Dimensionality and clustering in the semantic network of patients with Alzheimer's disease.

The organization of semantic memory in patients with Alzheimer's disease (AD) was investigated with a triadic comparison task. A multidimensional scaling statistic was used to analyze proximity data and to generate 3-dimensional cognitive maps that were then compared by a discriminant function analysis. The results suggest that the structure of semantic memory in AD patients differs from that of elderly normal controls (NC) in 2 ways. First, AD patients are less consistent in using the attributes (predation, domesticity, and size) of concepts. Second, AD patients focus primarily on concrete perceptual information (size), whereas NC Ss stress abstract conceptual knowledge (domesticity). These results are consistent with the notion that AD is characterized by a breakdown in the structure of semantic knowledge.