Conceptual organization in Alzheimer's dementia

Although episodic memory impairment is usually the earliest feature of Alzheimer's Disease (AD), semantic memory deficits often occur during the course of the disease. The present study is the first to examine the conceptual organization of semantic memory with Chinese AD patients in Hong Kong. In the attempt to minimize the effects of the level of formal education, our procedure involved pictorial sorting tasks similar to the ones used in developmental literature on preschool children. The first condition involved a triadic comparison in which subjects were instructed to find one out of two choice objects which was most related to the target object. This condition was followed by the second condition that involved more specific instructions asking the subjects to find the taxonomic, thematic and shape associate of the target object. Results indicated that AD patients as compared to the controls tended to use more perceptual cues in categorization. The tendency to use perceptual cues for categorization was found to increase with the severity of dementia. These results were discussed in light of the hypothesized structural alteration of semantic networks in AD.