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The experiment was designed to test Deci's (1975) informational/controlling analysis with verbal rewards and to assess the joint effects of type of verbal reward and level of surveillance. Compared to a no-reward control, the informational verbal reward enhanced interest in task engagement, but the controlling verbal reward did not. Regardless of type of reward, task interest decreased in linear fashion as surveillance was increased from low to medium to high.
Pittman et al. (Sun,) studied this question.