Breaking continuous flash suppression: competing for consciousness on the pre-semantic battlefield

The temporal dynamics of conscious and unconscious audio-visual semantic integration

We compared the time course of cross-modal semantic effects induced by both naturalistic sounds and spoken words on the processing of visual stimuli, whether visible or suppressed form awareness through continuous flash suppression. We found that, under visible conditions, spoken words elicited audio-visual semantic effects over longer time (-1000, -500, -250 ms SOAs) than naturalistic sounds (-500, -250 ms SOAs). Performance was generally better with auditory primes, but more so with congruent stimuli. Spoken words presented in advance (-1000, -500 ms) outperformed naturalistic sounds; the opposite was true for (near-)simultaneous presentations. Congruent spoken words demonstrated superior categorization performance compared to congruent naturalistic sounds. The audio-visual semantic congruency effect still occurred with suppressed visual stimuli, although without significant variations in the temporal patterns between auditory types. These findings indicate that: 1. Semantically congruent auditory input can enhance visual processing performance, even when the visual stimulus is imperceptible to conscious awareness. 2. The temporal dynamics is contingent on the auditory types only when the visual stimulus is visible. 3. Audiovisual semantic integration requires sufficient time for processing auditory information.

Learning to discriminate the eye-of-origin during continuous flash suppression

Helmholtz asked whether one could discriminate which eye is the origin of one's perception merely based on the retinal signals. Studies to date showed that participants' ability to tell the eye-of-origin most likely depends on contextual cues. Nevertheless, it has been shown that exogenous attention can enhance performance for monocularly presented stimuli. We questioned whether adults can be trained to discriminate the eye-of-origin of their perceptions and if this ability depends on the strength of the monocular channels. We used attentional feed-forward training to improve the subject's eye-of-origin discrimination performance with voluntary attention. During training, participants received a binocular cue to inform them of the eye-of-origin of an upcoming target. Using continuous flash suppression, we also measured the signal strength of the monocular targets to see any possible modulations related to the cues. We collected confidence ratings from the participants about their eye-of-origin judgements to study in further detail whether metacognition has access to this information. Our results show that, even though voluntary attention did not alter the strength of the monocular channels, eye-of-origin discrimination performance improved following the training. A similar pattern was observed for confidence. The results from the feedforward attentional training and the increase in subjective confidence point towards a high-level decisional mechanism being responsible for the eye-of-origin judgements. We propose that this high-level process is informed by subtle sensory cues such as the differences in luminance or contrast in the two monocular channels.

The role of identity priming on the (unconscious) bodily self-attribution

It has been recently demonstrated that hand stimuli presented in a first-, with respect to a third-, person perspective were prioritized before awareness independently from their identity (i.e., self, or other). This pattern would represent an unconscious advantage for self-related bodily stimuli rooted in spatial perspective. To deeper investigate the role of identity, we employed a breaking-Continuous Flash Suppression paradigm in which a self- or other-hand presented in first- or third-person perspective was displayed after a conscious identity-related prime (i.e., self or other face). We replicated the unconscious advantage of the first-person perspective but, crucially, we reported that within the first-person perspective, other-hand stimuli preceded by other-face priming slowed down the conscious access with respect to the other conditions. These findings demonstrate that a top-down conscious identity context modulates the unconscious self-attribution of bodily stimuli. Within a predictive processing framework, we suggest that, by adding ambiguous information, the prime forces a prediction update that slows conscious access.

A new 'CFS tracking' paradigm reveals uniform suppression depth regardless of target complexity or salience

When the eyes view separate and incompatible images, the brain suppresses one image and promotes the other into visual awareness. Periods of interocular suppression can be prolonged during continuous flash suppression (CFS) - when one eye views a static 'target' while the other views a complex dynamic stimulus. Measuring the time needed for a suppressed image to break CFS (bCFS) has been widely used to investigate unconscious processing, and the results have generated controversy regarding the scope of visual processing without awareness. Here, we address this controversy with a new 'CFS tracking' paradigm (tCFS) in which the suppressed monocular target steadily increases in contrast until breaking into awareness (as in bCFS) after which it decreases until it again disappears (reCFS), with this cycle continuing for many reversals. Unlike bCFS, tCFS provides a measure of suppression depth by quantifying the difference between breakthrough and suppression thresholds. tCFS confirms that (i) breakthrough thresholds indeed differ across target types (e.g. faces vs gratings, as bCFS has shown) - but (ii) suppression depth does not vary across target types. Once the breakthrough contrast is reached for a given stimulus, all stimuli require a strikingly uniform reduction in contrast to reach the corresponding suppression threshold. This uniform suppression depth points to a single mechanism of CFS suppression, one that likely occurs early in visual processing because suppression depth was not modulated by target salience or complexity. More fundamentally, it shows that variations in bCFS thresholds alone are insufficient for inferring whether the barrier to achieving awareness exerted by interocular suppression is weaker for some categories of visual stimuli compared to others.

Intra-group differences in skin tone influence evaluative and perceptual face processing

In an exploration of colorist biases across native Melanesian participants, we employed a multi-method approach across three studies to examine evaluative and perceptual processing of 'lighter' and 'darker' non-Melanesian facial targets controlled for attractiveness, sex, and ethnicity. In Study 1, 305 participants evaluated facial attractiveness using surveys. In Study 2, 153 participants alternately mapped lighter and darker faces with positive and neutral attributes across brief Implicit Association Tests. In Study 3, 61 participants underwent a manual sorting task followed by a 'breaking' continuous flash suppression (b-CFS) paradigm to probe 'non-conscious' perceptual biases. Across evaluative measures, male and female respondents consistently preferred lighter-skinned, highly attractive male faces. During b-CFS, lighter and attractive opposite-sex faces entered awareness ('broke suppression') faster than their darker counterparts. We speculate that skin tone may operate as a perceptually salient cue in the presence of facial configurations signaling high reproductive potential.

VWM-based bias in conscious access can be extended to a new sandwich masking task and real-life stimuli

Previous studies using breaking continuous flash suppression observed that the content of visual working memory (VWM) influences the priority for accessing visual awareness. However, most studies have used simple stimuli, whereas real-life objects are typically more meaningful and contain more perceptual information than simple objects. In this study, we intermixed a delayed match-to-sample task to manipulate the content of VWM, and a breaking repeated masking suppression (b-RMS) task to investigate whether this memory-based effect in conscious access can be extended to a new sandwich masking task and real-life stimuli. The results revealed that memory-congruent objects broke RMS faster than incongruent objects for both simple and real-life objects. Specifically, for simple objects, color-matching targets broke RMS faster than color-mismatching targets, whereas state-matching targets broke RMS faster than state-mismatching targets for real-life objects. These results suggest that the faster detection of VWM-matching over VWM mismatching stimuli-which has been mostly studied using only one type of task (b-CFS) and stimulus (colored shapes)-extends to (1) yet another masking technique (b-RMS) and to (2) a novel stimulus type (real-life objects), providing evidence that memory-based biases in conscious access are a ubiquitous phenomenon.

Revisiting the effects of configuration, predictability, and relevance on visual detection during interocular suppression

Statistical regularities and predictions can influence the earliest stages of visual processing. Studies examining their effects on detection, however, have yielded inconsistent results. In continuous flash suppression (CFS), where a static image projected to one eye is suppressed by a dynamic image presented to the other, the predictability of the suppressed signal may facilitate or delay detection. To identify the factors that differentiate these outcomes and dissociate the effects of expectation from those of behavioral relevance, we conducted three CFS experiments that addressed confounds related to the use of reaction time measures and complex images. In experiment 1, orientation recognition performance and visibility rates increased when a suppressed line segment completed a partial shape surrounding the CFS patch, demonstrating that valid configuration cues facilitate detection. In Experiment 2, however, predictive cues marginally affected visibility and did not modulate localization performance, challenging existing findings. In experiment 3, a relevance manipulation was introduced; participants pressed a key upon detecting lines of a particular orientation, ignoring the other possible orientation. Visibility and localization were enhanced for relevant orientations. Predictive cues modulated visibility, orientation recognition sensitivity, and response latencies, but not localization-an objective measure sensitive to partial breakthrough. Thus, while a consistent surround can strongly enhance detection during passive observation, predictive cueing primarily affects post-detection factors such as response readiness and recognition confidence. Relevance and predictability did not interact, suggesting that the contributions of these two processes to detection are mostly orthogonal.

Gestalt formation promotes awareness of suppressed visual stimuli during binocular rivalry

Continuous flash suppression leverages binocular rivalry to render observers unaware of a static image for several seconds. To achieve this effect, rapidly flashing noise masks are presented to the dominant eye while a static stimulus is presented to the non-dominant eye. Eventually "breakthrough" occurs, wherein awareness shifts to the static image shown to the non-dominant eye. We tested the hypothesis that Gestalt formation can promote breakthrough. In two experiments, we presented pacman-shaped objects that might or might not align to form illusory Kanizsa objects. To measure the inception of breakthrough, observers were instructed to press a key at the moment of partial breakthrough. After pressing the key, which stopped the trial, observers reported how many pacmen were seen and where they were located. Supporting the Gestalt hypothesis, breakthrough was faster when the pacmen were aligned and observers more often reported pairs of pacmen if they were aligned. To address whether these effects reflected illusory shape perception, a computational model was applied to the pacman report distributions and breakthrough times for an experiment with four pacmen. A full account of the data required an increased joint probability of reporting all four pacmen, suggesting an influence of a perceived illusory cross.

Guns Are Not Faster to Enter Awareness After Seeing a Black Face: Absence of Race-Priming in a Gun/Tool Task During Continuous Flash Suppression

In the Weapon Identification Task (WIT), Black faces prime the identification of guns compared with tools. We measured race-induced changes in visual awareness of guns and tools using continuous flash suppression (CFS). Eighty-four participants, primed with Black or Asian faces, indicated the location of a gun or tool target that was temporarily rendered invisible through CFS, which provides a sensitive measure of effects on early visual processing. The same participants also completed a standard (non-CFS) WIT. We replicated the standard race-priming effect in the WIT. In the CFS task, Black and Asian primes did not affect the time guns and tools needed to enter awareness. Thus, race priming does not alter early visual processing but does change the identification of guns and tools. This confirms that race-priming originates from later post-perceptual memory- or response-related processing.

Humans, fish, spiders and bees inherited working memory and attention from their last common ancestor

All brain processes that generate behaviour, apart from reflexes, operate with information that is in an "activated" state. This activated information, which is known as working memory (WM), is generated by the effect of attentional processes on incoming information or information previously stored in short-term or long-term memory (STM or LTM). Information in WM tends to remain the focus of attention; and WM, attention and STM together enable information to be available to mental processes and the behaviours that follow on from them. WM and attention underpin all flexible mental processes, such as solving problems, making choices, preparing for opportunities or threats that could be nearby, or simply finding the way home. Neither WM nor attention are necessarily conscious, and both may have evolved long before consciousness. WM and attention, with similar properties, are possessed by humans, archerfish, and other vertebrates; jumping spiders, honey bees, and other arthropods; and members of other clades, whose last common ancestor (LCA) is believed to have lived more than 600 million years ago. It has been reported that very similar genes control the development of vertebrate and arthropod brains, and were likely inherited from their LCA. Genes that control brain development are conserved because brains generate adaptive behaviour. However, the neural processes that generate behaviour operate with the activated information in WM, so WM and attention must have existed prior to the evolution of brains. It is proposed that WM and attention are widespread amongst animal species because they are phylogenetically conserved mechanisms that are essential to all mental processing, and were inherited from the LCA of vertebrates, arthropods, and some other animal clades.

The importance of awareness in face processing: A critical review of interocular suppression studies

Human faces convey essential information for understanding others' mental states and intentions. The importance of faces in social interaction has prompted suggestions that some relevant facial features such as configural information, emotional expression, and gaze direction may promote preferential access to awareness. This evidence has predominantly come from interocular suppression studies, with the most common method being the Breaking Continuous Flash Suppression (bCFS) procedure, which measures the time it takes different stimuli to overcome interocular suppression. However, the procedures employed in such studies suffer from multiple methodological limitations. For example, they are unable to disentangle detection from identification processes, their results may be confounded by participants' response bias and decision criteria, they typically use small stimulus sets, and some of their results attributed to detecting high-level facial features (e.g., emotional expression) may be confounded by differences in low-level visual features (e.g., contrast, spatial frequency). In this article, we review the evidence from the bCFS procedure on whether relevant facial features promote access to awareness, discuss the main limitations of this very popular method, and propose strategies to address these issues.

Learned value modulates the access to visual awareness during continuous flash suppression

Monetary value enhances visual perception and attention and boosts activity in the primary visual cortex, however, it is still unclear whether monetary value can modulate the conscious access to rewarding stimuli. Here we investigate this issue by employing a breaking continuous flash suppression (b-CFS) paradigm. We measured suppression durations of sinusoidal gratings having orthogonal orientations under CFS in adult volunteers before and after a short session of Pavlovian associative learning in which each orientation was arbitrarily associated either with high or low monetary reward. We found that monetary value accelerated the access to visual awareness during CFS. Specifically, after the associative learning, suppression durations of the visual stimulus associated with high monetary value were shorter compared to the visual stimulus associated with low monetary value. Critically, the effect was replicated in a second experiment using a detection task for b-CFS that was orthogonal to the reward associative learning. These results indicate that monetary reward facilitates the access to awareness of visual stimuli associated with monetary value probably by boosting their representation at the early stages of visual processing in the brain.

Priming of natural scene categorization during continuous flash suppression

Continuous Flash Suppression (CFS) reduces conscious awareness of stimuli. Whether stimuli suppressed by CFS are processed at categorical or semantic levels is still debated. Here, we approached this question using a large set of indoor and outdoor scene photographs in a priming paradigm. Perceptually suppressed primes were followed by visible targets. Participants rapidly reported whether the targets showed an indoor or an outdoor scene. Responses were faster (and fast responses more accurate) when primes and targets came from a congruent superordinate category (e.g., both were outdoor scenes). During CFS, priming effects were relatively small (up to 10 ms) and modulated by prime visibility and stimulus onset asynchrony (SOA) of prime and target. Without CFS, the stimuli elicited consistent and more robust priming effects (about 24 ms). Our results imply that scene category is processed during CFS, although some residual prime visibility is likely necessary for significant priming effects to occur.

Holistic processing of gaze cues during interocular suppression

Direct eye contact is preferentially processed over averted gaze and has been shown to gain privileged access to conscious awareness during interocular suppression. This advantage might be driven by local features associated with direct gaze, such as the amount of visible sclera. Alternatively, a holistic representation of gaze direction, which depends on the integration of head and eye information, might drive the effects. Resolving this question is interesting because it speaks to whether the processing of higher-level social information in the visual system, such as facial characteristics that rely on holistic processing, is dependent on conscious awareness. The Wollaston Illusion is a visual illusion that allows researchers to manipulate perceived gaze direction while keeping local eye features constant. Here we used this illusion to elucidate the driving factor facilitating the direct gaze advantage during interocular suppression. Using continuous flash suppression, we rendered Wollaston faces with direct and averted gaze (initially) invisible. These faces conveyed different gaze directions but contained identical eye regions. Our results showed clear evidence for a direct gaze advantage with Wollaston faces, indicating that holistic representations of gaze direction may drive the direct gaze advantage during interocular suppression.

Gaze direction and face orientation modulate perceptual sensitivity to faces under interocular suppression

Faces convey information essential for social interaction. Their importance has prompted suggestions that some facial features may be processed unconsciously. Although some studies have provided empirical support for this idea, it remains unclear whether these findings were due to perceptual processing or to post-perceptual decisional factors. Evidence for unconscious processing of facial features has predominantly come from the Breaking Continuous Flash Suppression (b-CFS) paradigm, which measures the time it takes different stimuli to overcome interocular suppression. For example, previous studies have found that upright faces are reported faster than inverted faces, and direct-gaze faces are reported faster than averted-gaze faces. However, this procedure suffers from important problems: observers can decide how much information they receive before committing to a report, so their detection responses may be influenced by differences in decision criteria and by stimulus identification. Here, we developed a new procedure that uses predefined exposure durations, enabling independent measurement of perceptual sensitivity and decision criteria. We found higher detection sensitivity to both upright and direct-gaze (compared to inverted and averted-gaze) faces, with no effects on decisional factors. For identification, we found both greater sensitivity and more liberal criteria for upright faces. Our findings demonstrate that face orientation and gaze direction influence perceptual sensitivity, indicating that these facial features may be processed unconsciously.

Semantic Expectation Effects on Object Detection: Using Figure Assignment to Elucidate Mechanisms

Recent evidence suggesting that object detection is improved following valid rather than invalid labels implies that semantics influence object detection. It is not clear, however, whether the results index object detection or feature detection. Further, because control conditions were absent and labels and objects were repeated multiple times, the mechanisms are unknown. We assessed object detection via figure assignment, whereby objects are segmented from backgrounds. Masked bipartite displays depicting a portion of a mono-oriented object (a familiar configuration) on one side of a central border were shown once only for 90 or 100 ms. Familiar configuration is a figural prior. Accurate detection was indexed by reports of an object on the familiar configuration side of the border. Compared to control experiments without labels, valid labels improved accuracy and reduced response times (RTs) more for upright than inverted objects (Studies 1 and 2). Invalid labels denoting different superordinate-level objects (DSC; Study 1) or same superordinate-level objects (SSC; Study 2) reduced accuracy for upright displays only. Orientation dependency indicates that effects are mediated by activated object representations rather than features which are invariant over orientation. Following invalid SSC labels (Study 2), accurate detection RTs were longer than control for both orientations, implicating conflict between semantic representations that had to be resolved before object detection. These results demonstrate that object detection is not just affected by semantics, it entails semantics.

A nasal visual field advantage in interocular competition

When our eyes are confronted with discrepant images (yielding incompatible retinal inputs) interocular competition (IOC) is instigated. During IOC, one image temporarily dominates perception, while the other is suppressed. Many factors affecting IOC have been extensively examined. One factor that received surprisingly little attention, however, is the stimulus’ visual hemifield (VHF) of origin. This is remarkable, as the VHF location of stimuli is known to affect visual performance in various contexts. Prompted by exploratory analyses, we examined five independent datasets of breaking continuous flash suppression experiments, to establish the VHF’s role in IOC. We found that targets presented in nasal VHF locations broke through suppression much faster than targets in temporal VHF locations. Furthermore, we found that the magnitude of this nasal advantage depended on how strongly the targets were suppressed: the nasal advantage was larger for the recessive eye than for the dominant eye, and was larger in observers with a greater dominance imbalance between the eyes. Our findings suggest that the nasal advantage reported here originates in processing stages where IOC is resolved. Finally, we propose that a nasal advantage in IOC serves an adaptive role in human vision, as it can aid perception of partially occluded objects.

Hidden intentions: Visual awareness prioritizes perceived attention even without eyes or faces

Eye contact is a powerful social signal, and it readily captures attention. Recent work has suggested that direct gaze is prioritized even unconsciously: faces rendered invisible via interocular suppression enter awareness faster when they look directly at (vs. away from) you. Such effects may be driven in a relatively low level way by the special visual properties of eyes, per se, but here we asked whether they might instead arise from the perception of a deeper property: being the focus of another agent's attention and/or intentions. We report five experiments which collectively explore whether visual awareness also prioritizes distinctly non-eye-like stimuli that nevertheless convey directedness. We first showed that directed (vs. averted) 'mouth' shapes also break through into awareness faster, after being rendered invisible by continuous flash suppression - a direct 'gaze' effect without any eyes. But such effects could still be specific to faces (if not eyes), so we next asked whether the prioritization of directed intentions would still occur even for stimuli that have no faces at all. In fact, even simple geometric shapes can be seen as intentional, as when numerous randomly scattered cones are all consistently pointing at you. And indeed, even such directed (vs. averted) cones entered awareness faster - a direct 'gaze' effect without any facial cues. Additional control experiments ruled out effects of both symmetry and response biases. We conclude that the perception of directed intentions is sufficient to boost objects into awareness, and that putative eye-contact effects might instead reflect more general phenomena of 'mind contact'.

Dimensions of Perception: 3D Real-Life Objects Are More Readily Detected Than Their 2D Images

Most of our interactions with our environment involve manipulating real 3D objects. Accordingly, 3D objects seem to enjoy preferential processing compared with 2D images, for example, in capturing attention or being better remembered. But are they also more readily perceived? Thus far, the possibility of preferred detection for real 3D objects could not be empirically tested because suppression from awareness has been applied only to on-screen stimuli. Here, using a variant of continuous flash suppression (CFS) with augmented-reality goggles ("real-life" CFS), we managed to suppress both real 3D objects and their 2D representations. In 20 healthy young adults, real objects broke suppression faster than their photographs. Using 3D printing, we also showed in 50 healthy young adults that this finding held only for meaningful objects, whereas no difference was found for meaningless, novel ones (a similar trend was observed in another experiment with 20 subjects, yet it did not reach significance). This suggests that the effect might be mediated by affordances facilitating detection of 3D objects under interocular suppression.

Slower access to visual awareness but otherwise intact implicit perception of emotional faces in schizophrenia-spectrum disorders

Schizophrenia-spectrum disorders are characterized by deficits in social domains. Extant research has reported an impaired ability to perceive emotional faces in schizophrenia. Yet, it is unclear if these deficits occur already in the access to visual awareness. To investigate this question, 23 people with schizophrenia or schizoaffective disorder and 22 healthy controls performed a breaking continuous flash suppression task with fearful, happy, and neutral faces. Response times were analysed with generalized linear mixed models. People with schizophrenia-spectrum disorders were slower than controls in detecting faces, but did not show emotion-specific impairments. Moreover, happy faces were detected faster than neutral and fearful faces, across all participants. Although caution is needed when interpreting the main effect of group, our findings may suggest an elevated threshold for visual awareness in schizophrenia-spectrum disorders, but an intact implicit emotion perception. Our study provides a new insight into the mechanisms underlying emotion perception in schizophrenia-spectrum disorders.

Unpredictive linguistic verbal cues accelerate congruent visual targets into awareness in a breaking continuous flash suppression paradigm

One of the most influential ideas within the domain of cognition is that of embodied cognition, in which the experienced world is the result of an interplay between an organism's physiology, sensorimotor system, and its environment. An aspect of this idea is that linguistic information activates sensory representations automatically. For example, hearing the word 'red' would automatically activate sensory representations of this color. But does linguistic information prioritize access to awareness of congruent visual information? Here, we show that linguistic verbal cues accelerate matching visual targets into awareness by using a breaking continuous flash suppression paradigm. In a speeded reaction time task, observers heard spoken color labels (e.g., red) followed by colored targets that were either congruent (red), incongruent (green), or neutral (a neutral noncolor word) with respect to the labels. Importantly, and in contrast to previous studies investigating a similar question, the incidence of congruent trials was not higher than that of incongruent trials. Our results show that RTs were selectively shortened for congruent verbal-visual pairings, and that this shortening occurred over a wide range of cue-target intervals. We suggest that linguistic verbal information preactivates sensory representations, so that hearing the word 'red' preactivates (visual) sensory information internally.

Subliminal temporal integration of linguistic information under discontinuous flash suppression

Whether unconscious complex visual information integration occurs over time remains largely unknown and highly controversial. Previous studies have tended to use a combination of strong masking or suppression and a weak stimulus signal (e.g., low luminance), resulting in a low signal-to-noise ratio during unconscious stimulus presentation. To lengthen the stimulus exposure, we introduced intermittent presentation into interocular suppression. This discontinuous suppression allowed us to insert a word during each suppression period and deliver multiple words over time unconsciously. We found that, after participants received the subliminal context, they responded faster to a syntactically incongruent target word in a lexical decision task. We later replicated the finding in a separate experiment where participants exhibited chance performance on locating the subliminal context. These results confirmed that the sentential context was both subjectively and objectively subliminal. Critically, the effect disappeared when the context was disrupted by presenting only partial sentences or sentences with a reversed word order. These control experiments showed that the effect was not merely driven by word-word association but instead required integration over multiple words in the correct order. These findings support the possibility of unconscious high-level, complex information integration.

Bottom-up processing of fearful and angry facial expressions is intact in schizophrenia

INTRODUCTION

Judgments of emotion from faces are reportedly impaired in schizophrenia. However, it is unclear whether this is due to a top-down cognitive deficit in evaluating sensory information or a fundamental bottom-up perturbation in the early stages of face encoding. This study examined whether deficits in emotion processing reflect imprecision in the initial preconscious registration of emotional face expressions within the visual system.

METHODS

Using continuous flash suppression (CFS), we presented participants (18 patients with schizophrenia, 8M/10F; 20 healthy controls, 13M/7F) with fearful and angry faces. Previous CFS research on healthy participants reveals that fearful facial expressions gain privileged access to awareness over angry faces-demonstrating the visual system's ability to discriminate these emotions at a preconscious level. We used this same approach to probe the integrity of early emotion encoding whilst minimising the potential contribution of any top-down cognitive biases on perceptual judgments.

RESULTS

In both groups, fearful faces were perceived faster than angry faces, with no differences observed between patients and controls.

CONCLUSIONS

Emotion processing difficulties in schizophrenia are unlikely to reflect an early sensory deficit, but rather a deficit in social cognition that has a top-down impact on the conscious evaluation of facial expressions.

Dissociating conscious and unconscious influences on visual detection effects

The scope of unconscious processing is highly debated, with recent studies showing that even high-level functions such as perceptual integration and category-based attention occur unconsciously. For example, upright faces that are suppressed from awareness through interocular suppression break into awareness more quickly than inverted faces. Similarly, verbal object cues boost otherwise invisible objects into awareness. Here, we replicate these findings, but find that they reflect a general difference in detectability not specific to interocular suppression. To dissociate conscious and unconscious influences on visual detection effects, we use an additional discrimination task to rule out conscious processes as a cause for these differences. Results from this detection-discrimination dissociation paradigm reveal that, while face orientation is processed unconsciously, category-based attention requires awareness. These findings provide insights into the function of conscious perception and offer an experimental approach for mapping out the scope and limits of unconscious processing.

Continuous flash suppression: Known and unknowns

Studies utilizing continuous flash suppression (CFS) provide valuable information regarding conscious and nonconscious perception. There are, however, crucial unanswered questions regarding the mechanisms of suppression and the level of visual processing in the absence of consciousness with CFS. Research suggests that the answers to these questions depend on the experimental configuration and how we assess consciousness in these studies. The aim of this review is to evaluate the impact of different experimental configurations and the assessment of consciousness on the results of the previous CFS studies. We review studies that evaluated the influence of different experimental configuration on the depth of suppression with CFS and discuss how different assessments of consciousness may impact the results of CFS studies. Finally, we review behavioral and brain recording studies of CFS. In conclusion, previous studies provide evidence for survival of low-level visual information and complete impairment of high-level visual information under the influence of CFS. That is, studies suggest that nonconscious perception of lower-level visual information happens with CFS, but there is no evidence for nonconscious high-level recognition with CFS.

Synesthesia does not help to recover perceptual dominance following flash suppression

Grapheme-colour synesthesia occurs when letters or numbers elicit an abnormal colour sensation (e.g., printed black letters are perceived as coloured). This phenomenon is typically reported following explicit presentation of graphemes. Very few studies have investigated colour sensations in synesthesia in the absence of visual awareness. We took advantage of the dichoptic flash suppression paradigm to temporarily render a stimulus presented to one eye invisible. Synesthetic alphanumeric and non-synesthetic stimuli were presented to 21 participants (11 synesthetes) in achromatic and chromatic experimental conditions. The test stimulus was first displayed to one eye and then masked by a sudden presentation of visual noise in the other eye (flash suppression). The time for an image to be re-perceived following the onset of the suppressive noise was calculated. Trials where there was no flash suppression performed but instead mimicked the perceptual suppression of the flash were also tested. Results showed that target detection by synesthetes was significantly better than by controls in the absence of flash suppression. No difference was found between the groups in the flash suppression condition. Our findings suggest that synesthesia is associated with enhanced perception for overt recognition, but does not provide an advantage in recovering from a perceptual suppression. Further studies are needed to investigate synesthesia in relation to visual awareness.

The neural substrates of subliminal attentional bias and reduced inhibition in individuals with a higher BMI: A VBM and resting state connectivity study

Previous studies have shown that individuals with overweight and obesity may experience attentional biases and reduced inhibition toward food stimuli. However, evidence is scarce as to whether the attentional bias is present even before stimuli are consciously recognized. Moreover, it is not known whether or not differences in the underlying brain morphometry and connectivity may co-occur with attentional bias and impulsivity towards food in individuals with different BMIs. To address these questions, we asked fifty-three participants (age M = 23.2, SD = 2.9, 13 males) to perform a breaking Continuous Flash Suppression (bCFS) task to measure the speed of subliminal processing, and a Go/No-Go task to measure inhibition, using food and nonfood stimuli. We collected whole-brain structural magnetic resonance images and functional resting-state activity. A higher BMI predicted slower subliminal processing of images independently of the type of stimulus (food or nonfood, p = 0.001, ε_p² = 0.17). This higher threshold of awareness is linked to lower grey matter (GM) density of key areas involved in awareness, high-level sensory integration, and reward, such as the orbitofrontal cortex [t = 4.55, p = 0.003], the right temporal areas [t = 4.18, p = 0.002], the operculum and insula [t = 4.14, p = 0.005] only in individuals with a higher BMI. In addition, individuals with a higher BMI exhibit a specific reduced inhibition to food in the Go/No-Go task [p = 0.02, ε_p² = 0.02], which is associated with lower GM density in reward brain regions [orbital gyrus, t = 4.97, p = 0.005, and parietal operculum, t = 5.14, p < 0.001] and lower resting-state connectivity of the orbital gyrus to visual areas [fusiform gyrus, t = -4.64, p < 0.001 and bilateral occipital cortex, t = -4.51, p < 0.001 and t = -4.34, p < 0.001]. Therefore, a higher BMI is predictive of non food-specific slower visual subliminal processing, which is linked to morphological alterations of key areas involved in awareness, high-level sensory integration, and reward. At a late, conscious stage of visual processing a higher BMI is associated with a specific bias towards food and with lower GM density in reward brain regions. Finally, independently of BMI, volumetric variations and connectivity patterns in different brain regions are associated with variability in bCFS and Go/No-Go performances.

How retaining objects containing multiple features in visual working memory regulates the priority for access to visual awareness

The content of visual working memory influences the access to visual awareness. Thus far, research has focused on retention of a single feature, whereas memoranda in real life typically contain multiple features. Here, we intermixed a delayed match-to-sample task to manipulate VWM content, and a breaking Continuous Flash Suppression (b-CFS) task to measure prioritization for visual awareness. Observers memorized either the color (Exp. 1), the shape (Exp. 2) or both the features (Exp. 3) of an item and indicated the location of a suppressed target. We observed that color-matching targets broke suppression faster than color-mismatching targets both when color was memory relevant or irrelevant. Shape only impacted priority for visual awareness through an interaction with color. We conclude that: (1) VWM can regulate the priority of visual information to access visual awareness along a single feature dimension; (2) different features of a memorandum vary in their potency to impact access to visual awareness, and the more dominant feature may even suppress the effect of the less dominant feature; (3) even stimuli that match an irrelevant feature dimension of the memorandum can be prioritized for visual awareness.

Reflections on Eriksen's seminal essay on discrimination, performance and learning without awareness

Early in his career C.W. Eriksen published in Psychological Review what turned out to be a highly impactful critique on methods and findings on the topic of unconscious influences on discrimination and awareness. His incisive commentary on extant methodology employed at that time - especially the heavy dependence on subjective reports - clearly was heard by others moving forward, as evidenced by the subsequent, lively discussions within the literature concerning the very definition of the notion of unconscious processing. Of equal importance, Eriksen's paper provided an impetus for the development of more refined techniques for manipulating perceptual awareness and for measuring the consequences of those manipulations. My purpose in this essay is to ensure that Eriksen's seminal contributions concerning unconscious phenomena remain within the awareness of the many current investigators working on this popular topic.

Perceptual Advantage of Animal Facial Attractiveness: Evidence From b-CFS and Binocular Rivalry

Research has shown that attractive human faces enjoy an advantage in both conscious and preconscious processing. Here we examined whether this preference for attractiveness is exclusive to human faces by measuring participants’ sensitivity to the attractiveness of cat and tiger faces. Experiment 1 measured the time taken to break continuous flash suppression (b-CFS), whereas Experiment 2 measured the dominant time in binocular rivalry (BR). The results showed that attractive cat faces were detected more quickly (Experiment 1) and dominated for longer time in visual awareness (Experiment 2). However, no effect of attractiveness was found for tiger faces in Experiment 1, while attractive tiger faces also dominated for longer time in visual awareness in Experiment 2. The results provide first evidence that the preference for attractive animal faces can be shown involuntarily or without apparent conscious control. The findings suggest that human preference for facial attractiveness may contain an aesthetic element rather than being a purely adaptive means for mate choice.

Faces under continuous flash suppression capture attention faster than objects, but without a face-evoked steady-state visual potential: Is curvilinearity responsible for the behavioral effect?

Face perception is a vital part of human social interactions. The social value of faces makes their efficient detection evolutionarily advantageous. It has been suggested that this might occur nonconsciously, but experimental results are equivocal thus far. Here, we probe nonconscious face perception using a novel combination of binocular rivalry with continuous flash suppression and steady-state visually evoked potentials. In the first two experiments, participants viewed either non-face objects, neutral faces (Study 1), or fearful faces (Study 2). Consistent with the hypothesis that faces are processed nonconsciously, we found that faces broke through suppression faster than objects. We did not, however, observe a concomitant face-selective steady-state visually evoked potential. Study 3 was run to reconcile this paradox. We hypothesized that the faster breakthrough time was due to a mid-level visual feature, curvilinearity, rather than high-level category membership, which would explain the behavioral difference without neural evidence of face-selective processing. We tested this hypothesis by presenting participants with four different groups of stimuli outside of conscious awareness: rectilinear objects (e.g., chessboard), curvilinear objects (e.g., dartboard), faces, and objects that were not dominantly curvilinear or rectilinear. We found that faces and curvilinear objects broke through suppression faster than objects and rectilinear objects. Moreover, there was no difference between faces and curvilinear objects. These results support our hypothesis that the observed behavioral advantage for faces is due to their curvilinearity, rather than category membership.

Task-induced attention load guides and gates unconscious semantic interference

The tight relationship between attention and conscious perception has been extensively researched in the past decades. However, whether attentional modulation extended to unconscious processes remained largely unknown, particularly when it came to abstract and high-level processing. Here we use a double Stroop paradigm to demonstrate that attention load gates unconscious semantic processing. We find that word and color incongruencies between a subliminal prime and a supraliminal target cause slower responses to non-Stroop target words-but only if the task is to name the target word (low-load task), and not if the task is to name the target's color (high-load task). The task load hypothesis is confirmed by showing that the word-induced incongruence effect can be detected in the color-naming task, but only in the late, practiced trials. We further replicate this task-induced attentional modulation phenomenon in separate experiments with colorless words (word-only) and words with semantic relationship but no orthographic similarities (semantics-only).

No evidence for mnemonic modulation of interocularly suppressed visual input

Visual working memory (VWM) allows for keeping visual information available for upcoming goal-directed behavior, while new visual input is processed concurrently. Interactions between the mnemonic and perceptual systems cause VWM to affect the processing of visual input in a content-specific manner: visual input that is initially suppressed from consciousness is detected faster when it matches rather than mismatches the content of VWM. It is currently under debate whether such mnemonic influences on perception occur prior to or after conscious access. To address this issue, we investigated whether VWM content modulates the neural response to visual input that remains suppressed from consciousness. We measured fMRI responses to interocularly suppressed stimuli in 20 human participants performing a delayed match-to-sample task: Participants were retro-cued to memorize one of two geometrical shapes for subsequent recognition. During retention, an interocularly suppressed peripheral stimulus (the probe) was briefly presented, which was either of the cued (memorized) or uncued (not memorized) shape category. We found no evidence that VWM content modulated the neural response to the probe. Substantial evidence for the absence of this modulation was found despite leveraging a highly liberal analysis approach: (1) selecting regions of interest that were particularly prone to detecting said modulation, and (2) using directional Bayesian tests favoring the presence of the hypothesized modulation. We did observe faster detection of memory-matching compared to memory-mismatching probes in a behavioral control experiment, thus validating the stimulus set. We conclude that VWM impacts the processing of visual input only once suppression is mostly alleviated.

Novel procedure for generating continuous flash suppression: Seurat meets Mondrian

Continuous flash suppression (CFS) entails presentation of a stationary target to one eye and an animated sequence of arrays of geometric figures, the mask, to the other eye. The prototypical CFS sequence comprises different sized rectangles of various colors, dubbed Mondrians. Presented as a rapid, changing sequence to one eye, Mondrians or other similarly constructed textured arrays can abolish awareness of the target viewed by the other eye for many seconds at a time, producing target suppression durations much longer than those associated with conventional binocular rivalry. We have devised an animation technique that replaces meaningless Mondrian figures with recognizable visual objects and scenes as inducers of CFS, allowing explicit manipulation of the visual semantic content of those masks. By converting each image of these CFS sequences into successively presented objects or scenes each comprised of many small, circular patches of color, we create pointillist CFS sequences closely matched in terms of their spatio-temporal power spectra. Randomly rearranging the positions of the pointillist patches scrambles the images so they are no longer recognizable. CFS sequences comprising a stream of different objects produces more robust interocular suppression than do sequences comprising a stream of different scenes, even when the two categories of CFS are matched in root mean square contrast and spatial frequency content. Factors promoting these differences in CFS potency could range from low-level, image-based features to high-level factors including attention and recognizability. At the same time, object- and scene-based CFS sequences, when themselves suppressed from awareness, do not differ in their durations of suppression, implying that semantic content of those images comprising CFS sequences are not registered during suppression. The pointillist technique itself offers a potentially useful means for examining the impact of high-level image meaning on aspects of visual perception other than interocular suppression.

No influence of eye gaze on emotional face processing in the absence of conscious awareness

The human brain has evolved specialised mechanisms to enable the rapid detection of threat cues, including emotional face expressions (e.g., fear and anger). However, contextual cues - such as gaze direction - influence the ability to recognise emotional expressions. For instance, anger paired with direct gaze, and fear paired with averted gaze are more accurately recognised compared to alternate conjunctions of these features. It is argued that this is because gaze direction conveys the relevance and locus of the threat to the observer. Here, we used continuous flash suppression (CFS) to assess whether the modulatory effect of gaze direction on emotional face processing occurs outside of conscious awareness. Previous research using CFS has demonstrated that fearful facial expressions are prioritised by the visual system and gain privileged access to awareness over other expressed emotions. We hypothesised that if the modulatory effects of gaze on emotional face processing occur also at this level, then the gaze-emotion conjunctions signalling self-relevant threat will reach awareness faster than those that do not. We report that fearful faces gain privileged access to awareness over angry faces, but that gaze direction does not modulate this effect. Thus, our findings suggest that previously reported effects of gaze direction on emotional face processing are likely to occur once the face is detected, where the self-relevance and locus of the threat can be consciously appraised.

Emotion in Chinese Words Could Not Be Extracted in Continuous Flash Suppression

Previous studies have demonstrated the automatic vigilance effect for faces and pictures and have attributed it to the brain's prioritized unconscious evaluation of early evolutionary stimuli that are critical to survival. Whether this effect exists for evolutionarily more recent stimuli, such as written words, has become the center of much debate. Apparently contradicting results have been reported in different languages, such as Hebrew, English, and Traditional Chinese (TC), with regard to the unconscious processing of emotional words in breaking continuous flash suppression (b-CFS). Our current study used two experiments (with two-character words or single-character words) to verify whether the emotional valence or the length of Simplified Chinese (SC) words would modulate conscious access in b-CFS. We failed to replicate the findings reported in Yang and Yeh (2011) using TC, but found that complex high-level emotional information could not be extracted from interocularly suppressed words regardless of their length. Our findings comply with the distinction between subliminal and preconscious states in Global Neuronal Workspace Theory and support the current notion that preconsciousness or partial awareness may be indispensable for high-level cognitive tasks such as reading comprehension.

Object Vision in a Structured World

In natural vision, objects appear at typical locations, both with respect to visual space (e.g., an airplane in the upper part of a scene) and other objects (e.g., a lamp above a table). Recent studies have shown that object vision is strongly adapted to such positional regularities. In this review we synthesize these developments, highlighting that adaptations to positional regularities facilitate object detection and recognition, and sharpen the representations of objects in visual cortex. These effects are pervasive across various types of high-level content. We posit that adaptations to real-world structure collectively support optimal usage of limited cortical processing resources. Taking positional regularities into account will thus be essential for understanding efficient object vision in the real world.

Individual differences in continuous flash suppression: Potency and linkages to binocular rivalry dynamics

Binocular rivalry (BR) and continuous flash suppression (CFS) are compelling psychophysical phenomena involving interocular suppression. Using an individual differences approach we assessed whether interocular suppression induced by CFS is predictable in potency from characteristics of BR that are plausibly governed by interocular inhibition. We found large individual differences in BR dynamics and, in addition, in the strength of CFS as gauged by the incidence and durations of breakthroughs in CFS during an extended viewing periods. CFS's potency waned with repeated trials, but stable individual differences persisted despite these mean shifts. We also discovered large individual differences in the strength of the post-CFS shift in BR dominance produced by interocular suppression. While CFS breakthroughs were significantly negatively correlated with shifts in BR dominance after CFS, there were no significant associations between individual differences in alternation rate during pre-CFS binocular rivalry and either breakthroughs during CFS or post-CFS dominance shifts. Bayesian hypothesis tests and highest posterior density intervals confirmed the weak association between these two forms of interocular suppression. Thus, our findings suggest that the substantial individual differences in BR dynamics and CFS effectiveness are modestly related but not entirely mediated by one common neural substrate.

Access to awareness of direct gaze is related to autistic traits

BACKGROUND

The atypical processing of eye contact is a characteristic hallmark of autism spectrum disorder (ASD). The severity of these symptoms, however, is thought to lie on a continuum that extends into the typical population. While behavioural evidence shows that differences in social cognitive tasks in typically developed (TD) adults are related to the levels of autistic-like traits, it remains unknown whether such a relation exists for the sensitivity to direct gaze.

METHODS

In two experiments, we measured reaction times to detect the faces with direct and averted gaze, suppressed from awareness, i.e. the access to awareness. In experiment 1, we tested N = 19 clinically diagnosed adults with ASD and N = 22 TD matched controls, while in experiment 2, we tested an independent sample of N = 20 TD adults.

RESULTS

In line with the literature, experiment 1 showed preferential processing of direct gaze in the TD group but not in the ASD group. Importantly, we found a linear relationship in both experiments between the levels of autistic traits within the groups of TD participants and their sensitivity to direct gaze: with increasing autistic characteristics, there was a decrease in sensitivity to direct gaze.

CONCLUSION

These results provide the first evidence that differences in gaze processing and the sensitivity to direct gaze are already present in individuals with subclinical levels of autistic traits. Furthermore, they lend support to the continuum view of the disorder and could potentially help in an earlier diagnosis of individuals at high risk for autism.

Prospectively reinstated memory drives conscious access of matching visual input

Maintaining information in visual working memory (VWM) biases attentional selection of concurrent visual input, by favoring VWM-matching over VWM-mismatching visual input. Recently, it was shown that this bias disappears when the same item is memorized on consecutive occasions (as memoranda presumably transit from VWM to long-term memory), but reemerges when observers anticipate to memorize a novel item on a subsequent trial. Here, we aimed to conceptually replicate and extend this intriguing finding, by investigating whether prospectively reinstated memory drives conscious access of memory-matching visual input. We measured the time it took for participants to detect interocularly suppressed target stimuli, which were either from the same color category as a concurrently memorized color or not. Our results showed that the advantage of memory-matching targets in overcoming suppression progresses non-monotonically across consecutive memorizations of the same color ('repetitions'): the advantage for memory-matching visual input initially declined to asymptote, before being fully revived on the last repetition. This revival was not observed in a control experiment in which targets were not interocularly suppressed. The results suggest that, as observers anticipate to memorize a novel item imminently, VWM usage is prospectively reinstated, causing memory-matching visual input to gain accelerated access to consciousness again.

Effects of Hunger on Visual Perception in Binocular Rivalry

The effect of hunger on visual perception is largely absent from contemporary vision science. Using a well-established visual phenomenon termed binocular rivalry, this study was carried out to investigate the effects of hunger on visual perception. A within-subject design was applied in which participants attended two sessions before and after their lunch or dinner, i.e., a hunger state and a satiated state. In Experiment 1, we found that the mean dominance times to food-related pictures were larger in the hungry condition than that in the satiated condition, while the mean dominance time to the non-food stimuli were unaffected. In Experiment 2, we found the times to break through continuous flash suppression (b-CFS) for both food-related and non-food-related pictures were not affected by hunger. In Experiment 3, a probe-detection task was conducted to address possible response-biases. Our findings provide evidence that hunger biases the dynamic process of binocular rivalry to unsuppressed and visible food stimuli, while processing suppressed and invisible food-related was unaffected. Our results support the notion that the top-down modulation by hunger on food-related visual perception is limited to visible stimuli.

Intact prioritisation of unconscious face processing in schizophrenia

INTRODUCTION

Faces provide a rich source of social information, crucial for the successful navigation of daily social interactions. People with schizophrenia suffer a wide range of social-cognitive deficits, including abnormalities in face perception. However, to date, studies of face perception in schizophrenia have primarily employed tasks that require patients to make judgements about the faces. It is, thus, unclear whether the reported deficits reflect an impairment in encoding visual face information, or biased social-cognitive evaluative processes.

METHODS

We assess the integrity of early unconscious face processing in 21 out-patients diagnosed with Schizophrenia or Schizoaffective Disorder (15M/6F) and 21 healthy controls (14M/7F). In order to control for any direct influence of higher order cognitive processes, we use a behavioural paradigm known as breaking continuous flash suppression (b-CFS), where participants simply respond to the presence and location of a face. In healthy adults, this method has previously been used to show that upright faces gain rapid and privileged access to conscious awareness over inverted faces and other inanimate objects.

RESULTS

Here, we report similar effects in patients, suggesting that the early unconscious stages of face processing are intact in schizophrenia.

CONCLUSION

Our data indicate that face processing deficits reported in the literature must manifest at a conscious stage of processing, where the influence of mentalizing or attribution biases might play a role.

Does emotion influence visual perception? Depends on how you look at it

One of the biggest challenges in the study of emotion-cognition interaction is addressing the question of whether and how emotions influence processes of perception as distinct from other higher-level cognitive processes. Most theories of emotion agree that an emotion episode begins with a sensory experience - such as a visual percept - that elicits a cascade of affective, cognitive, physiological, and/or behavioural responses (the ordering and inclusion of those latter components being forever debated). However, for decades, a subset of philosophers and scientists have suggested that the presumed perception → emotion relationship is in fact bidirectional, with emotion also altering the perceptual process. In the present review we reflect on the history and empirical support (or, some might argue, lack thereof) for the notion that emotion influences visual perception. We examine ways in which researchers have attempted to test the question, and the ways in which this pursuit is so difficult. As is the case with the ongoing debate about the cognitive penetrability of perception, we conclude that nothing is conclusive in the debate about the emotional penetrability of perception. We nonetheless don rose-coloured glasses as we look forward to the future of this research topic.

Pupil Size as a Gateway Into Conscious Interpretation of Brightness

Although retinal illumination is the main determinant of pupil size, evidence indicates that extra-retinal factors, including attention and contextual information, also modulate the pupillary response. For example, stimuli that evoke the idea of brightness (e.g., pictures of the sun) induce pupillary constriction compared to control stimuli of matched luminance. Is conscious appraisal of these stimuli necessary for the pupillary constriction to occur? Participants' pupil diameter was recorded while sun pictures and their phase-scrambled versions were shown to the left eye. A stream of Mondrian patterns was displayed to the right eye to produce continuous flash suppression, which rendered the left-eye stimuli invisible on some trials. Results revealed that when participants were aware of the sun pictures their pupils constricted relative to the control stimuli. This was not the case when the pictures were successfully suppressed from awareness, demonstrating that pupil size is highly sensitive to the contents of consciousness.

"Real-life" continuous flash suppression (CFS)-CFS with real-world objects using augmented reality goggles

Continuous flash suppression (CFS) is a popular method for suppressing visual stimuli from awareness for relatively long periods. Thus far, this method has only been used for suppressing two-dimensional images presented on screen. We present a novel variant of CFS, termed “real-life” CFS, in which a portion of the actual immediate surroundings of an observer—including three-dimensional, real-life objects—can be rendered unconscious. Our method uses augmented reality goggles to present subjects with CFS masks to the dominant eye, leaving the nondominant eye exposed to the real world. In three experiments we demonstrated that real objects can indeed be suppressed from awareness for several seconds, on average, and that the suppression duration is comparable to that obtained using classic, on-screen CFS. As supplementary information, we further provide an example of experimental code that can be modified for future studies. This technique opens the way to new questions in the study of consciousness and its functions.