Experimental design for testing the coordinate system of modulation of the gain of visual–motor transmission for pursuit eye movements. A, Example traces for a single trial of target motion. From top to bottom, traces are superimposed horizontal eye and target position, vertical eye and target velocity, and horizontal eye and target velocity. Dashed and continuous traces show target and eye motion; red and black traces show trials with versus without a brief perturbation of target motion. B, Sixty-four combinations of directions of target and perturbation directions. Arrows show the eight directions of baseline target motion. The endpoints of the solid octagons around each arrow show the eight directions of motion of the perturbation. Perturbation direction is defined according to the first half of the cycle sine wave of 10 Hz target motion. C, Perturbation responses of monkey U on an individual experiment. Error bars are 95% confidence intervals from the bootstrap analysis. To differentiate data from stimuli, octagons now have been rendered in dashed lines.