We examined whether interocular inhibition in binocular rivalry could occur at the interocular intersection of horizontal and vertical rectangular patches which are locally fusible but globally rivalrous between the two eyes. We measured contrast increment (and decrement) thresholds of a monocularly presented probe which was presented on the horizontal patch corresponding to the intersection. We found that the threshold was higher when the horizontal patch was perceptually suppressed than when it was dominant. In addition, threshold elevation did not occur when both patches were dominant, or when the horizontal patch was viewed in isolation. These results indicate that interocular inhibition occurs at the potentially fusible region, and the determination of binocular fusion or binocular rivalry does not depend on physical stimulus but rather perceptual state at the time.

We examined whether dynamic stimulation that surrounds a rival target influences perceptual alternations during binocular rivalry. We presented a rival target surrounded by dynamic random-dot patterns to both eyes, and measured dominance durations for each eye's rival target. We found that rival target dominance durations were longer when surrounds were dynamic than when they were static or absent. Additionally, prolonged dominance durations were more apparent when the dynamic surround was alternately presented between the two eyes than when it was presented simultaneously to both eyes. These results indicate that dynamic stimulation that surrounds a rival target plays a role in maintaining the current perceptual state, and causes less perceptual alternations during binocular rivalry. Our findings suggest that dynamic signals on the retina may suppress rivalry, and thus provide useful information for stabilizing perceptions in daily life.

This paper presents a model of how binocular single vision can be achieved. The model incorporates an inhibitory mechanism into the fusion theory, so we call it binocularinhibition theory. The essential property is an inhibitory mechanism in which a binocular unit yielding a fused image might inhibit two monocular neural units yielding double images in the network. To test the validity of the theory, we manipulated the binocular unit strength in the binocular network and measured the cumulative disappearance times of a monocular test stimulus in Panum's limiting case and in a single-line stereogram under fixation of the eyes. We found that the test stimulus in a single-line stereogram disappeared for longer periods of time than in Panum's limiting case. These results support the validity of the binocular-inhibition theory, assuming that the inhibitory effect on the monocular units might be directly proportional to the activity of the binocular units and that binocular single vision can be achieved using the inhibitory effects from a binocular unit to monocular units.

To study the effect of binocular disparity on apparent motion, we measured the cumulative time of its breakdown during a 30 s fixation viewing period. Two light spots, both on the left side of the fixation point, were alternately presented one by one on a CRT display (unilateral condition). These spots were binocularly disparate and viewed through a stereoscope. While one spot near the fixation point was presented on a zero disparity plane, the other spot (more peripheral) was either on a zero, uncrossed, or crossed disparity plane, so that three-dimensional motion could be seen depending on disparity values. We found that the duration of the breakdown of apparent motion was longer when uncrossed and zero-disparity spots were paired to produce apparent motion, and it was shorter when crossed and zero-disparity spots were paired. However, such disparity-specific tendencies were not obtained when the two spots were presented on both sides of the fixation point (bilateral condition). The disparity-specific tendencies in the unilateral condition can be explained by assuming that three-dimensional apparent motion that is consistent with the motion perspective may be stable because we experience it more frequently. Thus, we assume that perception of motion, both apparent and real, may develop through everyday experiences of moving to and fro in the environment rather than seeing objects move.

We examined how the binocular visual system behaves during perceptual filling-in. In these experiments an initial filled-in target was replaced with an interocularly matched (fusible) or unmatched (rivalrous) target immediately after the disappearance of the initial target induced by perceptual filling-in. We measured the times for the target to recover from the filling-in. We found that recovery times were faster when the target was replaced with an interocularly matched target than with an unmatched target: The matched visual input was immediately released from perceptual suppression by filling-in but the unmatched one was not. These results indicate that even during perceptual filling-in our visual system can use the information whether the visual inputs from the two eyes are interocularly matched or not, and the interocular matching stage (the initial stage of binocular fusion or binocular rivalry) is not inhibited by the perceptual filling-in processing. Our findings suggest that the interocular matching processing may serve to gate visual inputs accessing visual awareness.