Figure 1.

Stimulus and tasks. The arc started moving simultaneously with the flash, to which participants had to orient a pointer (perceptual task) or make a saccade (motion and gap tasks). The three flash positions (displacement, +15, 0, and −15°), the two motion directions (clockwise and counterclockwise), and the two stimulus presentation sides (right and left) are illustrated (the elements in black depict a prototypical trial). The angle between response direction (thick line or arrow) and flash direction (dashed line) was the directional error. For graphical purposes, the layout of the figure is somewhat arbitrary.