Research Article: Mapping collective variable and synergy dynamics to task outcome in a perceptual-motor skill

Date Published: April 18, 2019

Publisher: Public Library of Science

Author(s): Yeou-Teh Liu, Kuo-Liang Chuang, Karl M. Newell, Jeffrey M. Haddad.


In complex adaptive systems approaches to perceptual-motor control the mapping between the different categories of task dynamics: namely, task outcome, collective variable, neuromuscular synergies and individual joint configurations is a central theoretical issue, that has been primarily studied in bimanual tasks. Here we report an investigation in the roller ball task of how the task goal and multiple degrees of freedom of the arm-hand complex affords degeneracy between the respective properties of the task dynamics. The relation of the candidate collective variable, namely, the synchrony of the inner ball to outer shell motion of the roller ball and its relation to the task goal (continued increasing in ball speed), was examined as a function of the initial ball speed acting as a control parameter. Within trial analysis revealed initial search behavior for synchrony of ball and shell motion that was longer in duration with initial lower ball speed conditions. In contrast, higher initial ball speed conditions reduced the search time for and enhanced the rate of stabilization of the synchrony of inner ball and outer shell motion–features that facilitated the continued increase of ball speed and the probability of task success. Participants adopted one of three wrist-elbow neuromuscular synergies to manipulate the roller ball, the distribution of which was not influenced by either initial ball speed or task outcome. The pattern of findings over the different properties of task analysis of the roller ball provides evidence for the distinct but complementary dynamics of searching to form, stabilize and exploit a collective variable that satisfies the task goal through a small redundant set of arm-hand synergy motions.

Partial Text

A contemporary umbrella perspective to perceptual-motor control is that of complex adaptive dynamical systems [1–2]. There have been several theoretical and experimental instantiations in the perceptual-motor domain that reflect this perspective that have a number of common elements concerning movement coordination, control and skill (e.g., [3–6]). These include the system properties of multiple degrees of freedom (DFs), interacting subsystems within and between levels of analysis, emergence of movement coordination modes, and the exhibition of varying levels of the complexity of system output that continually evolve with learning and development over the lifespan [5].

The purpose of the present study was to investigate the mapping of collective variable and synergy dynamics with task outcome within the general context of the multi-layered framework of complex adaptive dynamical systems [2–6]. In particular, we examined the effect of a control parameter, namely, the initial condition of ball speed in the roller ball task, on short-term adaptation in task dynamic properties of the perceptual-motor system. The perceptual-motor properties analyzed were task outcome, the candidate collective variable (inner ball-outer shell relative motion) and neuromuscular synergies of the arm-hand kinematic chain.