Eye movements serve vision by placing the image of an object on the fovea of each retina, and by preventing slippage of images on the retina. The vestibulo-ocular reflex(VOR) subserves vision by generating conjugate eye movements that are equal and opposite to head movements. If the gain of VOR(the ratio of eye velocity to head velocity) is too high or too low, the target image is off the fovea, and head motion causes oscillopsia, an illusory to-and-fro movement of the environment.
