Psychology Ph.D. Dissertations


Incentive Contrast in Humans: Behavioral and Electroencephalographic Studies

Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)



First Advisor

Howard Cromwell (Advisor)

Second Advisor

Khani Begum (Other)

Third Advisor

William O’Brien (Committee Member)

Fourth Advisor

Sherona Garrett-Ruffin (Committee Member)


Incentive contrast effects occur when reward values change from previous experience and comparisons are made between the previous and current value. The value reupdating depends on the relative outcomes that are comparable. The changes occur after exposure to the identical reward whose value has changed depending upon the differences between previous and current experiences. Studies have been done to examine the incentive contrast effects using extrinsic rewards, such as money and points earned. However, no studies have been done to investigate if intrinsic rewards can induce incentive contrast effects in humans and in general, how brain oscillations change related to incentive contrast effects. We predicted that the order of exposure to different levels of difficulty of the game would lead to incentive contrast effects. Specifically, we hypothesized that the performance of game playing would be enhanced in the easier-level immediately preceded by the difficult-level (positive contrast) and impaired in the difficult-level when preceded by an easier-level (negative contrast). Moreover, the greater positive emotional response was predicted to lead to better performance, while negative emotion would result in bad performance. In Experiment 2, brain oscillations were recorded at Fz and Cz sites after each session of game playing. We hypothesized that the power of beta oscillation would increase in positive incentive contrast, while the power of theta oscillation would increase in negative incentive contrast. Furthermore, we believe the theta/beta ratio would decrease in positive incentive contrast and increase in negative incentive contrast. Results supported these predictions partially that only negative behavioral incentive contrast effect was revealed in Experiment 1. The performance in the games was positively related to motivation and positive affect and negatively related to negative affect (frustration). No incentive contrast effect was found in psychological measures and brain oscillations in experiment 2. However, beta oscillation was discovered to be positively related to game difficulty. Conversely, theta/beta ratio decreased with game difficulty. These explorative studies will broaden the research of incentive contrast effects to intrinsic reward and provide some new insights into the brain mechanism of reward processing and specifically, incentive contrast effects.