Figure 2.

Experiment 1: behavior. a, Illustration of the experimental procedures: participants performed visually guided reaching movements in the forward direction while grasping the handle of a robotic manipulandum. They performed movements with or without force-field (curl field) trials randomly interleaved. See Materials and Methods for more details. b, Hand velocity of individual trials from one representative participant. Ten traces were randomly selected for illustration from the pre- (orange), peri- (purple), and post-exposure to uncertain context (green). The peak hand speed computed for each trial is highlighted with dots following the same color code and the triangles are aligned with the average peak velocity in each condition. c, Group data of forward hand velocity in the pre-, peri-, and post-exposure to randomly applied disturbances. The figure shows the mean ± SEM across 20 trials in each phase (trials chosen from the peri-exposure were evenly spaced, n = 10 subjects). d, Left, Individual change in average peak velocity in the peri-exposure as a function of the average from the pre-exposure. Each dot represents one participant. The filled dots represent the participants who exhibited significant differences in the distribution of individual trials (Wilcoxon rank sum test, p < 0.05). Right, Same as the left for the data post-exposure as a function of the average in the peri-exposure. The arrow points to the participant chosen to illustrate the main effect in b. FF, Force Field.