Perception is increasingly viewed as an inferential process wherein sensory inputs are integrated with prior expectations. We employed time-resolved decoding on electroencephalography (EEG) data (n = 30 male participants) to investigate how expectations modulate sensory processing across varying levels of stimulus complexity and tested the effect of attention and NMDA receptor blockade. We designed a visual stimulus containing features of different complexity whose processing relies on distinct neural mechanisms: local contrast, collinearity, and the Kanizsa illusion, involving primarily feedforward, lateral, and feedback processes, respectively. EEG decoding revealed that expectations modulated lateral and feedback processing (better decoding for unexpected stimuli) but not feedforward processing. These expectation effects were confined to attended (task-relevant) features and were not observed for task-irrelevant features. The NMDA receptor antagonist memantine selectively enhanced decoding of the Kanizsa illusion, implicating NMDA-mediated feedback mechanisms in perceptual inference, but it did not modulate the effects of expectation or attention. These findings highlight the differential impact of expectations across different stages of sensory processing and reveal a distinct role of NMDA receptor-mediated feedback mechanisms.

The neural correlates of conscious perception remain debated, particularly regarding the role of extra-sensory regions such as the prefrontal cortex. One promising approach is to study the dynamical properties of neural processing in task-related and task-free contexts. A previous EEG study showed that conscious perception is associated with all-or-none late activations, giving rise to bifurcation dynamics even without a task. Here we used fMRI and near-threshold auditory stimulation to ask which brain networks give rise to these bifurcations, and how they diOer depending on task. In both contexts, stimulus intensity modulated activity within broad networks spanning sensory and extra-sensory regions, including the prefrontal cortex. These networks showed both shared and distinct components. Single-trial modelling further revealed bifurcation dynamics beyond primary sensory cortices and enabled single-trial prediction of conscious perception in both contexts. These findings resolve previous conflicting results and reveal common networks and dynamics underlying conscious perception irrespective of task.

What is the role of sensory processing in conscious perception? Current theories of consciousness are divided on this question. Some propose that conscious perception arises during the buildup of sensory representations. Others argue for a secondary process that broadcasts these representations to higher-level areas. This second view makes a counter-intuitive prediction: one could consciously perceive abstract representations untied to any low-level sensory feature. We tested this prediction by combining visual masking with retrospective cueing. We found that when visually masked words were followed by a semantically related auditory word, participants were better at detecting this past word and reporting its identity, but were strikingly unable to report its visual features (letter casing or position on screen). This suggests that retro-cueing can help a semantic representation reach awareness even after the associated sensory information has been masked. The mechanisms of conscious access might thus be largely independent of early sensory build-up.

Hemianopic patients with visual field defects due to cerebral damage sometimes demonstrate residual visual capacities in their contralesional field, known as blindsight. Its associated subjective experience remains poorly understood. We developed a novel task for patients combining forced-choice detection and discrimination paradigms with a confidence scale to assess individual objective sensitivity and metacognitive sensitivity and efficiency, addressing the unique challenges of probing subjective experience in hemianopia, where visual nature is rarely evident. Four patients participated, revealing distinct perceptual and metacognitive profiles. One patient exhibited remarkable contralesional objective capacities and some preserved metacognition despite rarely reporting visual perception, suggesting subjective content may not reflect the stimulus itself. Concomitantly, preliminary results reveal ipsilesional metacognitive impairments in three patients despite optimal objective performance. Overall, we present the first application of state-of-the-art metacognitive measures to hemianopia, bridging perceptual and metacognitive measures to explore subjective experience, offering new insights into blindsight and the dissociation between consciousness and metacognitive processes.

A recent publication in Nature aimed at enriching the progressive build-up of a valid theory of conscious processing using a valuable multicentric experimentation and massive data-sharing open to new analyses. It is important to stress that several of the analyses validate key predictions of the Global Neuronal Workspace Theory (GNWT) including (i) transient ignition following stimulus onset in the predicted time-window (200-800ms), (ii) irrespective of stimulus duration and (iii) of stimulus relevance, as well as (iv) decoding of ‘conscious content in visual, ventrotemporal and inferior frontal cortex, with sustained responses […] and content specific synchronization between frontal and early visual areas’. In other words, this article confirmed that stimuli that are clearly consciously visible elicit a brain-wide activation and synchronization between sensory areas and prefrontal cortex, even in the absence of task-relevance, validating a non-trivial prediction of the GNWT. Also given that this study only used clearly visible stimuli, it could not test the most central predictions of the GNWT which tackle the critical contrast between conscious and non-conscious processing. Hence, several conclusions drawn by the authors about GNWT predictions need to be reconsidered.

Conscious access is suggested to involve "ignition," an all-or-none activation across cortical areas. To elucidate this phenomenon, we carry out computer simulations of a detection task using a mesoscale connectome-based model for the multiregional macaque cortex. The model uncovers a dynamic bifurcation mechanism that gives rise to ignition in a network of associative regions. A hierarchical N-methyl-D-aspartate (NMDA)/α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor gradient plays a critical role: fast AMPA receptors drive feedforward signal propagation, while slow NMDA receptors in feedback pathways shape and sustain the ignited network. Intriguingly, the model suggests higher NMDA-to-AMPA receptor ratios in sensory areas compared to association areas, a prediction supported by in vitro autoradiography data. Furthermore, the model accounts for diverse behavioral and physiological phenomena linked to consciousness. This work sheds light on how receptor gradients along the cortical hierarchy enable distributed cognitive functions and provides a biologically constrained computational framework for investigating the neurophysiological basis of conscious access.

One of the goals of the neuroscience of consciousness is to identify neural markers capable of distinguishing brain dynamics in awake, healthy individuals from unconscious conditions. This problem also has a clinical diagnostic interest in disorders of consciousness. Recent research has shown that brain connectivity patterns characterized by long-range interactions and anticorrelations are associated with conscious states and diminish with loss of consciousness in human and non-human primates. However, the precise contribution of these patterns to conscious processing and subjective experience formation remains unclear. In this study, we investigated the functional role of these brain patterns in shaping conscious content by examining their influence on participants’ ability to process external information during wakefulness. Participants underwent fMRI recordings during an auditory detection task. Phase coherence-based functional connectivity and k-means clustering confirmed that the ongoing dynamics were underpinned by brain patterns consistent with those identified in previous research, including the “high pattern” characteristic of conscious states. We found that the detection of auditory stimuli at threshold was specifically improved when the connectivity pattern at the time of presentation corresponded to this high-pattern. In return, the occurrence of the high-pattern increased after detection, indicating that participants were more likely to transition to a high-pattern following stimulus detection. Our findings suggest that ongoing brain dynamics and conscious perception mutually influence each other and that certain brain configurations are more favorable for conscious processing of external stimuli. In the future, targeting these moments of favorable patterns in patients with disorders of consciousness may help us identify windows of greater receptivity to the external world, paving the way for developing individualized patient care protocols.### Competing Interest StatementThe authors have declared no competing interest.

The neuroscience of consciousness aims to identify neural markers that distinguish brain dynamics in healthy individuals from those in unconscious conditions. Recent research has revealed that specific brain connectivity patterns correlate with conscious states and diminish with loss of consciousness. However, the contribution of these patterns to shaping conscious processing remains unclear. Our study investigates the functional significance of these neural dynamics by examining their impact on participants’ ability to process external information during wakefulness. Using fMRI recordings during an auditory detection task and rest, we show that ongoing dynamics are underpinned by brain patterns consistent with those identified in previous research. Detection of auditory stimuli at threshold is specifically improved when the connectivity pattern at stimulus presentation corresponds to patterns characteristic of conscious states. Conversely, the occurrence of these conscious state-associated patterns increases after detection, indicating a mutual influence between ongoing brain dynamics and conscious perception. Our findings suggest that certain brain configurations are more favorable to the conscious processing of external stimuli. Targeting these favorable patterns in patients with consciousness disorders may help identify windows of greater receptivity to the external world, guiding personalized treatments.

Can we become aware of auditory stimuli retrospectively, even if they initially failed to reach awareness? Here, we tested whether spatial cueing of attention after a word had been played could trigger retrospective conscious access. Two sound streams were presented dichotically. One stream was attended for a primary task of speeded semantic categorization. The other stream included occasional target words, which had to be identified as a secondary task after the trial. We observed that cueing attention to the secondary stream improved identification accuracy, even when cueing occurred more than 500 ms after the target offset. In addition, such "retro-cueing" boosted the detection sensitivity and subjective audibility of the target. The effect was a perceptual one and not one based on enhancing or protecting conscious representations already available in working memory, as shown by quantitative models of the experimental data. In particular, the retro-cue did not gradually shift audibility but rather sharply changed the balance between fully audible and not audible trials. Together with remarkably similar results in vision, these results point to a previously unsuspected temporal flexibility of conscious access as a core feature of perception, across modalities. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Blindsight regroups the different manifestations of preserved discriminatory visual capacities following the damage to the primary visual cortex. Blindsight types differentially impact objective and subjective perception, patients can report having no visual awareness whilst their behaviour suggests visual processing still occurs at some cortical level. This phenomenon hence presents a unique opportunity to study consciousness and perceptual consciousness, and for this reason, it has had an historical importance for the development of this field of research. From these studies, two main opposing models of the underlying mechanisms have been established: (a) blindsight is perception without consciousness or (b) blindsight is in fact degraded vision, two views that mirror more general theoretical options about whether unconscious cognition truly exists or whether it is only a degraded form of conscious processing. In this article, we want to re-examine this debate in the light of recent advances in the characterization of blindsight and associated phenomena. We first provide an in-depth definition of blindsight and its subtypes, mainly blindsight type I, blindsight type II and the more recently described blindsense. We emphasize the necessity of sensitive and robust methodology to uncover the dissociations between perception and awareness that can be observed in brain-damaged patients with visual field defects at different cognitive levels. We discuss these different profiles of dissociation in the light of both contending models. We propose that the different types of dissociations reveal a pattern of relationship between perception, awareness and metacognition that is actually richer than what is proposed by either of the existing models. Finally, we consider this in the framework of current theories of consciousness and touch on the implications the findings of blindsight have on these.

A growing body of evidence suggests that conscious perception of a sensory stimulus triggers an all-or-none activity across multiple cortical areas, a phenomenon called ‘ignition’. In contrast, the same stimulus, when undetected, induces only transient activity. In this work, we report a large-scale model of the macaque cortex based on recently quantified structural connectome data. We use this model to simulate a detection task, and demonstrate how a dynamical bifurcation mechanism produces ignition-like events in the model network. The model predicts that feedforward excitatory transmission is primarily mediated by the fast AMPA receptors to ensure rapid signal propagation from sensory to associative areas. In contrast, a greater proportion of the inter-areal feedback projections and local recurrent excitation depend on the slow NMDA receptors, to ensure ignition of distributed frontoparietal activity. Our model predicts, counterintuitively, that fast-responding sensory areas contain a higher ratio of NMDA to AMPA receptors compared to association cortical areas that show slow, sustained activity. We validate this prediction using in-vitro receptor autoradiography data. Finally, we show how this model can account for various behavioral and physiological effects linked to consciousness. Together, these findings clarify the neurophysiological mechanisms of conscious access in the primate cortex and support the concept that gradients of receptor densities along the cortical hierarchy contribute to distributed cognitive functions.

Despite the tangible progress in psychological and cognitive sciences over the last several years, these disciplines still trail other more mature sciences in identifying the most important questions that need to be solved. Reaching such consensus could lead to greater synergy across different laboratories, faster progress, and increased focus on solving important problems rather than pursuing isolated, niche efforts. Here, 26 researchers from the field of visual metacognition reached consensus on four long-term and two medium-term common goals. We describe the process that we followed, the goals themselves, and our plans for accomplishing these goals. If this effort proves successful within the next few years, such consensus building around common goals could be adopted more widely in psychological science.

presents a synthesis of recent advances obtained within the large French team

We recently published the results of a study on the occurrence of blindsight among eight, post-stroke homonymous hemianopic (HH) patients (Garric et al., 2019), in whom we measured blindsight through forced-choice tasks and assessed perceptual experiences by a new awareness scale, the Sensation Awareness Scale (SAS). Within the cohort, we found different profiles of dissociation between objective and subjective performance. Importantly, we were able to describe several cases of a dissociation phenomenon that we named blindsense, whereby patients exhibited marked subjective sensitivity in their blind hemifield despite being unable to discriminate the different stimuli. Following publication of our article (Garric et al., 2019), Prof. Ian Phillips (Phillips, 2019) wrote a Commentary in which he questioned the methodology we used to measure and analyze objective and subjective perception in our HH patients. As opposed to our original interpretation of our results to describe the new profile of blindsense, based on a non-visual experience hypothesis (Kentridge, 2015), Prof. Phillips re-evaluated the different blindsight profiles that we identified in our study through the lens of a degraded conscious vision hypothesis (Overgaard, Fehl, Mouridsen, Bergholt, & Cleeremans, 2008). In the present response, we explain that, although we agree that dichotomous visual scales lead to highly conservative responses and mask conscious perceptual experience of patients, we still support the notion that nuanced report protocols can enable more-sensitive measurements of perceptual experiences in the hemianopic, so-called blind visual field. Furthermore, we affirm that the additional awareness-scale phenomenal levels that such protocols enable are more consistent with patients’ experiences and lead patients to provide more liberal responses when describing their subjective perceptions. Measuring subjective experiences in the contralesional hemianopic visual field Subjective reports are ambiguous because they depend on a series of elements: firstly, the actual perceptual experiences of patients; secondly, patients’ interpretation of these experiences; and finally, patients’ verbal reports of the interpretations. Moreover, the elements become more complex in the case of asking homonymous hemianopic (HH) patients to describe what is happening in their (clinically diagnosed) blind hemifield. In these cases, patients may respond with varying levels of confidence, doubt, and conservative or liberal responses. Therefore, investigating whether HH patients have any perceptual experience in their blind hemifield, and understanding whether their perceptions correspond to residual vision or to a more phenomenal or abstract experience, are critical and challenging issues in the blindsight literature. Unfortunately, such assessments have rarely been performed in groups of hemianopic patients. In order to address this gap, we recently proposed a fivelevel awareness scale, the SAS. Importantly this scale was not copied from those used in healthy participants, but based on spontaneous self-reporting by HH patients: (1) I did not see anything; (2) I don’t think that I saw nothing, but I’m not sure; (3) I felt something; (4) I saw something; and (5) I clearly saw something and can identify it. The distinction between (3) and (4) in particular was directly inspired from patients spontaneous reports, as it would not occur to subjects with normal vision that such distinction could exist. In his Commentary, Phillips (2020) argues that the SAS cannot be considered to be a scale because of the lack of continuity between the different levels—notably, as a consequence of level 3. In particular, Phillips claims that “someone could feel something [level 3] but see nothing [level 1]”. However, our aim was precisely to disentangle the feeling that ‘something was there’ from the visual, perceptual, experience in the blind visual field. Indeed, our aim in designing and using the SAS was to ascertain any possible distinction between a visual perception of a stimulus in the blind visual field and a subjective experience of the presence of that stimulus. Accordingly, our data indicated that a patient could acknowledge having had a subjective experience in their blind external visual field without having had perceived (per se) that stimulus. Moreover, although Phillips’ claim of a lack of continuity in the SAS could be defended from a strictly psychophysical point of view, it still seems reasonable to call “scale” a collection of categories with some form of ordering between them. Actually we have no guarantee of a strict continuity between the levels of the most commonly used awareness scale, the Perceptual Awareness Scale. During our subjective awareness task, we taught our patients to use a graduated scale and to respond with a number from 1 to 5. We clearly explained the labels of each level to the patients at the beginning of the experiment and displayed the levels on the screen to the patients each time that an SAS response was required. The graduated character of this scale is particularly reflected in the use of progressive degree of certainty (e.g. level 2: “I don’t think that I saw anything, but I’m not sure” and level 5: I clearly saw something and can identify it”). We have considered the possibility that a feeling could correlate with the first level of awareness; however, and as we mention in the original paper, we designed the SAS based on spontaneous-HH patients’ reports, who seem to employ phenomenal vocabulary principally when they perceive that something happens during stimulation. Finally, beyond the question of whether this specific level of our scale is at the right position relative to the others, the real question is whether this category is meaningful for describing the patients’ perception or not. If it is, our scale should capture nuances that cannot be captured by other measures. And this is exactly what we observe. In line with his claim about a purported lack of continuity in the SAS, Phillips suggests that the SAS cannot be statistically analyzed as a scale. He also suggests that the assessment of subjective sensitivity might be more accurate by “focusing on whether sensitivity in the two objective tasks corresponds to reported awareness “. He argues that in our paper, we wrongly classified patient P2 as having type I blindsight (the only case without any awareness of the stimuli), and he asserts that “If P2 has blindsight, it would seem to be type II.” Contrariwise, we believe that computing ROC curves and comparing the area under these curves (AUC) in target trials and catch trials (i.e. measuring whether the distribution of responses on the SAS were significantly different between the presence or absence of a stimulus on the screen), provides an accurate measure of subjective sensitivity, independent of response bias, as dictated by signal detection theory. In patient P2, although response distributions on the scale show slight differences for target and catch trials (see Garric et al., Fig. 5), our analysis confirms that they are not statistically different. In other words, this patient is not sensitive to the presence of the stimulus when using the subjective scale. Blindsight, blindsense or residual vision? By employing visual detection tasks, visual discrimination tasks, binary responses (stimulus is present or absent; and stimulus is X or O) and the SAS in our study on eight HH patients, we had expected to observe distinct patterns of dissociation between objective and subjective perception in the blind visual field. Gathering results from previous studies on blindsight and new predictions, we expected four profiles: Absence of blindsight: objective performance and subjective performance both at chance level; Type I blindsight: objective performance above chance level, without any statistically significant subjective sensitivity; Type II blindsight: objective performance and subjective performance both above chance level, without any conscious detection in the blind visual field; Blindsense: objective performance at chance level combined with a statistically significant subjective performance In our study, we identified blindsight profiles (types) according to literature definitions, and then quantified these profiles in our cohort. Nonetheless, one could argue that the definitions that we employed, originally proposed by distinct authors based on different case studies and methodologies, are less than optimal for classifying patient performance. On the one hand, classifying the performance of patients based on previous studies can generate confusion, as exemplified in what Phillips refers to as the “unremarked puzzle” of patients P6 and P7 in our study. These patients represented the two most striking blindsense profiles: they were at chance level for the two binary tasks (detection and discrimination) yet demonstrated significant subjective sensitivity on the SAS. We agree with Phillips that interpreting the chance-level performance on the detection binary task as an “absence of sensitivity” is confusing, as we argued that these patients had been able to feel ‘something’. However, this situation highlights the case of literature based on binary (conscious/unconscious) responses. Thus, the solution to this “puzzle” is what we had already provided as the main conclusion in our paper: “assessment of detection performance through a binary choice in patients strongly depends on the patients’ decision criteria”. Indeed, challenging the blind visual field of HH patients can provoke them to provide highly conservative responses. Ultimately, the debate hinges on the mechanism that underpins each patient’s blindsight behavior (e.g. unconscious/conscious or visual/non-visual), which shape the definition—and consequently, researchers’ understanding—of blindsight. On the other hand, using the pre-existing definitions, as we had, enabled u

Does conscious perception occur during initial sensory processing, or does it arise later in a supra modal fashion? If conscious access truly depends on supra modal processes, we may be able to induce “asensory perception”, where only the semantic features of a meaningful stimulus are accessed, untied to its sensory attributes. Here we tested this prediction by degrading the low-level sensory representations of visual words in the brain using pattern masking, and subsequently presenting audio words that were either semantically related to the masked word or not. We hypothesized these retrospective semantic cues would reactivate the remaining traces of the masked word in the brain, and induce awareness of any information that was not disrupted by masking. In three separate experiments we show that, when presented with retrospective cues that are semantically related to the masked word, participants are better at detecting the presence of the preceding masked word and naming it, while at the same time being unable to report its visual features. In other words, participants could consciously detect and recognize the preceding masked word, without knowing what it looked like. These findings suggest that non-sensory information can be consciously accessed in relative independence from the build-up of sensory representations. ### Competing Interest Statement The authors have declared no competing interest.

An outstanding challenge for consciousness research is to characterize the neural signature of conscious access independently of any decisional processes. Here we present a model-based approach that uses inter-trial variability to identify the brain dynamics associated with stimulus processing. We demonstrate that, even in the absence of any task or behavior, the electroencephalographic response to auditory stimuli shows bifurcation dynamics around 250–300 milliseconds post-stimulus. Namely, the same stimulus gives rise to late sustained activity on some trials, and not on others. This late neural activity is predictive of task-related reports, and also of reports of conscious contents that are randomly sampled during task-free listening. Source localization further suggests that task-free conscious access recruits the same neural networks as those associated with explicit report, except for frontal executive components. Studying brain dynamics through variability could thus play a key role for identifying the core signatures of conscious access, independent of report.

We recently published the results of a study on the occurrence of blindsight among eight, post-stroke homonymous hemianopic (HH) patients (Garric et al., 2019), in whom we measured blindsight through forced-choice tasks and assessed perceptual experiences by a new awareness scale, the Sensation Awareness Scale (SAS). Within the cohort, we found different profiles of dissociation between objective and subjective performance. Importantly, we were able to describe several cases of a dissociation phenomenon that we named blindsense, whereby patients exhibited marked subjective sensitivity in their blind hemifield despite being unable to discriminate the different stimuli. Following publication of our article (Garric et al., 2019), Prof. Ian Phillips (Phillips, 2019) wrote a Commentary in which he questioned the methodology we used to measure and analyze objective and subjective perception in our HH patients. As opposed to our original interpretation of our results to describe the new profile of blindsense, based on a non-visual experience hypothesis (Kentridge, 2015), Prof. Phillips re-evaluated the different blindsight profiles that we identified in our study through the lens of a degraded conscious vision hypothesis (Overgaard, Fehl, Mouridsen, Bergholt, & Cleeremans, 2008). In the present response, we explain that, although we agree that dichotomous visual scales lead to highly conservative responses and mask conscious perceptual experience of patients, we still support the notion that nuanced report protocols can enable more-sensitive measurements of perceptual experiences in the hemianopic, so-called blind visual field. Furthermore, we affirm that the additional awareness-scale phenomenal levels that such protocols enable are more consistent with patients' experiences and lead patients to provide more liberal responses when describing their subjective perceptions.

Recent studies have demonstrated that visually cueing attention towards a stimulus location after its disappearance can facilitate visual processing of the target and increase task performance. Here, we tested whether such retro-cueing effects can also occur across different sensory modalities, as cross-modal facilitation has been shown in pre-cueing studies using auditory stimuli prior to the onset of a visual target. In the present study, participants detected low-contrast Gabor patches in a speeded response task. These patches were presented in the left or right visual periphery, preceded or followed by a lateralized and task-irrelevant sound at 4 stimulus-onset asynchronies (SOA; −600 ms, −150 ms, +150 ms, +450 ms). We found that pre-cueing at the −150 ms SOA led to a general increase in detection performance irrespective of the sound’s location relative to the target. On top of this temporal effect, sound-cues also had a spatially specific effect, with further improvement when cue and target originated from the same location. Critically, the temporal effect was absent, but the spatial effect was present in the short-SOA retro-cueing condition (+150 ms). Drift-diffusion analysis of the response time distributions allowed us to better characterize the evidenced effects. Overall, our results show that sounds can facilitate visual processing, both pre- and retro-actively, indicative of a flexible and multisensory attentional system that underlies our conscious visual experience.