[Reciprocity and identity protection: reasons for rejection in the ultimatum game].

An ultimatum game and two impunity games, in which rejection by the Responder had no impact on the Proposer's earnings, were conducted with 228 participants. The impunity game was run in two conditions: with feedback information, where the Responder's choice was disclosed to the Proposer, and without feedback information, where the Responder's choice was not disclosed to the Proposer. These two conditions were used to determine whether the motivation for rejection in the impunity game was social punishment or identity protection. The three game conditions and the Responder or Proposer roles were manipulated between participants. The rejection rates in the two impunity games were about half the rate in the ultimatum game: there was no difference in the rejection rates between the two feedback conditions of the impunity game. These results indicate that rejection in the ultimatum game is largely based on identity protection. The adaptive role of maintaining self-image as a commitment device was discussed.