Figure 1.

The experimental paradigm for contrast and spatial frequency detection during pursuit. A circular ring (with an external size of ∼7.7° and an internal size of ∼6.2°) surrounded a small fixation circle (size ∼0.1°), moved smoothly at 6.2°/sec from right to left and vice versa. The subjects were asked to track the fixation circle. Each direction represents one trial, two seconds long. When the stimulus reached the center, a Gabor patch was flashed for 100 ms at the middle of the moving target in a pseudo-random order. The spatial frequency and the contrast of the Gabor patch were manipulated in two different experiments (see the Methods).