Processing capacity and sentence comprehension in patients with alzheimer's disease

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Abstract
A sentence-picture matching task was used to test the ability of patients with dementia of the Alzheimer's type (DAT) and age- and education-matched control subjects to interpret nine different sentences. These sentences differed on two dimensions…syntactic complexity and number of propositions. Subjects were tested on this task with no concurrent task (alone) and while concurrently remembering a digit load that was one less than their span or equivalent to their span. Neither group of subjects showed an effect of syntactic complexity, but DAT patients did show an effect of the number of propositions in a sentence. For all subjects, comprehension of sentences with more propositions was more greatly affected by larger digit loads, but comprehension of more complex syntactic structures was not. The performance of DAT patients was more affected than that of the control subjects on the digit task, but they were not disproportionately impaired on the sentence types which were more complex or had more propositions compared to normals. The results are discussed in relationship to the hypothesis that there is a sentence comprehension impairment in DAT that is related to the processing resource requirements of different aspects of the sentence comprehension process.