Head movement associated with performance of mandibular tasks.

The present study was designed to examine the hypothesis that the motor system controlling phonation is functionally coupled with the motor system controlling posture of the head and neck, as previously suggested (U. Haddar, T.J. Steiner, E.C. Grant and F.C. Rose Human Movement Science 2: 35 and Language and Speech 26: 117). Head tilt and trunk drift in the antero-posterior and right-left directions were measured simultaneously for 20 s before and during three types of speech sounds (/pa/, /ta/ and /ka/) as well during a maximum jaw open-close task in 14 healthy young subjects. The major findings obtained in all of the four tasks were: (i) the trunk drift measured in both directions was negligible in comparison with the head tilt; (ii) the head tilt in the antero-posterior direction was much larger than in the right-left direction and (iii) the head tilt during performance of the four tasks consisted of 'initial' and 'sustained' phases. In the initial phase, the head tilted posteriorly in association with the start of individual tasks. In the sustained phase, the head tilted either anteriorly or posteriorly when the task progressed. The magnitude of the net head tilt in the sustained phase negatively correlated with that of the initial head tilt. These findings indicate that phonation, in the form of jaw open-close, accompanies head movement in two consecutive phases.