Overjustification Effect

The overjustification effect is a phenomenon in which providing an expected external incentive, such as money or a prize, for an activity a person already finds intrinsically rewarding can reduce that person's intrinsic motivation to keep doing it. It is understood through the interaction of intrinsic and extrinsic motivation, in which an external reward can undermine a pre-existing intrinsic interest, a process researchers describe as motivational crowding out. The effect has been studied extensively by Edward Deci and Mark Lepper. Once the external reward is withdrawn, a person who has come to attribute their engagement in the activity to the reward rather than to their own interest may show reduced interest in continuing it, a shift described as cognitive re-evaluation, though how strongly this happens varies by context. In education, the overjustification effect bears directly on the use of grades, prizes and other extrinsic rewards to motivate students: rewarding an activity a student already enjoys risks teaching the student to see the reward, rather than the activity itself, as the reason to keep doing it.