Conjugate and disjunctive optokinetic eye movements in the rabbit, evoked by rotatory and translatory motion

SummaryHorizontal movements of both eyes of rabbits were recorded simultaneously, using a scleral search coil system. Several types of motion of the environment were produced: a) a circular striped drum rotating around the animal (‘true rotation’), b) flat striped patterns moving in parasagittal planes, one forward, the other backward (‘pseudorotation’), c) flat patterns moving both either backward or forward (‘tunnelmotion’).True rotation and pseudorotation evoked a regular optokinetic nystagmus (OKN). Systematic asymmetries in the OKN of the two eyes were found. As was already known, each eye apart is much more sensitive to forward than to backward motion. The eye that sees forward motion proves to have a larger slow phase velocity and amplitude of OKN and therefore a better gain than the crossed eye, which is to a great dealdriven by the other eye. This asymmetry is more clearly exposed by covering one eye; the seeing eye is then the leading one in both directions.Tunnelmotion elicited vergence movements in all rabbits. Bilateral forward motion induced convergence, backward motion divergence. The range between extreme convergence and divergence varied from 7–23°. Occasionally, a regular vergence nystagmus was elicited by forward motion; in this case some of the fast phases of the two eyes were oppositely directed.It is concluded that disjunctive eye movements can be induced in the rabbit by certain visual stimuli. It is doubtful whether vergence movements are ever normally used by the rabbit for binocular vision of objects at varying distances. A role in individual drift-correction for each eye appears more plausible.