Some Determinants of Overjustification and Behavioral Momentum

Abstract

The overjustification hypothesis posits that the delivery of external rewards diminishes an individual's intrinsic interest in the activity associated with the reward (Green & Lepper, 1974). This idea remains widely controversial across psychological perspectives. Cognitive and developmental researchers frequently find evidence of the phenomenon (Deci, Koestner, & Ryan, 2001), whereas behavioral researchers rarely observe the effect (Cameron & Pierce, 2002). Importantly, researchers have generally used methods of investigation common to their own field. This has occasioned consistent differences across perspectives in the rate and aggregate history of reward prior to tests of overjustification. Behavioral momentum literature indicates that baseline rate of reward has a central importance in governing response persistence during disruption (such as extinction, as applied in the overjustification effect). Similarly, baseline rate of reward may affect responding during tests of overjustification under conditions amenable to momentum. Aggregate reward history may have a similar relation to behavioral momentum (and possibly to overjustification), to the extent that heightened stimulus-reward associations may obtain over longer durations of stimulus-reinforcer pairings. Experiments 1 and 2 aimed to examine these parameters of reward delivery to determine how the overjustification effect may relate to behavioral momentum and to examine the extent to which the overjustification effect, like persistence, may be a function of stimulus-reinforcer relations. Specifically, Experiment 1 examined aggregate reinforcement history and Experiment 2 examined reinforcer and response rates and their relation to these phenomena. Results from Experiment 1 were generally in-line with our hypotheses: in 3 of 4 cases, overjustification effects were observed infrequently in the Reward-History Condition and persistence was stronger in the Reward-History Condition relative to the No-Reward History Condition. These results suggest longer histories of reward may strengthen responding as it relates to these phenomena. Notably, results also provided a novel demonstration of possible interactions between overjustification and behavioral persistence: patterns of responding consistently projected an inverse relation between these phenomena. In 3 of 4 cases, the Reward-History Condition was associated with very strong persistence and very infrequent overjustification effects. As well, in 3 of 4 cases, the No-Reward History Condition was associated with low to moderate persistence and relatively more frequent overjustification effects. Results from Experiment 2 were inconsistent and did not conform to our hypotheses: across conditions, with few exceptions, results indicated strong persistence and infrequent overjustification effects. Although overjustification effects were relatively rare, both studies provided some evidence to suggest the reinforcing efficacy of the stimuli affected the likelihood of obtaining overjustification effects: tests following rewards that provisionally functioned as reinforcers were less likely to result in overjustification effects.