Analyzing feature distinctiveness in the processing of living and non-living concepts in Alzheimer's disease.

The conceptual structure account (CSA) is a model specifying the role of the living and non-living domain dichotomy in the structure of semantic memory. According to this model, feature distinctiveness and the perceptual-functional inter-correlation of concepts are assumed to play a major role in impairing the ability to discriminate between living and non-living concepts in Alzheimer's disease (AD). The hypothesis was tested in this study by using naming and sorting tasks traditionally considered as assessing distinctiveness, and a property verification task where distinctiveness and perceptual-functional inter-correlation were objectively controlled against norms especially created for this purpose. Alzheimer's patients (n=59) with minimal, mild or moderate dementia and normal elderly adults (n=31) participated in the study. Overall, the findings did not support the CSA predictions. They revealed a distinctiveness effect on response accuracy with shared features dominating distinctive features regardless of domain. They also revealed more difficulties in the tasks involving effortful processes. The results stress the need to consider both cognitive demands of tasks and structural aspects of knowledge in the evaluation of semantic memory in AD.