Contextual constraint facilitates semantic decisions about object pictures by Alzheimer patients.

Semantic constraints produced by sentence context reduce the time normal adults take to decide whether a given stimulus constitutes a meaningful ending to that sentence. The mechanism responsible for this constraint effect is thought to involve generation of featural restrictions based on context. In the present study, participants heard a sentence whose last word was replaced by an object picture. They decided whether the object formed a sensible ending to that sentence. Contextual constraint present in the sentences greatly influenced decision time: the greater the constraint, the faster the decision. Alzheimer patients were as affected by contextual constraint as were normal adults. The normality of the constraint effect in Alzheimer patients suggests that they can generate featural restrictions and thus retain knowledge of the semantic attributes of objects.