Page 46 - Foundations of Cognitive Psychology : Core Readings

44 Daniel C. Dennett

But now, more seriously, was this an honest-to-goodness Turing test? Were
there tacit restrictions on the lines of questioning of the judges? Like the geolo-
gists interacting with LUNAR, the psychiatrists’ professional preoccupations
and habits kept them from asking the sorts of unlikely questions that would
have easily unmasked PARRY. After all, they realized that since one of the
contestants was a real, live paranoid person, medical ethics virtually forbade
them from toying with, upsetting, or attempting to confuse their interlocutors.
Moreover, they also knew that this was a test of a model of paranoia, so there
were certain questions that wouldn’t be deemed to be relevant to testing the
model as a model of paranoia. So, they asked just the sort of questions that
therapists typically ask of such patients, and of course PARRY had been ingen-
iously and laboriously prepared to deal with just that sort of question.
One of the psychiatrist judges did, in fact, make a rather half-hearted attempt
to break out of the mold and ask some telling questions:‘‘Maybe you’ve heard
of the saying ‘Don’t cry over spilled milk.’ What does that mean to you?’’
PARRY answered:‘‘Maybe it means you have to watch out for the Mafia.’’
When then asked ‘‘Okay, now if you were in a movie theater watching a movie
and smelled something like burning wood or rubber, what would you do?’’
PARRY replied:‘‘You know, they know me.’’ And the next question was, ‘‘If
you found a stamped, addressed letter in your path as you were walking down
the street, what would you do?’’ PARRY replied:‘‘What else do you want to
know?’’ 1
Clearly PARRY was, you might say, parrying these questions, which were
incomprehensible to it, with more or less stock paranoid formulas. We see a bit
of a dodge, which is apt to work, apt to seem plausible to the judge, only be-
cause the ‘‘contestant’’ is supposed to be paranoid, and such people are expected
to respond uncooperatively on such occasions. These unimpressive responses
didn’t particularly arouse the suspicions of the judge, as a matter of fact,
though probably they should have.
PARRY, like all other large computer programs, is dramatically bound by
limitations of cost-effectiveness. What was important to Colby and his crew
was simulating his model of paranoia. This was a massive effort. PARRY has a
thesaurus or dictionary of about 4500 words and 700 idioms and the grammati-
cal competence to use it—a parser, in the jargon of computational linguistics.
The entire PARRY program takes up about 200,000 words of computer mem-
ory, all laboriously installed by the programming team. Now once all the effort
had gone into devising the model of paranoid thought processes and linguistic
ability, there was little if any time, energy, money, or interest left over to build
in huge amounts of world knowledge of the sort that any actual paranoid, of
course, would have. (Not that anyone yet knows how to build in world
knowledge in the first place.) Building in the world knowledge, if one could
even do it, would no doubt have made PARRY orders of magnitude larger and
slower. And what would have been the point, given Colby’s theoretical aims?
PARRY is a theoretician’s model of a psychological phenomenon:paranoia.
It is not intended to have practical applications. But in recent years a branch
of AI (knowledge engineering) has appeared that develops what are now
called expert systems. Expert systems are designed to be practical. They are
software superspecialist consultants, typically, that can be asked to diagnose