Bauer, A., Jäncke, L. & Kalveram, K.Th. (1996) Mechanical
Perturbation of the jaw during speech in stutterers and nonstutterers.
In W. Hulstijn, H.F.M. Peters & P.H.H.M. van Lieshout (Hrsg..), Speech Production: Motor Control, Brain Research and Fluency Disorders. Amsterdam: Elsevier Science Publishers, 191-196.
Abstract
10 stuttering and 10 nonstuttering adults uttered the testword /sasasar/ repeatedly with normal or with slow speech rate and with stress either on the first or on the second syllable. In 17% randomly chosen trials of each condition, an unexpected and unpredictable mechanical perturbation was applied to the jaw during the utterance of the first syllable of the testword. In these trials, the jaw was suddenly loaded with 80 g via a spatula lying on the lower front teeth. This load was applied during the jaw opening movement at the moment when the jaw reached 70% of maximal opening as determined for the first syllable of the preceding utterance.
Assuming that stuttering is a temporal discoordination of speech movements, we hypothesized that the mechanical perturbation of the jaw would lead to a greater discoordination between jaw movement and phonation in the stutterers than in the nonstutterers. A semiautomatic analysis of the jaw movement and phonation signals showed that the reaction to the perturbation varies for both stutterers and nonstutterers from trial to trial and that in most cases, the perturbation is integrated into the ongoing opening movement of the jaw. In some trials, the application of the load evokes overshooting compensatory movements of the jaw in stutterers as well as in nonstutterers. Only two severe stutterers show cases of complete destruction of the jaw movement but preserved phonation. In some severe stutterers, there are cases of disturbed jaw movements in unperturbed trials following trials with perturbation. These results show that the sensorimotor speech control of both stutterers and nonstutterers is subject to temporary fluctuations and that most of the time, the reactions to the mechanical perturbation of the jaw are not different for both groups. On the other hand, the sensorimotor speech control of some severe stutterers occasionally is especially prone to disturbances.
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