| Many researchers have argued that defection is the rational strategy in the Prisoner's Dilemma (PD) because it maximizes individual gain regardless of what one's opponent does. Conversely, cooperation enhances group gains, but only if adopted by all. The payoff structure of the PD ensures that for any probability of opponent cooperation, defection will remain the dominating strategy. Classic game theory implicitly assumes that the perceived probability of an opponent's cooperation is independent of the player's own intended choice. In contrast, the present research suggests that individuals may sequentially evaluate the possible outcomes for each choice. When predicting opponent behavior, individuals may anchor predictions about their opponent on their own behavior. Cooperation would then be the optimal strategy in the PD, since payoffs to the individual and group are higher for mutual cooperation than for mutual defection. In Studies 1–3, individual differences in projection were used to predict PD behavior, but were not good predictors. In Study 4, participants were explicitly provided with reciprocity information. In this study, cooperation increased monotonically with the probability of matching response from an opponent. In Study 5, participants were provided with information about the probability of opponent cooperation, information independent of participant choice. Here, cooperation was uniformly low. In Study 6, individuals played the PD against an ingroup or outgroup member. Although projection varied with group status, cooperation did not, thereby eliminating projection as a possible mediator of the relationship between group status and cooperation. Overall, explicit manipulations of probability values consistent with projection (i.e., information about opponent reciprocation of one's response) were more effective in eliciting cooperation than more implicit manipulations. In Studies 2–6, increases in the difference in payoff between mutual cooperation and mutual defection were also shown to increase cooperation. |
