Newsgroups: bit.listserv.csg-l
Date:         Tue, 10 Nov 1992 14:48:17 EST
From:         "Bruce E. Nevin" <bnevin@CCB.BBN.COM>
Subject:      Hamming it up

(John Gabriel 921109:16:45 CST) --

> A perception of the real world can be put in terms of a set of
> propositions believd to be true (Aristotle - or if you want
> something more modern, Pattern Recognition, Human and Mechanical -
> Satosi Watanabe, pub John Wiley 1985).

Henry Hiz wrote some interesting papers on this socalled "aletheic
theory of truth" in the 1960s or '70s.  The direction I took it in my MA
thesis at Penn (1970) was to build an acceptability model of
propositions rather than a truth model.  Those operator-argument
combinations actually encountered in utterances (some of them sentences,
some not, Penni) accepted by my desired peers are ipso facto acceptable.
Others are acceptable by analogy over the classifier vocabulary of the
subject matter domain.  The simplest case:  (a) substituting a
classifier word Ncl for a word actually occurring in a given utterance
and (b) substituting for the classifier word Ncl each of the words that
is acceptable in an utterance of the form N is an Ncl.  This corresponds
to some of the sublanguage analysis work of Sager, Grishman, Hirshman,
and others.  The more remote the analogical extension, the lower the
acceptability or the expectation of encountering or producing a
particular operator-argument dependency.  From these differences follow
the enabling conditions for the reductions that make up most of the
messiness of language.

> The distance between "your" perception and "mine" is a Hamming
> distance(*), possibly weighted by value systems for the propositions.
> Note that you and I can disagree about the magnitude of the weighted
> Hamming distance because of differing value systems, unless we
> agree on everything in which case the Hamming distance is zero

The only way that you can arrive at a Hamming distance of zero in this
sense is if you (the observer arriving at the Hamming distance of zero)
occupy an external point of view able to look inside each of the two
parties and inspect their perceptions from the outside.  In general, the
Hamming distance can be no more than the count of propositions that one
person affirms and with which this person perceives that the other
disagrees.  There are ways of negotiating and testing agreements, of
course, but they are never complete.

Also, in PCT you are dealing with perceptions, not with propositions.
(Propositions are also perceptions, that is, the linguistic perceptions
whose control results in speech, but it is nonverbal perceptions that I
assume are the object of agreement and disagreement here.)  The division
into propositions and "weighting by value systems" is probably at least
in part an artifact of this confusion.  If you are representing
perceptions in your model by propositions, then it isn't a model of
perceptual control (a PCT model).

> In this framework, the PCT model has an error signal that is the
> weighted Hamming distance,

You mean in your model there is an elementary control system with a
perceptual input signal corresponding to the number of propositions
about which there is disagreement, weighted in some way according to the
values associated with the propositions in a value system, and a
reference input signal of zero, such that any perceived disagreements
result in a non-zero error output signal, right?

>and the purpose of communication,
> diplomacy, or in the last resort war, (von Clausewitz) is to
> change that distance either by change of perceived truth or
> change of (even imposing a different in case of war) value system.

This says that people control for agreement.  Or am I missing something?

	Bruce Nevin
	bn@bbn.com
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