Reference Articles on Turing

What is Artificial Intelligence?

By Jack Copeland

© Copyright B.J. Copeland, May 2000


Alan Turing and the Origins of AI

The earliest substantial work in the field was done by the British logician and computer pioneer Alan Mathison Turing.

In 1935, at Cambridge University, Turing conceived the modern computer. He described an abstract computing machine consisting of a limitless memory and a scanner that moves back and forth through the memory, symbol by symbol, reading what it finds and writing further symbols. The actions of the scanner are dictated by a program of instructions that is also stored in the memory in the form of symbols. This is Turing's "stored-program concept", and implicit in it is the possibility of the machine operating on, and so modifying or improving, its own program. Turing's computing machine of 1935 is now known simply as the universal Turing machine. All modern computers are in essence universal Turing machines.

During the Second World War Turing was a leading cryptanalyst at the Government Code and Cypher School, Bletchley Park (where the Allies were able to decode a large proportion of the Wehrmacht's radio communications). Turing could not turn to the project of building a stored-program electronic computing machine until the cessation of hostilities in Europe in 1945. Nevertheless, during the wartime years he gave considerable thought to the issue of machine intelligence. Colleagues at Bletchley Park recall numerous off-duty discussions with him on the topic, and at one point Turing circulated a typewritten report (now lost) setting out some of his ideas. One of these colleagues, Donald Michie (who later founded the Department of Machine Intelligence and Perception at the University of Edinburgh), remembers Turing talking often about the possibility of computing machines (1) learning from experience and (2) solving problems by means of searching through the space of possible solutions, guided by rule-of-thumb principles. The modern term for the latter idea is "heuristic search", a heuristic being any rule-of-thumb principle that cuts down the amount of searching required in order to find the solution to a problem. Programming using heuristics is a major part of modern AI, as is the area now known as machine learning.

At Bletchley Park Turing illustrated his ideas on machine intelligence by reference to chess. (Ever since, chess and other board games have been regarded as an important test-bed for ideas in AI, since these are a useful source of challenging and clearly defined problems against which proposed methods for problem-solving can be tested.) In principle, a chess-playing computer could play by searching exhaustively through all the available moves, but in practice this is impossible, since it would involve examining an astronomically large number of moves. Heuristics are necessary to guide and to narrow the search. Michie recalls Turing experimenting with two heuristics that later became common in AI, minimax and best-first. The minimax heuristic (described by the mathematician John von Neumann in 1928) involves assuming that one's opponent will move in such a way as to maximise their gains; one then makes one's own move in such a way as to minimise the losses caused by the opponent's expected move. The best-first heuristic involves ranking the moves available to one by means of a rule-of-thumb scoring system and examining the consequences of the highest-scoring move first.

In London in 1947 Turing gave what was, so far as is known, the earliest public lecture to mention computer intelligence, saying "What we want is a machine that can learn from experience", adding that the "possibility of letting the machine alter its own instructions provides the mechanism for this". In 1948 he wrote (but did not publish) a report entitled "Intelligent Machinery". This was the first manifesto of AI and in it Turing brilliantly introduced many of the concepts that were later to become central, in some cases after reinvention by others. One of these was the concept of "training" a network of artificial neurons to perform specific tasks.

In 1950 Turing introduced the test for computer intelligence that is now known simply as the Turing test. This involves three participants, the computer, a human interrogator, and a human "foil". The interrogator attempts to determine, by asking questions of the other two participants, which is the computer. All communication is via keyboard and screen. The interrogator may ask questions as penetrating and wide-ranging as he or she likes, and the computer is permitted to do everything possible to force a wrong identification. (So the computer might answer "No" in response to "Are you a computer?" and might follow a request to multiply one large number by another with a long pause and an incorrect answer.) The foil must help the interrogator to make a correct identification. A number of different people play the roles of interrogator and foil, and if sufficiently many interrogators are unable to distinguish the computer from the human being then (according to proponents of the test) it is to be concluded that the computer is an intelligent, thinking entity. In 1991, the New York businessman Hugh Loebner started the annual Loebner Prize competition, offering a $100,000 prize for the first computer program to pass the Turing test (with $2,000 awarded each year for the best effort). However, no AI program has so far come close to passing an undiluted Turing test.

In 1951 Turing gave a lecture on machine intelligence on British radio and in 1953 he published a classic early article on chess programming. Both during and after the war Turing experimented with machine routines for playing chess. (One was called the Turochamp.) In the absence of a computer to run his heuristic chess program, Turing simulated the operation of the program by hand, using paper and pencil. Play was poor! The first true AI programs had to await the arrival of stored-program electronic digital computers.

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