Normal binocular vision emerges from the combination of neural signals arising within separate monocular pathways. It is natural to wonder whether both eyes contribute equally to the unified cyclopean impression we ordinarily experience. Binocular rivalry, which occurs when the inputs to the two eyes are markedly different, affords a useful means for quantifying the balance of influence exerted by the eyes (called sensory eye dominance, SED) and for relating that degree of balance to other aspects of binocular visual function. However, the precise ways in which binocular rivalry dynamics change when the eyes are unbalanced remain uncharted. Relying on widespread individual variability in the relative predominance of the two eyes as demonstrated in previous studies, we found that an observer’s overall tendency to see one eye more than the other was driven both by differences in the relative duration and frequency of instances of that eye’s perceptual dominance. Specifically, larger imbalances between the eyes were associated with longer and more frequent periods of exclusive dominance for the stronger eye. Increases in occurrences of dominant eye percepts were mediated in part by a tendency to experience “return transitions” to the predominant eye – that is, observers often experienced sequential exclusive percepts of the dominant eye’s image with an intervening mixed percept. Together, these results indicate that the often-observed imbalances between the eyes during binocular rivalry reflect true differences in sensory processing, a finding that has implications for our understanding of the mechanisms underlying binocular vision in general.

Starting from early scientific explorations of binocular rivalry, researchers have wondered about the degree to which an observer can exert voluntary attentional control over rivalry dynamics. The answer to this question would not only reveal the extent to which we may determine our own conscious visual experience, but also advance our understanding of the neural mechanisms underlying binocular rivalry. Classic studies, intriguingly, reached contradictory conclusions, ranging from an absence of attentional control, as advocated by Breese, to nearly complete control of rivalry dynamics, as reported by Helmholtz. Recent investigations have revisited this question, but the results have continued to echo the conflicting findings of earlier studies, seemingly precluding a comprehensive understanding of attentional effects on rivalry. Here, we review both classic and modern studies, and propose a unifying framework derived from the biased competition theory of attention. The key assumption of this theory is that the nature of stimulus conflict determines the limits of attentional modulation. For example, a condition in which unresolved stimulus conflict transpires through many levels of visual processing should be very susceptible to attentional control. When applied to binocular rivalry, this framework predicts strong attentional modulations under conditions of unresolved stimulus conflict (e.g., initial selection) and conditions where conflict is resolved at higher levels of visual processing (e.g., stimulus rivalry). Additionally, the efficacy of attentional control over rivalry can be increased by utilization of demanding, behaviorally relevant tasks, and likely through perceptual training paradigms. We show that this framework can help facilitate the understanding and synthesis of a diverse set of results on attentional control over rivalry, and we propose several directions for future research on this interesting topic.

Segregation of objects from their backgrounds is a fundamental visual function and one that is particularly effective when objects are in motion. Theoretically, suppressive center-surround mechanisms are well suited for accomplishing motion segregation. This longstanding hypothesis, however, has received limited empirical support. We report converging correlational and causal evidence that spatial suppression of background motion signals is critical for rapid segmentation of moving objects. Motion segregation ability is strongly predicted by both individual and stimulus-driven variations in spatial suppression strength. Moreover, aging-related superiority in perceiving background motion is associated with profound impairments in motion segregation. This segregation deficit is alleviated via perceptual learning, but only when motion segregation training also causes decreased sensitivity to background motion. We argue that perceptual insensitivity to large moving stimuli effectively implements background subtraction, which, in turn, enhances the visibility of moving objects and accounts for the observed link between spatial suppression and motion segregation.

How does attention interact with incoming sensory information to determine what we perceive? One domain in which this question has received serious consideration is that of bistable perception: a captivating class of phenomena that involves fluctuating visual experience in the face of physically unchanging sensory input. Here, some investigations have yielded support for the idea that attention alone determines what is seen, while others have implicated entirely attention-independent processes in driving alternations during bistable perception. We review the body of literature addressing this divide and conclude that in fact both sides are correct – depending on the form of bistable perception being considered. Converging evidence suggests that visual attention is required for alternations in the type of bistable perception called binocular rivalry, while alternations during other types of bistable perception appear to continue without requiring attention. We discuss some implications of this differential effect of attention for our understanding of the mechanisms underlying bistable perception, and examine how these mechanisms operate during our everyday visual experiences.

Attentional influence over perception is particularly pronounced when sensory stimulation is ambiguous, where attention can reduce stimulus uncertainty and promote a stable interpretation of the world. However, binocular rivalry, an extensively studied visual ambiguity, has proved to be comparatively resistant to attentional modulation. We hypothesize that this apparent inconsistency reflects fluctuations in the degree of unresolved competition during binocular rivalry. Namely, attentional influence over rivalry dynamics should be limited to phases of relatively unresolved stimulus competition, such as ends of individual dominance periods. We found that transient cues congruent with the dominant stimulus prolonged dominance durations, while cues matching the suppressed stimulus hastened its return to dominance. Notably, this only occurred when cues were presented near the end of individual dominance periods. These findings reveal that unresolved competition, which gates attention across a variety of domains, is also crucial in determining the susceptibility of binocular rivalry to selective influences.