Kinematic correlates of speaking rate changes in stuttering and normally fluent adults.

Articulatory kinematics were analyzed to determine if adults who stutter are generally poorer at speech movement pattern generation and if changing speech rate affects their stability in the same way that it affects normally fluent controls. Adults who stutter (n = 14) and a matched group of controls produced fluent repetitions of a simple phrase at normal, slow, and fast rates. A composite index of spatiotemporal stability (STI), as well as independent measures of timing and spatial variability, revealed that adults who stutter can operate within normal movement parameter ranges under low-demand speaking conditions. However, some of the stuttering participants showed evidence of abnormal instability even when repeating a simple utterance at habitual rate. Also, measures of relative timing indicated that adults who stutter, unlike their matched controls, are not better timers at habitual vs. nonpreferred speech rates. Overall, the results suggest that the kinematic characteristics of the fluent speech of adults who stutter generally overlap that of normally fluent speakers; however, subtle differences in kinematic parameters are interpreted to reveal their susceptibility to speech motor breakdown when performance demands increase.