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.     

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.     

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.     

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.     

Emotional pictures predominate in binocular rivalry

This study used binocular rivalry to examine whether emotionally relevant pictures are processed preferentially in the visual system. Binocular rivalry occurs when two incompatible pictures are presented to both eyes. If the pictures cannot be merged to a single unambiguous percept, binocular rivalry results in an alternation of the two percepts. However, it has been controversial whether emotional picture content can influence a picture's relative predominance. Twenty pairs of emotional and neutral pictures from the International Affective Picture System (IAPS) were presented to 45 healthy participants. As hypothesised, emotional pictures significantly predominated over neutral pictures, both with respect to the first percept and the total viewing time across each trial. We conclude that the relative predominance of emotional pictures in binocular rivalry provides further support for the preferential processing of emotional stimuli in the visual system.     

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.     

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.     

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.     

Stochastic properties of binocular rivalry alternations

The extent to which binocular rivalry phases are sequentially related was assessed by theν statistic and by autocorrelation. Both measures indicate that the duration of successive phases are independent. The frequency distributions of suppression phases and of nonsuppression phases can be fitted by gamma distributions. These results are consistent with models of the rivalry process that incorporate independence assumptions.     

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.     

The effect of practice on binocular rivalry control

The effects of passive viewing and the practice of the control instructions, “slow rate” and “rapid rate,” on a measure of binocular rivalry (BR) control was investigated. Four groups of 8 Ss each had different amounts of passive viewing of BR followed by different amounts of control instructions to complete a total of 50 min of testing spaced over lOdays. There were increases of passive rate as long as Ss practiced only the “passive rate“ instructions. This had an effect of increasing the rapid rate and slow rate of the first control practice day. However, “passive rate” practice had no significant effect on the measure of BR control. Successive practice days of “rapid rate” and “slowrate” instructions produced an increase in rapid rate and decrease in slow rate resulting in an increase in the measure of control.     

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.

     

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.     

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.