Timing and stiffness in speech motor control of stuttering and nonstuttering adults

Twelve stutterers and 12 nonstutterers were investigated in order to measure speech movements of the jaw. They spoke the nonsense word /papapas/ with stress on either the first or second syllable and with three speech rates (fast, moderate, and slow). During these trials, jaw movements were analyzed with a selspot-like optical tracking system. It was shown that stutters and nonstutterers applied the same strategies for realizing jaw movements of accented and unaccented syllables. The first strategy (stiffness variation) was used to achieve fast jaw movements while the second strategy (timing) was used in order to realize jaw movements for accented syllables. These results were taken as evidence for the assumption that, in general, stutterers and nonstutterers used the same control strategies when speaking fluently. However, it was also evident that stutterers produced lengthened jaw opening and closing durations as well as reduced peak velocities and maximal opening and closing displacements. This deviating movement pattern was supposed to reflect motor compensations necessary to achieve fluent speech rather than anomalies of the speech neuromotor system.