Article Figures & Data
Figures
- Figure 1.
A, Participants used a robotic manipulandum to move an on-screen cursor from a central start circle to one of 8 possible target locations (0°, 45°…315°): target order was randomized within each bin of eight trials such that each target appeared once within each bin. No direct visual feedback of the hand was available. Online movement corrections were disincentivized by only making feedback of hand position available for the last 4 cm of the 9 cm start-target distance. Feedback of hand position was also removed as soon the 9 cm start-target distance was achieved. B, Trial sequence for the aiming trials. Before the start of each aiming block (where each block = 10 bins, or 80 trials), participants were instructed to aim away from the presented target at angles of varying sizes (0°, 30°, 60°, 120°, 135°, 150°, 165°; C). In each aiming trial, participants saw a target that jumped mid-movement (4 cm into the 9 cm start-target distance) by the instructed aiming angle relative to the target. As the target jump was not linked to sensory properties of the participant movements, the target jump did not result in sensory prediction errors (i.e., discrepancies between predicted and actual sensory outcomes of movements). Instead, the target-jump results in task errors, or failures to achieve the task goal of hitting the target, if the participant fails to aim by the instructed angle.
- Figure 2.
Trial-by-trial performance changes within the first 8 trials (i.e., the first bin) averaged across all aiming angles and across training and follow-up sessions for accuracy (A), reaction times (B), and peak velocity (C). Right panels show changes in individual participant data from trial 1 to trial 8. Trial-wise reductions in reaction times were evident for both the levodopa (pink) and the placebo (gray) groups (B, left panel). The levodopa group showed smaller mean errors than the placebo group in the first trial and maintained this level of accuracy across the first eight trials, whereas the placebo group reduced errors across trials. D, Mean error for the first eight trials for the training session compared with the follow-up session. Bin-by-bin performance averaged across the training and follow-up sessions and aiming angles for accuracy (E), reaction times (F), peak velocity (G), and error variability (H). Right panels show changes in individual participant data from bin 1 to bin 10. Reaction time and error variability reduced across bins. Values are covariate-adjusted estimated marginal means and standard errors of the mean.
- Figure 3.
Session-by-session performance improvements in accuracy and the speed of movement planning and movement execution, as evidenced in reduced error, reaction time, and increased peak velocity from training (lighter colors) to follow-up sessions (darker colors), for the levodopa and the placebo group. Values are covariate-adjusted estimated marginal means and standard errors of the mean.
- Figure 4.
Levodopa modulated accuracy and the speed of movement planning both at training (left panels) and follow-up (middle panels), as shown by effects of levodopa in reducing errors (A) while lengthening reaction times (B). Levodopa also resulted in slower peak velocity at training (D), although this effect was less prominent at follow-up. Values are covariate-adjusted estimated marginal means and standard errors of the mean. Right panels show individual participant data averaged across trial bins across both sessions, for each aiming angle. Values are covariate-adjusted estimated marginal means and standard errors of the mean.
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