Motor performance of stutterers: a search for mechanisms

A continuing program of research, which is concerned with identifying brain mechanisms underlying stuttering through an analysis of manual motor control, is described. Clear evidence has been found that the neural mechanisms associated with sequential responding (and, by implication, with speech) are lateralized in stutterers as they are in nonstutterers. Although no gross or general incoordination has been found in motor performance by most stutterers, their left hemisphere mechanisms appear to be inefficient for organizing and initiating new sequences of responses and vulnerable to interference from other neural activities. Results of research on bimanual coordination in stutterers are consistent with a model that attributes the interference, in part, to interhemispheric processes, possibly involving the supplementary motor area. One implication of the research is that the disfluency of stuttering is only one manifestation of a more general disfunction in motor and cognitive organization and planning.