Abstract
An assessment is made of the effects of an antiepileptic drug, diphenylhydantoin sodium on the performance of 20 normal subjects. The subjects were presented with a binary classification task. Performance in the drug condition was compared with that in the placebo condition. The primary dependent variable was the response accuracy. Although the subjects were given instructions which stressed speed of decision, reaction time was not measured. The analysis of the data revealed that the drug enhanced performance by reducing the number of errors made. In order to understand the effect of the drug on performance better, it was necessary to obtain a much more detailed account of the subjects' performance. In a second experiment, error rate and reaction time were measured and related to the complexity of the decisions on each trial. The analysis of the data revealed that the drug reduced the error rate and the reaction time. This effect depended on the complexity of the decisions, and the rate at which decisions were made. The inverted-U hypothesis which related arousal to performance changes was presented as a possible explanation for the effect of the drug. It is proposed that the drug may reduce the level of over-arousal to an optimum level and facilitate performance by this normalizing effect.