Eleah Sunde

Date Approved


Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department or School


Committee Member

James Todd, Ph.D.

Committee Member

Rusty McIntyre, Ph.D.

Committee Member

Kenneth Rusiniak, Ph.D.


The overjustification effect posits that rewards undermine intrinsic motivation, such that an individual’s engagement in previously intrinsically motivating tasks will decrease when a previously reliable reward is withdrawn. This study aimed to determine if this overjustification effect can be demonstrated in rats, with typical confounds related to social and verbal aspects of reward delivery controlled for. Baseline “intrinsic” wheel-running rates of seven SpragueDawley rats were compared to rates that followed administration and withdrawal of a contingent sucrose reward, and to rates of rats in control conditions (n = 7). Consistent with the author’s hypothesis, the reward group’s wheel-running did not decrease below the initial baseline following this procedure, as would be predicted by the overjustification hypothesis. This suggests that the overjustification effect demonstrated in humans may be better conceptualized as being related to social and verbal aspects of rewards rather than as an inherent feature of reward administration and withdrawal.