TIMING AND STIFFNESS IN SPEECH MOTOR CONTROL OF STUTTERING AND NONSTUTTERING ADULTS

Twelve stutterers and 12 nonstutterers were investigated in order to m easure speech movements of the jaw. They spoke the nonsense word /papa pas/ with stress on either the first or second syllable and with three speech rates (fast, moderate, and slow). During these trials, jaw mov ements were analyzed with a selspot-like optical tracking system. It w as shown that stutters and nonstutterers applied the same strategies f or realizing jaw movements of accented and unaccented syllables. The f irst strategy (stiffness variation) was used to achieve fast jaw movem ents while the second strategy (timing) was used in order to realize j aw movements for accented syllables. These results were taken as evide nce for the assumption that, in general, stutterers and nonstutterers used the same control strategies when speaking fluently. However, it w as also evident that stutterers produced lengthened jaw opening and cl osing durations as well as reduced peak velocities and maximal opening and closing displacements. This deviating movement pattern was suppos ed to reflect motor compensations necessary to achieve fluent speech r ather than anomalies of the speech neuromotor system. (C) 1997 Elsevie r Science Inc.