Mind, Body, World- Foundations of Cognitive Science, 2013a

In the most abstract sense, both a model and a modelled agent can be viewed as
opaque devices, black boxes whose inner workings are invisible. From this perspective,
both are machines that convert inputs or stimuli into outputs or responses;
their behaviour computes an input-output function (Ashby, 1956, 1960). Thus the
most basic point of contact between a model and its subject is that the input-output
mappings produced by one must be identical to those produced by the other.
Establishing this fact is establishing a relationship between model and subject at
the computational level.
To say that a model and subject are computing the same input-output function
is to say that they are weakly equivalent. It is a weak equivalence because it is established
by ignoring the internal workings of both model and subject. There are an
infinite number of different algorithms for computing the same input-output function
(Johnson-Laird, 1983). This means that weak equivalence can be established
between two different systems that use completely different algorithms. Weak
equivalence is not concerned with the possibility that two systems can produce the
right behaviours but do so for the wrong reasons.
Weak equivalence is also sometimes known as Turing equivalence. This is
because weak equivalence is at the heart of a criterion proposed by computer pioneer
Alan Turing, to determine whether a computer program had achieved intelligence
(Turing, 1950). This criterion is called the Turing test.
Turing (1950) believed that a device’s ability to participate in a meaningful conversation
was the strongest test of its general intelligence. His test involved a human
judge conducting, via teletype, a conversation with an agent. In one instance, the
agent was another human. In another, the agent was a computer program. Turing
argued that if the judge could not correctly determine which agent was human then
the computer program must be deemed to be intelligent. A similiar logic was subscribed
to by Descartes (2006). Turing and Descartes both believed in the power
of language to reveal intelligence; however, Turing believed that machines could
attain linguistic power, while Descartes did not.
A famous example of the application of the Turing test is provided by a model of
paranoid schizophrenia, PARRY (Kosslyn, Ball, & Reiser, 1978). This program interacted
with a user by carrying on a conversation—it was a natural language communication
program much like the earlier ELIZA program (Weizenbaum, 1966).
However, in addition to processing the structure of input sentences, PARRY
also computed variables related to paranoia: fear, anger, and mistrust. PARRY’s
responses were thus affected not only by the user’s input, by also by its evolving
affective states. PARRY’s contributions to a conversation became more paranoid as
the interaction was extended over time.
A version of the Turing test was used to evaluate PARRY’s performance (Colby
et al., 1972). Psychiatrists used teletypes to interview PARRY as well as human
Elements of Classical Cognitive Science 95