Dynamics and coordinate systems in skilled sensorimotor activity

Skilled sensorimotor activities entail the creation of complex kinematic patterns by actors using their limbs and speech articulators. Examples of kinematic patterns include trajectories over time of a reaching hand's position, velocity, or acceleration variables, the spatial shape of the path taken by a hand-held pen during handwriting, or the relative timing of the speech articulators to produce the phonemes Ipl, lei, and In! in the word "pen". The term dynamics is used to refer to the vector field of forces that underlies and gives rise to an action's observable kinematic patterns. In this chapter, a dynamical account of skilled activity is reviewed in which skilled behavior is characterized as much as possible as that of a relatively autonomous, self-organizing dynamical system. In such systems, task-appropriate kinematics are viewed as emerging from the system's underlying dynamical organization (e.g., Beek, 1989; Saltzman & Munhall, 1989; Schoner & Kelso, 1988; Turvey, 1990). Thus, the emphasis of the present account is on a dynamical description, rather than a kinematic one, of sensorimotor skills. For example, an extreme and admittedly exaggerated "straw man" counter-hypothesis is that of a central executive or homunculus that produces a given movement pattern with reference to an internal kinematic template of the form, tracing out the form provided by the template, and using the articulators as a