The invention of the steam engine and industrial mass production astonished a society familiar only with manual labor, generating visions of a leisurely future in which human toil was no longer necessary and machines provided all of the necessities of life. Similarly, the power of digital computer technology to perform amazing feats of calculation has raised the hope of scientists that computers might be built which have the ability to perform complex tasks, make sound decisions in novel situations, initiate activity and learn from mistakes--in a word, to think . One of the most important figures in the early study of artificial intelligence was Alan Turing (1912-1954), an English mathematician and logician. Turing proposed a means by which one could determine whether a computer is "intelligent." Place a computer, Turing said, in one room and place a keyboard attached to the computer in another room...