[A comparison between orienting rapid eye movements accompanying active or passive head movement in the cat]

Gaze is shifted by means of eye saccades which, in most instances, are synchronized with head rotations. During eye-head movements performed by cats in the dark, most of the rapid eye movements start after the head has begun to move (mean time lag was 45 msec). This pattern resembles that observed when the cat, as a whole, is suddenly rotated passively and consists of a short lasting vestibularly induced slow phase component followed by a rapid eye movement that takes the eye in the same direction as the head. We have compared the passively and actively induced eye-head movements. The rapid eye movements are similar in both cases in that they terminate at a fixed position ("goal") in the orbit irrespective of the eye's starting position. They differ primarily in the fact that the eccentricity of the "goal" during active head rotations increases much more rapidly with velocity than it does during the passive condition. The results suggest that the rapid eye movement that accompanies an active head movement in the dark is not simply a vestibularly induced quick phase.