Effects of phenytoin withdrawal on matching to sample and workshop performance of mentally retarded persons.

The present study was designed to examine the effects of gradual phenytoin withdrawal on the matching to sample performance of three mentally retarded person. The percentage of correct responses per session served as the dependent variable, and the sample and comparison stimuli were red, green, and blue illuminations of translucent response windows. With two of the subjects, the sensitivity of a workshop assembly task to phenytoin effects was explored retrospectively. The dependent variables were percentage of time on task, number of completions, and number and type of prompts required per session. The results showed that doses of phenytoin considerably lower than the suggested optimum therapeutic level impaired the performance of mentally retarded individuals on both matching to sample and workshop assembly tasks. As doses were reduced for each subject, there were increases in the percentage of correct responding on the matching to sample task with the highest percentage correct being obtained after, and only after, the 0-mg dose was reached. In the workshop setting, the greatest number of assemblies completed and the lowest number of prompts required occurred only after the 0-mg dose was reached. The results are discussed in terms of generality, the tasks being well suited ot the study of drug effects with mentally retarded individuals, and implications for habilitation.