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

In order to assess the hypotheses that Alzheimer's disease (AD) results in a property level restructuring, loss, or degradation of lexical-semantic knowledge, Alzheimer's patients and normal elderly subjects were presented with a property verification task in which they were asked to judge the truth value of telegraphic statements which paired objects with their properties (e.g., ''Apple is red.''). Objects with either high- or low-typical exemplars of categories (e.g., ''oak'' is a high typical exemplar of the category ''tree,'' while ''palm'' is a less typical item), Properties were varied with respect to normatively determined dominance (e.g, ''fins'' is a high dominant property of ''trout,'' while ''slimy'' is a less dominant property) and whether they were distinctive (i.e., served to distinguish between subsets of exemplars within a category) or shared among most or all category members (e.g,, ''stem'' for the category ''fruit''). Analyses of accuracy and reaction time data suggested that AD results in neither a loss per se of representation 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 properties, results suggested that AD patients have degraded representations of lower dominant properties and properties of low-typical category exemplars. (C) 1995 Academic Press, Inc.