Article Figures & Data
Figures
- Figure 1.
Experimental paradigm. A, Illustration of targets and forces for the first main experiment. Participants were asked to perform reaching movements of 20 cm between the home target and the goal target, which could either be a rectangle or a square. For trials with target switch, the change occurred during the movement (from rectangle to square or vice versa). For trials with mechanical perturbations, rightward or leftward step loads were applied during the movement. The onset of the target switch and step loads is represented by the dotted line at 6 cm in the y-direction from the home target. This line was not visible to the participants, who saw only targets and a cursor representing the position of their hand. B, Schematic of the second main experiment. The instructions were the same as for the first experiment but in this case, participants were exposed to a velocity-dependent force field
- Figure 2.
Kinematics. A–C, Mean x–y traces across trials for each participant (light traces) and across participants (thick trace) with the FF (Exp. 2, purple) or without FF (Exp. 1, blue) from trials in which there was no step load for (A) a rectangle goal target, (B) a square goal target, and (C) a square goal target initially which became a rectangle during movement. D, Evolution of the x-position (mean across participants ± SE) over time during the movement with FF (purple) or without FF (blue) for a rectangle target (solid line), a square target (dotted line), or a switch from a square to a rectangle target (dashed line). Note that the curves for the square target and the switch from a square to a rectangle target are nearly superimposing each other. E, Evolution of the y-position (mean across participants ± SE) over time during the movement for all conditions. Note that all the curves are nearly superimposing each other F–J. Same as panels A–E for trials with a right step load.
- Figure 3.
Exploitation of target redundancy. A, B, Average final x-position along the rectangle width without force field (blue) and with force field (purple) following a right step load for each trial (mean across participants ± SE) when (A) the goal target was a rectangle and there was no visual switch and (B) the goal target switched from a square to a rectangle. C, D, Evolution of intrasubject variance with time (mean across participants ± SE) when (C) there was no visual switch of the rectangle target and (D) the goal target switched from a square to a rectangle. E, F, Mean of the difference between the maximal and the final variance for each experimental group when there is (E) no switch of the goal target and (F) a switch from square to rectangle. Positive values mean the endpoint variance was smaller than the peak variance across trials.
- Figure 4.
Muscular activity. For the first main experiment (without FF), (A) muscular activity in the pectoralis major (solid line) and in the posterior deltoid (dotted line) following a right step load when the target was a square (dark blue) or a square which became a rectangle (light blue). B, Mean muscular activity over 25 ms bins for a square target (dark blue) or a target switching from a square to a rectangle (light blue). C, Log-scale evolution of the p value over a 25 ms sliding window. Time index corresponds to the timing of the end of the window. Red horizontal line represents p = 0.05. D–F, Same as A–C, but for the second main experiment, with FF. G, Mean muscular activity for each target condition during the long-latency and voluntary windows. H, Mean muscular activity across all trials in the pectoralis major and posterior deltoid in a window of 300 ms before the step load for the experiment without FF (blue) and with FF (purple).
- Figure 5.
Motor adaptation. A, Maximal deviation (with respect to the straight line between the home and goal target) across trials for which participants are exposed to the force field for the experiment with target switch and step load in addition to the force field (purple) and the control experiment with the force field only (red). Trials toward a square target are represented against their index. B, Maximal deviation during catch trials represented against their index for both experiments (mean across participants + SEM; left part) and median deviation across the ten last catch trials (right part). C, Distribution of the b and c parameters of the exponential regression after 106 resampling of the population with replacement. Horizontal lines below the graphs represent the 95% HDIs. D, Comparison across all control experiments. Mean traces for the first (left) and last (right) 30 trials exposed to the force field for the experiment with the force field only (red), the experiment with target switch and step loads in addition to the force field (purple), the experiment with only target redundancy (rectangle and switch from square to rectangle, brown), and the experiment with step loads in addition to the force field (orange). Each line represents the mean for one trial across participants. E, Value of the c parameter of the exponential regression for the same four experiments. The 95% HDIs are projected on the y-axis.
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