DOUBLE DISSOCIATION OF SEMANTIC CATEGORIES IN ALZHEIMERS-DISEASE

Data that demonstrate distinct patterns of semantic impairment in Alzh eimer's disease (AD) are presented. Findings suggest that while groups of mild-moderate patients may not display category specific impairmen ts, some individual patients do show selective impairment of either na tural kinds or artifacts. We present a model of semantic organization in which category specific impairments arise from damage to distribute d features underlying different types of categories. We incorporate th e crucial notions of intercorrelations and distinguishing features, al lowing us to demonstrate (1) how category specific impairments can res ult from widespread damage and (2) how selective deficits in AD reflec t different points in the progression of impairment. The different pat terns of impairment arise from an interaction between the nature of th e semantic categories and the progression of damage. (C) 1997 Academic Press.