Amplitude of visual suppression during the control of binocular rivalry

To investigate the precise mechanism of control of binocular rivalry, Ss were instructed to attend actively to whichever pattern was momentarily in the nonsuppression phase. Test stimuli were presented tachistoscopically for recognition in either phase of rivalry. Because the differential recognition between nonsuppressed and suppressed phases was no greater for an active condition than for a passive viewing condition, it was concluded that control is not mediated by varying the amplitude of the suppression effect. This result was consistent with control that is exercised by selecting the eye to receive a constant amplitude suppression. In addition, it was found that visual sensitivity of rivalry nonsuppression and nonrivalry were the same for the ocular dominant eye but different for the nondominant eye.     

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.     

Analysis of temporal suppression mechanism in binocular rivalry

A method for analyzing the temporal suppression mechanism in binocular rivalry is described. A test pattern was presented to one eye and a suppressing pattern to the other eye after varying time intervals. The subject was instructed to report the frequency of nonsuppression phases of the test pattern immediately after presentation of the suppressing pattern. Analysis indicated that the test pattern was never suppressed at the 0-msec. stimulus onset asynchrony and the nonsuppression probabilities decreased as the onset asynchrony increased. Moreover, resistivity to contralateral suppression was greater when the test pattern was projected to the dominant eye.     

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.     

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.     

On the inhibitory nature of binocular rivalry suppression

During binocular rivalry the average duration of a suppression phase depends on the stimulus strength (e.g., contrast) of the input to the suppressed eye. To determine if a similar relationship exists between stimulus strength and the inhibitory effect of suppression on test probe detectability, a series of experiments was performed. Using two-alternative forced-choice procedures, increment detection thresholds were measured during phases of dominance and suppression. Results from three trained observers show that detection performance is significantly impaired during suppression by an amount that is independent of any difference in contrast between the rivalrous stimuli. These data indicate that the magnitude of the inhibitory effect of suppression is governed by a mechanism other than that which determines suppression duration.     

Binocular rivalry and dichoptic masking: suppressed stimuli do not mask stimuli in a dominating eye

Reaction time was used to gauge the sensitivity of an eye during its dominant and suppressed phases of binocular rivalry. During dominance, performance was uniformly good in detecting both stimuli that were spatially identical to the suppressed stimulus and those that were different in spatial frequency. When suppressed eyes were tested, performance was poor when the stimulus was different from the dominating stimulus, but even worse when the test stimulus and the dominating stimulus were spatially identical. The results favor the view that suppression operates nonselectively on a monocular visual channel, prior to the point at which dichoptic pattern masking occurs.     

Binocular rivalry and reciprocal inhibition

Any explanation of binocular rivalry based on a reciprocal inhibition mechanism would require that unilateral increases in the stimulus strength of the rivalry target in one eye produce increases in the mean nonsuppression duration of that eye and concommitant decreases in the mean nonsuppression duration of the contralateral eye. To test that hypothesis, the stimulus strength (in this case, contrast) of one rivalry target was varied (0.1, 1, 10, and 100 ft-L) while the strength of the target in the other eye remained constant. The data, obtained from six experienced Ss, indicate that variations in stimulus strength do not alter the mean nonsuppression duration of the recipient eye. This outcome offers a fundamental difficulty for the reciprocal inhibition concept. A model that assumes partially independent suppression and dominance mechanisms is suggested as a more adequate alternative.     

Possible monocular predictors of binocular rivalry of contours

An analysis of contour disappearances in conflicting patterned stereograms is made from the knowledge of two monocular events: contrast effects associated with contours and phasic local adaptation. It is argued that the percepts resulting from these monocular processes are combined simply by some more central process and that a suppression mechanism may not be necessary to account for contour rivalry. Predictions were tested in three experiments and the results tend to support the argument given.     

Dichoptic reading: The role of meaning in binocular rivalry

These experiments sought to determine whether meaning influences the predominance of one eye during binocular rivalry. In Experiment 1, observers tried to read meaningful text under conditions in which different text streams were viewed by the two eyes, a situation mimicking the classic dichotic listening paradigm. Dichoptic reading proved impossible even when the text streams were printed in different fonts or when one eye received a 5-sec advantage. Under non-rivalry conditions, the observers were able to read text presented at twice the rate used for dichoptic testing, indicating that cognitive overload does not limit performance under conditions of rivalry. In Experiment 2, observers were required to detect repeated presentations of a probe target within a string of characters presented to one eye. Although this task was easily performed under monocular viewing conditions, it proved difficult when the two eyes received dissimilar character strings. This was true regardless of whether the probed eye viewed nonsense strings, real words, or meaningful text. In a condition designed to encourage semantic processing of one eye’s view, the observers were required to detect animal names as well as to detect the probe target. Performance remained inferior to that measured under monocular conditions. Even the observer’s own name proved insufficient to influence the predominance of one eye under conditions of dichoptic stimulation. When two text strings were physically superimposed and viewed monocularly, essentially no probes were detected, indicating that the failure to see some probes during rivalry reflects a limitation unique to dichoptic viewing. These results contradict theories attributing binocular rivalry to an attentional process that operates on monocular inputs that have received refined analysis. This conclusion may be limited to rival stimuli whose meaning is defined linguistically, not structurally.     

Briefly presented stimuli can disrupt constant suppression and binocular rivalry suppression

An earlier study has shown that the intermittent suppression of one monocular stimulus by another in binocular rivalry does not occur when normally rivalrous stimuli are briefly presented. Constant suppression of stimuli presented to one eye is a common consequence of esotropia during development. A study is reported which demonstrates that constant suppression does not occur when stimuli are briefly presented. The dependence of suppression on stimulus duration is similar in both forms of 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.     

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.     

Binocular rivalry and semantic processing: out of sight, out of mind

Previous studies of binocular rivalry have shown that some aspects of a phenomenally suppressed stimulus remain available for visual analysis. The question remains, however, whether this analysis extends to the case of semantic information. This experiment examines that question using a semantic-priming paradigm in which prime words were briefly flashed to an eye during either dominance or suppression phases of binocular rivalry. Reaction times on a lexical-decision task were significantly shortened (the semantic-priming effect) only when prime words were presented to an eye during dominance; suppression acted to impair word recognition and to eliminate semantic priming. These results are inconsistent with certain cognitive models of binocular rivalry.     

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.     

Monocular and binocular rivalry between contours.

The temporal characteristics of binocular and monocular rivalry between orthogonal gratings of the same or complementary colours were investigated. Rivalry was measured in terms of the dominance of either grating or the visibility of composites comprised of parts of both gratings. The total duration for which either grating was dominant was significantly longer in binocular rivalry between gratings of complementary colours. A comparison of binocular and monocular rivalry indicated considerable phenomenal differences between them. Dominance in binocular rivalry corresponds to the visibility of one grating alone; this occurs rarely in monocular rivalry, which is characterized by fluctuations in the distinctiveness of the gratings. The changes in distinctiveness are influenced by colour in a similar manner to that in binocular rivalry, and the frequencies of fluctuations are higher for gratings of complementary colours.     

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.     

Interocular conflict attracts attention

During binocular rivalry, perception alternates.between dissimilar images presented dichoptically. Since.its discovery, researchers have debated whether the phenomenon is subject to attentional control. While it is now clear that attentional control over binocular rivalry is possible, the opposite is less evident: Is interocular conflict (i.e., the situation leading to binocular rivalry) able to attract attention?In order to answer this question, we used a change blindness paradigm in which observers looked for salient changes in two alternating frames depicting natural scenes. Each frame contained two images: one for the left and one for the right eye. Changes occurring in a single image (monocular) were detected faster than those occurring in both images (binocular). In addition,monocular change detection was also faster than detection in fused versions of the changed and unchanged regions. These results show that interocular conflict is capable of attracting attention, since it guides visual attention toward salient changes that otherwise would remain unnoticed for longer. The results of a second experiment indicated that interocular conflict attracts attention during the first phase of presentation, a phase during which the stimulus is abnormally fused [added].     

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.     

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.