Thursday 1/31

The Turing Test

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Synopsis

We began today by revisiting the two threads--one philosophical leading to machine functionalism; the other mathematical leading to machine intelligence, whereby thought itself is conceived as a matter of the rule-governed manipulation of strings of 'symbols'--and discussed how they neatly mesh to make the optimistic case for 1) the possibility of Artificial Intelligence and 2) the possibility of understanding the Mind in light of Dretske's Dictum.

Of course, the notion that intelligence can ultimately be boiled down to mechanical processes raises two crucial questions:

1. What is intelligence?

and,

2. What is mechanism?

We began today with the puzzle of intelligence.

A.M. Turing provides answers to both questions. Turing's biography, you may recall, is both fascinating and historically eventful, including as it does Bletchley Park, World War II, the German U-Boat "wolf-packs", and the Naval Enigma Cypher machine.

Andrew Hodges' "Alan Turing: The Enigma" is an excellent source for more material on this important bit of history.

To be sure, Turing's importance only begins with his contributions towards cracking naval enigma. For, on the one hand, he helped us grapple with the thorny question of intelligence, while on the other hand he, more than anyone, provided the theoretical foundation upon which the modern computer is built.

Turing's key insight on the puzzle of intelligence, which we will have many opportunities to critically examine, can be simply put as the proposition that

The perfect imitation of intelligence is intelligence.

That is, in his unusually accessible essay "Computing Machinery and Intelligence", Turing suggests that the question of whether a machine is intelligent is hopelessly ill-formed and perhaps unanswerable in that form. After all, there are many things we might mean by 'intelligent', and it is not clear what all of them have to do with one another. Turing proposed that we replace the question of machine intelligence with an imitation game in which an interlocutor interrogates a machine and a person by teletype (today: chatroom) to determine which is which. This is a strictly behavioral test. If the machine can fool the interlocutor better than average number of times, then the machine is behaviorally indistinguishable from a person insofar as 'verbal' behavior is concerned.

It is enough, in other words, to satisfy any questions about 'intelligence' we could meaningfully ask. (It bears noting that psychometrics, the study of the measure of psychological phenomena, has thus far born out his suspician: We really have no idea what intelligence is.)

However, let us be absolutely clear what we mean by the significance of the Turing Test for machine intelligence.

It would be a mistake to argue that passing the Turing Test is both necessary and sufficient for intelligence. That is, it would be a mistake to assert that

1. X passes the Turing Test if, and only if, X is intelligent.

(1) is clearly false. Consider that (1), logically speaking, is bi-conditional, where a bi-conditional is defined (or can be defined) as simply the conjunction of two distinct conditionals:

1a. If X passes the Turing Test, then X is intelligent. (The Turing Test, we say, is according to this proposition a sufficient condition on, or suffices for, intelligence. Passing the Turing Test means successfully having intelligence.)

1b. If X is intelligent, then X passes the Turing Test. (The Turing Test, we say, is according to this proposition a necessary condition on, or necessary for, intelligence. Failing the Turing Test means failing to have intelligence.)

(1b), though, is false. For if the question of intelligence is at all meaningful, one can be intelligent without passing the Turing Test. There are lots of reasons why an intelligent being might lose the Turing Test. Inability to type would be one reason; speaking another language would be another.

The interesting question, from our standpoint, is whether passing the Turing Test is a sufficient condition on intelligence--i.e., is (1a) true?

There are roughly two skeptical responses to the assertion (1a) that passing the Turing Test suffices for intelligence: The Turing Test is too strong a sufficient condition on intelligence, or the Turing Test is too weak a condition on intelligence to suffice

The Turing Test is Too Strong (aka, The Problem of False Negatives).

First, one might argue, as researchers in computer science and robotics sometimes do, that the Turing Test is simply too strong a condition on intelligence because intelligence is not always expressed verbally. Witness the Mars rovers Spirit and Opportunity. The rovers would fail the Turing Test miserably, yet it can be argued that they have behavioral capacities on a par with insect-level intelligence. Intelligence has evolved, and so too with our machines. It may be a very long time before we can create machines that can reliably pass the Turing Test, yet we should not for that reason refuse to see the fantastically complicated and sophisticated behavioral repertoire of their predecessors as anything but intelligence.

In short, this objection holds that the Turing Test is too strong in the sense that it ignores as intelligent many things that should rightfully be considered intelligent. Perhaps dog and dolphin-lovers will agree.

The Turing Test is Too Weak (aka, The Problem of False Positives).

A much more common objection to the Turing Test, at least within the philosophical community, is that it is simply too weak. According to this objection, the Turing Test could in principle result in false positives: things that pass the test but ought not be considered intelligent. The most common source of these objections has been the philosophical community, and many of these bear careful scrutiny, as we shall see.

Whether the Turing Test is too strong, too weak, or, as a robotic Goldilocks might wish, just right, it is clear that Turing has done much to help us sharpen the debate over the possibility of artificial intelligence.

Here are some useful links for further reading about Alan Turing and the Turing Test:

Next time we dive into a thicket of much thornier questions: What is the nature of mechanism? (We are, after all, considering the possibility of machine intelligence. We can't make any progress on that puzzle without first knowing what to count as a machine!) And what are the capacities and, crucially, limitations of mechanism? This part of the course takes a decidedly technical, perhaps even mathematical turn which some students find off-putting. Rest assured as past classes have amply demonstrated, this material can be mastered, and mastered quite readily and thoroughly given patience and time.