the incentive was provided for one session and was then arbitrarily withdrawn in the next and such incentive plans do not exist in the real world. Also, the reduced intrinsic interest seen in subjects may be explained by a negative reaction when the reward was withheld. Eisenberger and his colleges also claimed that the validity of the dependent measure is highly questionable in the Deci study. Laboratory results that used the amount of free time spend on the task as the dependent measure are shown to be far weaker than when self reports are used for these measures. The Deci study gives far less weight to self reports, however self-reports about subjects' level of internal motivation seem to be a more direct measure of the psychological state of interest. Considerable research has also shown that rewards tend to enhance feelings of competence and autonomy and high standards, pressure and competitiveness are able to increase these effects. For example, employees view earning incentives as enjoyable rather than a dreaded tool of management control. These findings are in contrast with the psychological mechanism for effects that Deci and his colleges had claimed in the past. Also in the past 30 years, notable academic reviews of rewards have confirmed that monetary incentives have shown to significantly increase performance. Additionally, some activities require a significant level of mastery or engagement before its attractiveness becomes apparent to an individual, in such cases external incentives may be useful to build individuals up to that level. Token economy programs represent one example in which there is evidence showing that such programs have successfully implemented extrinsic rewards to increase interest in certain broad classes of activities. There are also differences in effect among the different age groups. According to Deci et al. (1999), 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 behavior, which causes them to operate with performance-goal orientations. It is therefore speculated that such differences are far greater between children and employed workers. A rebuttal defended the original findings, concluding that this analysis by Cameron (2001) was flawed and that Cameron's inclusion of boring tasks in analyzing