Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Dr. R. Wayne Fuqua

Second Advisor

Dr. Jack Michael

Third Advisor

Dr. Richard Malott


Four mentally retarded adults participated twice daily in assessments of their performance of a titrating delayed matching to sample discrimination. Trials began with the center of three response panels illuminated by one of three colors. Depression of the center panel terminated the light on the center panel and, following a delay, resulted in the presentation of two comparison colors on the side panels. Pressing the side panel illuminated by the same color which had been presented on the center panel yielded a reinforcer, while incorrect responses produced a brief timeout. The delay between depression of the center response panel and presentation of the comparison stimuli varied according to the accuracy of the subject's performance. Following four consecutive correct responses at a given delay, the delay was increased for the subsequent trial to the next higher step in a specified progression. Each error decreased the delay for the next trial to the previous step in this progression. The primary dependent variable was the limit of delay, defined as the longest delay at which the subject emitted four consecutive correct responses in a 30 minute session. Concurrent with these assessments, the subjects' chronic doses of thioridazine were reduced systematically in a multiple baseline across subjects design. For all of the subjects, the limit of delay increased after, and only after, reductions in the daily thioridazine dose had been implemented. The latencies to press the center and side response panels either increased or remained stable for all subjects as the dose was reduced. Informal observations of the subjects in their institutional living environments revealed no systematic increases in inappropriate behavior for any of the subjects following drug reductions. The results indicate that the withdrawal of chronically administered thioridazine resulted in increased accuracy in a delayed matching to sample task, suggesting strongly that the drug impairs performance of this discrimination. Until further research is conducted to determine the extent to which this disruption affects adaptation to the environment, caution should be used in prescribing thioridazine and its indiscriminate use should be curtailed.

Access Setting

Dissertation-Open Access

Included in

Psychology Commons