Conditions of perceptual selection and suppression during interocular rivalry in strabismic and normal cats

Presenting the two eyes with incongruent stimuli leads to the phenomenon of interocular rivalry. At any given time, one of the stimuli is perceptually suppressed in order to avoid double vision. In squinting subjects, rivalry occurs permanently also for congruent stimuli because of developmental rea rrangement of cortical circuitry. In this study, we have investigated the d ynamics and stimulus dependence of rivalry in six esotropic, four exotropic and three non-strabismic cats. As an indicator for perception, we used opt okinetic nystagmus that was induced by moving gratings. The esotropic cats were tested for their visual acuity by means of a jumping stand procedure. The results show that one eye can dominate perception even if both eyes hav e equal Visual acuity and are presented with stimuli of equal contrast. Str ong eye dominance asymmetry was found in all but one of the tested cats. No tably, all three of the normal cats showed a clear asymmetry in perceptual selection. Measurements with varying contrast and velocity of the stimuli r evealed that the influence of these parameters on perceptual selection was independent of the presence of strabismus. In all cats, the time during whi ch a given eye dominated perception increased with the contrast and decreas es with the velocity of the stimulus presented to this eye. (C) 2001 Elsevi er Science Ltd. All rights reserved.