The overjustification effect is a phenomenon in psychology in which providing expected external incentive, such as money or prizes, for an already intrinsically rewarding activity can reduce a person's intrinsic motivation to perform that activity. It is commonly understood in terms of the interaction between intrinsic and extrinsic motivation, where external rewards may undermine pre-existing intrinsic interest, a process often described as motivational "crowding out". The effect has been widely discussed in research by Edward Deci and Mark Lepper. Once rewards are no longer offered, individuals may show reduced interest in the activity, namely, cognitive re-evaluation, although the extent of this effect can vary depending on contexts.
Theoretical mechanisms Several theoretical frameworks have been used to explain the overjustification effect, particularly focusing on the distinction between intrinsic motivation (when a person does the activity in the absence of a reward contigency or control) and extrinsic motivation (the activity with a reward contigency or control).
Self-perception theory According to self-perception theory, developed by psychologist Daryl Bem, a person infers their own internal states based on external conditions and constraints to some extent. Bem’s self-perception theory believes that when a salient external incentive is present, individuals may attribute their behaviour to that external cause rather than to intrinsic interest. This process of self-inference is particularly likely when external constraints are strong (such as the presence of a reward) or when internal cues are weak or ambiguous. As a result, the activity may be reinterpreted as being performed for the rewards rather than for its inherent enjoyment. Over time, this would lead a person to conclude that they are performing the behavior solely for the reward, which shifts the person's motivation from intrinsic to extrinsic.
A classic example comes from an experiment by Leon Festinger and James M. Carlsmith (1959), in which participants were asked to complete a boring task and then tell another fellow student that it was enjoyable. Afterwards, participants were asked how much they had enjoyed the task. Those who were paid only $1 evaluated the task as significantly more enjoyable than those who received $20. This is because individuals who receive low compensation ($1) are more likely to rule out financial incentive as a motivating factor in their thinking process, and instead infer that their behaviour reflected genuine interest. When the external reward is subsequently removed, individuals may be less likely to engage in the activity, providing a theoretical explanation for the overjustification effect.
Cognitive evaluation theory Laboratory studies in the 1970s indicated that individuals under conditions with extrinsic rewards showed diminished intrinsic motivation. Deci and his colleagues developed the cognitive evaluation theory to explain the underlying causes. As a sub-theory of self-determination theory, cognitive evaluation theory proposes that intrinsic motivation is shaped by individuals’ perceived locus of causality (PLOC), referring to whether individuals feel free to follow their inner interests, as well as by individuals’ experience of autonomy and competence.
According to this framework, external rewards and other contextual factors can influence intrinsic motivation by shifting individuals’ PLOC. Intrinsic motivation may increase if rewards are interpreted as pertaining positive information about an individual’s competence and self-control. In contrast, if individuals perceive the results as indicative of external control, this decreases their feelings of self-control and competence, which in turn decreases intrinsic motivation. It underlies the overjustification effect, as rewards perceived as controllong would shift the locus of causality and reduce intrinsic motivation.
In general, this account is broadly consistent with Self-perception theory, which similarly emphasises the importance of external cues in changing individuals’ intrinsic motivation, although the Cognitive evaluation theory specifies more on the extent to which people feel like they originate their behaviour.
Self-determination theory Self-determination theory (SDT) is a theory of human motivation that focuses on how individuals internalise, or take on, goals and values as their own. It further distinguishes between different forms of extrinsic motivation, ranging from external regulation to more autonomous forms such as identified and integrated regulation. This continuum highlights that the impact of rewards on intrinsic motivation depends on the extent to which behaviours are internalised and experienced as self-determined. The distinction answers why some rewards undermine intrinsic motivation while others do not.
SDT is also a broad theory that extends the predictions of Cognitive evaluation theory to a wider range of contexts, including work organisations.The theory differentiates between various types of motivational states, distinguishes the organisational conditions where extrinsic rewards are more effective than intrinsic rewards, examines individual differences in orientation toward intrinsic versus extrinsic motivation and discusses managerial behaviour that can enhance intrinsic motivation.
Findings from the Deci et al. (1989) study have supported Self-determination theory as an approach to work motivation by showing how managers can impact the work attitudes of their employees. For example, the study reported that managerial autonomy support which included provision of options, giving relevant information in a non-autonomous way, acknowledging subordinates' perspectives and cultivating self-initiation resulted in employees having more positive work-related attitudes such as higher level of job satisfaction and increased level of trust in corporate management. This perspective suggests that the overjustification effect is not universal, but depends on whether rewards are perceived as supporting or constraining basic psychological needs.
Experimental evidence The overjustification effect has been widely demonstrated in many settings. These empirical research demonstrates that the impact of external rewards on intrinsic motivation relies on how rewards are structured and interpreted.
In one of the earliest demonstrations of this effect, Edward Deci and his colleagues conducted a laboratory experiment in 1971 where subjects showing baseline interest in solving a puzzle were exposed to two different conditions. The control group were not paid on all three days while the experimental group were not paid on the first day, were paid on the second day and were not paid again on the third day. The subjects were given a break in the middle of each session and were being observed while doing whatever they wanted. The results showed that the experimental group spent significantly more time than the control group playing the puzzle during their break time on day 2 when they were paid but significantly less on day 3 when they were not paid. This was interpreted as evidence that the extrinsic monetary reward significantly reduced their intrinsic motivation to engage in the task.
Researchers at Southern Methodist University conducted an experiment on 188 female university students in which they measured the subjects' continued interest in a cognitive task (a word game) after their initial performance under different incentives. The subjects were divided into two groups. Members of the first group were told that they would be rewarded for competence. Above-average players would be paid more and below-average players would be paid less. Members of the second group were told that they would be rewarded only for completion. Their pay was scaled by the number of repetitions or the number of hours playing. Afterwards, half of the subjects in each group were told that they over-performed, and the other half were told that they under-performed, regardless of how well each subject actually did. Members of the first group generally showed greater interest in the game and continued playing for a longer time than the members of the second group. "Over-performers" continued playing longer than "under-performers" in the first group, but "under-performers" continued playing longer than "over-performers" in the second group. This study showed that, when rewards do not reflect competence, higher rewards lead to less intrinsic motivation. But when rewards do reflect competence, higher rewards lead to greater intrinsic motivation.
Richard Titmuss suggested that paying for blood donations might reduce the supply of blood donors. To test this, a field experiment with three treatments was conducted. In the first treatment, the donors did not receive compensation. In the second treatment, the donors received a small payment. In the third treatment, donors were given a choice between the payment and an equivalent-valued contribution to charity. None of the three treatments affected the number of male donors, but the second treatment almost halved the number of female donors. However, allowing the contribution to charity fully eliminated this effect.
Overall, these findings show that the overjustification effect is not uniform, and is consistent with the explanations in Cognitive evaluation theory and Self-determination theory.
Moderating factors There remains considerable ambiguity regarding the conditions under which the overjustification effect occurs and continue to be the subject of ongoing research. For instance, a commonly cited illustration shows a young man who initially enjoys reading, but may become to view it as ‘work’ if external rewards are introduced.
The major moderators are task characteristics, reward structures, and individual differences (e.g., age group).
1. Initial intrinsic interest Initial interest is an essential moderator in the motivation-undermining process. Researchers consistently found rewards reduced individuals’ motivation in high interest group in educational settings. Outside of the classrooms, a recent study indicates that in video game play situations, there is also a decrease in game-play willingness for participants with high initial interest.
In contrast, extensive evidence suggests that rewards may have the opposite effect when initial interest is low. A 2001 meta-analysis showed that rewards can increase intrinsic motivation for tasks that initially hold little intrinsic interest. Similarly, another separate meta-analysis found that tangible rewards offered for outperforming others and for performing uninteresting tasks (in which intrinsic motivation is low) lead to increased intrinsic motivation.
In either direction, these findings collectively suggest that initial interest plays a critical role in deciding whether external rewards undermine or enhance intrinsic motivation.
2. Age group There are also differences in effect among the different age groups. The negative effects extrinsic contingencies have on intrinsic motivation seem to be more severe for children than college students. One possible explanation is that college students have greater cognitive capacity, enabling them to better separate informational and controlling aspects of rewards. Hence they are able to interpret rewards as indicators of effective performance rather than controlling their behaviour, which causes them to operate with performance-goal orientations. Meanwhile, it has been suggested that older individuals may have more stable intrinsic interests, making them less susceptible to small rewards. It is therefore speculated that such differences are far greater between children and employed workers.