Fig. 1.

A modified helping game. Control condition (shaded cells): Producer may help or not, Consumer makes no choice; possible outcomes are inaction or gift. Tokens condition (all cells): players have tokens. Producer chooses a row: no help, give help, or sell help in exchange for a token. Consumer simultaneously chooses a column: do nothing, transfer a token unilaterally, or buy help in exchange for a token. Possible outcomes are inaction, gift, donation, or trade. When Consumer has no tokens, the actions available in the Tokens and Control conditions coincide (trade impossible). Numbers are payoffs in CUs.