Coordination of the head and eyes in pursuit of predictable and random target motion.

Subjects were required to use their head and eyes in pursuit of visual targets which moved randomly or sinusoidally in the horizontal plane. All subjects disliked moving their heads to pursue the random motion, apparently because the motion broke fixation which resulted in a predominance of the vestibulo-ocular compensatory reflex over the smooth pursuit reflex. As a consequence gaze (head plus eye movement) was at times in the opposite direction to the motion of the target. In steady state pursuit of sinusoidal targets, eye movement consisted of a combination of pursuit and vestibulo-ocular reflex eye movements. At frequencies below 0.8 HZ, the vestibular reflex was used at times of minimum target velocity to stabilize fixation whereas during maximum target velocity the head movement was slowed and the smooth pursuit reflex predominated. At 1 HZ and over, there was a failure to suppress the compensatory vestibulo-ocular reflex; however, the saccades of vestibular nystagmus were used to "catch up" the target. There was a preference not to use the head in predictable pursuit.