Compensation for the gravitational force on the jaw during speech

• Main Author: Shiller, Douglas M.
• Other Authors: Ostry, David (advisor)
• Format: Others
• Language: en
• Published: McGill University 1998
• Subjects: Biomechanics; Jaws > Mechanical properties; Speech > Physiological aspects
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20469

External loads, such as those due to the orientation of body segments relative to gravity, affect the extent to which control signals result in the achievement of desired goals. The degree to which subjects adjust control signals to compensate for loads provides a measure of what the nervous system knows about forces affecting motion and gives an indication of the complexity of control signals needed for voluntary movement. In the present study, we have explored the hypothesis that subjects take no account of the orientation of the head relative to gravity when making jaw movements during speech. We used a simulation model of the jaw to predict the kinematic effect of using a single set of motor commands (which take no account of the relative direction of the gravitational force) to produce speech-like movements while the body was in three different orientations: upright, prone and supine. The simulations predict a systematic change in jaw pitch angle and horizontal translation resulting from the change in body orientation. Empirical results for five subjects tested under the same conditions as those explored in the simulations are for the most part consistent with the pattern predicted by the model. This suggests that in the case of jaw movements during speech, control signals are not adjusted to account for changes in head and body orientation relative to gravity.