Learned Optimism: How to Change Your Mind and Your Life

by Martin E.P. Seligman

This view ran against the existing belief about achievement, the classic demonstration of which was called PREE—the partial reinforcement extinction effect. PREE is an old chestnut of learning theory. If you give a rat a food pellet every time he presses a bar, this is called “continuous reinforcement”; the ratio of reward to effort is one-to-one, one pellet for one bar-press. If you then stop giving him food for pressing the bar (“extinction”), he’ll press the bar three or four times and then quit completely, because he can see he’s never getting fed anymore, since the contrast is so great. If, on the other hand, instead of one-for-one reinforcement, you give the rat “partial” reinforcement—say, an average of only one pellet for every five or ten times he presses—and then start extinction, he’ll press the bar a hundred times before he gives up.