Anomaly judgments of subject-predicate relations in Alzheimer's disease

Claims that patients with probable Alzheimer's disease (AD) have semantic memory difficulty have received equivocal support. A common assumption has been that defining or core information determines the truth value of word meaning on measures requiring semantic memory such as category membership judgments or confrontation naming, but this assumption may not be valid. In the present study, we assessed the comprehension of subject-predicate sentences independent of their truth value by asking AD patients to judge the coherence of statements such as "The tulip is tall" or "*The tulip is jealous." We found that AD patients are significantly more impaired than controls at judging the coherence of these simple subject-predicate sentences. Moreover, AD patients were more successful at judging the coherence of statements that contain attributes with a narrow scope of reference compared to attributes with a broad scope of reference. These findings support the hypothesis that AD patients have a semantic memory impairment and suggest a specific deficit processing the network of semantic relations underlying word meaning in semantic memory.