• cooperation;
  • prisoner's dilemma;
  • punishment delay;
  • punishment magnitude;
  • reward delay;
  • reward magnitude;
  • tit for tat


Parties in real-world conflicts often attempt to punish each other's behavior. If this strategy fails to produce mutual cooperation, they may increase punishment magnitude. The present experiment investigated whether delay reduction—potentially less harmful than magnitude increase—would generate mutual cooperation as interactions are repeated. The participants played a prisoner's dilemma game against a computer that played a tit-for-tat strategy, cooperating after a participant cooperated, defecting after a participant defected. For half the participants, the delay between their choice and the computer's next choice was long relative to the delay between the computer's choice and their next choice. For the other half, long and short delays were reversed. The tit-for-tat contingency reinforces the other player's cooperation (by cooperating) and punishes the other player's defection (by defecting). Both the rewards and the punishments are discounted by delay. Consistent with delay discounting, the participants cooperated more when the delay between their choice and the computer's cooperation (reward) or defection (punishment) was relatively short. These results suggest that, in real-world tit-for-tat conflicts, the decreasing delay of reciprocation or retaliation may foster mutual cooperation as effectively as (or more effectively than) the more usual tactic of increasing magnitude of reciprocation or retaliation. Copyright © 2011 John Wiley & Sons, Ltd.