Figure 2.

Examples of trial events. A) The 200 and 400 ms perturbations were intermixed in a single data collection for half the subjects (with 0 and 200 ms intermixed for the other half of the subjects). Note that within the conditions in each panel of the figure the perturbation location remained consistent. Also, for a given subject the conditions in a single data collection remained consistent for interception and control sessions. Initial target location is represented by the asterisk and moved in the direction of the arrows along the trajectory without leaving a trace. When it reached the location of the GO signal (filled black circle) it changed from cyan to yellow to indicate to the subject to begin the interception movement. Abrupt speed changes could occur when the target reached the positions marked with the open circle. The target continued along the trajectory until it was successfully intercepted or it completed two full rotations of the trajectory (10 seconds). B) Target, eye and finger data from three individual trials (Subject 2). The target started at the asterisk and moved along the thin, dashed, black line in the direction indicated by the arrows. The GO signal was located at the filled black dot and if there was a perturbation it occurred at the location of the open circle. Smooth pursuit (thin solid colored lines near the target trajectory) from 200 ms before the GO signal to the time of interception follows along the target path, occasionally interrupted by saccades (solid thicker magenta lines). The path of the finger is shown with the thickest solid line, and is color-coded for the slower perturbation (−0.5, blue, left panel), the faster perturbation (+1.5, red, right panel) and the control situation (0, green, center panel). Since there was no requirement to stop at the target, this subject chose a strategy where her finger continued past the interception location, which is why in all three trials the finger movement path extends past the target trajectory. In each case the straight dashed lines that begin at the finger start location point ~150 ms ahead of where the target was when the finger started moving. In all panels the green dashed-dotted line represents the prediction if the perturbation was not included and the colored dotted line (blue, red) represents if the prediction took the perturbation into account. All panels in B) are from interception sessions.