Understanding attentional modulation of binocular rivalry: a framework based on biased competition

Abstract

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.

Keywords: biased competition; binocular rivalry; bistable perception; visual attention.

Figure 1

Binocular rivalry occurs when different images are presented, one to each eye. In this situation, observers do not perceive a blend of the two stimuli, but instead experience irregular perceptual alternations between the two images such that only one image is typically perceived at a time. Head image courtesy of Jamie Simon.

Figure 2

A study by McMains and Kastner (2011) demonstrates that susceptibility to attentional modulation is dependent on the degree of unresolved stimulus conflict. (A–C) Inducer stimuli used in the experiment, which varied in the strength of perceptual grouping, ranging from strong grouping (A) to no perceptual grouping (C). In these displays, stimulus conflict decreases as the strength of perceptual grouping increases. (D,E) Illustrations of experimental conditions and tasks. In the sequential condition (D), inducers are presented in sequence, which precludes competitive interactions among stimuli. In the simultaneous condition (E), all inducers are presented at the same time. This typically results in suppressive interactions among stimuli – a result thought to indicate their competition for neural resources (Kastner et al., ; Reynolds et al., 1999). To estimate susceptibility to attentional modulation, observers were asked to perform either a demanding RSVP task at fixation (attention diverted task) or luminance detection task on one of the inducers (attention deployed task). This allowed computation of attentional modulation indices (AMI), which quantified how much responses increased when attention was directed toward the inducer stimuli. (F) The results showed that attentional modulation was strongest in the simultaneous condition and when inducer stimuli did not from a perceptual group. This key finding indicates that the unresolved competition between stimuli is linked with strong susceptibility to attentional modulation. Adopted from McMains and Kastner (2011) with permission from the Society for Neuroscience.

Figure 3

Exogenous attention biases initial dominance in binocular rivalry. In a study by Mitchell et al. (2004), rivalry was initiated between conflicting rotating surfaces, one of which was cued during preceding binocular presentation by a brief translation period (A). After rivalry was initiated, observers reported which of the two surfaces was dominant at the end of variable dichoptic viewing periods (B). After 150 ms of dichoptic viewing, in most cases observers did not perceive exclusive dominance of either surface, consistent with previous reports (Wolfe, 1983). However, for viewing periods between 300 and ∼1500 ms, the cued surface was the predominant percept, indicating a strong effect of attention on the initial dominance during rivalry. Adopted from Mitchell et al. (2004). Adapted by permission from Macmillan Publishers Ltd.: Nature, copyright 2004.

Figure 4

In a study by Meng and Tong (2004), observers were asked to willfully affect dynamics of Necker cube reversals (A) and binocular rivalry (B) by trying to hold one of two possible perceptual interpretations. This was an easy task for the Necker cube stimulus (C). When asked to “attempt to perceive the cube from the bottom view for as long as possible,” observers were able to do that regardless of the fixation position [denoted by crosses in (A)]. However, the degree of attentional control over binocular rivalry was considerably smaller (D). When asked to “try to maintain the percept of the face for as long as possible,” observers exhibited only weak ability hold the face dominant over a range of stimulus contrasts. Adopted with permission from Meng and Tong, ; ARVO^©).

Figure 5

Performing a demanding attentional task promotes selective attentional control over rivalry dynamics. (A) Stimuli used by Chong et al. (2005). One eye views a control stimulus (a radial checkerboard), while the other eye is shown a bullseye pattern. In two separate attentional tasks, observers were instructed to track either shape changes (black arrows) or shading changes (gray arrows) of the bullseye pattern. These tasks were demanding and required sustained attention. For illustration purposes, the magnitudes of the shape and shading changes are greatly exaggerated. Results (B) indicate that completing a demanding task that directs attention toward a rival stimulus lengthens its average dominance duration. On the other hand, an equally demanding task where attention was directed to the same location in space but not to rival stimulus per se did not affect rivalry dynamics. Adopted with permission from Chong et al., ; ARVO^©).