The overjustification effect occurs when an external incentive such as money or prizes decreases a person's intrinsic motivation to perform a task. According to self-perception theory, people pay more attention to the incentive, and less attention to the enjoyment and satisfaction that they receive from performing the activity. The overall effect is a shift in motivation to extrinsic factors and the undermining of pre-existing intrinsic motivation.
In one of the earliest demonstrations of this effect, Mark Lepper and Richard Nisbett promised a group of 3–5-year-old children that they would receive a "good player" ribbon for drawing with felt-tipped pens. A second group of children played with the pens and received an unexpected reward (the same ribbon), and a third group was not given a reward. All of the children played with the pens, a typically enjoyable activity for preschoolers. Later, when observed in a free-play setting, the children who received a reward that had been promised to them played significantly less with the felt-tipped pens. The researchers concluded that expected rewards undermine intrinsic motivation in previously enjoyable activities.[1] A replication of this experiment found that rewarding children with certificates and trophies decreased intrinsic interest in playing math games.[2]
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One explanation of the overjustification effect is self-perception theory. According to this approach, people infer causes about their behavior based on external constraints. The presence of a strong constraint (such as a reward) would lead people to conclude that they are performing the behavior for the reward.[3] This would shift the individual's motivation from intrinstic to extrinsic.
The most detailed explanation for the overjustification effect is cognitive evaluation theory. This theory proposes that tangible rewards (like money) are perceived as controlling or coercive, and act to decrease perceived self-determination and undermine intrinsic motivation. Because unexpected tangible rewards do not motivate behavior during a task, they are less likely to be perceived as controlling, and thus less likely to undermine intrinsic motivation. Informational rewards (like praise) increase perceived self-determination and feelings of competence, and consequently tend to enhance intrinsic motivation.[4]
The overjustification effect is controversial because it challenges previous findings in psychology on the general effectiveness of reinforcement on increasing behavior, and also the widespread practice of using incentives in the classroom. Nevertheless, two meta-analyses found that intrinsic motivation is diminished by expected, tangible rewards in both children and adults, especially when the reward is given for simply performing a task, regardless of the results. Nontangible rewards, such as verbal praise, and unexpected rewards do not undermine intrinsic motivation. In fact, praise may actually increase intrinsic motivation.[5][6]
These conclusions were challenged in a separate meta-analysis which found that tangible rewards offered for outperforming others and for performing uninteresting tasks (in which intrinsic motivation is low) lead to increased intrinsic motivation.[7] A rebuttal defended the original findings and concluded that this analysis was flawed.[8]
Research in this area suggests that parents and educators should rely on intrinsic motivation and preserve feelings of autonomy and competence as much as possible.[9] When the task is unattractive and intrinsic motivation is insufficient (e.g. household chores), then extrinsic rewards are useful to provide incentives for behavior. Student grades may not undermine intrinsic motivation because grades convey information about competence, much like praise.[10]
School programs that provide money or prizes for reading books have been criticized for their potential to reduce intrinsic motivation by overjustification. However, a study of the Pizza Hut program, Book It!, found that participation in the program neither increased nor decreased reading motivation.[11] Although motivating students to read by rewarding them may undermine their interest in reading, it may also encourage the reading skills necessary for developing an interest in reading.