Figure 1.
Experimental setup and typical trajectory data. A, Subjects move a hidden cursor from a starting position to a target (yellow) by moving their occluded right index finger. We measure the generalization of the learned variance of a perturbation using the response to a noisy midpoint cursor feedback (red dots). B, Experiment 1, with zero mean perturbation, and a SD (σp) of either 4° or 12° (shown example trajectories are for σp = 12°). Subject's hand and cursor position during learning trials. Each thin red line represents the trajectory of the real hand position (hand, left) or of the hidden cursor position (cursor, right) during a trial toward the learning direction (yellow target). The black solid line represents the average trajectory toward the learning direction. Average trajectories for generalizing directions are shown as black dashed lines (corresponding targets are black dots). The position where midpoint feedback is triggered is denoted by the red circle. Left, Hand trajectories are also superimposed on the workspace shown in A. C, Experiments 2 and 3, where the absolute mean perturbation is 30° (introduced abruptly in Experiment 2 and progressively in Experiment 3) and the SD is either 4° or 12° (shown example trajectories are from Experiment 2 with σp = 12°). Same notation as B. Note that, because the cursor is rotated 30° on average, the subjects' hand has to move on average in a −30° direction (relative to the target) so that the cursor hits the target.