Résumé
Changes that occur during motor learning can be assessed by two kinds of variables. Performance variables refer to the efficiency of behavior for reaching the goal of the task, in terms of speed or accuracy. Coordination variables, in contrast, account for the qualitative organization of behavior, in terms of spatio-temporal relationships between body segments, and between the body and the environment. Motor learning studies have for a long time focus on performance variables, for assessing learning, transfer and retention of motor skills. We argue, however, that learning essentially lies on changes in coordination variables, and that relevant test for assessing the effectiveness of learning and retention should consider these variables. The aim of this experiment was to test the retention of a complex motor skill, after a long term delay. 10 years ago, five participants where involved in an experiment during which they practiced for 39 sessions of ten 1-min trials on a ski-simulator. All participants volunteered for a retention test, ten years after, for one session of ten 1-min trials. Analyses focused on the oscillations of the platform of the simulator. Performance was assessed in terms of amplitude and frequency. Coordination was accounted for by an analysis of dynamical properties of the motion of the platform, and especially the nature of the damping function that was exploited for sustaining the limit cycle dynamics. Results showed a significant decrement in performance variables. In contrast, all participants adopted from the first trial the coordination mode they learned 10 years ago. These results confirm the strong persistence of coordination modes, once acquired and stabilized in the behavioral repertoire. They also support the importance of coordination variables, for a valid assessment of learning and retention.