Associative and Orthographic Neighborhood Density Effects in Normal Aging and Alzheimer's Disease

A group of patients with Alzheimer's disease and a group of healthy elderly controls were tested with a lexical-decision task that included words with dense or sparse orthographic and associative neighborhoods to investigate whether there is automatic orthographic and semantic activation of related representations in these populations similar to that found with younger samples. Although some studies support the idea of deteriorated connections in semantic networks in Alzheimer's disease, other studies propose that the automatic spread of activation at lexicosemantic levels remains intact and that intergroup differences are a consequence of impaired retrieval or attentional deficits. In this study, participants responded to words with dense orthographic and associative neighborhoods faster than they did to words with sparse neighborhoods, providing evidence in favor of a preserved automatic spread of activation through intact orthographic and semantic representations. Furthermore, no differences were found between the two groups regarding the magnitude of the effects, although control participants responded significantly faster than patients.