Timing and spatial accuracy of reaching movements do not improve off-line


Consolidation, a time-dependant process allowing the newly acquired motor skill to be stored in long-term memory, is essential to motor learning. In sequence production tasks, consolidation has even been associated with performance gains without additional practice (i.e., off-line learning). However, the movement characteristics improved off-line and causing the performance gains remain poorly understood. To investigate this question, thirty-eight subjects (15 males, 23 females; mean age: 23.9 ± 3.4) were trained to produce a sequence of planar reaching movements toward four different visual targets. The task required that participants learn the relative timing of the movements of the sequence (i.e., the duration of each movement in proportion to the other movements), the absolute timing (i.e., the speed at which the whole sequence should be executed) and aim accurately at each target. Participants performed a first training session (150 trials) during which they received visual and temporal feedback following each trial. Off-line learning was assessed by comparing the performance of two groups performing a no-feedback retention test either 10-min or 24-hour after the initial practice session. Our results indicated that a 24-hour consolidation interval did not result in better temporal or spatial precision (p > 0.11, np2 > 0.07) nor a decrease in the participants' variability (p > 0.39, np2 < 0.02). This absence of off-line gains, also observed in other paradigms using gross motor tasks, suggests that off-line learning may be restricted to sequence production tasks in which the different sub-movements must be regrouped ("chunked") together to accelerate their execution.

Acknowledgments: Luc Proteau, Marcel Beaulieu