Naming from definition, semantic relevance and feature type: the effects of aging and Alzheimer's disease

The principal aim of the present study was to evaluate the impact of semantic relevance and feature type on the ability to name from definition.

Thirty-two normal young subjects (Study 1) and 20 probable Alzheimer's disease patients (pAD) with 20 matched older controls (Study 2) were tested with verbal definitions consisting of 4 features, combining feature type (sensory vs. nonsensory) and semantic relevance (high vs. low). The subjects were asked to provide a name corresponding to the definition and to select which individual features they considered most important in justifying their answer.

Feature selection results showed that high-relevance features first (d = 2.13 in Study 1; d = 1.44 in Study 2) and nonsensory features second (d = 0.81 in Study 1; d = 0.36 in Study 2) were the main dimensions driving correct performance. Overall, naming performance was affected by the age of acquisition (AoA) of the concept, and differences between the groups in all measures were mainly quantitative.

These findings suggest that semantic relevance and feature type are important feature dimensions in conceptual representation and in conceptual access and retrieval. Moreover, results suggest that the former dimension may be more important than the latter, at least in the case of naming from definition. Finally, these results extend previous findings with other tasks, supporting the importance of AoA for correct performance and suggesting that the poorer performance of pAD patients on semantic tasks may represent an exaggeration of difficulties found also in normal older subjects.