Stochastic properties of binocular rivalry alternations

Previous researches have demonstrated that the successive phase durations in binocular rivalry are independent. These findings are confirmed and extended to chromatic stimuli. The nature of the function that is shown to describe the distribution of the dominance phase durations is consistent with the independence of successive phases and suggests that a parallel may exist between binocular rivalry and the perceptual reversal of ambiguous figures.

     

Shifting spatial attention makes you flip: Exogenous visual attention triggers perceptual alternations during binocular rivalry

Although it has been argued that visual attention and the dynamics of binocular rivalry are closely linked, strong evidence for this proposition is still lacking. Here, we investigate how perceptual alternations during binocular rivalry are affected by spatial attention by employing a cuing paradigm. We show a tight link between the occurrence of perceptual alternations and the spatiotemporal properties of visual attention: Alternations occurred earlier and more frequently at locations where visual attention was summoned by an exogenous cue. We argue that cuing a location where rival images are presented leads to a transient increase in the effective contrast of these rival images. This transient increase in effective contrast increases the probability of an alternation at that location. Furthermore, we suggest that an occipito-fronto-parietal network known to be involved in selective attention and binocular rivalry mediates perceptual alternations by boosting the neural response at attended locations.     

Aftereffects in binocular rivalry

Five experiments are reported in which the aftereffect paradigm was applied to binocular rivalry. In the first three experiments rivalry was between a vertical grating presented to the left eye and a horizontal grating presented to the right eye. In the fourth experiment the rivalry stimuli consisted of a rotating sectored disc presented to the left eye and a static concentric circular pattern presented to the right. In experiment 5 rivalry was between static radiating and circular patterns. The predominance durations were systematically influenced by direct (same eye) and indirect (interocular) adaptation in a manner similar to that seen for spatial aftereffects. Binocular adaptation produced an aftereffect that was significantly smaller than the direct aftereffect, but not significantly different from the indirect one. A model is developed to account for the results; it involves two levels of binocular interaction in addition to monocular channels. It is suggested that the site of spatial aftereffects is the same as that for binocular rivalry, rather than sequentially prior.     

Attention speeds binocular rivalry

During binocular rivalry, incompatible images presented dichoptically compete for perceptual dominance. It has long been debated whether binocular rivalry can be controlled by attention. Most studies have shown that voluntary control over binocular rivalry is limited. We sought to remove attention from binocular rivalry by presenting a concurrent task. Diverting attention slowed the rivalry alternation rate, and did so in proportion to the difficulty of the concurrent task. Even a very demanding distractor task, however, did not arrest rivalry alternations completely. Given that diverting attention was equivalent to lowering the contrast of the rival stimuli, the ability of attention to speed binocular rivalry is most likely due to an increase in the effective contrast of the stimuli through boosting the gain of the cortical response. This increase in effective contrast will ultimately lead to a perceptual switch, thereby limiting voluntary control. Thus, attention speeds rivalry alternations, but has no inherent control over the rivalry process.     

Neural bases of binocular rivalry

During binocular rivalry, conflicting monocular images compete for access to consciousness in a stochastic, dynamical fashion. Recent human neuroimaging and psychophysical studies suggest that rivalry entails competitive interactions at multiple neural sites, including sites that retain eye-selective information. Rivalry greatly suppresses activity in the ventral pathway and attenuates visual adaptation to form and motion; nonetheless, some information about the suppressed stimulus reaches higher brain areas. Although rivalry depends on low-level inhibitory interactions, high-level excitatory influences promoting perceptual grouping and selective attention can extend the local dominance of a stimulus over space and time. Inhibitory and excitatory circuits considered within a hybrid model might account for the paradoxical properties of binocular rivalry and provide insights into the neural bases of visual awareness itself.     

Temporal perturbations of binocular rivalry

Successive durations of binocular rivalry are sequentially independent, random variables. To explore the underlying control process, we perturbed the cycle during a 30-sec viewing period by immediately forcing an eye to return to dominance whenever it became suppressed. During this period of forced dominance, that eye's individual dominance durations were unusually brief, but immediately following the period of forced dominance that eye's suppression durations were unusually long. However, no long-term change in the sequential pattern of rivalry occurred, and the stochastic independence of successive durations was maintained during and following the period of forced dominance. The same pattern of results was obtained with even longer periods of forced dominance. These results are consistent with the existence of a short-term adaptation, or fatigue, process responsible for transitions from dominance to suppression.     

Oculomotor effects upon binocular rivalry

Summary Binocular rivalry was generated by projecting dissimilar Julesz-type patterns to each eye. The minimum angular width of the patterns needed to observe rivalry was measured at four retinal eccentricities for two simulated viewing distances: 200 and 20 cm. The angular width needed to just detect rivalry was up to 50% greater for the 20 cm viewing distance as compared with the threshold width measured at 200 cm. This increased tolerance for rivalry for near fixation was inversely proportional to the change in apparent size. The results suggest that the lateral geniculate nucleus is the site of size-scaling or zooming.Supported by the U. S. Air Force under contract No. AFOSR-F44620-67-C0085, with supplementary funding to Prof. H.-L. Teuber, Chairman, from NASA and NIMH under grants NsG 496 and MH 05673.     

Contour synchrony in binocular rivalry

Afterimages of rivalrous vertical and horizontal lines were generated simultaneously in each eye. Either a horizontal and a vertical line or two vertical lines were presented to one eye with the complementary rivalrous pair to the other eye. Synchrony of line pairs presented to the same eye was longer than predicted on the basis of independence, irrespective of the monocular configuration. Furthermore, there appeared to be a facilitatory effect for lines of the same orientation if they were presented to one eye rather than combined from both eyes.     

A neural theory of binocular rivalry

When the two eyes view discrepant monocular stimuli, stable single vision gives way to alternating periods of monocular dominance; this is the well-known but little understood phenomenon of binocular rivalry. This article develops a neural theory of binocular rivalry that treats the phenomenon as the default outcome when binocular correspondence cannot be established. The theory posits the existence of monocular and binocular neurons arrayed within a functional processing module, with monocular neurons playing a crucial role in signaling the stimulus conditions instigating rivalry and generating inhibitory signals to implement suppression. Suppression is conceived as a local process happening in parallel over the entire cortical representation of the binocular visual field. The strength of inhibition causing suppression is related to the size of the pool of monocular neurons innervated by the suppressed eye, and the duration of a suppression phase is attributed to the strength of excitation generated by the suppressed stimulus. The theory is compared with three other contemporary theories of binocular rivalry. The article closes with a discussion of some of the unresolved problems related to the theory.     

A statistical model for binocular rivalry

A probabilistic model is presented for the phase durations in binocular rivalry experiments. The hypothetical construct of inhibition or reaction inhibition is used to account for the length of the successive phases of left‐eye dominance and right‐eye dominance. In accordance with Hull's Postulate X.B. it is assumed that the inhibition increases linearly at rate a₁ during periods of left‐eye dominance and decreases linearly at rate a₀ during periods of right‐eye dominance. Two different versions of the proposed model are presented: the beta and the Bessel inhibition models. Inhibition fluctuates between the boundaries 0 and 1 in the beta inhibition model and between ?∞ and +∞ in the Bessel inhibition model. The transition rates λ₁(t) for switches from a state of left‐eye dominance to a state of right‐eye dominance, and λ₀(t) for switches from a state of right‐eye dominance to a state of left‐eye dominance depend on inhibition: , , where l₁ is a non‐decreasing function and l₀ is a non‐increasing function. In the beta inhibition model and . In the Bessel inhibition model and . Special attention is given to the derivation of the expectation of the stationary phase durations.     

Spatial interactions in binocular rivalry.

Observers tracked binocular rivalry between a pair of small, foveally viewed gratings whose orientation differed between the 2 eyes. In Experiment 1, a textured annulus surrounding 1 eye's grating increased the total duration of exclusive visibility of the grating only when the grating-annulus separation was less than 0.5 degree. In Experiment 2, observers tracked the visibility of a monocular annulus that surrounded a foveally viewed grating that was either engaged in rivalry or fused with a grating alone viewed by the other eye. The visibility of the annulus was greater when the grating it surrounded was not undergoing rivalry fluctuations. In Experiment 3, the predominance of a rival grating was greater when the contours in the surrounding annulus were orthogonal to those of the rival grating. In Experiment 4, total exclusive visibility of a given grating-annulus target was greater when the grating and the annulus contained the same orientation.     

Microsaccadic eye movements and binocular rivalry

Eye movements were monitored with a sensitive binocular measuring device during presentation of stimuli that caused binocular rivalry. It was found that the number of microsaccades was approximately 50% higher when measured during rivalry than when measured during periods of normal viewing. The level of microsaccadic activity is greater at the beginning than toward the end of the suppression interval. The results suggest that the depth of suppression associated with binocular rivalry is not constant over the duration of a rivalry interval.     

Conditions required for binocular rivalry suppression

When the two eyes are presented with incompatible stimuli, the two monocular stimuli are seen alternately in a never-ending cycle. It is now widely accepted that the neural processes underlying this phenomenon, binocular rivalry, are distributed across a number of cortical stages. It is not clear, however, where binocular rivalry is initiated. We performed two experiments whose aim was to clarify this issue. In the first experiment, rivalry was induced, and brief test stimuli were delivered to an eye while its inducing stimulus was either dominant or suppressed. Sensitivity to a test stimulus with features similar to those of the suppressed inducing stimulus was reduced only when the test was presented to the eye whose inducing stimulus was suppressed. This indicates that suppression of a monocular channel is a prerequisite for binocular rivalry suppression. The second experiment showed that to induce rivalry, local interocular stimulus incompatibilities were necessary and that conflicting global percepts were not sufficient. These results suggest that low-level visual processes are required for the initiation of binocular rivalry.     

The site of binocular rivalry suppression.

Two experiments were performed to localize the site of binocular rivalry suppression in relation to the locus of grating adaptation. In one experiment it was found that phenomenal suppression of a high-contrast adaptation grating presented to one eye had no influence on the strength of the threshold-elevation aftereffect measured interocularly. Evidently information about the adaptation grating arrives at the site of the aftereffect (presumably binocular neurons) even during suppression. In a second experiment 60 s of grating adaptation was found to produce a short-term reduction in the predominance of the adapted eye during binocular rivalry. These findings provide converging lines of evidence that suppression occurs at a site in the human visual system after the locus of grating adaptation and, hence, after the striate cortex.     

Afterimages, binocular rivalry, and the temporal properties of dominance and suppression

When different contours are presented to the two eyes, an unstable percept, binocular rivalry, is the result. Parts of each set of contours may be seen but the two sets are not seen in the same place at the same time. The contours need not be physically present. Afterimages will produce binocular rivalry. Normal rivalry can be prevented if intermittent stimulation is used. Previous work has shown that orthogonal gratings, flashed for less than 150 ms and separated by more than 150 ms, will appear to fuse into a plaid or checkerboard pattern. In the present experiment this phenomenon is examined with afterimages used to produce rivalry. This abnormal 'fusion' is seen when negative afterimages are stroboscopically illuminated at less than 5 Hz. The results obtained with afterimages are predictable from the previous results obtained with stimuli external to the eye.     

An astable multivibrator model of binocular rivalry

The behavior of a neural network model for binocular rivalry is explored through the development of an analogy between it and an electronic astable multivibrator circuit. The model incorporates reciprocal feedback inhibition between signals from the left and the right eyes prior to binocular convergence. The strength of inhibitory coupling determines whether the system undergoes rivalrous oscillations or remains in stable fusion: strong coupling leads to oscillations, weak coupling to fusion. This implies that correlation between spatial patterns presented to the two eyes can affect the strength of binocular inhibition. Finally, computer simulations are presented which show that a reciprocal inhibition model can reproduce the stochastic behavior of rivalry. The model described is a counterexample to claims that reciprocal inhibition models as a class cannot exhibit many of the experimentally observed properties of rivalry.     

Increment detection thresholds during binocular rivalry suppression

In two experiments, two-choice forced-choice duration thresholds for increment test flashes were estimated during phases of rivalry suppression and nonsuppression and for a nonrivalry monocular control condition. In both experiments thresholds of both eyes of each S were measured and, to maximize correct detections, feedback was given after every trial and Ss were relieved of the task of continually reporting changes in rivalry phases. Results of both experiments support the conclusion that suppression constitutes an elevation in threshold, on the order of .5 log units relative to thresholds found during nonsuppression and monocular conditions. These data, in concert with others, reinforce the general conclusion that rivalry suppression is an inhibitory state that nonselectively attenuates all classes of inputs falling within the spatial boundaries of the suppressed target.     

How context influences predominance during binocular rivalry

Variations in the predominance of an object engaged in binocular rivalry may arise from variations in the durations of dominance phases, suppression phases, or both. Earlier work has shown that the predominance of a binocular rival target is enhanced if that target fits well-via common color, orientation, or motion-with its surrounding objects. In the present experiments, the global context outside of the region of rivalry was changed during rivalry, to learn whether contextual information alters the ability to detect changes in a suppressed target itself. Results indicate that context will maintain the dominance of a rival target, but will not encourage a suppressed target to escape from suppression. Evidently, the fate of the suppressed stimulus is determined by neural events distinct from those responsible for global organization during dominance. To reconcile diverse findings concerning rivalry, it may be important to distinguish between processes responsible for selection of one eye's input for dominance from processes responsible for the implementation and maintenance of suppression.