Article Figures & Data
Figures
- Figure 1.
Task paradigms. A, Representation of the task paradigm of experiment 1. Participants controlled a hand-aligned cursor represented by the black dot on a virtual reality display. They had to reach for the goal target, represented by the magenta goal target in front of them. This goal target could have a low, medium, or high reward (1, 5, or 10 points). The bottom part of the panel represents the load profiles that participants could experience. B, Representation of the task paradigm of experiment 2. Participants had to reach for any of the three targets presented in front of them. The central target always had a high reward whereas the two others either had a low or a high reward. The bottom part of the panel represents the load profiles that participants could encounter during movements. C, Representation of the task paradigm of experiment 3. Participants had to reach for any of the three targets presented in front of them. During the second half of the trials, a background load force directed leftward was applied prior and during the movement (dashed line bottom panel). The bottom part of the panel represents the possible profiles of the total load forces (perturbation load + background load). EMG data from PM and PD were collected during all experiments.
- Figure 2.
Experiment 1, kinematics. A, Mean hand path across participants for the different conditions of the first experiment. The magenta, green, and blue traces, respectively, correspond to the low, medium and high reward conditions. The dashed line represents the onset of the mechanical perturbation. B, Mean difference in forward velocity between the high and low (dash-dot line) and medium and low (full line) for the unperturbed (top) and perturbed (bottom) trials. The time axis is aligned on the force onset. C, Mean hand deviation across participants for the perturbed trials. The hand deviation has been obtained by subtracting the mean hand path to the perturbed hand path in the same reward condition for every subjects. The top part of the graph represents the trials perturbed to the right whereas the bottom part of the graph represents the trials perturbed to the left. D, Group mean (black) and individual means (gray) of the differential forward peak velocity for the unperturbed trials (top) and perturbed trials (bottom) as a function of the reward condition with respect to average forward peak velocity. E, Group mean (black) and individual means (gray) of the difference in hand deviation with respect to the mean hand deviation for leftward (top) and rightward (bottom) perturbation in the three reward conditions with respect to the average hand deviation; p < 0.05 (*), p < 0.01 (**), p < 0.005 (***).
- Figure 3.
Experiment 1, EMG activity. A, Mean EMG activity collapsed across muscles and participants for unperturbed trials. The time axis is aligned on force onset. B, Mean differences in EMG activity collapsed across muscles and participants between high and low (dash-dot line) and medium and low (full line) reward conditions for unperturbed trials. C, Group mean (black) and individual means (gray) PM EMG activity binned between 0 and 200 ms after force onset for unperturbed trials. D, Group mean (black) and individual means (gray) PD EMG activity binned between 0 and 200 ms after force onset for unperturbed trials. E, Group mean EMG activity in PM (top) and PD (bottom) when they were stretched (full lines) or shortened (dashed lines) by mechanical perturbations. F, Mean differences in EMG activity collapsed across muscles and participants between high and low (dash-dot line) and medium and low (full line) reward conditions for agonist muscles in presence of perturbation load. G, Group mean (black) and individual means (gray) differential EMG activity in PM binned in the long latency (50–100 ms, top) and voluntary epochs (100–180 ms, bottom) as a function of the reward condition. H, Group mean (black) and individual means (gray) of the differential EMG activity in PD binned in the long latency (50–100 ms, top) and voluntary epochs (100–180 ms, bottom) as a function of the reward condition; p < 0.05 (*), p < 0.01 (**), p < 0.005 (***).
- Figure 4.
Experiment 2, kinematics. A, Representation of hand path of individual trials for a representative subject in the same condition on top (all the targets had the same reward) and in the different condition on bottom (the central target had a higher reward than the other two). The different columns represent the different force levels (from right to left, large leftward perturbation to large rightward perturbation). Magenta, blue, and green paths, respectively, represent the paths that reached the left, central, and right targets. B, Group mean (black) and individual means (gray) of the switch proportion (i.e., fraction of trials that reached either the left or right targets) as a function of the applied load for the same condition. C, Group mean (black) and individual means (gray) of the switch proportion (i.e., fraction of trials that reached either the left or right targets) as a function of the applied load for the different condition. D–G, Comparison of the switch proportion for the same (left) and different (right) conditions for the trials with large leftward force, small leftward force, small rightward force and large rightward force, respectively; p < 0.05 (*), p < 0.01 (**), p < 0.005 (***).
- Figure 5.
Experiment 2, EMG activity. A, Mean EMG activity in PM (top) while responding to rightward (first column) and leftward perturbations (second column) and in PD (bottom) while responding to rightward (first column) and leftward (second column) perturbations in the second experiment. The magenta, blue, and green traces represent the mean EMG activity measured when participants reached the left, center or right target, respectively. B, Binned EMG activity before force onset in PM (top) and PD (bottom) for the leftward and rightward perturbation loads, for the trials that reached the central (left bin) and lateral (right bin) targets. C, Group mean and SEM of the differences in forward velocities across participants between the center and lateral trials for trials with rightward (left) and leftward (right) perturbations. D, Comparison of the forward velocity at force onset for the trials that reached the central (blue) and lateral (green or magenta) targets with a rightward or leftward perturbation load; p < 0.05 (*), p < 0.01 (**), p < 0.005 (***).
- Figure 6.
Experiment 3. A, Group mean (full line) and individual means (dashed lines) of the reach proportion to the left and right targets for the conditions without (top row, black) and with (bottom row, gray) the leftward background load as a function of perturbation load. B, Comparison of the reach proportion of the left and right targets (left and right columns, respectively) with (gray boxes) and without (black boxes) the leftward background force. C, Group mean of the EMG activity in PM (left) and PD (right) before movement onset for trials without (black) and with (gray) a background load. The time axis is aligned with the perturbation load onset. D, Comparison of the binned EMG activity between 500 and 300 ms (corresponding to the gray box in panel C) before force onset in PM and PD for the conditions with and without background; p < 0.05 (*), p < 0.01 (**), p < 0.005 (***).
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