Motor learning : a nonlinear , irreversible and fractal process

1. Motorlearning: a nonlinear, irreversible and fractal process 1.5 0 Sujet 4 essais -1.5 Discovery stage 0 50 100 150 200 250 300 350 400 Final stage « Van der Pol » Transition Phase • Nourrit-Lucas, D.1,Tossa, A.O.1, Zelic, G. 2 & Delignières,D. 2. • MAPMO Laboratory, University of Orléans, France; (2) Movement to HealthLaboratory , University of Montpellier, France • e-mail:deborah.lucas@univ-orleans.fr On discontinuities in motor learning A bi-stable transition The transition between Rayleigh and van der Pol damping A longitudinal study of 39 sessions of ten-1 min trials . Aim: examine the qualitative behavioral reorganizations that occurred during the acquisition of a complex motor skill. Procedure: the motion of the apparatus platform modelled as a self-sustained oscillator Van der Pol Rayleigh Position Damping Stiffness Results: 2 stages during practice. An initial stage characterized by a highly non-linear stiffness function and a Rayleigh damping function which provides a prolonged dwelling time when subjects approach the reversal points of the movement. These behaviours contributed also to well control the reversal points. On the other hand a final stage characterized by the linearization of stiffness and a van der Pol damping function where the decrease of non-linear stiffness are revealing a better storing energy in the rubber belts and a van der Pol damping allows subjects to adopt high frequencies and large amplitude that characterize skilled performance (expert behaviour in ski-simulator). Initial stage « Rayleigh » A saddle-node bifurcation: Practice (time) Van der Pol Rayleigh Mono-stable phase (initial stage) Bi-stable phase (transition phase) Mono-stable phase (final stage) Drift before transition The non-linearity of the motor learning seems to have the form of a prolonged phase transition (like in a saddle-node bifurcation) ,which permits access to the skilled behavior. The same task 5 subjects, instructed to oscillate on a ski simulator “as ample and frequent as possible”. Movements recorded by a VICON motion analyzer (Biometrics) . The persistent coordination patterns after 10 years delay Fractal properties for the expert : close to 1/fnoise A retention test: ten 1-min trials, with a 1 min break between trials, 10 years later. A comparative test between 5 experts and 5 novices during one-10 min trial. Time series of ski-simulator movements analysed by DFA. C01(Rayleigh) is the linear damping coefficient obtained with this forcing procedure. C01(Rayleigh) is negative when the limit cycle is sustained by a Rayleigh behavior, and positive for a van der Pol behavior. The exploitation of the previous damping behavior, the van der Pol damping, appeared quite durable during the time.Any transformation in the attractors landscape is “catastrophic” in sense of René Thom (1983), the space of phases is modified in an irreversible way. One allows us to validate the old saying : “Once one learns to ride a bicycle, one never forgets that skill”. Novice Expert 1/f noise is an adaptation- stability trade-off : a localized perturbation will not necessarily alter the stability of the global. The expert’s time series have revealed a noise close to the pink noise. We consider the 1/f noise as an indicator of efficiency of the system. References : - Nourrit, D., Delignières, D., Caillou, N., Deschamps, T. & Lauriot, B. (2003) On discontinuities in motor learning: A longitudinal study of complex skill acquisition on a ski-simulator. Journal of Motor Behavior, 35, 151-170. - Thom, R. (1983). Paraboles et Catastrophes. coll.: Champs, ed.: Flammarion, Paris. - Teulier, C., Nourrit, D. & Delignières, D. (2006). The evolution of oscillatory behavior during learning on a ski simulator. Research Quaterly for Exercise and Sport. 77, n°3, 464-475. - Nourrit-Lucas, D., Zélic, G.; Deschamps, T., Hilpron, M. & Delignières, D.(Submitted) “Once you have learned how to ride a bicycle, you never forget!”. Persistent coordination patterns in a complex task after 10 years delay. Journal of Motor Behavior. .