Psychology ETDs

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The primary purpose of this experiment was to demonstrate how different percentages of reinforcement can result in differential amounts of stimulus control. The initial conditions were designed to see if organisms could distinguish between different reinforcement percentages of different stimuli, even though these stimuli always appeared in compound and never in isolation. In Condition I, four stimuli were used with the following absolute reinforcement percentages: 75, 75, 50, and 0, corresponding to three different tones and a light. Results showed that the light had become a conditioned inhibitor but that no difference in stimulus control was obtained between the 75% and 50% reinforced stimuli. Condition II showed that when reinforcement percentages were changed to 75, 75, 25, and 0, a difference in percent responding between 75% and 25% reinforced tones could be obtained. The light again demonstrated strong controlling properties as a conditioned inhibitor. Due to discrepant results in the first two conditions, and due to the strong effect of the light as a conditioned inhibitor, only three stimuli were used in Condition III, where reinforcement percentages were 75, 75, and 50 for three tones. Data analysis indicated a significant difference between response percentages of 75% and 50% reinforced cues. Acquisition data demonstrated that the task was difficult and the discrimination poor. Condition IV examined the effect of different percentages of reinforcement on two stimuli in the same modality. Results showed that whether the discrimination between a 75% and 50% reinforced cue was obtained depended upon the physical similarities and differences of the tones. Large differences were obtained when stimuli were farther apart in intensity. Condition V investigated these same reinforcement percentages with stimuli in two different modalities. Large differences in stimulus control were obtained. Results from all five conditions indicate that cue relevance may be viewed as a continuum, but that differences in stimulus control also depend on the number of stimulus modalities involved, the differences and similarities of stimuli, and their saliencies. Furthermore, a conditioned inhibitor was demonstrated for the first time within an instrumental appetitive conditioning paradigm.

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First Committee Member (Chair)

Frank Anderson Logan

Second Committee Member

G. Robert Grice

Third Committee Member

Thomas Patrick Friden



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Psychology Commons