The Influence of Opponent Strategy and Psychopathic Traits on Point Gains and Cooperation in the Iterated Prisoner’s Dilemma

Mary Baggio


The Prisoner’s Dilemma game is a paradigm used to model and measure social cooperation. Uncooperative behavior may be one manifestation of the unstable interpersonal functioning in psychopathy. I investigated the effect of opponent strategy as well as psychopathic traits of fearless dominance (FD) and impulsive antisociality (IA) on cooperation rates and total and competitive point gains in a sample of 177 undergraduates playing long, finitely iterated Prisoner’s Dilemma games against computerized opponents who varied in their interpersonal styles from very harsh to very lenient. I analyzed rates of cooperation during each game, participants’ total points gained, and the difference in points earned between participant and opponent (competitive point gain). These variables were analyzed across the experiment overall and across trials after either participant or computer cooperation or defection on the previous trial. Across the experiment overall, there was significantly less cooperation and total and competitive point gains in the second half compared to the first half of each opponent block of trials, there was a positive association with leniency of opponent strategy and cooperation and total and competitive point gains, and there was a negative association with inconsistent opponent conditions and total and competitive point gains. However, opposing patterns emerged for each when comparing after cooperation and defection on the previous trial. For psychopathy, there were no effects of computer opponent’s strategy on these three variables. In the second half of each block of trials, those higher in FD tended to score more total points. Implications and future directions are discussed.