Figure 1.

Experimental design. A, In each one-shot ultimatum game, participants viewed a photograph of the Proposer, the amount of the stake, and the offer, and decided whether to accept or reject the offer while the offer was on the screen. B, In the No-Choice condition of the ultimatum game, participants viewed an identical set of offers but their decisions were determined randomly. C, Offers in the ultimatum game. Each bubble represents an offer. The size of the bubble represents its magnitude, and its vertical position corresponds to its fairness. Offer magnitude and offer fairness were not significantly correlated (r = 0.006, p = 0.968), which permitted us to detect BOLD responses to fairness over and above responses to magnitude.