas writes:

>	may not be much difference between a classical view augmented to...
>	*arbitrary* boolean expressions of features...and a probabilistic view

I agree that such a probabilistic representation is possible. Now the question
is, will it work, is it economical (and is it right)? Note, though, that even
graded (probabilistic) individual features must yield an all-or-none feature
SET. So even this would not be evidence of graded membership. (I don't think
you'd disagree.)

>	need to...explain...typicality and reaction time results...interpreted
>	as supporting probabilistic and exemplar-based category representations 

Yes, but it seems only appropriate that we should account for the
categorization performance capacity itself before we worry about its
fine tuning. (Experimental psychology has a long history of bypassing
the difficult but real problems underlying our behavioral capacities
and fixating instead on fine-tuning.) 

>	may [be] 2 representations for categories: a 'core' of defining features
>	and a heuristic categorizer... 2 pathways [grounding] categories

You may be right. It's an empirical question whether the heuristic component
will be necessary to generate successful performance. If it is, it is still not
obvious that the need for it would be directly related to the grounding problem.

>	[Re:] Anders Weinstein [on] the semantic meaning of...thunder/...`angry
>	gods nearby'...: The terms in the definition presumably are grounded
>	via the 2 routes discussed above... [now] Consider a sentence with 2
>	variables, e.g. FISH SWIM... Obviously, many bindings would satisfy
>	the sentence. [But]...by adding many more true sentences, the possible
>	bindings of the variables become much more constrained.

I accepted this argument the first time you made it. I think it's
right; I've made similar degrees-of-freedom arguments against Quine myself,
and I've cross-referenced your point in my response to Weinstein. I
don't believe, though, that this reduction of the degrees of freedom
of the interpretation (even to zero) is sufficient to ground a symbol
system. Even if there's only one way to interpret an entire language,
the decryption must be performed; and it's not enough that the mapping
should be into a natural language (that's still a symbol/symbol
relation, leaving the entire edifice hanging by a skyhook of derived
rather than intrinsic meaning). The mapping must be into the world.

But, in any case, you seem to rescind your degrees-of-freedom
argument immediately after you make it:

>	On the other hand... Maybe a Martian [or] your neighbor... could
>	figure out [an alternative] way to do it consistently... but as long
>	as you both agree on the truthfulness of all the sentences you are
>	mutually aware of, there is no way to tell! Shades of the Turing test...

This is standard Quinean indeterminacy again! So you don't believe
your degrees-of-freedom argument! Well I do. And it's partly because
of degrees-of-freedom and convergence considerations that I am so
sanguine about the TTT. (I called this the "convergence" argument in
"Minds, Machines and Searle": There may be many arbitrary ways to
successfully model a toy performance, but as you move toward the TTT,
the degrees of freedom shrink.)

>	would this method of 'grounding' the semantics of categories be
>	sufficient to do the job? Only in theory? Potentially in practice? ...

I think it would not (although it may simplify the task of grounding
somewhat). Even if only one interpretation is possible, it must be
intrinsic, not derivative.

>	Are you assuming a representation of episodes (more generally,
>	exemplars) that is iconic rather than symbolic? 

Yes, I am assuming that episodic representations would be iconic. This is
related to the distinction in the human memory literature concering
"episodic" vs. "semantic" memory. The former involves qualitative
recall for when something happened (e.g., Kennedy's assassination) and
the particulars of the experience; the latter involves only the
*product* of past learning (e.g., knowing how to ride a bicycle, do
calculus or speak English). It's much harder to imagine how the former
could be symbolic (although, of course, there are "constructive" memory
theories such as Bartlett's that suggest that what we remember as an
episode may be based on reconstruction and logical inference...).

>	*no* category representation method can generate category boundaries
>	when there is significant interconfusability among categories!

I would be very interested to know your basis for this assertion
(particularly as "significant interconfusability" is not exactly a
quantitative predicate). If I had said "complete indeterminacy," or even
"radical underdetermination" (say, features that would require
exponential search to find), I could understand why you would say this
-- but significant interconfusability... Can you remember first
looking at cellular structures under a microscope? Have you seen Inuit snow
taxonomies? Have you ever tried serious mushroom-picking? Or chicken
sexing? Or tumor identification? Art classification? Or, to pick some
more abstract examples: paleolinguistic taxonomy? ideological
typologizing? or problems at the creative frontiers of pure mathematics?
-- 

Stevan Harnad                                  (609) - 921 7771
{bellcore, psuvax1, seismo, rutgers, packard}  !princeton!mind!harnad
harnad%mind@princeton.csnet       harnad@mind.Princeton.EDU