A PROPERTY LEVEL ANALYSIS OF LEXICAL SEMANTIC REPRESENTATION IN ALZHEIMERS-DISEASE

In order to assess the hypotheses that Alzheimer's disease (AD) result s in a property level restructuring, loss, or degradation of lexical-s emantic knowledge, Alzheimer's patients and normal elderly subjects we re presented with a property verification task in which they were aske d to judge the truth value of telegraphic statements which paired obje cts with their properties (e.g., ''Apple is red.''). Objects with eith er high- or low-typical exemplars of categories (e.g., ''oak'' is a hi gh typical exemplar of the category ''tree,'' while ''palm'' is a less typical item), Properties were varied with respect to normatively det ermined dominance (e.g, ''fins'' is a high dominant property of ''trou t,'' while ''slimy'' is a less dominant property) and whether they wer e distinctive (i.e., served to distinguish between subsets of exemplar s within a category) or shared among most or all category members (e.g ,, ''stem'' for the category ''fruit''). Analyses of accuracy and reac tion time data suggested that AD results in neither a loss per se of r epresentation of properties, nor a reorganization of relations between objects' properties. However, results were consistent with a property level degradation of AD patients' object concepts. While there was no evidence for a differential degradation of distinctive vs shared prop erties, results suggested that AD patients have degraded representatio ns of lower dominant properties and properties of low-typical category exemplars. (C) 1995 Academic Press, Inc.