Human smooth pursuit gain is modulated by a signal related to gaze velocity

The gain in smooth pursuit eye movements in primates depends on the ongoing pursuit velocity. To address the question of whether eye or gaze (equal to eye and head) velocity is the relevant signal that controls gain, patients were instructed to pursue a continuously moving target with (headfree) and without (headfixed) the use of head movements. Eye velocity differed significantly between the head-fixed and headfree conditions. To estimate the gain, the response to a brief perturbation of the target velocity was measured. Analysis of variance revealed that the target ([almost equal to]gaze) velocity had a significant and equal influence in both headfixed and headfree conditions. This finding indicates that gaze velocity modulates the response.