THE EQUILIBRIUM-POINT HYPOTHESIS AND ITS APPLICATION TO SPEECH MOTOR CONTROL

In this paper, we address a number of issues in speech research in the context of the equilibrium point hypothesis of motor control. The hyp othesis suggests that movements arise from shifts in the equilibrium p osition of the limb or the speech articulator. The equilibrium is a co nsequence of the interaction of central neural commands, reflex mechan isms, muscle properties, and external loads, but it is under the contr ol of central neural commands. These commands act to shift the equilib rium via centrally specified signals acting at the level of the motone urone (MN) pool. In the context of a model of sagittal plane jaw and h yoid motion based on the lambda version of the equilibrium point hypot hesis, we consider the implications of this hypothesis for the notion of articulatory targets. We suggest that simple linear control signals may underlie smooth articulatory trajectories. We explore as well the phenomenon of intraarticulator coarticulation in jaw movement. We sug gest that even when no account is taken of upcoming context, that appa rent anticipatory changes in movement amplitude and duration may arise due to dynamics. We also present a number of simulations that show in different ways how variability in measured kinematics can arise in sp ite of constant magnitude speech control signals.