Effects of task difficulty on sentence comprehension performance of aphasic subjects.

Twenty aphasic subjects participated in an auditory comprehension task in which they were asked to point to pictures named by the examiner. The spoken commands delivered to each subject were either "easy" or "difficult," as determined by the subject's performance in a preexperimental session. Difficulty was determined by the number of items that the subject was asked to point to in sequence. Each subject performed in two conditions. In the Low Error Condition, a small number of difficult commands (as determined in the preexperimental session) was interspersed in a larger number of easy commands (as determined in the preexperimental session). In the High Error Condition, a small number of easy commands was interspersed in a larger number of difficult commands. Analysis of the results indicated that presentation of a series of difficult commands interfered with subject's subsequent performance to commands that would ordinarily be very easy.