Figure 6.

Testing the influence of microsaccades on early visual motion processing. A, Our ocular following paradigm aimed to simulate full-field retinal-image motion at different times relative to microsaccades. Monkeys first fixated a stationary stimulus consisting of a fixation point and a vertical sine wave grating (left). After steady fixation, we enabled a process to detect microsaccades, and we triggered a horizontal (rightward or leftward) motion of the grating at different times relative to microsaccade detection (right; the arrows are just an illustration of grating motion and were not actually visible). B, Average radial eye velocity of one monkey (N) aligned on motion onset of the grating. Full-field image motion elicited a short-latency increase in radial eye velocity. We analyzed the peak of the initial upswing of this velocity (in the shown rectangular analysis window) as our “open-loop” response. C, Same analysis as in B but for the case in which the motion was triggered during microsaccades (black curve; note the upswing in average eye velocity around motion onset, corresponding to the velocity of the triggering microsaccades). Compared with the baseline with no microsaccades (gray curve; identical to that in B), there was a strong and long-lasting suppression of the initial ocular following response (arrow labeled suppression). D, When the image motion was started ∼50 ms after the end of a microsaccade (black curve), the initial ocular following response was greatly enhanced. Error bars in all plots indicate 95% confidence intervals.