Three-dimensional organization of optokinetic responses in the rabbit

1. Three-dimensional rotations of both eyes were measured in alert rabbits during optokinetic stimulation about axes lying in the horizontal plane or about an earth-vertical axis, with either one or both eyes viewing the stimulus. Optokinetic stimulus speed was 2 degrees /s, either continuous or alternating in polarity (triangular stimulus). In addition to the gains of the responses, the orientations of the response axes relative to the stimulus axes were determined. 2. In comparison to the response to constant-speed optokinetic stimulation about the vertical axis, the response to constant-speed optokinetic stimulation about horizontal axes was characterized by the lack of a speed buildup. In many cases, slow phase tracking was good as long as the eye was within the central oculomotor range but deteriorated when eye deviation became more eccentric and fast phases failed to be generated. These features suggest that the optokinetic reflex about horizontal axes functions as a position-control system, rather than as a velocity-control system. 3. Binocular optokinetic stimulation at constant speed (2 degrees/s) about the roll axis (0 degrees azimuth horizontal axis) elicited disconjugate responses. Although the gain of the response was not significantly different in the two eyes (0.38 for downward and 0.44 for upward stimulation), the response axes of the two eyes differed by as much as 51 degrees. 4. Monocular, horizontal axis optokinetic stimulation at constant speed elicited responses that were grossly dissociated between the two eyes. The magnitude of the responses was anisotropic in that it varied with the azimuthal orientation of the stimulus axis; the maximum gain for each eye (0.41 for the seeing and 0.33 for the covered eye) was at 135 degrees azimuth for each eye. The axis orientation and direction (sense of rotation) of the optokinetic stimulus eliciting the maximal response for each eye coincided with the optic flow normally associated with the maximal excitation of the corresponding ipsilateral anterior canal. 5. Binocular, triangular optokinetic stimulation with small excursions (+/- 10 degrees), which avoided the saturation problems of constant-speed stimulation, elicited adequate responses without systematic directional asymmetries. Gain was approximately 0.9 for all stimulus axis orientations in the horizontal plane. 6. During monocular stimulation with triangular stimuli, the response of the seeing eye showed a gain of approximately 0.5 for all orientations of the stimulus axis. In contrast, the covered eye showed anisotropic responses, with a maximum gain of approximately 0.5 during stimulation of the seeing eye about its 45 degree axis.(ABSTRACT TRUNCATED AT 400 WORDS)