Kinematic analysis of multiple movement coordination during speech in stutterers.

This study addresses the long-standing claim that stuttering reflects an impairment in the neuromotor coordination of multiple speech movements. Upper lip (UL), lower lip (LL), and jaw (J) kinematics for nonstuttered speech behaviours in stutterers and normal speakers were examined using quantitative indices of normal multiple movement coordination reported in recent studies of gait, reaching, grasping, and speech. While two measures of coordination--dynamic movement composition and intermovement motor equivalence--did not distinguish between stutterers and normals, stutterers manifested striking differences from normal on a third measure, the sequencing of UL, LL, and J movement onsets and velocity peaks. These findings suggest that, contrary to previous hypotheses, stutterers do not manifest general problems of coordination of speech movement. Instead, stuttering appears to be associated with a specific impairment in multiple movement coordination associated with sequencing of those movements.