Probability of reciprocation in repeated prisoner's dilemma games

Both social cooperation and self-control require reciprocation. In social cooperation situations a single person's cooperative act, if not reciprocated by others, would be unreinforced both immediately and in the long term. Similarly, a single act of self-control (refusing a single cigarette, for example), if not followed up by other such acts, would also be unreinforced immediately and in the long term. The present experiments varied probability of reciprocation in a prisoner's dilemma-like game that could resemble a social cooperation or a self-control situation. Participants earned points by playing against a computer. The computer offered the participant a choice between 5 or 6 points ('cooperation' by the computer) or between 1 or 2 points ('defection' by the computer). The participant's choice of the lesser alternative ('cooperation') or the greater alternative ('defection') on the current trial led, respectively, to cooperation or defection by the computer on the next trial with a probability (probability of reciprocation, PR) which could vary. When PR was greater than 63%, consistent cooperation maximized the participant's earnings. When PR was less than 63%, defection maximized earnings. Three conditions were studied: PR signaled by spinners; PR unsignaled; PR unsignaled with participants believing that they were playing with another person, not the computer. With PR = 100% ('tit-for-tat') and PR = 50%, the modal participant maximized earnings under all three conditions. With PR = 75%, participants maximized earnings only when PR was signaled. These results indicate that differences between people's tendency to cooperate with other people (social cooperation) and their tendency to cooperate with their own future interests (self-control) may lie indifferences in subjective PR. Copyright (C) 2001 John Wiley gr Sons, Ltd.