Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)




Timothy A. Shahan


Preference for one stimulus context over another and resistance to disruption within those contexts are a function of the conditions of reinforcement arranged within those contexts. According to behavioral momentum theory, these measures are converging expressions of the concept of response strength. Most studies have found that preference in concurrent chains and resistance to change are greater in contexts presenting higher rates or larger magnitudes of reinforcement. The present series of experiments attempted to extend behavioral momentum theory by examining whether differences in reinforcer type affect relative response strength with rats lever pressing for different types of food. In Experiment 1 of Chapter 2, several nonuniform disrupter types were examined that provided free access to a food type that was the same as one reinforcer type. Responding decreased more in the context presenting the same type of reinforcer as the disrupter, suggesting that many traditional disrupters (e.g., satiation) are inappropriate for examining how reinforcer type impacts response strength. Therefore, extinction was used throughout the remainder of the experiments to more uniformly disrupt responding across contexts. In Experiment 2 of Chapter 2, resistance to extinction was assessed when food pellets and a sucrose solution maintained responding across contexts. Moreover, relative reinforcer type was manipulated by changing the sucrose concentration across conditions. Relative response rates were systematically affected by changing sucrose concentration, but relative resistance to extinction was not. In Experiment 3 of Chapter 2, qualitative difference between reinforcers was enhanced and preference also was assessed to provide a converging measure of response strength. Preference and relative response rates were systematically affected, but relative resistance to extinction again was not. Finally, in Chapter 3, relative reinforcer rate and type were manipulated while assessing preference and resistance to extinction using the matching law. Preference, but not resistance to extinction, consistently was affected by changes in reinforcer rate and type. Systematic deviations in sensitivity and bias, however, suggested that different reinforcer types interacted with reinforcer rate. Overall, these findings suggest that the overall context of reinforcement, including interactions between different reinforcer types, should be considered when assessing preference and relative resistance to change.

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