Controlling binocular rivalry.

Binocular rivalry is the alternating perception that occurs when the two eyes are presented with incompatible stimuli. We have developed a new method for controlling binocular rivalry and measuring its progress. One eye views a static grating while the fellow eye views a grating that smoothly and cyclically varies between two orientations, one the same as the static grating and the other orthogonal. Contrast sensitivity was tested monocularly a number of times during the stimulus cycle. When the eye viewing the static grating was tested, sensitivity varied between maximum and minimum values as the conditioning stimulus varied from binocularly compatible to incompatible. The interocular suppression thus demonstrated was limited to the eye viewing the static grating; variations in the fellow eye's sensitivity were due to interocular masking alone.     

Adaptive center-surround interactions in human vision revealed during binocular rivalry

We used binocular rivalry as a psychophysical probe to explore center-surround interactions in orientation, motion and color processing. Addition of the surround matching one of the rival targets dramatically altered rivalry dynamics. For all visual sub-modalities tested, predominance of the high-contrast rival target matched to the surround was greatly reduced-a result that disappeared at low contrast. At low contrast, addition of the surround boosted dominance of orientation and motion targets matched to the surround. This contrast-dependent modulation of center-surround interactions seems to be a general property of the visual system and may reflect an adaptive balance between surround suppression and spatial summation.     

Functional asymmetries of the human visual system as revealed by binocular rivalry and binocular brightness matching.

Two techniques, a binocular rivalry task and a binocular brightness matching task, were designed to yield indices of asymmetry (relative dominance weights) for the two eyes, the crossed and uncrossed visual pathways, and the two cerebral hemispheres. Twenty subjects with normal vision were run on all conditions. Intercorrelations of the dominance weights obtained by the two methods showed no relationship between the two methods, but produced three hypotheses about visual functioning: (1) the left hemisphere appears more dominant for rivalry; (2) the right hemisphere appears more dominant for brightness matching; (3) the uncrossed visual pathways are dominant over the crossed pathways in the binocular rivalry task.     

Compound binocular rivalry

Binocular rivalry was examined with random dot patterns consisting of three colours: red, green and grey. The microstructure of the patterns was defined by the individual dots, and the correspondence between the microstructures in the two eyes was manipulated. The macrostructures were defined by the distributions of red, green and grey dots over the displays, so that they consisted of orthogonally striped patterns. The degree of correspondence between the microstructures was varied in Expt 1, together with the spatial frequency of the microstructure. Rivalry periods of the macrostructures were briefer when the microstructures were in correspondence, In Expt 2 the spatial frequencies of the macrostructures were varied. The lower spatial frequency predominated for longer than the higher. The results are discussed in terms of independent pathways for corresponding and rivalry stimulation. In addition a stimulus pairing that produces clear dichoptic colour mixtures is presented.     

Dynamics of perceptual filling-in of visual phantoms revealed by binocular rivalry

How do selective and constructive visual mechanisms interact to determine the outcome of conscious perception? Binocular rivalry involves selective perception of one of two competing monocular images, whereas visual phantoms involve perceptual filling-in between two low-contrast collinear gratings. Recently, we showed that visual phantoms lead to neural filling-in of activity in V1 and V2, which can be dynamically gated by rivalry suppression (M. Meng, D. A. Remus, & F. Tong, 2005). Here, we used psychophysical methods to study the temporal dynamics of filling-in, by applying rivalry or flash suppression to trigger the suppression or appearance of visual phantoms. Experiments revealed that phantom filling-in involves an active, time-dependent process that depends on the phenomenal visibility of the phantom-inducing gratings. Shortly after the inducing gratings became dominant during rivalry, the likelihood of perceiving phantoms in the intervening gap increased over time, with larger gaps requiring more time for filling-in. In contrast, suppression of the inducing gratings promptly led to the disappearance of visual phantoms, with response times independent of gap size. The fact that binocular rivalry can prevent the formation of visual phantoms rules out the possibility that rivalry suppression occurs after the site of phantom filling-in. This study provides novel evidence that visual phantoms result from a slow time-dependent filling-in mechanism; possible models to account for its time course are discussed.     

Rival ideas about binocular rivalry.

Binocular rivalry has been used to investigate neural correlates of visual awareness. For this investigation to succeed, however, it is necessary to know what rivals during binocular rivalry. Recent work has raised questions about whether rivalry is between eyes or between stimuli. We find that stimulus rivalry occurs only within a limited range of spatial and temporal parameters--otherwise eye rivalry dominates.     

Stochastic resonance in binocular rivalry

When a different image is presented to each eye, visual awareness spontaneously alternates between the two images--a phenomenon called binocular rivalry. Because binocular rivalry is characterized by two marginally stable perceptual states and spontaneous, apparently stochastic, switching between them, it has been speculated that switches in perceptual awareness reflect a double-well-potential type computational architecture coupled with noise. To characterize this noise-mediated mechanism, we investigated whether stimulus input, neural adaptation, and inhibitory modulations (thought to underlie perceptual switches) interacted with noise in such a way that the system produced stochastic resonance. By subjecting binocular rivalry to weak periodic contrast modulations spanning a range of frequencies, we demonstrated quantitative evidence of stochastic resonance in binocular rivalry. Our behavioral results combined with computational simulations provided insights into the nature of the internal noise (its magnitude, locus, and calibration) that is relevant to perceptual switching, as well as provided novel dynamic constraints on computational models designed to capture the neural mechanisms underlying perceptual switching.     

Audiovisual interactions in binocular rivalry

When the two eyes are presented with dissimilar images, human observers report alternating percepts-a phenomenon coined binocular rivalry. These perceptual fluctuations reflect competition between the two visual inputs both at monocular and binocular processing stages. Here we investigated the influence of auditory stimulation on the temporal dynamics of binocular rivalry. In three psychophysics experiments, we investigated whether sounds that provide directionally congruent, incongruent, or non-motion information modulate the dominance periods of rivaling visual motion percepts. Visual stimuli were dichoptically presented random-dot kinematograms (RDKs) at different levels of motion coherence. The results show that directional motion sounds rather than auditory input per se influenced the temporal dynamics of binocular rivalry. In all experiments, motion sounds prolonged the dominance periods of the directionally congruent visual motion percept. In contrast, motion sounds abbreviated the suppression periods of the directionally congruent visual motion percepts only when they competed with directionally incongruent percepts. Therefore, analogous to visual contextual effects, auditory motion interacted primarily with consciously perceived visual input rather than visual input suppressed from awareness. Our findings suggest that auditory modulation of perceptual dominance times might be established in a top-down fashion by means of feedback mechanisms.     

Laughter abolishes binocular rivalry

Background : Binocular rivalry is an increasingly popular technique for the study of consciousness, which changes quasi‐regularly during rivalry, despite the unchanging sensory stimuli presented to each eye. For example, if a small patch of horizontal stripes is presented constantly to the fovea of one eye and a small patch of vertical stripes is similarly presented constantly to the fovea of the other eye, most subjects experience an alternation between stimuli rather than a simultaneous mixed percept of both. Methods : Binocular rivalry was induced, superimposed on normal viewing, using liquid crystal shutters and a short persistence monitor, which produced a one degree circular patch of horizontal gratings to the right eye and an identical patch of vertical gratings in the same location for the left eye. The subject signalled with key presses the three possible perceptual states that alternated with each other, namely horizontal, vertical and mixed percept (where horizontal and vertical were simultaneously visible). Results : The present study builds on an incidental observation that laughter stopped the rivalry alternations between horizontal and vertical and induced the mixed percept instead. A physical explanation for this effect was ruled out by using stabilised imagery in the form of retinal after‐images of the rivalling gratings. Under conditions of retinal stabilisation, laughter also produced the mixed percept. Conclusions : The results are discussed in the light of recent work that indicates the inadequacy of low‐level explanation of rivalry, with laughter being another complex multi‐level contribution to the neural basis of rivalry, along with other aspects of mood. The results are discussed in relation to the interesting literature on the neurology and postulated functions of laughter.     

Local binocular fusion is involved in global binocular rivalry

We examined whether interocular inhibition in binocular rivalry could occur at the interocular intersection of horizontal and vertical rectangular patches which are locally fusible but globally rivalrous between the two eyes. We measured contrast increment (and decrement) thresholds of a monocularly presented probe which was presented on the horizontal patch corresponding to the intersection. We found that the threshold was higher when the horizontal patch was perceptually suppressed than when it was dominant. In addition, threshold elevation did not occur when both patches were dominant, or when the horizontal patch was viewed in isolation. These results indicate that interocular inhibition occurs at the potentially fusible region, and the determination of binocular fusion or binocular rivalry does not depend on physical stimulus but rather perceptual state at the time.     

Grouping and segmentation in binocular rivalry

Dichoptic presentation of dot arrays produces binocular rivalry if the arrays are of opposite contrast relative to background. Rivalry can occur even if individual dots in one eye's array do not overlap with the dots in the contralateral eye's array. The amount of unitary perception of only one array is a measure of the probability that the stimuli rival as textured surfaces rather than as portions of arrays or as individual dot elements. In accordance with Gestalt grouping principles, arrays of uniform brightness or color produced more unitary perception than mixed arrays. However, experiments with parametric variation of dot motion coherence suggested that segmentation mechanisms based on detection of collinearity can also influence perceptual selection and suppression in binocular rivalry.     

Minimal physiological conditions for binocular rivalry and rivalry memory

Binocular rivalry entails a perceptual alternation between incompatible stimuli presented to the two eyes. A minimal explanation for binocular rivalry involves strong competitive inhibition between neurons responding to different monocular stimuli to preclude simultaneous activity in the two groups. In addition, strong self-adaptation of dominant neurons is necessary to enable suppressed neurons to become dominant in turn. Here a minimal nonlinear neural model is developed incorporating inhibition, self-adaptation, and recurrent excitation. The model permits derivation of an equation for mean dominance duration as a function of the underlying physiological variables. The dominance duration equation incorporates an explicit representation of Levelt's second law. The same equation also shows that introduction of a simple compressive response nonlinearity can explain Levelt's fourth law. Finally, addition of brief, recurrent synaptic facilitation to the model generates properties of rivalry memory.     

Integration of motion information during binocular rivalry.

When two moving gratings are superimposed in normal viewing they often combine to form a pattern that moves with a single direction of motion. Here, we investigated whether the same mechanism underlies pattern motion when drifting gratings are presented independently to the two eyes. We report that, with relatively large circular grating patches (4 deg), there are periods of monocular dominance in which one eye's orientation alone is perceived, usually moving orthogonal to the contours (component motion). But, during the transitions from one monocular view to the other, a fluid mosaic is perceived, consisting of contiguous patches, each containing contours of only one of the gratings. This entire mosaic often appears to move in a single direction (pattern motion), just as when two gratings are literally superimposed. Although this implies that motion signals from the perceptually suppressed grating continue to influence the perception of motion, an alternative possibility is that it reflects a strategy that involves integrating directional information from the contiguous single-grating patches. To test between these possibilities, we performed a second experiment with very small grating stimuli that were about the same size as the contiguous single-grating patches in the mosaic (1-deg diameter). Despite the fact that the form of only one grating was perceived, we report that pattern motion was still perceived on about one third of trials. Moreover, a decrease in the occurrence of pattern motion was apparent when the contrast and spatial frequency of the gratings were made more different from each other. This phenomenon clearly demonstrates an independent binocular interaction for form and motion.     

Hysteresis effects in stereopsis and binocular rivalry

Neural hysteresis plays a fundamental role in stereopsis and reveals the existence of positive feedback at the cortical level [Wilson, H. R., & Cowan, J. D. (1973). A mathematical theory of the functional dynamics of cortical and thalamic nervous tissue. Kybernetik 13(2), 55-80]. We measured hysteresis as a function of orientation disparity in tilted gratings in which a transition is perceived between stereopsis and binocular rivalry. The patterns consisted of sinusoidal gratings with orientation disparities (0 degrees, 1 degrees, 2 degrees,..., 40 degrees) resulting in various degrees of tilt. A movie of these 41 pattern pairs was shown at a rate of 0.5, 1 or 2 pattern pairs per second, in forward or reverse order. Two transition points were measured: the point at which the single tilted grating appeared to split into two rivalrous gratings (T1), and the point at which two rivalrous gratings appeared to merge into a single tilted grating (T2). The transitions occurred at different orientation disparities (T1=25.4 degrees, T2=17.0 degrees) which was consistent with hysteresis and far exceeded the difference which could be attributed to reaction time. The results are consistent with a cortical model which includes positive feedback and recurrent inhibition between neural units representing different eyes and orientations.     

Effects of dominant and nondominant eyes in binocular rivalry.

PURPOSE: To investigate the relation between sighting and sensory eye dominance and attempt to quantitatively examine eye dominance using a balance technique based on binocular rivalry. METHODS: The durations of exclusive visibility of the dominant and nondominant eye target in binocular rivalry were measured in 14 subjects. The dominant eye was determined by using the hole-in-card test (sighting dominance). In study 1, contrast of the target in one eye was fixed at 100% and contrast of the target in the other eye was varied from 100% to 80% to 60% to 40% to 20%, when using rectangular gratings of 1, 2, and 4 cycles per degree (cpd) at 2 degrees, 4 degrees , and 8 degrees in size. In study 2, contrast of the target in the nondominant eye was fixed at 100% and contrast of the target in the dominant eye was varied from 100% to 80% to 60% to 40% to 20%, when using a rectangular grating of 2 cpd at 4 degrees in size. RESULTS: In study 1, the total duration of exclusive visibilities of the dominant eye target; that is, the target seen by the eye that had sighting dominance was longer compared with that of the nondominant eye target. When using rectangular gratings of 4 cpd, mean total duration of exclusive visibility of the dominant eye target was statistically longer than that of the nondominant eye target (p < 0.05). In study 2, reversals (in which duration of exclusive visibility of the nondominant eye becomes longer than the dominant eye when the contrast of the dominant eye target is decreased) were observed for all contrasts except for 100%. CONCLUSIONS: The dominant sighting eye identified by the hole-in-card test coincided with the dominant eye as determined by binocular rivalry. The contrast at which reversal occurs indicates the balance point of dominance and seems to be a useful quantitative indicator of eye dominance to clinical applications.     

A physiological model of binocular rivalry

This paper presents a modified reciprocal inhibition model for the temporal dynamics of binocular rivalry. The model is based on neurophysiological mechanisms and is derived from human psychophysical data. A simple reciprocal inhibition oscillator may be described with a set of four coupled differential equations with a neurophysiological interpretation. However, such a circuit does not account for some aspects of the temporal behavior of binocular rivalry, including the effects of contrast change on alternation rate and on the magnitudes of changes in duration of the suppressed and dominant phases. To better account for these phenomena, the equations and their stimulation are modified to include three new components: (1) presynaptic inhibition of the reciprocal inhibition by the input, (2) the motor delays that occur when a human observer tracks rivalry and (3) a minimum threshold for each neuron's state variable. The result is a much improved fit to psychophysically-obtained data on the temporal behavior of binocular rivalry. Finally, the model is incorporated into a larger model to suggest how rivalry might occur in a network that usually exhibits binocular fusion.     

Center-surround inhibition deepens binocular rivalry suppression

When dissimilar stimuli are presented to each eye, perception alternates between both images--a phenomenon known as binocular rivalry. It has been shown that stimuli presented in proximity of rival targets modulate the time each target is perceptually dominant. For example, presenting motion to the region surrounding the rival targets decreases the predominance of the same-direction target. Here, using a stationary concentric grating rivaling with a drifting grating, we show that a drifting surround grating also increases the depth of binocular rivalry suppression, as measured by sensitivity to a speed discrimination probe on the rival grating. This was especially so when the surround moved in the same direction as the grating, and was slightly weaker for opposed directions. Suppression in both cases was deeper than a no-surround control condition. We hypothesize that surround suppression often observed in area MT (V5)-a visual area implicated in visual motion perception-is responsible for this increase in suppression. In support of this hypothesis, monocular and binocular surrounds were both effective in increasing suppression depth, as were surrounds contralateral to the probed eye. Static and orthogonal motion surrounds failed to add to the depth of rivalry suppression. These results implicate a higher-level, fully binocular area whose surround inhibition provides an additional source of suppression which sums with rivalry suppression to effectively deepen suppression of an unseen rival target.     

Subjective contours and binocular rivalry suppression

Binocular rivalry probably involves distributed neural processes, some responsible for dominance, others for suppression and still others for fluctuations in perception. Focusing on the suppression process, the present study asks whether neural events underlying rivalry suppression take place prior to, or subsequent to those underlying the synthesis of subjective contours. Specifically, we examined whether (i) a subjective contour could prematurely return a suppressed target to dominance and (ii) whether suppression of a Kanizsa-type inducer precludes the formation of a subjective contour. Suppression durations were not abbreviated by the subjective contour, but suppression did prevent the formation of a subjective contour. Evidently suppression precedes the synthesis of subjective contours in the visual processing hierarchy.