Story of Psychology - Morton Hunt [356]
In the mid-1950s, when Simon and Newell undertook to create Logic Theorist, the first program that simulated thinking, they posed a problem to themselves: How do human beings solve problems? Logic Theorist took them a year and a half, but the question occupied them for more than fifteen. The resulting theory, published in 1972, has been the foundation of work in that field ever since.
Their chief method of working on it, according to Simon’s autobiography, was two-man brainstorming. This involved deductive and inductive reasoning, analogical and metaphoric thinking, and flights of fancy—in short, any kind of reasoning, orderly or disorderly:
From 1955 to the early 1960s, when we met almost daily… [we] worked mostly by conversations together, with the explicit rule that one could talk nonsensically and vaguely, but without criticism unless you intended to talk accurately and sensibly. We could try out ideas that were half-baked or quarter-baked or not baked at all, and just talk and listen and try them again.73
They also did a good deal of laboratory work. Singly and together they recorded and analyzed the steps by which they and others solved puzzles and then wrote out the steps as programs. A favorite puzzle, of which they made extensive use for some years, is a child’s toy known as the Tower of Hanoi. In its simplest form, it consists of three disks of different sizes (with holes in their centers) piled on one of three vertical rods mounted on flat bases. At the outset, the largest disk is on the bottom, the middle-sized one in the middle, the smallest one on top. The problem is to move them one at a time in the fewest possible moves, never putting any disk on top of one smaller than itself, until they are piled in the same order on another rod.
The perfect solution takes seven steps, although with errors leading to dead ends and backtracking to correct them, it can take several times that many. In more advanced versions, the solution requires complex strategies and many moves. A perfect five-disk game takes thirty-one moves, a perfect seven-disk game 127 moves, and so on.* Simon has said, quite seriously, that “the Tower of Hanoi was to cognitive science what fruit flies were to modern genetics—an invaluable standard research setting.”74 (Sometimes, however, he ascribes this honor to chess.)
Another laboratory tool used by the team was cryptarithmetic, a type of puzzle in which a simple addition problem is presented in letters instead of numbers. The goal is to figure out what digits the letters stand for. This is one of Simon and Newell’s simpler examples:
The obvious first step: M must be 1, since no two digits—S + M in this case—can add up to more than 19, even with a carry.† Simon and Newell had volunteers talk out loud as they worked on such a puzzle, recorded everything they said, and afterward diagrammed the steps of their thought process in the form of a search track of moves, decisions at forks with more than one option, wrong choices pursued to dead ends, reversals to try another route from the last fork, and so on.
Simon and Newell made particular use of chess, a vastly more complex problem than either the Tower or cryptarithmetic. In a typical chess game of sixty moves, at each step there are on average thirty possible moves; to “look ahead” only three moves would mean visualizing twenty-seven thousand possibilities. A key question for Simon and Newell was how chess players deal with such impossibly large sets of contingencies. The answer: A skilled chess player does not consider all the possible moves he might make next and all the moves his opponent might make in response but only those few moves that make good sense and that follow elementary guidelines like “Guard the King” and “Don’t give away a piece for