Figure 4

Circle-writing task. Exemplificative trajectories of one healthy and one dystonic subject, in the 3 conditions (A, B and C). The first four and the last four trials are indicated in black dashed and thicklines, respectively, while the intermediate ones in blue for healthy and in red for dystonic. The yellow arrows represent the disturbing force along x-axis, i.e. horizontal. Note: for the few trials where the subjects lost the leaning on the virtual surface, the data portion where the user end-effector was not touching the surface was cut (event detection); and such trial was reconstructed and included into the analysis if the re-started path passed back for the falling point.