| Recent research has demonstrated that behavioral variability is modulated by reinforcement expectation. These experiments have largely been conducted in rats, and have typically examined the behavioral effects of manipulating reinforcement probability. The effects of other aspects of reinforcement on behavioral variability have been largely ignored. This dissertation is comprised of a number of studies that investigate the associative factors that modulate behavioral variability. Chapter 1 serves as a thorough review of the literature that informs the current research. Chapter 2 details the results of two experiments that indicate that reinforcement probability controls behavioral variation in pigeons in both the spatial and temporal dimensions. Chapter 3 details two experiments that investigate the effects of reward magnitude and delay to reinforcement on operant variability of behavior in pigeons. This paper demonstrates that a large reward size mitigates the behavioral effects of a reduced probability of reinforcement. Similarly, the delay of reinforcement produces an upward shift in the level of behavioral variability. Chapter 4 demonstrates that the effects of expectation on behavioral variability are instantiated in a task that is behaviorally neutral (i.e., a Pavlovian task). Chapter 5 details a study in which the effect of reward probability was examined with respect to foraging behavior in rats. This study indicates that behavioral variability increases with reduced expectation of foraging success, which suggests that the relationship between behavioral variability and expectation may be an adaptive one. Chapter 6 examines the effect of differential reward probability on the production of behavioral variability across a set of operant behavioral options. Chapter 7 details the effects of three different reinforcement schedules (i.e., positive reinforcement, Pavlovian, omission) on behavioral variability in pigeons. Results indicated that behavioral variability was differentially affected by reinforcement schedule; indeed, reinforcement probability was not as great a predictor in the production of variability as the schedule of reinforcement. The results are discussed with respect to the potentially adaptive nature of the relationship between expectation and variability. |
