Figure 1.

The Prisoner’s Dilemma Game apparatus consisted of two similar but independent trays (one for each player) operating in a seesaw-like fashion that delivered rewards to the players. Each player had control over one of the two trays. For instance, Player 1 would decide whether to choose the blue side (i.e., defect, as it delivers one reward to Player 1) or the yellow side (i.e., cooperate, as it delivers three rewards to Player 2) while Player 2 would decide whether to choose the orange side (i.e., defect) or the green side (i.e., cooperate).