Figure 1

Experimental design. (A) Preliminary test. On the left, the scheme represents participants’ placement and the manipulandum used. Participants were asked to grasp a handle (gray cylinder) located below the screen with their right hand, which position was displayed on the screen in real time with a cursor (white dot). Black rectangles are schematic representations of the screen displayed in front of participants. The trial started with the appearance of a red fixation cross and the starting point (gray dot). Once participants placed their cursor into the starting point for 1.5 to 2.5 s, two targets appeared on the screen. The location of the left target varied across trials (all possible locations are represented with the dotted blue circles). The percentage of right target choices as a function of left target locations was fitted with a psychometric function to extract the PSE (i.e., left target location corresponding to the 50th percentile of right target choice). (B) Test. Participants’ placement was similar to the one used in the preliminary test. Trial timeline was also similar, except that at target onset the red fixation cross turned into a stimulus indicating the choice context (arrows: instructed, lines: free) and the direction of the target to reach in the case of an instructed choice (direction indicated by the central arrow). Movement onset was considered as the first time point at which the position of the cursor was located outside of the starting point. If the cursor ended inside of one of the two presented targets in free choices or inside of the target indicated by the central arrow in the case of instructed choices, the selected target turned green.