The effect of contextual constraint on semantic judgments by Alzheimer patients.

Subjects (Alzheimer patients, normal young and elderly individuals) heard a sentence the last word of which was missing. A visual word then appeared and the subjects decided whether it made a sensible ending to the sentence. Sentences varied in the degree to which their semantic context constrained possible endings to the sentence. The degree of contextual constraint greatly influenced response time--the greater the constraint, the faster subjects made their decisions. While Alzheimer patients were slower than normals, their decision time was affected by contextual constraint to the same degree as that of normals. Thus, the performance of Alzheimer patients was sensitive to the amount of semantic context present in sentences, and this context facilitated their ability to make conscious semantic judgements. These findings suggest that Alzheimer patients are capable of using semantic information in a task requiring attention-dependent processes.