Skilled actions: A task-dynamic approach.

Abstract

A task-dynamic approach to skilled movements of multi-degree-of-freedom effector systems is developed in which task-specific, relatively autonomous action units are specified within a functionally defined dynamical framework. Qualitative distinctions among tasks (e.g., the body maintaining a steady vertical posture or the hand reaching to a single spatial target versus cyclic vertical hopping or repetitive hand motion between two spatial targets) are captured by corresponding distinctions among dynamical topologies (e.g., point attractor versus limit cycle dynamics) defined at an abstract task space (or work space) level of description. The approach provides a unified account for several signature properties of skilled actions: trajectory shaping (e.g., hands move along approximately straight lines during unperturbed reaches) and immediate compensation (e.g., spontaneous adjustments occur over an entire effector system if a given part is disturbed en route to a goal). Both of these properties are viewed as implicit consequences of a task's underlying dynamics and, importantly, do not require explicit trajectory plans or replanning procedures. Two versions of task dynamics are derived (control law, network coupling) as possible methods of control and coordination in artificial (robotic, prosthetic) systems, and the network coupling version is explored as a biologically relevant control scheme.

Using task dynamics to quantify the affordances of throwing for long distance and accuracy.

“…Task dynamics was originally formulated to capture the complexity of human movement (Bingham, 1988;Saltzman & Kelso, 1987) and has since been used to identify the perceptual information created by tasks (e.g. Siegler et al, 2013;Warren & Whang, 1987).…”

Timing an attacking forehand drive in table tennis.

“…Although perception and action can be analytically separated, such a separation does not have an onto 1 ~gical foundation (Bootsma, 1989;Fitch & Turvey, 1978;Turvey, in press). Rather, it appears to be the case that the task constraints, defined in task space (Saltzman & Kelso, 1987), provide the organizing principles for perception and action at the same time. Whether the act is performed a bit faster, initiated somewhat later, or performed more slowly, initiated somewhat earlier, appears to be inconsequential as long as a coupling between perceptual and movement variables is sustained.…”

“…A control strategy on movement time, such as suggested in the operational timing hypothesis of Tyldesley and Whiting, has been interpreted to have the advantage of reducing the number of decisions to be made before performing the drive to only one, namely, when to initiate it. Put differently, producing a consistent movement time reduces the number of degrees of freedom that have to be controlled in task space (Fitch & Turvey, 1978;Saltzman & Kelso, 1987).…”

Speech sound acquisition, coarticulation, and rate effects in a neural network model of speech production.

“…Investigation of the orosensory-to-articulatory mapping also reveals that articulators automatically organize into task-specific groupings or coordinate structures (Easton, 1972;see Developing Coordinative Structures: The Orosensory-to-Articulatory Mapping) during the learning process. Coordinative structures have long been hypothesized to play an important role in efficient movement control (Fowler, 1980;Saltzman & Kelso, 1987) and have been observed in experimental data (e.g., Kelso et al, 1984).…”