KNOWLEDGE OF CONCEPT MEANINGS IN ALZHEIMERS-DISEASE

The present study focuses on semantic deficits in Alzheimer's disease (AD). We distinguish three different levels of semantic knowledge: (1) lexical, (2) semantic-conceptual, (3) conscious understanding. We dev ised methods that tap levels (2) and (3). Our aim was to determine how much guidance AD patients need to consciously access a given semantic -conceptual field and how well they can understand the meanings of con cepts and semantic relations. Four different tasks were used to tap di fferent kinds of concepts the relationships between concepts and their attributes, and the hierarchical structure among different concepts. The retrieval demands of the tasks were eased by presenting guiding qu estions. The results revealed that AD patients have deficient voluntar y access to semantic-conceptual representations. The deficits persist even in passive recognition and forced-choice tasks. We conclude that AD patients have a generalized access deficit, although some aspects o f the results are suggestive of storage deficit.