Rivalry Stimuli Research Articles

Measuring the reliability of binocular rivalry.

Binocular rivalry is a widely used tool in sensory and cognitive neuroscience to investigate different aspects of vision and cognition. The dynamics of binocular rivalry (e.g., duration of perceptual dominance phases and mixed percept proportions) differ across individuals; based on rivalry dynamics, it is also possible to calculate an index of ocular dominance (by comparing the perceptual dominance of the images in the two eyes). In this study, we investigated the reliability of binocular rivalry dynamics using different methods for dichoptic stimulation and different rivalry stimuli. For the three main indices we defined (ocular dominance, phase durations and mixed percept proportions), we found a high test-retest reliability across sessions. Moreover, the test-retest reliability of the ocular dominance index was predictable from its internal consistency, supporting its stability over time. Phase durations and mixed percept proportions, in contrast, had worse test-retest reliability than expected based on internal consistency, indicating that these parameters are susceptible to state-dependent changes. Our results support the use of the ocular dominance index and binocular rivalry in the measurement of sensory eye dominance and its plasticity, but advise caution when investigating the association between phase durations or mixed percepts and stable characteristics like psychological traits or disorders.

Atypical responses to faces during binocular rivalry in early glaucoma.

Glaucoma is a progressive optic neuropathy that damages retinal ganglion cells and a neurodegenerative disease as it affects neural structures throughout the brain. In this study, we examined binocular rivalry responses in patients with early glaucoma in order to probe the function of stimulus-specific cortical areas involved in face perception. Participants included 14 individuals (10 females, mean age 65 ± 7 years) with early pre-perimetric glaucoma and 14 age-matched healthy controls (7 females, mean age 59 ± 11 years). The 2 groups were equivalent in visual acuity and stereo-acuity. Three binocular rivalry stimulus pairs were used: (1) real face/house, (2) synthetic face/noise patch, and (3) synthetic face/spiral. For each stimulus pair, the images were matched in size and contrast level; they were viewed dichotically, and presented centrally and eccentrically at 3 degrees in the right (RH) and in the left hemifield (LH), respectively. The outcome measures were rivalry rate (i.e., perceptual switches/min) and time of exclusive dominance of each stimulus. For the face/house stimulus pair, rivalry rate of the glaucoma group (11 ± 6 switches/min) was significantly lower than that of the control group (15 ± 5 switches/min), but only in the LH location. The face dominated longer than the house in the LH for both groups. Likewise, for the synthetic face/noise patch stimulus pair, rivalry rate of the glaucoma group (11 ± 6 switches/min) was lower than that of the control group (16 ± 7 switches/min) in the LH, but the difference failed to reach significance. Interestingly, the mixed percept dominated less in glaucoma than in the control group. For the synthetic face/spiral stimulus pair, the glaucoma group had lower rivalry rate at all 3 stimulus locations. This study reveals atypical responses to faces during binocular rivalry in patients with early glaucoma. The results may be suggestive of early neurodegeneration affecting stimulus-specific neural structures involved in face processing starting in the pre-perimetric phase of the disease.

Priming and reversals of the perceived ambiguous orientation of a structure-from-motion shape and relation to personality traits.

We demonstrate contributions of top-down and bottom-up influences in perception as explored by priming and counts of perceived reversals and mixed percepts, as probed by an ambiguously slanted structure-from-motion (SFM) test-cylinder. We included three different disambiguated primes: a SFM cylinder, a still image of a cylinder, and an imagined cylinder. In Experiment 1 where the prime and test sequentially occupied the same location, we also administered questionnaires with the Big-5 trait openness and vividness of visual imagery to probe possible relations to top-down driven priming. Since influences of gaze or position in the prime conditions in Experiment 1 could not be ruled out completely, Experiment 2 was conducted where the test cylinder appeared at a randomly chosen position after the prime. In Experiment 2 we also measured the number of perceptual reversals and mixed percepts during prolonged viewing of our ambiguous SFM-cylinder, and administered questionnaires to measure all Big-5 traits, autism, spatial and object imagery, and rational or experiential cognitive styles, associated with bottom-up and top-down processes. The results revealed contributions of position-invariant and cue-invariant priming. In addition, residual contributions of low-level priming was found when the prime and test were both defined by SFM, and were presented at the same location, and the correlation between the SFM priming and the other two priming conditions were weaker than between the pictorial and imagery priming. As previously found with ambiguous binocular rivalry stimuli, we found positive correlations between mixed percepts and the Big-5 dimension openness to experience, and between reversals, mixed percepts and neuroticism. Surprisingly, no correlations between the scores from the vividness of imagery questionnaires and influence from any of the primes were obtained. An intriguing finding was the significant differences between the positive correlation from the experiential cognitive style scores, and the negative correlation between rational style and the cue invariant priming. Among other results, negative correlations between agreeableness and all priming conditions were obtained. These results not only support the notion of multiple processes involved in the perception of ambiguous SFM, but also link these processes in perception to specific personality traits.

Perceptual Grouping During Binocular Rivalry in Mild Glaucoma.

PurposeThis study tested perceptual grouping during binocular rivalry to probe the strength of neural connectivity of the visual cortex involved in early visual processing in patients with mild glaucoma.MethodsSeventeen patients with mild glaucoma with no significant visual field defects and 14 healthy controls participated. Rivalry stimuli were 1.8°-diameter discs, containing horizontal or vertical sine-wave gratings, viewed dichoptically. To test the grouping, two spatially separated identical stimuli were presented eccentrically to the same or different eyes and to the same or different hemifields. The outcome measures were the time of exclusive dominance of the grouped percept (i.e., percept with synchronized orientations), the rivalry rate, and the epochs of exclusive dominance.ResultsFor both groups, the grouping occurred primarily for the matching orientations in the same eye/same hemifield (MO SE/SH) and for the matching orientations in the same eye/different hemifield (MO SE/DH) conditions. Time dominance of the grouped percept of the glaucoma group was similar to that of the control group in all conditions. The rivalry rates in the MO SE/SH and MO SE/DH conditions were significantly larger in the control group than in the glaucoma group. The epochs of exclusive dominance of the grouped percept in the MO SE/SH condition were a median of 48-ms longer for the control group, but a median of 116-ms shorter for the glaucoma group when compared to those in the MO SE/DH condition.ConclusionPatients with mild glaucoma show clear impairments in binocular rivalry while evidence for deficits in perceptual grouping could be inferred only indirectly. If these deficits truly exist, they may have implications for higher levels of visual processing, such as object recognition and scene segmentation, but these predictions remain to be tested in future studies.

Interocular Grouping in Perceptual Rivalry Localized with fMRI

Bistable perception refers to a broad class of dynamically alternating visual illusions that result from ambiguous images. These illusions provide a powerful method to study the mechanisms that determine how visual input is integrated over space and time. Binocular rivalry occurs when subjects view different images in each eye, and a similar experience called stimulus rivalry occurs even when the left and right images are exchanged at a fast rate. Many previous studies have identified with fMRI a network of cortical regions that are recruited during binocular rivalry, relative to non-rivalrous control conditions (termed replay) that use physically changing stimuli to mimic rivalry. However, we show here for the first time that additional cortical areas are activated when subjects experience rivalry with interocular grouping. When interocular grouping occurs, activation levels broadly increase, with a slight shift towards right hemisphere lateralization. Moreover, direct comparison of binocular rivalry with and without grouping highlights strong focused activity in the intraparietal sulcus and lateral occipital areas, such as right-sided retinotopic visual areas LO1 and IP2, as well as activity in left-sided visual areas LO1, and IP0-IP2. The equivalent analyses for comparable stimulus (eye-swap) rivalry showed very similar results; the main difference is greater recruitment of the right superior parietal cortex for binocular rivalry, as previously reported. Thus, we found minimal interaction between the novel networks isolated here for interocular grouping, and those previously attributed to stimulus and binocular rivalry. We conclude that spatial integration (i.e,. image grouping/segmentation) is a key function of lateral occipital/intraparietal cortex that acts similarly on competing binocular stimulus representations, regardless of fast monocular changes.

Divergent Thinking Influences the Perception of Ambiguous Visual Illusions.

This study investigated the relationships between personality and creativity in the perception of two different ambiguous visual illusions. Previous research has suggested that Industriousness and Openness/Intellect (as measured by the Big Five Aspects Scale) are both associated with individual differences in perceptual switching rates for binocular rivalry stimuli. Here, we examined whether these relationships generalise to the Necker Cube and the Spinning Dancer illusions. In the experimental phase of this study, participants viewed these ambiguous figures under both static and dynamic, as well as free-view and fixation, conditions. As predicted, perceptual switching rates were higher: (a) for the static Necker Cube than the Spinning Dancer, and (b) in free-view compared with fixation conditions. In the second phase of the study, personality type and divergent thinking were measured using the Big Five Aspects Scale and the Alternate Uses Task, respectively. Higher creativity/divergent thinking (as measured by the Alternate Uses Task) was found to predict greater switching rates for the static Necker Cube (but not the Spinning Dancer) under both free-view and fixation conditions. These findings suggest that there are differences in the perceptual processing of creative individuals.

Does Cortical Inhibition Explain the Correlation Between Bistable Perception Paradigms?

When observers view a perceptually bistable stimulus, their perception changes stochastically. Various studies have shown across-observer correlations in the percept durations for different bistable stimuli including binocular rivalry stimuli and bistable moving plaids. Previous work on binocular rivalry posits that neural inhibition in the visual hierarchy is a factor involved in the perceptual fluctuations in that paradigm. Here, in order to investigate whether between-observer variability in cortical inhibition underlies correlated percept durations between binocular rivalry and bistable moving plaid perception, we used center-surround suppression as a behavioral measure of cortical inhibition. We recruited 217 participants in a test battery that included bistable perception paradigms as well as a center-surround suppression paradigm. While we were able to successfully replicate the correlations between binocular rivalry and bistable moving plaid perception, we did not find a correlation between center-surround suppression strength and percept durations for any form of bistable perception. Moreover, the results from a mediation analysis indicate that center-surround suppression is not the mediating factor in the correlation between binocular rivalry and bistable moving plaids. These results do not support the idea that cortical inhibition can explain the between-observer correlation in mean percept duration between binocular rivalry and bistable moving plaid perception.

Binocular rivalry from luminance and contrast

Binocular rivalry is the phenomenon that when two incompatible images are simultaneously presented, one to each eye, the two images compete with each other to be the dominant percept. Studying the underlying neural mechanisms of binocular rivalry is useful for understanding the mechanisms of interocular inhibition. Levelt’s Propositions, a set of four propositions that were originally published over fifty years ago, are not only useful for characterizing the perceptual dynamics of binocular rivalry, but can also provide a metric for assessing the common or differential neural mechanisms of binocular rivalry when diverse stimulus types are used. In the present study, we conducted a series of psychophysics experiments, where we compared the rivalry dynamics of two quite different types of stimuli. Orthogonal gratings, a classic type of rivalry stimulus, were contrasted with luminance patches, a type of rivalry stimulus that is relatively less studied. Our results showed that, similar to the orthogonal gratings, the alternate percepts in luminance-only rivalry were described by the modified Levelt’s Propositions, despite the clearly slower alternation rates for luminance patches. However, unlike the mixed percepts observed during transitions between oriented gratings, fusion percepts during luminance rivalry were common, could be lustrous, and obeyed the same Propositions, suggesting a regime of tri-stability. Overall, both types of rivalry are consistent with recent models that posit separate binocular and monocular channels embedded within neural circuits that also accomplish contrast normalization. Finally, luminance rivalry is discussed in the contexts of binocular summation and suppression, as well as Fechner’s paradox.

Symmetry of generalized rivalry network models determines patterns of interocular grouping in four-location binocular rivalry.

Previously, symmetry of network models has been proposed to account for interocular grouping during binocular rivalry. Here, we construct and analyze generalized rivalry network models with different types of symmetry (based on different kinds of excitatory coupling) to derive predictions of possible perceptual states in 12 experiments with four retinal locations. Percepts in binocular rivalry involving more than three locations have not been empirically investigated due to the difficulty in reporting simultaneous percepts at multiple locations. Here, we develop a novel reporting procedure in which the stimulus disappears when the subject is cued to report the simultaneously perceived colors in all four retinal locations. This procedure ensures that simultaneous rather than sequential percepts are reported. The procedure was applied in 12 experiments with six binocular rivalry stimulus configurations, all consisting of dichoptic displays of red and green squares at four locations. We call configurations with an even or odd number of red squares even or odd configurations, respectively. In experiments using even stimulus configurations, we found that even percepts were more frequently observed than odd percepts, whereas in experiments using odd stimulus configurations even and odd percepts were observed with equal probability. The generalized rivalry network models in which couplings depend on stimulus features and spatial configurations was in better agreement with the empirical results. We conclude that the excitatory coupling strength in the horizontal and vertical configurations are different and the coupling strengths between the same color and between different colors are different.NEW & NOTEWORTHY Wilson network models of interocular groupings during binocular rivalry are constructed by considering features that indicate equal coupling strengths. Network symmetries, based on equal couplings, predict percepts. For a four-location rivalry experiment with red or green squares at each location, we analyze different possible Wilson networks. In our experiments we develop a novel reporting procedure and show that networks in which stimulus features and spatial configurations are distinguished best agree with experiments.

On Sensory Eye Dominance Revealed by Binocular Integrative and Binocular Competitive Stimuli.

PurposeTwo core processes underlie 3-D binocular vision. The first, a binocular combination/summation process, integrates similar feature signals from the two eye channels to form a binocular representation. The second, a binocular inhibitory process, suppresses interocular conflicting signals or falsely matched binocular representations to establish single vision. Having an intrinsic interocular imbalance within one or both processes can cause sensory eye dominance (SED), related to imbalances of combination (SEDcombo) and/or inhibition (SEDinhibition). While much has recently been revealed about SEDcombo and SEDinhibition, the relationship between them is still unknown.MethodsWe measured observers' foveal SEDcombo and SEDinhibition, respectively, with a pair of dichoptic horizontal sine wave gratings with different phases and binocular rivalry stimulus with vertical and horizontal gratings. We then measured horizontal and vertical monocular contrast thresholds using sinusoidal grating stimuli, and stereo thresholds using random-dot stereograms.ResultsThere exists a strong correlation between SEDcombo and SEDinhibition. An observer's interocular difference in contrast threshold was not always consistent with his/her SEDcombo and SEDinhihition, suggesting a partial binocular origin for the underlying imbalances. We also found stereo thresholds significantly increased with the magnitudes of SEDcombo, as well as with the magnitude of SEDinhibition.ConclusionsOur findings suggest a common origin for interocular imbalance in the two different binocular processes and that both types of sensory eye dominance are significant factors in impeding stereopsis.

Genomic Analyses of Visual Cognition: Perceptual Rivalry and Top-Down Control.

Visual cognition in humans has traditionally been studied with cognitive behavioral methods and brain imaging, but much less with genetic methods. Perceptual rivalry, an important phenomenon in visual cognition, is the spontaneous perceptual alternation that occurs between two distinct interpretations of a physically constant visual stimulus (e.g., binocular rivalry stimuli) or a perceptually ambiguous stimulus (e.g., the Necker cube). The switching rate varies dramatically across individuals and can be voluntarily modulated by observers. Here, we adopted a genomic approach to systematically investigate the genetics underlying binocular rivalry, Necker cube rivalry and voluntary modulation of Necker cube rivalry in young Chinese adults (Homo sapiens, 81% female, 20 ± 1 years old) at multiple levels, including common single nucleotide polymorphism (SNP)-based heritability estimation, SNP-based genome-wide association study (GWAS), gene-based analysis, and pathway analysis. We performed a pilot GWAS in 2441 individuals and replicated it in an independent cohort of 943 individuals. Common SNP-based heritability was estimated to be 25% for spontaneous perceptual rivalry. SNPs rs184765639 and rs75595941 were associated with voluntary modulation, and imaging data suggested genotypic difference of rs184765639 in the surface area of the left caudal-middle frontal cortex. Additionally, converging evidence from multilevel analyses associated genes such as PRMT1 with perceptual switching rate, and MIR1178 with voluntary modulation strength. In summary, this study discovered specific genetic contributions to perceptual rivalry and its voluntary modulation in human beings. These findings may promote our understanding of psychiatric disorders, as perceptual rivalry is a potential psychiatric biomarker.SIGNIFICANCE STATEMENT Perceptual rivalry is an important visual phenomenon in which our perception of a physically constant visual input spontaneously switches between two different states. There are individual variations in perceptual switching rate and voluntary modulation strength. Our genomic analyses reveal several loci associated with these two kinds of variation. Because perceptual rivalry is thought to be relevant to and potentially an endophenotype for psychiatric disorders, these results may help understand not only visual cognition, but also psychiatric disorders.

Stimulus rivalry and binocular rivalry share a common neural substrate.

When two incompatible images are shown separately to each eye, a perceptual process known as binocular rivalry occurs by which the two images compete for awareness. The site of competition for binocular rivalry has been a topic of debate, and recent theories are that it may occur either at low levels of the visual system where the inputs from the two eyes are combined or at high levels of the visual system where the two images are processed. One of the major pieces of evidence for a high-level image account of rivalry is a phenomenon known as stimulus rivalry, in which two competing stimuli are swapped between the eyes at 3 Hz. However, there is little available neurophysiological evidence for a neural substrate for this high-level competition. Here, we used frequency tagging of two competing stimuli in binocular rivalry and stimulus rivalry in humans to evaluate whether the steady-state visually evoked potentials (SSVEPs) show similar signatures of neural competition for both conditions. We found that flickering the stimuli generates spectral power at the tagged frequencies in both types of rivalry in the early visual cortex. We then quantified dynamic signatures of competition by tracking amplitude changes in the frequency tags, which showed that both types of rivalry colocalized in occipital regions of the cortex. Thus, contrary to our hypothesis that stimulus rivalry was being mediated by high-level competition between the images, we find that neural competition measured by the SSVEP instead suggests that the sites of competition for stimulus rivalry and binocular rivalry may similarly include the occipital pole and middle temporal gyrus (hMT+/V5) of the visual system, consistent with a low-level, binocular interpretation.

Neural representations of orientation and motion direction in human visual cortex during binocular rivalry

Binocular rivalry occurs when sensory inputs from two eyes are incongruent. Our visual system resolves the ambiguity by preferring one of the stimuli at a particular moment, creating alternating percepts. It is yet unclear how neural representations of low-level visual features are modulated by perceptual alternations in human visual areas. In two experiments, we used fMRI-based encoding models to reconstruct channel responses to suppressed/dominant orientations and motion directions during binocular rivalry. For orientation rivalry, participants first underwent an fMRI session and viewed contrast-reversing sinusoidal gratings of six possible orientations with both eyes. BOLD response patterns were used to train an encoding model of six orientation-selective channels. In binocular orientation rivalry sessions, we presented two orthogonally oriented gratings to the two eyes, and each binocular rivalry run was followed by a replay run to simulate the perceptual effect in the immediately preceding run. Relative to the reconstructed channel responses from the replay runs, we found that, in V1, the channel response to the suppressed orientation was higher during binocular rivalry, while the channel response to the dominant orientation was weaker. These effects were also found in V2 and V3, albeit less pronounced. In V4, the channel response profiles in the rivalry and replay conditions became indistinguishable. For motion direction rivalry, we used RDKs moving in opposite directions with 100% motion coherence as rivalry stimuli. Compared with the reconstructed channel responses from the replay runs, we found elevated responses to the suppressed direction and lowered responses to the dominant direction in V1-V3, V3A, and MT+. Similar to the orientation rivalry experiment, no significant difference was found between the rivalry and replay conditions in V4. Taken together, our findings suggest that during the binocular rivalry of low-level visual features, the suppressed information is substantially represented in early and intermediate visual areas. Meeting abstract presented at VSS 2018

Autistic Traits Are Not a Strong Predictor of Binocular Rivalry Dynamics.

It has been suggested that differences in binocular rivalry switching rates and mixed percept durations in ASD could serve as a biomarker of excitation/inhibition imbalances in the autistic brain. If so, one would expect these differences to extend to neurotypical groups with high vs. low levels of autistic tendency. Previous studies did not detect any correlations between binocular rivalry dynamics and Autism Spectrum Quotient (AQ) scores in neurotypical control groups; however it is unclear whether this was due to the characteristics of the rivalry stimuli that were used. We further investigated this possibility in a sample of neurotypical young adults. The binocular rivalry stimuli were simple gratings, complex objects, or scrambled objects, which were presented dichoptically, either at fixation or in the periphery. A Bayesian correlation analysis showed that individuals with higher AQ scores tended to have lower perceptual switching rates for the centrally presented, simple grating rival stimuli. However, there was no evidence of a relationship between AQ and switching rates, reversal rates or mixed percept durations for any of the other binocular rivalry conditions. Overall, our findings suggest that in the non-clinical population, autistic personality traits are not a strong predictor of binocular rivalry dynamics.

The functional effects of prior motion imagery and motion perception

The functional sensory effects and commonalties between mental imagery of different visual features such as color, form or motion remains largely unknown. Mental imagery of static visual features, including color and orientation, can have a facilitative, priming effect on subsequent perception. However, whether motion imagery can have a similar effect remains unknown. Here we used the binocular rivalry method as a measure of motion mental imagery. After imagining or viewing motion of a particular direction, participants were required to report the dominant motion direction in a brief motion rivalry stimulus. We found that motion imagery can have a facilitative priming effect on subsequent motion rivalry perception, and this effect can be attenuated by concurrent expanding and contracting perceptual motion, but not by static or flickering uniform luminance. Unlike color or orientation imagery, the effect of motion imagery on subsequent rivalry was location independent. We also observed this facilitative priming effect with prior low-contrast perceptual motion, but prior high-contrast motion induced a suppressive effect. Simultaneous imagery and perceptual motion in opposite directions induced priming, while congruent directions did not. Counter to prior findings, these results suggest motion imagery can have a priming effect on perception and that the rivalry method can be used to assess visual motion imagery. These results provide evidence for visual imagery as a multi-feature structure.

Attention model of binocular rivalry.

When the corresponding retinal locations in the two eyes are presented with incompatible images, a stable percept gives way to perceptual alternations in which the two images compete for perceptual dominance. As perceptual experience evolves dynamically under constant external inputs, binocular rivalry has been used for studying intrinsic cortical computations and for understanding how the brain regulates competing inputs. Converging behavioral and EEG results have shown that binocular rivalry and attention are intertwined: binocular rivalry ceases when attention is diverted away from the rivalry stimuli. In addition, the competing image in one eye suppresses the target in the other eye through a pattern of gain changes similar to those induced by attention. These results require a revision of the current computational theories of binocular rivalry, in which the role of attention is ignored. Here, we provide a computational model of binocular rivalry. In the model, competition between two images in rivalry is driven by both attentional modulation and mutual inhibition, which have distinct selectivity (feature vs. eye of origin) and dynamics (relatively slow vs. relatively fast). The proposed model explains a wide range of phenomena reported in rivalry, including the three hallmarks: (i) binocular rivalry requires attention; (ii) various perceptual states emerge when the two images are swapped between the eyes multiple times per second; (iii) the dominance duration as a function of input strength follows Levelt's propositions. With a bifurcation analysis, we identified the parameter space in which the model's behavior was consistent with experimental results.

Chromatic interocular-switch rivalry.

Interocular-switch rivalry (also known as stimulus rivalry) is a kind of binocular rivalry in which two rivalrous images are swapped between the eyes several times a second. The result is stable periods of one image and then the other, with stable intervals that span many eye swaps (Logothetis, Leopold, & Sheinberg, 1996). Previous work used this close kin of binocular rivalry with rivalrous forms. Experiments here test whether chromatic interocular-switch rivalry, in which the swapped stimuli differ in only chromaticity, results in slow alternation between two colors. Swapping equiluminant rivalrous chromaticities at 3.75 Hz resulted in slow perceptual color alternation, with one or the other color often continuously visible for two seconds or longer (during which there were 15+ eye swaps). A well-known theory for sustained percepts from interocular-switch rivalry with form is inhibitory competition between binocular neurons driven by monocular neurons with matched orientation tuning in each eye; such binocular neurons would produce a stable response when a given orientation is swapped between the eyes. A similar model can account for the percepts here from chromatic interocular-switch rivalry and is underpinned by the neurophysiological finding that color-preferring binocular neurons are driven by monocular neurons from each eye with well-matched chromatic selectivity (Peirce, Solomon, Forte, & Lennie, 2008). In contrast to chromatic interocular-switch rivalry, luminance interocular-switch rivalry with swapped stimuli that differ in only luminance did not result in slowly alternating percepts of different brightnesses.

Visible and invisible stimulus parts integrate into global object representations as revealed by combining monocular and binocular rivalry.

Our visual system faces the challenging task to construct integrated visual representations from the visual input projected on our retinae. Previous research has provided mixed evidence as to whether visual awareness of the stimulus parts is required for such integration to occur. Here, we address this issue by taking a novel approach in which we combine a monocular rivalry stimulus (i.e., a bistable rotating cylinder) with binocular rivalry. The results of Experiment 1 show that in a rivalry condition, where one half of the cylinder is perceptually suppressed, significantly more perceptual switches occur that are consistent with visual integration of the whole cylinder than occur in a control condition, where only half of the cylinder is presented at a time and the presentation of the two images is physically alternated. In Experiment 2, stimulation in the observer's dominant eye was kept dominant by presenting the half cylinder in this eye at higher contrast and by surrounding it with a flickering context. Results show that the strong convexity bias that was found in a control condition, where no stimulus was presented in the suppressed eye, almost completely disappears when the unseen half is presented in the suppressed eye, indicating that both halves visually integrate and, subsequently, compete for convexity. These findings provide evidence that unseen visual information is biased towards a representation that is congruent with the current visible representation and, hence, that principles of perceptual organization also apply to parts of the visual input that remain unseen by the observer.

Intracranial Recordings of Occipital Cortex Responses to Illusory Visual Events.

Ambiguous visual stimuli elicit different perceptual interpretations over time, creating the illusion that a constant stimulus is changing. We investigate whether such spontaneous changes in visual perception involve occipital brain regions specialized for processing visual information, despite the absence of concomitant changes in stimulation. Spontaneous perceptual changes observed while viewing a binocular rivalry stimulus or an ambiguous structure-from-motion stimulus were compared with stimulus-induced perceptual changes that occurred in response to an actual stimulus change. Intracranial recordings from human occipital cortex revealed that spontaneous and stimulus-induced perceptual changes were both associated with an early transient increase in high-frequency power that was more spatially confined than a later transient decrease in low-frequency power. We suggest that the observed high-frequency and low-frequency modulations relate to initiation and maintenance of a percept, respectively. Our results are compatible with the idea that spontaneous changes in perception originate from competitive interactions within visual neural networks. Ambiguous visual stimuli elicit different perceptual interpretations over time, creating the illusion that a constant stimulus is changing. The literature on the neural correlates of conscious visual perception remains inconclusive regarding the extent to which such spontaneous changes in perception involve sensory brain regions. In an attempt to bridge the gap between existing animal and human studies, we recorded from intracranial electrodes placed on the human occipital lobe. We compared two different kinds of ambiguous stimuli, binocular rivalry and the phenomenon of ambiguous structure-from-motion, enabling generalization of our findings across different stimuli. Our results indicate that spontaneous and stimulus-induced changes in perception (i.e., "illusory" and "real" changes in the stimulus, respectively) may involve sensory regions to a similar extent.

Canonical Cortical Circuit Model Explains Rivalry, Intermittent Rivalry, and Rivalry Memory.

It has been shown that the same canonical cortical circuit model with mutual inhibition and a fatigue process can explain perceptual rivalry and other neurophysiological responses to a range of static stimuli. However, it has been proposed that this model cannot explain responses to dynamic inputs such as found in intermittent rivalry and rivalry memory, where maintenance of a percept when the stimulus is absent is required. This challenges the universality of the basic canonical cortical circuit. Here, we show that by including an overlooked realistic small nonspecific background neural activity, the same basic model can reproduce intermittent rivalry and rivalry memory without compromising static rivalry and other cortical phenomena. The background activity induces a mutual-inhibition mechanism for short-term memory, which is robust to noise and where fine-tuning of recurrent excitation or inclusion of sub-threshold currents or synaptic facilitation is unnecessary. We prove existence conditions for the mechanism and show that it can explain experimental results from the quartet apparent motion illusion, which is a prototypical intermittent rivalry stimulus.