Predictive Context Influences Perceptual Selection during Binocular Rivalry

Spatiotemporal brain hierarchies of auditory memory recognition and predictive coding

Our brain is constantly extracting, predicting, and recognising key spatiotemporal features of the physical world in order to survive. While neural processing of visuospatial patterns has been extensively studied, the hierarchical brain mechanisms underlying conscious recognition of auditory sequences and the associated prediction errors remain elusive. Using magnetoencephalography (MEG), we describe the brain functioning of 83 participants during recognition of previously memorised musical sequences and systematic variations. The results show feedforward connections originating from auditory cortices, and extending to the hippocampus, anterior cingulate gyrus, and medial cingulate gyrus. Simultaneously, we observe backward connections operating in the opposite direction. Throughout the sequences, the hippocampus and cingulate gyrus maintain the same hierarchical level, except for the final tone, where the cingulate gyrus assumes the top position within the hierarchy. The evoked responses of memorised sequences and variations engage the same hierarchical brain network but systematically differ in terms of temporal dynamics, strength, and polarity. Furthermore, induced-response analysis shows that alpha and beta power is stronger for the variations, while gamma power is enhanced for the memorised sequences. This study expands on the predictive coding theory by providing quantitative evidence of hierarchical brain mechanisms during conscious memory and predictive processing of auditory sequences.

Temporal integration by multi-level regularities fosters the emergence of dynamic conscious experience

The relationship between integration and awareness is central to contemporary theories and research on consciousness. Here, we investigated whether and how information integration over time, by incorporating the underlying regularities, contributes to our awareness of the dynamic world. Using binocular rivalry, we demonstrated that structured visual streams, constituted by shape, motion, or idiom sequences containing perceptual- or semantic-level regularities, predominated over their nonstructured but otherwise matched counterparts in the competition for visual awareness. Despite the apparent resemblance, a substantial dissociation of the observed rivalry advantages emerged between perceptual- and semantic-level regularities. These effects stem from nonconscious and conscious temporal integration processes, respectively, with the former but not the latter being vulnerable to perturbations in the spatiotemporal integration window. These findings corroborate the essential role of structure-guided information integration in visual awareness and highlight a multi-level mechanism where temporal integration by perceptually and semantically defined regularities fosters the emergence of continuous conscious experience.

Building a decoder of perceptual decisions from microsaccades and pupil size

Many studies have reported neural correlates of visual awareness across several brain regions, including the sensory, parietal, and frontal areas. In most of these studies, participants were instructed to explicitly report their perceptual experience through a button press or verbal report. It is conceivable, however, that explicit reporting itself may trigger specific neural responses that can confound the direct examination of the neural correlates of visual awareness. This suggests the need to assess visual awareness without explicit reporting. One way to achieve this is to develop a technique to predict the visual awareness of participants based on their peripheral responses. Here, we used eye movements and pupil sizes to decode trial-by-trial changes in the awareness of a stimulus whose visibility was deteriorated due to adaptation-induced blindness (AIB). In the experiment, participants judged whether they perceived a target stimulus and rated the confidence they had in their perceptual judgment, while their eye movements and pupil sizes were recorded. We found that not only perceptual decision but also perceptual confidence can be separately decoded from the eye movement and pupil size. We discuss the potential of this technique with regard to assessing visual awareness in future neuroimaging experiments.

Eye-specific attentional bias driven by selection history

Attention helps in selection among competing stimuli, but attentional selection also biases subsequent information processing as a prior experience. Previous studies have demonstrated that intertrial repetition of target features or locations facilitates perceptual processing as selection history guides attention. In the current study, we found that eye selection history in binocular rivalry induces eye-specific attentional bias. In four experiments, participants responded to the target presented at one of the locations on either eye. The results showed that the target was detected faster when presented to the same eye as in the previous trial under binocular rivalry. However, the effect of eye repetition was not observed when the interocular conflict was reduced by presenting stimuli to only one eye on each trial. Our result indicates that eye selection history can affect eye dominance during binocular rivalry as attention amplifies selected information among competing inputs. These findings suggest that prior experience of attentional deployment modulates subsequent information processing owing to the residual effect of attentional amplification.

Object expectations alter information use during visual recognition

Prior expectations influence how we perceive and recognize objects. However, how they do so remains unclear, especially in the case of real-world complex objects. Expectations of objects may affect which features are used to recognize them subsequently. In this study, we used reverse correlation to reveal with high precision how the use of information across time is modulated by real-world object expectations in a visual recognition task. We show that coarse information leads to accurate responses earlier when an object is expected, indicating that observers use diagnostic features earlier in this situation. We also demonstrate an increased variability in the use of coarse information depending on the expected object, indicating that observers adopt a more specialized recognition strategy when they expect a specific object. In summary, our results reveal potential mechanisms underlying the effect of expectations on the recognition of complex objects.

Mistaking imagination for reality: Congruent mental imagery leads to more liberal perceptual detection

Visual experiences can be triggered externally, by signals coming from the outside world during perception; or internally, by signals from memory during mental imagery. Imagery and perception activate similar neural codes in sensory areas, suggesting that they might sometimes be confused. In the current study, we investigated whether imagery influences perception by instructing participants to imagine gratings while externally detecting these same gratings at threshold. In a series of three experiments, we showed that imagery led to a more liberal criterion for reporting stimulus presence, and that this effect was both independent of expectation and stimulus-specific. Furthermore, participants with more vivid imagery were generally more likely to report the presence of external stimuli, independent of condition. The results can be explained as either a low-level sensory or a high-level decision-making effect. We discuss that the most likely explanation is that during imagery, internally generated sensory signals are sometimes confused for perception and suggest how the underlying mechanisms can be further characterized in future research. Our findings show that imagery and perception interact and emphasize that internally and externally generated signals are combined in complex ways to determine conscious perception.

Circular inference in bistable perception

When facing ambiguous images, the brain switches between mutually exclusive interpretations, a phenomenon known as bistable perception. Despite years of research, a consensus on whether bistability is driven primarily by bottom-up or top-down mechanisms has not been achieved. Here, we adopted a Bayesian approach to reconcile these two theories. Fifty-five healthy participants were exposed to an adaptation of the Necker cube paradigm, in which we manipulated sensory evidence and prior knowledge. Manipulations of both sensory evidence and priors significantly affected the way participants perceived the Necker cube. However, we observed an interaction between the effect of the cue and the effect of the instructions, a finding that is incompatible with Bayes-optimal integration. In contrast, the data were well predicted by a circular inference model. In this model, ambiguous sensory evidence is systematically biased in the direction of current expectations, ultimately resulting in a bistable percept.

Predictive activation of sensory representations as a source of evidence in perceptual decision-making

Our brains can represent expected future states of our sensory environment. Recent work has shown that, when we expect a specific stimulus to appear at a specific time, we can predictively generate neural representations of that stimulus even before it is physically presented. These observations raise two exciting questions: Are pre-activated sensory representations used for perceptual decision-making? And, do we transiently perceive an expected stimulus that does not actually appear? To address these questions, we propose that pre-activated neural representations provide sensory evidence that is used for perceptual decision-making. This can be understood within the framework of the Diffusion Decision Model as an early accumulation of decision evidence in favour of the expected percept. Our proposal makes novel predictions relating to expectation effects on neural markers of decision evidence accumulation, and also provides an explanation for why we sometimes perceive stimuli that are expected, but do not appear.

The predictive global neuronal workspace: A formal active inference model of visual consciousness

The global neuronal workspace (GNW) model has inspired over two decades of hypothesis-driven research on the neural basis of consciousness. However, recent studies have reported findings that are at odds with empirical predictions of the model. Further, the macro-anatomical focus of current GNW research has limited the specificity of predictions afforded by the model. In this paper we present a neurocomputational model - based on Active Inference - that captures central architectural elements of the GNW and is able to address these limitations. The resulting 'predictive global workspace' casts neuronal dynamics as approximating Bayesian inference, allowing precise, testable predictions at both the behavioural and neural levels of description. We report simulations demonstrating the model's ability to reproduce: 1) the electrophysiological and behavioural results observed in previous studies of inattentional blindness; and 2) the previously introduced four-way taxonomy predicted by the GNW, which describes the relationship between consciousness, attention, and sensory signal strength. We then illustrate how our model can reconcile/explain (apparently) conflicting findings, extend the GNW taxonomy to include the influence of prior expectations, and inspire novel paradigms to test associated behavioural and neural predictions.

Individual differences in the tendency to see the expected

Prior knowledge has been shown to facilitate the incorporation of visual stimuli into awareness. We adopted an individual differences approach to explore whether a tendency to 'see the expected' is general or method-specific. We administered a binocular rivalry task and manipulated selective attention, as well as induced expectations via predictive context, self-generated imagery, expectancy cues, and perceptual priming. Most prior manipulations led to a facilitated awareness of the biased percept in binocular rivalry, whereas strong signal primes led to a suppressed awareness, i.e., adaptation. Correlations and factor analysis revealed that the facilitatory effect of priors on visual awareness is closely related to attentional control. We also investigated whether expectation-based biases predict perceptual abilities. Adaptation to strong primes predicted improved naturalistic change detection and the facilitatory effect of weak primes predicted the experience of perceptual anomalies. Taken together, our results indicate that the facilitatory effect of priors may be underpinned by an attentional mechanism but the tendency to 'see the expected' is method-specific.

Predictive context biases binocular rivalry in children and adults with no positive relation to two measures of social cognition

Integration of prior experience and contextual information can help to resolve perceptually ambiguous situations and might support the ability to understand other peoples' thoughts and intentions, called Theory of Mind. We studied whether the readiness to incorporate contextual information for resolving binocular rivalry is positively associated with Theory-of-Mind-related social cognitive abilities. In children (12 to 13 years) and adults (18 to 25 years), a predictive temporal context reliably modulated the onset of binocular rivalry to a similar degree. In contrast, adult participants scored better on measures of Theory of Mind compared to children. We observed considerable interindividual differences regarding the influence of a predictive context on binocular rivalry, which were associated with differences in sensory eye dominance. The absence of a positive association between predictive effects on perception and Theory of Mind performance suggests that predictive effects on binocular rivalry and higher-level Theory-of-Mind-related abilities stem from different neurocognitive mechanisms. We conclude that the influence of predictive contextual information on basic visual processes is fully developed at an earlier age, whereas social cognitive skills continue to evolve from adolescence to adulthood.

Does task relevance shape the 'shift to global' in ambiguous motion perception?

Perception can differ even when the stimulus information is the same. Previous studies have demonstrated the importance of experience and relevance on visual perception. We examined the influence of perceptual relevance in an auxiliary task on subsequent perception of an ambiguous stimulus. Observers were presented with an ambiguous motion stimulus that could either be perceived as rotating dot pairs ("local") or pulsating geometrical figures ("global"). Prolonged perception of this stimulus is characterized by a "shift to global", but it remained unclear whether this process is due to relevance of the global percept or mere exposure to the stimulus. During a relevance learning phase over 5 successive days, participants were divided into conditions determining the relevant percept in an auxiliary task: local, global, or none (active exposure). In a pre- and posttest, individual points of subjective equality between local and global percepts were measured. Results indicate that there is indeed a shift to global. Interestingly, auxiliary task relevance does not seem to modify this process.

Associative Prediction of Visual Shape in the Hippocampus

Perception can be cast as a process of inference, in which bottom-up signals are combined with top-down predictions in sensory systems. In line with this, neural activity in sensory cortex is strongly modulated by prior expectations. Such top-down predictions often arise from cross-modal associations, such as when a sound (e.g., bell or bark) leads to an expectation of the visual appearance of the corresponding object (e.g., bicycle or dog). We hypothesized that the hippocampus, which rapidly learns arbitrary relationships between stimuli over space and time, may be involved in forming such associative predictions. We exposed male and female human participants to auditory cues predicting visual shapes, while measuring high-resolution fMRI signals in visual cortex and the hippocampus. Using multivariate reconstruction methods, we discovered a dissociation between these regions: representations in visual cortex were dominated by whichever shape was presented, whereas representations in the hippocampus reflected only which shape was predicted by the cue. The strength of hippocampal predictions correlated across participants with the amount of expectation-related facilitation in visual cortex. These findings help bridge the gap between memory and sensory systems in the human brain.SIGNIFICANCE STATEMENT The way we perceive the world is to a great extent determined by our prior knowledge. Despite this intimate link between perception and memory, these two aspects of cognition have mostly been studied in isolation. Here we investigate their interaction by asking how memory systems that encode and retrieve associations can inform perception. We find that upon hearing a familiar auditory cue, the hippocampus represents visual information that had previously co-occurred with the cue, even when this expectation differs from what is currently visible. Furthermore, the strength of this hippocampal expectation correlates with facilitation of perceptual processing in visual cortex. These findings help bridge the gap between memory and sensory systems in the human brain.

The influence of action-effect anticipation on bistable perception: differences between onset rivalry and ambiguous motion

Perception is strongly shaped by the actions we perform. According to the theory of event coding, and forward models of motor control, goal-directed action preparation activates representations of desired effects. These expectations about the precise stimulus identity of one's action-outcomes (i.e. identity predictions) are thought to selectively influence perceptual processing of action-contingent effects. However, the existing evidence for such identity-prediction effects is scarce and mixed. Here, we developed a new paradigm to capture such effects and examined whether action-outcome predictions can bias the perception of binocular onset rivalry (Experiments 1a and 1b) and bistable motion (Experiment 2). Participants performed learning tasks in which they were exposed to action-outcome associations. On test trials, actions were followed by bistable stimuli that could be perceived as being either congruent or incongruent with the aforementioned associations (i.e. rivalrous oriented gratings in Experiments 1a and 1b and spheres with ambiguous rotation directions in Experiment 2). Across three experiments, we show that, whilst exposure to action-effect associations can bias the apparent motion direction of ambiguous spheres, it fails to influence perceptual selection of grating orientations in binocular onset rivalry. This pattern of results extends previous work on ambiguous motion by demonstrating that action-induced modulations do not generalize to all types of bistable percepts.

Differentiating aversive conditioning in bistable perception: Avoidance of a percept vs. salience of a stimulus

Alternating conscious visual perception of bistable stimuli is influenced by several factors. In order to understand the effect of negative valence, we tested the effect of two types of aversive conditioning on dominance durations in binocular rivalry. Participants received either aversive classical conditioning of the stimuli shown alone between rivalry blocks, or aversive percept conditioning of one of the two possible perceptual choices during rivalry. Both groups showed successful aversive conditioning according to skin conductance responses and affective valence ratings. However, while classical conditioning led to an immediate but short-lived increase in dominance durations of the conditioned stimulus, percept conditioning yielded no significant immediate effect but tended to decrease durations of the conditioned percept during extinction. These results show dissociable effects of value learning on perceptual inference in situations of perceptual conflict, depending on whether learning relates to the decision between conflicting perceptual choices or the sensory stimuli per se.

Out of sight, out of mind: Occlusion and eye closure destabilize moving bistable structure-from-motion displays

Our brain constantly tries to anticipate the future by using a variety of memory mechanisms. Interestingly, studies using the intermittent presentation of multistable displays have shown little perceptual persistence for interruptions longer than a few hundred milliseconds. Here we examined whether we can facilitate the perceptual stability of bistable displays following a period of invisibility by employing a physically plausible and ecologically valid occlusion event sequence, as opposed to the typical intermittent presentation, with sudden onsets and offsets. To this end, we presented a bistable rotating structure-from-motion display that was moving along a linear horizontal trajectory on the screen and either was temporarily occluded by another object (a cardboard strip in Exp. 1, a computer-generated image in Exp. 2) or became invisible due to eye closure (Exp. 3). We report that a bistable rotation direction reliably persisted following occlusion or interruption only (1) if the pre- and postinterruption locations overlapped spatially (an occluder with apertures in Exp. 2 or brief, spontaneous blinks in Exp. 3) or (2) if an object's size allowed for the efficient grouping of dots on both sides of the occluding object (large objects in Exp. 1). In contrast, we observed no persistence whenever the pre- and postinterruption locations were nonoverlapping (large solid occluding objects in Exps. 1 and 2 and long, prompted blinks in Exp. 3). We report that the bistable rotation direction of a moving object persisted only for spatially overlapping neural representations, and that persistence was not facilitated by a physically plausible and ecologically valid occlusion event.

Recent cross-modal statistical learning influences visual perceptual selection

Incoming sensory signals are often ambiguous and consistent with multiple perceptual interpretations. Information from one sensory modality can help to resolve ambiguity in another modality, but the mechanisms by which multisensory associations come to influence the contents of conscious perception are unclear. We asked whether and how novel statistical information about the coupling between sounds and images influences the early stages of awareness of visual stimuli. We exposed subjects to consistent, arbitrary pairings of sounds and images and then measured the impact of this recent passive statistical learning on subjects' initial conscious perception of a stimulus by employing binocular rivalry, a phenomenon in which incompatible images presented separately to the two eyes result in a perceptual alternation between the two images. On each trial of the rivalry test, subjects were presented with a pair of rivalrous images (one of which had been consistently paired with a specific sound during exposure while the other had not) and an accompanying sound. We found that, at the onset of binocular rivalry, an image was significantly more likely to be perceived, and was perceived for a longer duration, when it was presented with its paired sound than when presented with other sounds. Our results indicate that recently acquired multisensory information helps resolve sensory ambiguity, and they demonstrate that statistical learning is a fast, flexible mechanism that facilitates this process.

Why and How. The Future of the Central Questions of Consciousness

In this review, we deal with two central questions of consciousness how and why, and we outline their possible future development. The question how refers to the empirical endeavor to reveal the neural correlates and mechanisms that form consciousness. On the other hand, the question why generally refers to the “hard problem” of consciousness, which claims that empirical science will always fail to provide a satisfactory answer to the question why is there conscious experience at all. Unfortunately, the hard problem of consciousness will probably never completely disappear because it will always have its most committed supporters. However, there is a good chance that its weight and importance will be highly reduced by empirically tackling consciousness in the near future. We expect that future empirical endeavor of consciousness will be based on a unifying brain theory and will answer the question as to what is the function of conscious experience, which will in turn replace the implications of the hard problem. The candidate of such a unifying brain theory is predictive coding, which will have to explain both perceptual consciousness and conscious mind-wandering in order to become the truly unifying theory of brain functioning.

fMRI-based decoding of reward effects in binocular rivalry

Binocular rivalry is a phenomenon where the simultaneous presentation of two different stimuli to the two eyes leads to alternating perception of the two stimuli. The temporary dominance of one stimulus over the other is influenced by several factors. Here, we studied the influence of reward on binocular rivalry dynamics and its neural representation in visual cortex. Orthogonal rotating grating stimuli were shown continuously, while monetary reward was given during the conscious perception of one stimulus but not the other. Periods of perceptual dominance were assessed both through participants’ subjective report and objectively using functional magnetic resonance imaging and multi-voxel pattern analysis. Results did not confirm previous evidence for an effect of reward on perceptual dominance durations. Exploratory post-hoc analyses indicated that knowledge regarding both the reward contingency and the subjective nature of perceptual alternations may have interfered with potential reward effects on perceptual phase durations, suggesting a moderating role of meta-cognitive awareness in reward-based perceptual inference. Future studies of top-down influences on bistable perception should carefully consider the methodological challenges related to meta-cognitive awareness.

Perceptual suppression of predicted natural images

Perception is shaped not only by current sensory inputs but also by expectations generated from past sensory experience. Humans viewing ambiguous stimuli in a stable visual environment are generally more likely to see the perceptual interpretation that matches their expectations, but it is less clear how expectations affect perception when the environment is changing predictably. We used statistical learning to teach observers arbitrary sequences of natural images and employed binocular rivalry to measure perceptual selection as a function of predictive context. In contrast to previous demonstrations of preferential selection of predicted images for conscious awareness, we found that recently acquired sequence predictions biased perceptual selection toward unexpected natural images and image categories. These perceptual biases were not associated with explicit recall of the learned image sequences. Our results show that exposure to arbitrary sequential structure in the environment impacts subsequent visual perceptual selection and awareness. Specifically, for natural image sequences, the visual system prioritizes what is surprising, or statistically informative, over what is expected, or statistically likely.

How previous experience shapes perception in different sensory modalities

What has transpired immediately before has a strong influence on how sensory stimuli are processed and perceived. In particular, temporal context can have contrastive effects, repelling perception away from the interpretation of the context stimulus, and attractive effects (TCEs), whereby perception repeats upon successive presentations of the same stimulus. For decades, scientists have documented contrastive and attractive temporal context effects mostly with simple visual stimuli. But both types of effects also occur in other modalities, e.g., audition and touch, and for stimuli of varying complexity, raising the possibility that context effects reflect general computational principles of sensory systems. Neuroimaging shows that contrastive and attractive context effects arise from neural processes in different areas of the cerebral cortex, suggesting two separate operations with distinct functional roles. Bayesian models can provide a functional account of both context effects, whereby prior experience adjusts sensory systems to optimize perception of future stimuli.

Onset rivalry: factors that succeed and fail to bias selection

This project examined whether previous visual history can bias perceptual dominance during onset rivalry. A predictive sequence of non-rivalrous stimuli preceded dichoptically presented rivalrous displays. One of the dichoptic images was the implied next step of the preceding sequence while the other was not. Observers reported their initial dominant percept. Across five experiments, we found that motion sequences biased perceptual selection such that a rivalrous stimulus that continued a motion sequence tended to dominate one that did not. However, signals generated by complex pattern of motion information or verbal-semantic information had no influence on selection. These results are consistent with the view that onset rivalry is an early phase of rivalry that is likely insensitive to modulation by factors originating beyond the visual system.

Brain activity dynamics in human parietal regions during spontaneous switches in bistable perception

The neural mechanisms underlying conscious visual perception have been extensively investigated using bistable perception paradigms. Previous functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) studies suggest that the right anterior superior parietal (r-aSPL) and the right posterior superior parietal lobule (r-pSPL) have opposite roles in triggering perceptual reversals. It has been proposed that these two areas are part of a hierarchical network whose dynamics determine perceptual switches. However, how these two parietal regions interact with each other and with the rest of the brain during bistable perception is not known. Here, we investigated such a model by recording brain activity using fMRI while participants viewed a bistable structure-from-motion stimulus. Using dynamic causal modeling (DCM), we found that resolving such perceptual ambiguity was specifically associated with reciprocal interactions between these parietal regions and V5/MT. Strikingly, the strength of bottom-up coupling between V5/MT to r-pSPL and from r-pSPL to r-aSPL predicted individual mean dominance duration. Our findings are consistent with a hierarchical predictive coding model of parietal involvement in bistable perception and suggest that visual information processing underlying spontaneous perceptual switches can be described as changes in connectivity strength between parietal and visual cortical regions.

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Two parietal regions involve spontaneous perceptual switches.

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The two parietal regions and V5/MT form hierarchical model.

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Strength of DCM parameters predicts individual switch frequency.

An aberrant precision account of autism

Autism is a neurodevelopmental disorder characterized by problems with social-communication, restricted interests and repetitive behavior. A recent and thought-provoking article presented a normative explanation for the perceptual symptoms of autism in terms of a failure of Bayesian inference (Pellicano and Burr, 2012). In response, we suggested that when Bayesian inference is grounded in its neural instantiation—namely, predictive coding—many features of autistic perception can be attributed to aberrant precision (or beliefs about precision) within the context of hierarchical message passing in the brain (Friston et al., 2013). Here, we unpack the aberrant precision account of autism. Specifically, we consider how empirical findings—that speak directly or indirectly to neurobiological mechanisms—are consistent with the aberrant encoding of precision in autism; in particular, an imbalance of the precision ascribed to sensory evidence relative to prior beliefs.

Perceptual memory drives learning of retinotopic biases for bistable stimuli

The visual system exploits past experience at multiple timescales to resolve perceptual ambiguity in the retinal image. For example, perception of a bistable stimulus can be biased toward one interpretation over another when preceded by a brief presentation of a disambiguated version of the stimulus (positive priming) or through intermittent presentations of the ambiguous stimulus (stabilization). Similarly, prior presentations of unambiguous stimuli can be used to explicitly “train” a long-lasting association between a percept and a retinal location (perceptual association). These phenonema have typically been regarded as independent processes, with short-term biases attributed to perceptual memory and longer-term biases described as associative learning. Here we tested for interactions between these two forms of experience-dependent perceptual bias and demonstrate that short-term processes strongly influence long-term outcomes. We first demonstrate that the establishment of long-term perceptual contingencies does not require explicit training by unambiguous stimuli, but can arise spontaneously during the periodic presentation of brief, ambiguous stimuli. Using rotating Necker cube stimuli, we observed enduring, retinotopically specific perceptual biases that were expressed from the outset and remained stable for up to 40 min, consistent with the known phenomenon of perceptual stabilization. Further, bias was undiminished after a break period of 5 min, but was readily reset by interposed periods of continuous, as opposed to periodic, ambiguous presentation. Taken together, the results demonstrate that perceptual biases can arise naturally and may principally reflect the brain's tendency to favor recent perceptual interpretation at a given retinal location. Further, they suggest that an association between retinal location and perceptual state, rather than a physical stimulus, is sufficient to generate long-term biases in perceptual organization.

Amygdala, pulvinar, and inferior parietal cortex contribute to early processing of faces without awareness

The goals of the present study were 2-fold. First, we wished to investigate the neural correlates of stimulus-driven processing of stimuli strongly suppressed from awareness and in the absence of top-down influences. We accomplished this using a novel approach in which participants performed an orthogonal task atop a flash suppression noise image to prevent top-down search. Second, we wished to investigate the extent to which amygdala responses differentiate between suppressed stimuli (fearful faces and houses) based on their motivational relevance. Using continuous flash suppression (CFS) in conjunction with fMRI, we presented fearful faces, houses, and a no stimulus control to one eye while participants performed an orthogonal task that appeared atop the flashing Mondrian image presented to the opposite eye. In 29 adolescents, we show activation in subcortical regions, including the superior colliculus, amygdala, thalamus, and hippocampus for suppressed objects (fearful faces and houses) compared to a no stimulus control. Suppressed stimuli showed less activation compared to a no stimulus control in early visual cortex (EVC), indicating that object information was being suppressed from this region. Additionally, we find no activation in regions associated with conscious processing of these percepts (fusiform gyrus and/or parahippocampal cortex) as assessed by mean activations and multi-voxel patterns. A psychophysiological interaction analysis (PPI) that seeded the amygdala showed task-specific (fearful faces greater than houses) modulation of right pulvinar and left inferior parietal cortex. Taken together, our results support a role for the amygdala in stimulus-driven attentional guidance toward objects of relevance and a potential mechanism for successful suppression of rivalrous stimuli.

Predictive feedback and conscious visual experience

The human brain continuously generates predictions about the environment based on learned regularities in the world. These predictions actively and efficiently facilitate the interpretation of incoming sensory information. We review evidence that, as a result of this facilitation, predictions directly influence conscious experience. Specifically, we propose that predictions enable rapid generation of conscious percepts and bias the contents of awareness in situations of uncertainty. The possible neural mechanisms underlying this facilitation are discussed.

Onset rivalry: the initial dominance phase is independent of ongoing perceptual alternations

Binocular rivalry has been used to study a wide range of visual processes, from the integration of low-level features to the selection of signals that reach awareness. However, many of these studies do not distinguish between early and late phases of rivalry. There is clear evidence that the “onset” stage of rivalry is characterized by stable, yet idiosyncratic biases that are not evident in the average dominance of sustained rivalry viewing. Low-level stimulus features also have robust effects in the onset phase that are not seen in sustained rivalry, suggesting these phases may be driven at least partly by different neural mechanisms. The effects of high-level cognitive and affective factors at onset are less clear but also show differences from their effects in sustained viewing. These findings have important implications for the interpretation of any rivalry experiments using brief presentation paradigms and for understanding how the brain copes with binocular discrepancies in natural viewing conditions in which our eyes constantly move around an ever-changing environment. This review will summarize current research and explore the factors influencing this “onset” stage.