Abstract

The purpose of this study is to investigate the underlying mechanism of decrease of intrinsic motivation with extrinsic rewards. Two competing explanations about these phenomena, self-attribution and Crespi's (1942) incentive amount shift effect, were tested. High school girl students were told to solve two hinds of very similar word puzzles successively. A large(or no) amount of incentive was given with one task and small(or no) amount was given with other task. After finishing the first task and before beginning the second one, interest scale was administered. In Experiment 1, intrinsic motivation was found to be undermined by task-contingent rewards, through the mecahnism of self-attribution(or unpleasant feeling). In Experiment 2, task-noncontingent rewards, which were given as gratitude, did not undermine intrinsic motivation. In this situation, the change of intrinsic motivation according to reward shift(amount shift, but not existence shift) was found. In Experiment 3, the results of Experiment 2 were replicated.