Figure 1. Schematic of pursuit tasks and sample behavior. A, Each box depicts the monitor display at an important point in the trial for two-stimuli (top) and single-stimulus (bottom) trials. In a single experiment, stimuli moved along either the cardinal axes or diagonal axes (shown). For single-stimulus trials, stimuli that moved in each of the four directions were presented with equal probability, and for two-stimuli trials any two adjacent stimuli were presented on a given trial. B, The trajectory of smooth pursuit is plotted for single stimuli moving toward the upper right or lower right quadrant (gray) and, for both stimuli presented together (blue), in steps of 3 ms for the first 50 ms from pursuit onset. C, Horizontal and vertical eye velocities for single-stimulus trials (black) and two-stimuli trials (blue) from smooth pursuit onset (vertical gray line), averaged over ∼36 (single-stimulus) or 72 (two-stimuli) trials. Saccades have been removed for clarity. The first 50 ms of pursuit, used to calculate the initial pursuit response, are highlighted by the yellow shading. D, The mean horizontal and vertical velocities during the first 50 ms of smooth pursuit, shown in B and C, are plotted as vectors for single-stimulus trials (solid black) and for two-stimuli trials (solid blue). The weights for each stimulus are given and plotted as scaled vectors (dashed blue), which sum up to the response for the two-stimuli trials.