Article Figures & Data
Figures
- Figure 1.
Experimental paradigms. A, Schematic representation of the task paradigm. Participants had to perform reaching movement from the home target to the goal target, initially represented as a 30-cm-wide rectangle. During movement, they could experience mechanical step forces triggered in position at 6 cm (experiment 1, black line) or 8 cm (experiment 2, gray line) from the home target and visual changes in target width (triggered as they exited the home target). B, Evolution of the target width with respect to time in the different target conditions. The time axis is aligned on the visual perturbation onset defined by the onset of movement. The vertical dashed lines represent the median force onsets for experiments 1 and 2. C, Histograms of the distribution of the time interval between the visual and mechanical perturbation onset (respectively, target and force onset) across all participants and conditions in experiments 1 (black) and 2 (gray). D, Histograms of the distribution of the target width at force onset for the two dynamical conditions (fast in blue and slow in green) across all participants in experiments 1 (top) and 2 (bottom).
- Figure 2.
Experiment 1, hand kinematics during movement. A, Group mean of the hand path for unperturbed and perturbed trials in the no change (black), slow (green), fast (blue), and switch (magenta) conditions. B, Group mean and SEM of the x-position of participants’ hand as a function of time (aligned on force onset) for trials perturbed with rightward mechanical perturbations in the four target conditions. The black dashed line represents the onset of the mechanical perturbation. C, Group mean and SEM of the x-position of participants’ hand as a function of time for trials perturbed with leftward mechanical perturbations in the four target conditions. The black dashed line represents the onset of the mechanical perturbation. D, Group mean (black) and individual means (gray) of the maximal hand deviation in presence of a rightward perturbation for the four target conditions. E, Group mean (black) and individual means (gray) of the final position for trials with rightward perturbation for the four target conditions. F, Group mean (black) and individual means (gray) of the maximal hand deviation in presence of a rightward perturbation for the four target conditions. G, Group mean (black) and individual means (gray) of the final position for trials with rightward perturbation for the four target conditions; **p < 0.005.
- Figure 3.
Experiment 1, EMG activity. A, Group mean for the stretched (Pect. Maj., full lines) and shortened (Post. Delt., dashed lines) responses to rightward perturbations in the different target conditions. The gray rectangles represent the LL and VOL epochs where the EMG activity was averaged to perform statistical analyses. The black dashed line represents mechanical perturbation onset and the time axis is aligned with force onset. B, Group mean for the stretched (Post. Delt., full lines) and shortened (Pect. Maj., dashed lines) responses to leftward perturbations in the different target conditions. C, Group mean of target-specific EMG responses to perturbation for Pect. Maj. in the presence of rightward perturbation for the switch (magenta), fast (blue), and slow (green) target conditions. Time axis is aligned with force onset. The small insets represent the mean and SEM target-specific EMG responses at the end of the movement. D, Group mean of target-specific EMG responses to perturbation for Post. Delt. in the presence of leftward perturbation for the switch (magenta), fast (blue), and slow (green) target conditions. Time axis is aligned with force onset. The small insets represent the mean and SEM target-specific EMG responses at the end of the movement. E, F, Group mean (black) and individual means (gray) of the binned EMG activity in the LL (E) and VOL (F) time windows for Pect. Maj. in the presence of rightward perturbations for the different target conditions. G, H, Group mean (black) and individual means (gray) of the binned EMG activity in the LL (G) and VOL (H) time windows for Post. Delt. in the presence of leftward perturbations for the different target conditions; *p < 0.05, **p < 0.005.
- Figure 4.
Normalized EMG across experiments. A, Distribution histogram of the target width at perturbation onset in the slow target condition in experiments 1 (black) and 2 (gray). B, Distribution histogram of the target width at force onset in the fast target condition in experiments 1 (black) and 2 (gray). C, Group mean and SEM collapsed across participants of the normalized Pect. Maj. EMG activities in the LL time window in experiments 1 (black) and 2 (gray) across conditions in presence of rightward perturbations. D, Group mean and SEM collapsed across participants of the normalized Post. Delt. EMG activities in the LL time window in experiments 1 (black) and 2 (gray) across conditions in presence of leftward perturbations. E, Group mean and SEM collapsed across participants of the normalized Pect. Maj. EMG activities in the VOL time window in experiments 1 (black) and 2 (gray) across conditions in presence of rightward perturbations. F, Group mean and SEM collapsed across participants of the normalized Post. Delt. EMG activities in the VOL time window in experiments 1 (black) and 2 (gray) across conditions in presence of leftward perturbations. G, Group mean across participants, experiments and muscles of the stretched muscle activity for the different target conditions. The gray rectangles represent the LL and VOL time epochs. The time axis is aligned on force onset and the insets at the right of the panel represent the mean and SEM of the stretched muscles activity at the end of movement; *p < 0.05, **p < 0.005.
- Figure 5.
Between trials analyses. A, Group mean and SEM collapsed across participants of the first (full line) and last (dashed line) trials in the fast condition with rightward mechanical perturbation. Time axis is aligned on force onset. B, Group mean and SEM collapsed across participants of the first (full line) and last (dashed line) trials in the fast condition with leftward mechanical perturbation. The black dashed line corresponds to the difference between the first and last trials. Time axis is aligned on force onset. C, Group mean of the acceleration profiles of the first (full line) and last (dashed line) trials in the fast condition with rightward mechanical perturbation. Time axis is aligned with force onset. D, Group mean of the acceleration profiles of the first (full line) and last (dashed line) trias in the fast condition with leftward mechanical perturbation. Time axis is aligned with force onset. E, Cumulative density function of the lag between the last and first acceleration profiles for both perturbation directions. The blue vertical line corresponds to the median value. F, Group mean (black) and individual means (gray) of the integral of the absolute value of the jerk for the first and last trials in the fast target condition. G, Group mean (black) and individual means (gray) of the integral of the absolute value of the jerk for the first and last trials in the slow target condition; **p < 0.005.
- Figure 6.
Modified goal-directed feedback control architecture. The inner loop (in gray), combining sensory feedbacks and efference copy is the one responsible for the goal-directed feedback responses observed behaviorally. The latency of this inner loop is 50–100 ms depending on the sensory modalities involved. The outer feedback loop (in black) that modifies the task definition and the feedback control policy captures the online adjustments in control policy elicited by continuous alteration of the target structure during movement.
Tables
No change Slow Fast Switch No 20 6 6 6 Left 10 4 4 4 Right 10 4 4 4
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