Tongue kinematics in palate relative coordinate spaces for electro-magnetic articulography

This paper describes a method for constructing a three-dimensional model of the hard palate using electro-magnetic articulography, and defines two algorithms to derive constriction degree and constriction location values from the trajectories of tongue coils using this model. The kinematics of tongue motion that have been transformed into constriction degree and constriction location values are investigated in detail to determine whether this type of representation obeys the constraints theorized to operate over higher level motor control. Results show that palate-relative coordinate spaces decouple mechanical dependencies present in the tongue, while maintaining low-level kinematic properties. They additionally preserve the 1/3 power law for speed and curvature observed across many motor systems. Finally, it is shown that tongue movements in a palate relative coordinate space more closely correspond to their optimal, jerk-minimized trajectories. These results suggest that this type of coordinate space provides a closer match to higher level motor-planning, in line with production models that specify control units in terms of vocal tract constriction parameters.