Abnormal semantic network for "animals" but not "tools" in patients with Alzheimer's disease

The effects of Alzheimer's disease (AD) on the organization of semantic kno wledge (i.e., thr: semantic network) for living (e.g., animals) and non-liv ing (e.g., tools) categories was examined. Multidimensional scaling and Pat hfinder analyses of data from triadic comparison tasks showed that the sema ntic network for "animals", but not the network for "tools", was abnormal i n patients with AD. Specifically, patients with AD tended to use a differen t primary dimension than control subjects for categorizing animals and thei r network was characterized by atypical associations between concepts. The differences in the integrity of the AD patients' networks for "animals" and "tools" was not likely to be an artifact of differences in the difficulty in identifying the stimuli in the two categories as all stimuli were identi fied on simple naming or matching tasks. These findings support the results of previous studies that have shown the presence of category-specific sema ntic deficits in patients with AD.