Fig. 1.

Schematic diagram of the public goods game (PGG). (a) The game consists of 3 steps. Step 1. After receiving the initial money from the experimenter, all participants anonymously decide to cooperate or to free ride. Step 2. Whether the group earned the reward is presented (success/failure). Step 3. The number of cooperators is presented and if the group succeeded, an equal amount of bonus money is distributed to the group members. (b) Three tables display the payoff matrix of each of the 3 conditions. Each of the 2 main motivations to free ride were removed from the standard PGG (condition I). Possible monetary loss was controlled (removed) in condition II (fear-free; right-top in condition II) and greed was controlled in condition III (greed-free; left-bottom in condition III). Free: free ride; Coop.: cooperate.