利害葛藤のない場面において互酬性の期待が順社会的行動に及ぼす影響 : 繰り返し二者間囚人のジレンマゲームを用いて

Abstract

The present study investigated whether expectations of reciprocity influence prosocial behaviors in a situation when there is no conflict of interests using an iterated two-person Prisoner's Dilemma. Thirty-six university students participated in the experiment. The task was to run a hamburger shop competing with the other one in an imaginative small village. The owner of the other shop was in fact the computer, which controlled the experimental sessions. Two mutually unfamiliar participants were allocated to a shop whose cost (300, 000 yen per month) was lower than that of the other (600, 000 yen per month). They were rewarded (300 yen) when their earnings exceeded the cost after several trials ("days"). There were two experimental conditions (between-subject design). In the Alternation condition, they were instructed to change their position from the owner of low cost shop to that of the other in the second session. In the Maintenance condition, they were instructed to keep their position of the owner of low cost shop during two sessions. It was shown that once they had earned enough to get the reward, the participants in the Alternation condition changed their attitude to be cooperative, while those in the Maintenance condition did not. This clearly shows that even when there is no conflict of interests, people tend to display prosocial behavior due to the expectation of reciprocity in the immediate future.