When words fail: Higher cooperation in the absence of communication in the prisoner's dilemma

The Prisoner's Dilemma has a structure that rewards bilateral trust, but carries the risk of the sucker's payoff (your opponent gets everything, you get nothing). We investigated two factors that might influence a player's cooperativeness: (1) communication between players about their intentions, and (2) trait agreeableness. In a multi-level design (10 rounds per game), participants were allocated to either a communication or non-communication condition. In the communication condition, the participants could choose one of four short statements to convey to the opponent: (1) they will cooperate, (2) cooperate if they know the opponent will cooperate, (3) they will defect, or (4) choose not to communicate. After seeing each other's message, players made their decision (cooperate or defect) with no further communication and could change their strategy. In the non-communication condition, there was zero communication between players. After the game ended, participants completed an agreeableness questionnaire. Using a Bayesian analysis, we found that cooperation was about 20 % higher in the non-communication condition. We also found dishonest communication (offering to cooperate, but then defecting) led to a breakdown in cooperation and points accumulated. We found no significant effects of agreeableness. In summary, players focused on the opponent's actions more than their words.