Date of Award:

8-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Psychology

Committee Chair(s)

Timothy A. Shahan

Committee

Timothy A. Shahan

Committee

Gregory J. Madden

Committee

Christopher M. Warren

Committee

Emily R. Weichart

Committee

Erin Beckman

Abstract

Every living organism, including humans, has a finite amount of time available: 24 hours in a day, 365 days in a year, and a certain number of years in its life. At every moment, such an organism will be engaging in one of a multitude of possible activities, such as eating, sleeping, or reading this dissertation. We use the term choice to denote the way in which the organism distributes its time among all these activities, and some of these choice patterns are more beneficial to the organism than others, showcasing the importance of understanding the mechanisms underlying choice. A recent mathematical model known as the augmented matching law proved useful in describing how rats distribute their time among two levers that occasionally produce food when pressed, an arrangement called concurrent schedules of reinforcement that is commonly used to study choice in the laboratory. The experiments described in this dissertation explore several ways in which this model might be extended to account for variables known to affect how animals distribute their time among the activities they have available. Experiment 1 in Chapter II exposed rats to a choice experiment that manipulated the time required to go from one lever to the other. This variable is well-known to affect the amount of time spent at each lever, and the model was able to capture this effect. Experiment 2 in Chapter II attempted to manipulate the difficulty of distinguishing the source of each food reward the rats obtained, which is also known to affect choice, but the manipulation proved ineffective and so the results were uninformative. The experiment described in Chapter III showed how to extend the model to situations where there are more than two activities available. The model was able to describe the results, extending its applicability to situations with any number of alternatives. Given the results of the three experiments, the augmented matching law stands as a general theory of choice in concurrent schedules of reinforcement that has the potential to yield light on other areas such as how animals in the wild forage for food.

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