TRACKING OF ILLUSORY TARGET MOTION - DIFFERENCES BETWEEN GAZE AND HEAD RESPONSES

We compared ocular and eye-head tracking responses to an illusion of d iagonal motion produced when vertical movement of a small visual targe t was synchronized to horizontal movement of a background display. In response to sinusoidal movement, smooth ocular pursuit followed vertic al target motion, with only a small horizontal component, In response to regular stepping movement, all anticipatory saccades were in the di rection of the illusion; these erroneous oblique movements were follow ed by corrective horizontal saccades. When the head was free to move, it usually showed a diagonal trajectory that, for both sinusoidal and stepping target motion, was always in the direction of the illusion; n o corrective movements were present. Thus, for our illusory stimuli, e ye and head tracking showed qualitative differences that imply that oc ular tracking was ultimately controlled by actual target motion but he ad tracking was controlled by illusory target motion.