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A major concern in psychology and education is that rewards decrease intrinsic motivation to perform activities. Over the past 30 years, more than 100 experimental studies have been conducted on this topic. In 1994, Cameron and Pierce conducted a meta-analysis of this literature and concluded that negative effects of reward were limited and could be easily prevented in applied settings. A more recent meta-analysis of the literature by Deci, Koestner, and Ryan (1999) shows pervasive negative effects of reward. The purpose of the present article is to resolve differences in previous meta-analytic findings and to provide a meta-analysis of rewards and intrinsic motivation that permits tests of competing theoretical explanations. Our results suggest that in general, rewards are not harmful to motivation to perform a task. Rewards given for low-interest tasks enhance free-choice intrinsic motivation. On high-interest tasks, verbal rewards produce positive effects on free-choice motivation and self-reported task interest. Negative effects are found on high-interest tasks when the rewards are tangible, expected (offered beforehand), and loosely tied to level of performance. When rewards are linked to level of performance, measures of intrinsic motivation increase or do not differ from a nonrewarded control group. Overall, the pattern of results indicates that reward contingencies do not have pervasive negative effects on intrinsic motivation. Theoretical and practical implications of the findings are addressed.

Meta-analyses indicated that rewards increase perceived self-determination and that rewards' effects on intrinsic motivation depend on the performance requirement. Reward for meeting vague performance standards reduced the subsequent choice to carry out the task and did not affect self-reported interest. Reward for meeting absolute performance standards did not affect free choice but increased self-reported interest. Reward for exceeding others increased both free choice and self-reported interest. Applied studies commonly found positive or null relationships between reward and intrinsic motivation. The findings suggest that reward procedures requiring ill-defined or minimal performance convey task triviality, thereby decreasing intrinsic motivation. Reward procedures requiring specific high task performance convey a task's personal or social significance, increasing intrinsic motivation.

Pigeons' choice between reliable (100%) and unreliable (50%) reinforcement was studied using a concurrent-chains procedure. Initial links were fixed-ratio 1 schedules, and terminal links were equal fixed-time schedules. The duration of the terminal links was varied across conditions. The terminal link on the reliable side always ended in food; the terminal link on the unreliable side ended with food 50% of the time and otherwise with blackout. Different stimuli present during the 50% terminal links signaled food or blackout outcomes under signaled conditions but were uncorrelated with outcomes under unsignaled conditions. In signaled conditions, most pigeons displayed a nearly exclusive preference for the 100% alternative when terminal links were short (5 or 10 s), but with terminal links of 30 s or longer, preference for the 100% alternative was sharply reduced (often to below .5). In unsignaled conditions, most pigeons showed extreme preference for the 100% alternative with either short (5 s) or longer (30 s) terminal links. Thus, pigeons' choice between reliable and unreliable reinforcement is influenced by both the signal conditions on the unreliable alternative and the duration of the terminal-link delay. With a long delay and signaled outcomes, many pigeons display a suboptimal tendency to choose the unreliable side.

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This article reviews research on the effects of reinforcement/reward on intrinsic motivation. The main meta-analysis included 96 experimental studies that used between-groups designs to compare rewarded subjects to nonrewarded controls on four measures of intrinsic motivation. Results indicate that, overall, reward does not decrease intrinsic motivation. When interaction effects are examined, findings show that verbal praise produces an increase in intrinsic motivation. The only negative effect appears when expected tangible rewards are given to individuals simply for doing a task. Under this condition, there is a minimal negative effect on intrinsic motivation as measured by time spent on task following the removal of reward. A second analysis was conducted on five studies that used within-subject designs to evaluate the effects of reinforcement on intrinsic motivation; results suggest that reinforcement does not harm an individual’s intrinsic motivation.

Cross-sectional studies have suggested that total and bioavailable testosterone levels are reduced in some male athletes. Such changes may be related to loss of body weight, increased serum cortisol, and/or alterations in LH pulsatile release. To determine how endurance training may affect androgen levels, we measured serum total testosterone, sex hormone-binding globulin, free androgen index, LH, FSH, PRL, cortisol, and weight in 15 previously sedentary males. We also examined pulsatile LH release in a subset of 5 subjects. Over 6 months of training, the men increased weekly running mileage to an average of 56 km/week. Total testosterone and free androgen index levels decreased significantly. PRL and cortisol also decreased, while single sample LH and FSH remained unchanged. There was a significant reduction in weight, which did not correlate with changes in serum testosterone levels. LH pulsatile release was not altered by training in the subset of 5 runners. These data confirm previous findings of physiological reduction in serum testosterone and PRL levels and suggest that the testosterone decrease is not related to changes in LH pulsatile release, weight, or increased serum cortisol levels.

This review concerns human performance on concurrent schedules of reinforcement. Studies indicate that humans match relative behavior to relative rate of reinforcement. Herrnstein's proportional matching equation describes human performance but most studies do not evaluate the equation at the individual level. Baum's generalized matching equation has received strong support with humans as subjects. This equation permits the investigation of sources of deviation from ideal matching and a few studies have suggested variables which control such deviations in humans. While problems with instructional control are raised, the overall findings support the matching law as a principle of human choice.