One way to examine the dynamics of word processing is to investigate how processing is affected by the co-activation of similar words ("neighbors"). A unique prediction of attractor dynamicalmodels is that near neighbors should exert inhibitory effects and distant neighbors should exert facilitative effects. In study 1, data from 62 unselected chronic aphasia patients revealed a higher rate of semantic errors for words with many near semantic neighbors and fewer semantic errors for words with many distant semantic neighbors. In study 2, this basic result was replicated incontrols using a speeded picturenaming paradigm. Together, these two studies provide strong new evidence consistent with the attractor dynamics view of neighborhood effects. In addition, analyses of correlations between effect sizes and lesion locations, and comparisons with the existing literature on semantic deficits in aphasia and the speeded picture-naming paradigm, all provide converging evidence that the semantic error patterns found in the present studies were due to disruptions of cognitive control mechanisms. © Psychonomic Society, Inc. 2010.