Alan Turing, in a 1951 paper, proposed a test called "The Imitation Game" that might finally settle the issue of machine intelligence. The first version of the game he explained involved no computer intelligence whatsoever. Imagine three rooms, each connected via computer screen and keyboard to the others. In one room sits a man, in the second a woman, and in the third sits a person - call him or her the "judge". The judge's job is to decide which of the two people talking to him through the computer is the man. The man will attempt to help the judge, offering whatever evidence he can (the computer terminals are used so that physical clues cannot be used) to prove his man-hood. The woman's job is to trick the judge, so she will attempt to deceive him, and counteract her opponent's claims, in hopes that the judge will erroneously identify her as the male.
What does any of this have to do with machine intelligence? Turing then proposed a modification of the game, in which instead of a man and a woman as contestants, there was a human, of either gender, and a computer at the other terminal. Now the judge's job is to decide which of the contestants is human, and which the machine. Turing proposed that if, under these conditions, a judge were less than 50% accurate, that is, if a judge is as likely to pick either human or computer, then the computer must be a passable simulation of a human being and hence, intelligent. The game has been recently modified so that there is only one contestant, and the judge's job is not to choose between two contestants, but simply to decide whether the single contestant is human or machine.
The dictionary.com entry on the Turing Test
here) is short, but very clearly stated. A longer, but point-form review
of the imitation game and its modifications written by Larry Hauser, click
here (if link fails, click here
for a local copy) is also available. Hauser's page may not contain enough detail
to explain the test, but it is an excellent reference or study guide and contains
some helpful diagrams for understanding the interplay of contestant and judge.
The page also makes reference to John Searle's Chinese Room, a thought experiment
developed as an attack on the Turing test and similar "behavioural" intelligence
tests. We will discuss the Chinese Room in the next section.
Natural Language Processing (NLP)
Partly out of an attempt to pass Turing's test, and partly just for the fun of it, there arose, largely in the 1970s, a group of programs that tried to cross the first human-computer barrier: language. These programs, often fairly simple in design, employed small databases of (usually English) language combined with a series of rules for forming intelligent sentences. While most were woefully inadequate, some grew to tremendous popularity. Perhaps the most famous such program was Joseph Weizenbaum's ELIZA. Written in 1966 it was one of the first and remained for quite a while one of the most convincing. ELIZA simulates a Rogerian psychotherapist (the Rogerian therapist is empathic, but passive, asking leading questions, but doing very little talking. e.g. "Tell me more about that," or "How does that make you feel?") and does so quite convincingly, for a while. There is no hint of intelligence in ELIZA's code, it simply scans for keywords like "Mother" or "Depressed" and then asks suitable questions from a large database. Failing that, it generates something generic in an attempt to elicit further conversation. Most programs since have relied on similar principles of keyword matching, paired with basic knowledge of sentence structure. There is however, no better way to see what they are capable of than to try them yourself. We have compiled a set of links to some of the more famous attempts at NLP. Students are encouraged to interact with these programs in order to get a feeling for their strengths and weaknesses, but many of the pages provided here link to dozens of such programs, don't get lost among the artificial people.
Online Examples of NLP
A series of online demos (many are Java applets, so be sure you are using a Java-capable browser) of some of the more famous NLP programs.
Opponents of Turing's behavioural criterion of intelligence argue that it is either not sufficient, or perhaps not even relevant at all. What is important, they argue, is that the computer demonstrates cognitive ability, regardless of behaviour. It is not necessary that a program speak in order for it to be intelligent. There are humans that would fail the Turing test, and unintelligent computers that might pass. The test is neither necessary nor sufficient for intelligence, they argue. In hopes of illuminating the debate, we have assigned two papers that deal with the Turing Test from very different points of view. The first is a criticism of the test, the second comes to its defense.
Previous (Can Machines Think?) | Home | Next (The Chinese Room)