Perseverations and anticipations in aphasia: primed intrusions from the past and future.

In this article, we review an account of movement errors that is based on a model of serial order and an interactive spreading activation model of word production. This account makes two claims. First, anticipations and perseverations arise from malfunctions of a mechanism that maintains serial order in speech production and that has three components: (1) a means to turn off past utterances, (2) a means to activate the present utterance (3) a means to prime the future utterance. Second, the probabilities of such movement errors are further determined by the same variables that influence the production of ordinary word and sound substitutions, such a frequency and feature overlap. We review relevant studies of movement errors produced by aphasic and nonaphasic individuals and make suggestions for further investigation of these phenomena.