Semantic memory, or general knowledge about objects and events in the world, appears to be severely affected in most patients with Alzheimer's Disease (AD). The goal of the proposed research is a deeper understanding of semantic processing in AD. In overview, the following issues concerning semantic memory will be addressed. First of all, is semantic memory impaired, or does the appearance of impairment come from an attentional impairment? Second, are certain types of semantics knowledge more vulnerable to AD, and if so, why? Third, can an impairment of semantic memory account for other problems that seem, on the face things, not semantic but perceptual or lexical? Fourth, what is the relation between semantic impairments and visual impairments in the confrontation naming difficulties of AD patients? Finally, what is the status of the visual-semantic process of mental imagery in AD? The methods to be used include empirical studies of patients with AD and normal subjects, and computer simulation. We have drawn on the theoretical framework of cognitive psychology in designing studies of semantic memory, vision, and mental imagery in AD. In addition, concepts from parallel distributed processing (PDP) have guided the formulation of hypotheses concerning semantic memory in AD, and PDP computer simulations will provide tests of the computational adequacy of these hypotheses. In addition, new predictions of the computational hypotheses have been derived and will form the basis of further empirical tests with human subjects.