The study of bilingualism in individuals with neurological dysfunction (primarily unilateral focal lesions) has yielded a number of mixed findings. These include cases of parallel breakdown in both languages, breakdown of only one of a patient's languages (either first or second) with a relative sparing of the other language, and initial loss of both languages with differential recovery (i.e. one language improves more than the other). The use of bilingual AD offers an opportunity to better identify the nature of language breakdown under neurological insult for the following three reasons. First of all, patients with AD suffer from progressive bilateral patterns of cortical degeneration. This provides a larger homogeneity than studies with patients suffering form unilateral focal lesions. Second, the identification of patients in the early stages of AD will permit us to identify patterns of language dominance before the disease has run its course. Finally, the progressive nature of AD should help to elucidate the differential patterns of maintenance and loss that are observed in both of a patient's languages at various points in time. Two on-line tasks will be used to test bilingual language processing. In the cross-modal word pronunciation paradigm, subjects will presented with auditory texts and probed during the text with semantically or linguistically congruent and incongruent words. The second on-line task, the sentence interpretation task, is a forced choice task in which subjects will be asked to pick the subject of sentences with two nouns and a verb. These two paradigms will be employed with AD patients and elderly controls. AD patients will be tested only once. This longitudinal design should provide us the essential information about the effect of diffuse neurological insult on the pattern of syntactic and semantic sparing or breakdown in bilingual AD patients. These results, when compared to those of normal elderly controls and college aged controls, should help to reveal the impact of aging and dementia on bilingual language processing.
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