Fig. 1

Task conditions. The target and cursor are the upper and lower white bars, respectively. Their lengths were independently varied over time. The target horizontally moved unpredictably. Participants were instructed to track the center of target with the center of cursor. In the Precise condition (a), visual markers (black lines) were presented at the centers of both target and cursor and therefore there was no need to estimate cursor position. In the Obscure condition (b), no visual markers were provided and therefore estimating cursor position was somewhat helpful for tracking. In the No condition (c), while the visual marker was provided only for the target, the actual cursor (dotted bar) was invisible; instead, a fake cursor (white bar) was displayed which automatically and completely followed the target independently of input signals from the joystick. Therefore, positions of the actual and fake cursors were independent of each other and the demand for estimating position of the actual cursor was maximized