SENTENCE COMPREHENSION IN ALZHEIMERS-DISEASE

A visual sentence-picture matching task was used to clarify the nature of the comprehension deficit in Alzheimer's Disease (AD). Test senten ces varied according to how crucial the processing of syntax was in co mputing a correct interpretation. Half the sentences could be understo od through the comprehension of semantic cues alone; the other half re quired the processing of syntactic cues. In the first experiment, sent ences were removed from view before the test pictures were presented; in the second, sentences and pictures were presented together to decre ase demands on working memory. Two factors determined the accuracy of sentence comprehension: whether a syntactic analysis was needed and wh ether additional working-memory resources were needed for temporary st orage. When storage demands were minimized, patients were able to use semantic cues to guide comprehension. When semantic cues were unavaila ble, comprehension was impaired, regardless of whether or not there we re additional storage requirements, providing evidence for a genuine s yntactic deficit that is not due to coexisting semantic impairment or working-memory dysfunction.