Working memory and on-line sentence comprehension in patients with Alzheimer's disease.

We examined the ability of patients with dementia of the Alzheimer's type (DAT) and normal controls to perform a sentence acceptability judgment task that required determining the referent for a reflexive pronoun. Performance on three different sentence types that differed in terms of syntactic complexity was assessed. Subjects performed the task alone and under two different dual-task conditions which required continuous, externally paced responses. DAT patients were more affected than controls by the dual-task conditions, but were not disproportionately impaired on the more complex sentence types. The failure of DAT patients to be disproportionately affected on the most complex sentence types in the dual-task conditions provides evidence for the separation of the processing resources that are used in sentence comprehension from those involved in other tasks.