Kevin C. Dieter

Understanding Attentional Modulation of Binocular Rivalry: A Framework Based on Biased Competition

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.

Kinesthesis Can Make an Invisible Hand Visible

Self-generated body movements have reliable visual consequences. This predictive association between vision and action likely underlies modulatory effects of action on visual processing. However, it is unknown whether actions can have generative effects on visual perception. We asked whether, in total darkness, self-generated body movements are sufficient to evoke normally concomitant visual perceptions. Using a deceptive experimental design, we discovered that waving one’s own hand in front of one’s covered eyes can cause visual sensations of motion. Conjecturing that these visual sensations arise from multisensory connectivity, we showed that grapheme-color synesthetes experience substantially stronger kinesthesis-induced visual sensations than nonsynesthetes do. Finally, we found that the perceived vividness of kinesthesis-induced visual sensations predicted participants’ ability to smoothly track self-generated hand movements with their eyes in darkness, which indicates that these sensations function like typical retinally driven visual sensations. Evidently, even in the complete absence of external visual input, the brain predicts visual consequences of actions.

When can attention influence binocular rivalry

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, feature-based cues congruent with the dominant stimulus prolonged dominance durations, while cues matching the suppressed stimulus hastened its return to dominance. Notably, the effect of cues depended on when the cues are presented. Cues presented late, but not early, during a given episode of perceptual dominance influenced rivalry dynamics. This temporal pattern mirrors known changes in the relative competitive dynamics of rival stimuli, revealing that selective effects occur only during temporal windows containing weak resolution of visual competition. In conclusion, 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.

Motion-induced blindness continues outside visual awareness and without attention.

Visual phenomena demonstrating striking perceptual disappearances of salient stimuli have fascinated researchers because of their utility in identifying neural processes that underlie subjective visibility and invisibility. Motion-induced blindness (MIB) is appealing for such purposes because it, like a class of ostensibly related paradigms such as binocular rivalry, features periods of unequivocal subjective disappearances despite constant physical stimulation. It remains unclear, however, exactly how the mechanisms that cause MIB are related to subjectively observed fluctuations in visual awareness. To address this question, we used continuous flash suppression (CFS) to present the MIB stimulus outside visual awareness. Results indicated that MIB occasionally reappeared from suppression with its salient yellow target absent. To quantify this observation, we measured reaction times (RTs) to detect the yellow dot target following visible or perceptually suppressed MIB and indeed found no difference in RTs between these conditions. We also provide evidence that MIB fluctuations can occur without attention. In sum, these experiments indicate that MIB fluctuations are effectively changes in stimulus strength, which under typical conditions result in unmistakable subjective disappearances, but are not inherently fluctuations in stimulus visibility. More broadly, these results challenge the assumed privileged link between bistable stimuli and visual awareness.

Individual differences in sensory eye dominance reflected in the dynamics of binocular rivalry

HighlightsA large subset of observers experience imbalance between their two eyes.The stronger eye is dominant longer and more frequently during binocular rivalry.Large eye imbalance also predicts frequent return transitions to the dominant eye.Sighting and sensory eye dominance are unrelated. ABSTRACT 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.

Perceptual training profoundly alters binocular rivalry through both sensory and attentional enhancements

Significance Attention can exert a strong influence over perception, especially when multiple stimuli compete for processing resources. However, attention has relatively modest effects on binocular rivalry. Competitive interactions between the two eyes/stimuli unfold largely automatically, with observers unable to strongly bias perception toward either stimulus. Here, we demonstrate that this limitation can be overcome following prolonged perceptual training. Trained observers exhibited substantial changes in rivalry dynamics, with individual percepts occasionally stabilizing for tens of seconds. These large changes were mediated through both eye-specific changes in visual processing and enhanced attention to task-relevant features in the trained eye. Evidently, strong modulation of binocular rivalry can be achieved through training-induced plasticity of bottom-up sensory and top-down attentional mechanisms in low-level vision. The effects of attention, as well as its functional utility, are particularly prominent when selecting among multiple stimuli that compete for processing resources. However, existing studies have found that binocular rivalry—a phenomenon characterized by perceptual competition between incompatible stimuli presented to the two eyes—is only modestly influenced by selective attention. Here, we demonstrate that the relative resistance of binocular rivalry to selective modulations gradually erodes over the course of extended perceptual training that uses a demanding, feature-based attentional task. The final result was a dramatic alteration in binocular rivalry dynamics, leading to profound predominance of the trained stimulus. In some cases, trained observers saw the trained rival image nearly exclusively throughout 4-min viewing periods. This large change in binocular rivalry predominance was driven by two factors: task-independent, eye-specific changes in visual processing, as well as an enhanced ability of attention to promote predominance of the task-relevant stimulus. Notably, this strengthening of task-driven attention also exhibited eye specificity above and beyond that from observed sensory processing changes. These empirical results, along with simulations from a recently developed model of interocular suppression, reveal that stimulus predominance during binocular rivalry can be realized both through an eye-specific boost in processing of sensory information and through facilitated deployment of attention to task-relevant features in the trained eye. Our findings highlight the interplay of attention and binocular rivalry at multiple visual processing stages and reveal that sustained training can substantially alter early visual mechanisms.

Does visual attention drive the dynamics of bistable perception

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.

Persistent Biases in Binocular Rivalry Dynamics within the Visual Field

Binocular rivalry is an important tool for measuring sensory eye dominance—the relative strength of sensory processing in an individual’s left and right eye. By dichoptically presenting images that lack corresponding visual features, one can induce perceptual alternations and measure the relative visibility of each eye’s image. Previous results indicate that observers demonstrate reliable preferences for several image features, and that these biases vary within the visual field. However, evidence about the persistence of these biases is mixed, with some suggesting they affect only the onset (i.e., first second) of rivalry, and others suggesting lasting effects during prolonged viewing. We directly investigated individuals’ rivalry biases for eye and color within the visual field and interestingly found results that mirrored the somewhat contradictory pattern in the literature. Each observer demonstrated idiosyncratic patterns of biases for both color and eye within the visual field, but consistent, prolonged biases only for the eye of presentation (sensory eye dominance, SED). Furthermore, the strength of eye biases predicted one’s performance on a stereoacuity task. This finding supports the idea that binocular rivalry and other binocular visual functions may rely on shared mechanisms, and emphasizes the importance of SED as a measure of binocular vision.

Motion-induced blindness without awareness or attention

Motion-induced blindness (MIB) distinctly visible stimuli are made to periodically disappear by placement within a moving pattern. MIB has been widely utilized to investigate the neural and cognitive mechanisms of visual awareness. We probed observers’ perceptual states after periods of MIB outside of awareness (suppressed by continuous flash suppression: CFS), unattended (concurrent rapid serial visual presentation task), or both. If the target fluctuates during these manipulations (without awareness and/or attention), it should sometimes be perceptually suppressed after this period due to MIB, resulting in longer reaction times (RT) to report the target. We found that CFS and/or inattention had no significant effect on RTs for target detection compared to normal MIB. This suggests that the dynamics of MIB were unaffected by removing awareness, attention or both. A baseline condition in which the target dot was physically absent during the manipulation period only, produced reliably faster RTs for all of our manipulations, including CFS. To ensure that target suppression was due to MIB and not CFS, we ran a stationery MIB control and found no effect of CFS. Together, these results suggest that the phenomenon of MIB is unaffected by the removal of awareness, attention, or both.