Figure 1.

The motor skill learning task

(A) Time course of a trial in the motor skill learning task. Each trial started with the appearance of a sidebar and a target. After a variable preparatory phase (800-1000ms), a cursor appeared in the sidebar, playing the role of a “Go” signal. At this moment, participants were required to pinch the force transducer to bring the cursor into the target as quickly as possible and maintain it there until the end of the task (2000ms). Notably, on most trials, the cursor disappeared halfway toward the target (as displayed here). Then, a reinforcement feedback was provided in the form of a colored circle for 1000ms and provided binary knowledge of performance (Success or Failure in Block_-SR and Block_-SRR) or was non-informative (Block-S). The reinforcement feedback was determined based on the comparison between the Error on the trial and the individual success threshold (computed in the Calibration block, see STAR Methods). Finally, each trial ended with a reminder of the color/feedback association and potential reward associated to good performance (1500ms).

(B) Experimental procedure. On Day 1, all participants performed two familiarization blocks in a Block_-SR condition. The first one involved full vision of the cursor while the second one provided only partial vision and served to calibrate the difficulty of the task on an individual basis (See STAR Methods). Then, Pre- and Post-training Block_-SR assessments were separated by 6 blocks of training in the condition corresponding to each individual group (Block_-S for Group_-S, Block_-SR for Group_-SR and Block_-SRR for Group_-SRR). Day 2 involved a Familiarization block (with partial vision) followed by a Re-test assessment (4 Block_-SR pooled together). There was no recalibration on Day 2.

(C) Example of a force profile. Force applied (in % of MVC) during the task. Participants were asked to approximate the Target_Force as quickly and accurately as possible to minimize the Error (gray shaded area). As shown on the Figure, this Error depended on the speed of force initiation (Force_Initiation) and on the accuracy of the maintained force, as reflected by its amplitude with respect to the Target_Force (Force_AmplError) and its variability (Force_Variability). Note that the first 150ms of each trial were not considered for the computation of the Error.