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Abstract:
This paper focuses on recent studies in which we have used a
servo-controlled robotic manipulator to deliver precise
mechanical perturbations to the jaw. The overall goal is to
understand the relationship between neural signals and properties
of the biomechanical plant in the production of jaw movement in
speech. This experiment is the first in a series of studies that
are related by the common aim of understanding the relationship
between neural and biomechanical determinants of movements. The
studies will extend from the basic properties of the plant, the
jaw's mechanical behavior and its relation to speech variability,
to the contribution of reflexes, and the degree to which control
signals compensate for the dynamics of the mechanical apparatus.
The aim of this study is to document the pattern of jaw impedance
in statics and its relation to kinematic variability in speech.
We test the hypothesis that, as in the arm and in simulation
studies of jaw stiffness, the position of the jaw in the
workspace is a primary determinant of the orientation and shape
of the jaw stiffness field. We also examine the influence of
vocal tract mechanical behavior on kinematic variability.
Articulator stiffness, in particular, could contribute to
differences in variability in different movement directions.
Directions associated with high stiffness resist position change
more than directions of low stiffness. Accordingly, movements in
directions characterized by high stiffness may be less variable
than movements in directions with low stiffness. One may
therefore hypothesize that the pattern of variability in jaw
position that accompanies the production of different sounds may
reflect at least in part the directional asymmetries of stiffness
of the jaw.
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