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.     

The effect of contrast on the completeness of binocular rivalry suppression

Binocular rivalry between orthogonal sine wave gratings was studied by asking subjects to indicate when they saw just one or the other grating, as opposed to a composite. Using this measure, it was found that the completeness of rivalry (1) usually increased with grating contrast; (2) increased as a trial progressed, up to about 40 sec; and (3) depended on spatial frequency, with the optimal spatial frequency being lower than that at which contrast sensitivity was maximal. These findings supplement what has been learned about rivalry by other methods.     

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.     

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.     

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.     

The effect of orientation in binocular contour rivalry of real images and afterimages

Binocular rivalry was investigated using gratings of different orientations in three experiments. No consistent effects of orientation were found for predominance measures of rivalry between real images. Rivalrous afterimages, on the other hand, did exhibit orientation selectivity: vertical gratings were visible for longer than were 45-deg gratings. This effect was compared to the similar orientation selectivity found for monocular observation of grating afterimages. Comparisons of binocular rivalry between real images and afterimages were made in terms of the frequency distributions of the dominance periods.     

The role of accommodation in the control of binocular rivalry

The role of accommodation in the control of binocular rivalry (BR) has been granted various degrees of importance by Es in the past. The most recent investigation by Fry (1936) concluded that accommodation provides the basis of BR control through the blurring of retinal images. However, the present study found that the introduction of very small artificial pupils (0.5 mm) did not reduce BR control. It was concluded that if accommodation changes are occurring with large pupils, the resulting image blurring plays no part in control of rivalry. Experiment 2 tested the effect of paralyzed intrinsic eye muscles and found almost the same degree of control as in the normal state. The slight decrease of control that was present was attributed to a general performance decrement, since slight performance decrements with eye paralysis were also found in a visual reaction-time task and hand dynamometer test. In Experiment 3, it was found that the increased control that was obtained over several practice sessions was mostly retained during subsequent eye paralysis. These findings and, in addition, a very significant control of rivaling afterimage stimuli under eye paralysis strongly suggest a central component of BR control rather than one based on accommodation.     

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.     

The depth and selectivity of suppression in binocular rivalry

Binocular rivalry occurs when the two eyes are presented with incompatible stimuli and the perceived image alternates between the two stimuli. The aim of this study was to find out whether the periodic perceptual loss of a monocular stimulus during binocular rivalry is mirrored by a comparable loss of contrast sensitivity. We presented brief test stimuli to one eye while its conditioning stimulus was dominant or suppressed. The test stimuli were varied widely across four stimulus domains--namely, the relative stimulation of medium- and long-wavelength-sensitive cones, duration, spatial frequency, and grating orientation. The result in each case was the same. Suppression depended slightly or not at all on the type of test stimulus, and contrast sensitivity during suppression was around 64% of that during dominance. The effect of suppression on sensitivity is therefore very weak, relative to its effect on the perceived image. Furthermore, suppression was largely independent of the similarity between the conditioning and the test stimuli, indicating that our results are better explained by eye suppression than by stimulus suppression. A model is presented to account for the small, monocular sensitivity loss during suppression: It assumes that test detection precedes conditioning stimulus perception in the visual pathway.     

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.     

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.     

The temporal course of suppression during binocular rivalry

Orthogonally oriented sinusoidal luminance gratings were dichoptically presented to the observers' left and right eyes. During the subsequent binocular rivalry, a small target was briefly presented (4AFC) to probe the strength of interocular suppression at various temporal latencies. Both stationary and moving rivalrous patterns were investigated. The purpose of experiment 1 was to compare the temporal characteristics of stationary and motion rivalry (0 and 1.2 deg s-1), while that of experiment 2 was to examine rivalry suppression for higher speeds (2 and 4 deg s-1). In all cases, it was found that the strength of suppression remained essentially constant throughout a single phase of binocular rivalry. The results of the investigation also revealed that moving rivalrous patterns lead to greater magnitudes of interocular suppression than static patterns. Despite these differences in the strength of suppression, the results of both experiments show that the temporal characteristics of motion and static rivalry are essentially identical.     

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.