Learning to juggle: on the assembly of functional subsystems into a task-specific dynamical organization

Abstract

We examined the development of task-specific couplings among functional subsystems (i.e., ball circulation, respiration, and body sway) when learning to juggle a three-ball cascade, with a focus on learning-induced changes in the coupling between ball movements and respiration and the coupling between ball movements and body sway. Six novices practiced to juggle three balls in cascade fashion for one hour per day for twenty days. On specific days (7 in total), ball movements, center-of-pressure (CoP) trajectories and respiration traces were measured simultaneously. Discrete, time-continuous and spectral analyses revealed that the spatio-temporal variability of the juggling patterns decreased with practice and that the degree to which the task constraints were satisfied increased gradually. No conclusive evidence was found for ball movement-respiration coupling. In contrast, clear-cut evidence was found for the presence of 1:3 and 2:3 frequency locking between the vertical component of the ball trajectories and both the anterior-posterior and the medio-lateral components of the CoP. Incidence and expression of these mode locks varied across individuals and altered in the course of learning. Gradual changes in locking strength, appearances and disappearances of mode locks, as well as abrupt transitions between coupled states were observed. These results indicate that dissimilar learning dynamics may arise in the functional embedding of subsystems into a task-specific organization and that motor equivalence is an inherent property of such emerging task-specific organizations.

Multiple Time Scales and Multiform Dynamics in Learning to Juggle

“…Newell et al (2001). Recently, these insights were confirmed for the evolution of postural sway, as novices learned to juggle the 3-ball cascade (Huys, Daffertshofer, & Beek, 2003), in that the stability of juggling performance and the dynamics of postural sway evolved in disparate fashion: Whereas the former improved gradually, the latter showed both gradual and abrupt changes in frequency locking. Is this the only evidence for the co-existence of distinct, relatively autonomous dynamical processes in learning?…”

“…The number of components required for reconstructing the pattern varied with tempo, as the quality of performance decreased when speed of juggling increased from preferred to high. Building on these findings, Huys et al (2003) investigated changes in the patterning of the balls during the acquisition of 3-ball cascade juggling. Besides an asymptotic improvement in the consistency and stability of performance, changes in time-continuous cross-links, as revealed by cross-spectral and relative phase analyses, suggested a reduction in the dimensionality of the control structure.…”

“…Apparently, the expert shooters had fully integrated whole-body posture stabilization with shooting, whereas the novices had not. Although these works suggest that postural sway patterns differ as a function of expertise, studies of the actual evolution of the sway patterns during the learning of suprapostural tasks are few and far between (but see Huys et al, 2003).…”

“…However, besides an increase in the number of consecutively juggled balls, extensive practice is likely to result in an asymptotic reduction of variability in the juggling patterns due to increases in the degree of frequency and phase locking between the ball trajectories (Beek & Van Santvoord, 1992;Huys et al, 2003) which, in principle, allows for detection of multiple time scales within the goal behavior itself. Furthermore, given the cyclic nature of juggling, similar changes in coordination may be expected to occur between the oscillatory features of postural sway, and head and eye movements on the one hand, and the ball trajectories on the other-opening up the possibility to examine how, and at what rate, these subsystems evolve in relation to the evolution of the goal behavior.…”

Dynamical structure of center-of-pressure trajectories in patients recovering from stroke

“…1, C m (r) scales with r m ) acquisition (cf. Huys and Beek 2002;Harbourne and Stergiou 2003;Huys et al 2003Huys et al , 2004Milton et al 2004). In line with this interpretation, the introduction of a cognitive dual task reduced the cognitive contribution to postural control, resulting in less regular COP trajectories of larger dimension but similar stability.…”