The levels of perceptual processing and the neural correlates of increasing subjective visibility

According to the levels-of-processing hypothesis, transitions from unconscious to conscious perception may depend on stimulus processing level, with more gradual changes for low-level stimuli and more dichotomous changes for high-level stimuli. In an event-related fMRI study we explored this hypothesis using a visual backward masking procedure. Task requirements manipulated level of processing. Participants reported the magnitude of the target digit in the high-level task, its color in the low-level task, and rated subjective visibility of stimuli using the Perceptual Awareness Scale. Intermediate stimulus visibility was reported more frequently in the low-level task, confirming prior behavioral results. Visible targets recruited insulo-fronto-parietal regions in both tasks. Task effects were observed in visual areas, with higher activity in the low-level task across all visibility levels. Thus, the influence of level of processing on conscious perception may be mediated by attentional modulation of activity in regions representing features of consciously experienced stimuli.     

A Multi‐Factor Account of Degrees of Awareness

In this paper we argue that awareness comes in degrees, and we propose a novel multi‐factor account that spans both subjective experiences and perceptual representations. At the subjective level, we argue that conscious experiences can be degraded by being fragmented, less salient, too generic, or flash‐like. At the representational level, we identify corresponding features of perceptual representations—their availability for working memory, intensity, precision, and stability—and argue that the mechanisms that affect these features are what ultimately modulate the degree of awareness. We conclude the paper by demonstrating why the original interpretations of certain empirical findings that apparently pose problems for our account are, in fact, flawed.     

Gradedness of visual awareness depends on attentional scope: Global perception is more graded than local perception

The gradedness or discreteness of our visual awareness has been debated. Here, we investigate the influence of spatial scope of attention on the gradedness of visual awareness. We manipulated scope of attention using hierarchical letter-based tasks (global: broad scope; local: narrow scope). Participants reported the identity of a masked hierarchical letter either at the global level or at the local level. We measured subjective awareness using the perceptual awareness scale ratings and objective performance. The results indicate more graded visual awareness (lesser slope for the awareness rating curve) at the global level compared to the local level. Graded perception was also observed in visibility ratings usage with global level task showing higher usage of the middle PAS ratings. Our results are in line with the prediction of level of processing hypothesis and show that global/local attentional scope and contextual endogenous factors influence the graded nature of our visual awareness.     

Subjective awareness scale length influences the prevalence,not the presence,of graded conscious states

There is an ongoing debate about the graded or dichotomous form of visual consciousness. Studies involved in the disagreement have typically employed subjective awareness ratings in psychophysical experiments. Variations in scale length have made comparisons across studies difficult and have even been suspected of influencing conclusions about the form of consciousness. We tested the proposal that a 21-point awareness scale produces dichotomous awareness state reports. The experiment described in this article randomly assigned participants to use one of four scale lengths used in previous studies in a backward masking task. Our findings suggest that all scales indicate the presence of graded awareness states, but that the resulting proportion of degraded state reports differed across the scales. Consequently, we argue that the decision of whether the form of consciousness observed in a given study is dichotomous or graded is dependent on an interpretation of the relative degree of degradation.     

Subjective visibility depends on level of processing

Is visual awareness graded or binary? Experimental work has provided support for both possibilities, leading to two coexisting but contradictory theoretical accounts. Here we propose a promising candidate factor through which to integrate both accounts: the depth of stimulus processing required by the task. We compared color identification (a low-level task) with numerical judgements (a high-level task) performed on the very same colored number stimuli. Psychophysical curves were analyzed for both objective discrimination performance and subjective visibility ratings on a trial-by trial basis. We observed a graded relationship between stimulus duration and visibility in the low-level task, but a more non-linear relationship in the high-level task. Both patterns of results have previously been consistently associated with the graded and the dichotomous account, respectively. Follow-up experiments that manipulate the level of processing can further unify previously inconsistent results, thus integrating two major theories of visual awareness.     

The role of levels of processing in disentangling the ERP signatures of conscious visual processing

We aimed to distinguish electrophysiological signatures of visual awareness from other task-related processes through manipulating the level of processing of visual stimuli. During an event-related EEG experiment, 36 subjects performed either color (low-level condition) or magnitude (high-level condition) evaluations of masked digits. Participants also assessed subjective visibility of each stimulus using the Perceptual Awareness Scale (PAS). Mean amplitude of the components of interest was analyzed (VAN − 140–240 ms; LP − 380–480 ms) with weighted regression mixed model. In the VAN component time window the mean amplitude correlated with PAS rating in both conditions. Mean amplitude in the LP time window correlated with PAS ratings in the high-level condition, but not in the low-level condition. Our results support the temporal unfolding of ERP makers of conscious processing, with an early component reflecting the initial perceptual experience and a late component being a correlate of the conscious experience of non-perceptual information.     

Conscious awareness is required for holistic face processing

Investigating the limits of unconscious processing is essential to understand the function of consciousness. Here, we explored whether holistic face processing, a mechanism believed to be important for face processing in general, can be accomplished unconsciously. Using a novel “eyes-face” stimulus we tested whether discrimination of pairs of eyes was influenced by the surrounding face context. While the eyes were fully visible, the faces that provided context could be rendered invisible through continuous flash suppression. Two experiments with three different sets of face stimuli and a subliminal learning procedure converged to show that invisible faces did not influence perception of visible eyes. In contrast, surrounding faces, when they were clearly visible, strongly influenced perception of the eyes. Thus, we conclude that conscious awareness might be a prerequisite for holistic face processing.     

Balancing awareness: Vestibular signals modulate visual consciousness in the absence of awareness

The processing of visual and vestibular information is crucial for perceiving self-motion. Visual cues, such as optic flow, have been shown to induce and alter vestibular percepts, yet the role of vestibular information in shaping visual awareness remains unclear. Here we investigated if vestibular signals influence the access to awareness of invisible visual signals. Using natural vestibular stimulation (passive yaw rotations) on a vestibular self-motion platform, and optic flow masked through continuous flash suppression (CFS) we tested if congruent visual–vestibular information would break interocular suppression more rapidly than incongruent information. We found that when the unseen optic flow was congruent with the vestibular signals perceptual suppression as quantified with the CFS paradigm was broken more rapidly than when it was incongruent. We argue that vestibular signals impact the formation of visual awareness through enhanced access to awareness for congruent multisensory stimulation.     

A dissociation between selective attention and conscious awareness in the representation of temporal order information

Previous electrophysiological studies have shown that attentional selection processes are highly sensitive to the temporal order of task-relevant visual events. When two successively presented colour-defined target stimuli are separated by a stimulus onset asynchrony (SOA) of only 10 ms, the onset latencies of N2pc components to these stimuli (which reflect their attentional selection) precisely match their objective temporal separation. We tested whether such small onset differences are accessible to conscious awareness by instructing participants to report the category (letter or digit) of the first of two target-colour items that were separated by an SOA of 10, 20, or 30 ms. Performance was at chance level for the 10 ms SOA, demonstrating that temporal order information which is available to attentional control processes cannot be utilized for conscious temporal order judgments. These results provide new evidence that selective attention and conscious awareness are functionally separable, and support the hypothesis that attention and awareness operate at different stages of cognitive processing.     

Different subjective awareness measures demonstrate the influence of visual identification on perceptual awareness ratings

We compare four subjective awareness measures in the context of a visual identification task and investigate quantitative differences in terms of scale use and correlation with task performance. We also analyse the effect of identification task decisions on subsequent subjective reports. Results show that awareness ratings strongly predict accuracy for all scale types, although the type of awareness measure may influence the reported level of perceptual awareness. Surprisingly, the overall relationship between awareness ratings and performance was weaker when participants rated their awareness before providing identification responses. Furthermore, the Perceptual Awareness Scale was most exhaustive only when used after the identification task, whereas confidence ratings were most exhaustive when used before the identification task. We conclude that the type of subjective measure applied may influence the reports on visual awareness. We also propose that identification task decisions may affect subsequent awareness ratings.     

Emotion regulation and emotional information processing: The moderating effect of emotional awareness

The aim of this study was to examine the moderating role of emotional awareness in the relationship between emotion regulation strategies and emotional information processing. A total of 120 female students regulated emotions while watching an unpleasant film. Before and after emotion induction, participants completed a set of tasks that required matching facial expressions. The results demonstrated that participants who were high in emotional awareness showed a significantly smaller increase in error responses (i.e., incorrect matches) than participants who were low in emotional awareness. However, this effect was observed only in suppression (i.e., inhibition of an emotionally expressive behavior), masking (i.e., emotion experienced with a happy expression) and control (i.e., no regulation) conditions. Among reappraisers, who were instructed to adopt a neutral attitude toward the film, regardless of whether they were high or low in emotional awareness, there was not a significant increase in error responses. This study shows that the potentially damaging impact of negative emotions on the processing of emotional information can be prevented by a high emotional awareness or with the implementation of reappraisal as an emotion regulation strategy.     

Integrating the global neuronal workspace into the framework of predictive processing: Towards a working hypothesis

Hohwy (2013) proposed an account of conscious access that integrates the global neuronal workspace (GNW) into the framework of predictive processing, a view that I term the predictive global neuronal workspace (PGNW). Whilst promising, the PGNW is theoretically underdeveloped and empirically underexplored. The aim of this article is to outline the empirical predictions that distinguish the PGNW from other workspace models. I do so by (i) placing the PGNW in close contact with experimental work and cashing out a set of predictions that distinguish it from the standard formulation of the GNW, (ii) exploring the evidence for the first of these predictions in the context of bistable perception and the conscious processing of auditory regularities, and (iii), contrasting the PGNW with Chanes and Barrett (2016) limbic workspace. Combined, these arguments show that the PGNW is both testable and supported by current evidence.     

Finding ERP-signatures of target awareness: Puzzle persists because of experimental co-variation of the objective and subjective variables

Using masking techniques combined with electrophysiological recordings is a promising way to study neural correlates of visual awareness, as shown in recent studies. Here I comment on the following puzzling aspects typical for this endeavour that have made obstacles for a potentially even more impressive progress. First, the continuing practice of confounds between objective stimulus variables and subjective dependent measures. Second, complexity of timing the emergence of subjective conscious percept which is partly due to complex interactivity between target and mask. Third, the ambiguity of the concept of neural correlates of awareness.     

A critical review of the physicalistic approaches of the mind and consciousness

The aim of this paper is to construct a critical evaluation of the advantages and disadvantages of the physicalistic theory concerning mental phenomena and consciousness. Physicalism can, better than other theories, explain mental phenomena, such as intentionality and reasonability of human beings and other biological organisms. Modern neuroscience corroborates the conviction that the brain is a physical mind capable of giving meaning to, evaluating and further cognitively and behaviorally transforming complex aspects of the world. On the other hand, the emergence of consciousness from brain states seems to be a paradoxical, intransparent, physical coincidence hardly explained by the mental function of the brain at the physical level. Moreover, the intentionality and reasonability of psychic phenomena per se cannot be explained as a repercussion of the same attributes characterizing the brain function. In conclusion, the old debate between physicalism and other philosophical theories remains open. It can be expected that the progress of sciences will inspire novel approaches to the problem of the relations between matter, mind and consciousness.     

Motion-induced blindness does not affect the formation of negative afterimages

Aftereffects induced by invisible stimuli constitute a powerful tool to investigate what type of neural information processing can occur in the absence of visual awareness. This approach has been successfully used to demonstrate that awareness of oriented gratings or translating stimuli is not necessary to obtain a robust orientation-specific or motion-specific aftereffect. We exploit motion-induced blindness (MIB, Bonneh, Cooperman, & Sagi, 2001) to investigate the related question of the influence of visual awareness on the formation of negative afterimages. Our results show that MIB does not affect the persistence and intensity of afterimages. Thus, there is no significant contribution to the formation of afterimages beyond the sites mediating MIB.     

Retention of word pairs as a function of level of processing,instruction to remember,and delay

ABSTRACT

Modern research on the efficacy of levels of processing (LoP) tasks on memory has focused on less than 1-day retention delays, while assuming that the observed benefits of deep tasks will continue across remote delays. However, direct tests of the continued benefits of deep processes for accuracy and organisation in remote memory are rare. The current set of experiments, using auditorily-presented lists of scrambled word pairs, tested whether deep LoP tasks produced better free recall and organisation over one week (Experiment 1) and four weeks (Experiments 2 and 3). All experiments revealed significant LoP effects on free recall and organisation at immediate and delayed test, with no effect of intention to remember. However, Experiments 2 and 3 revealed poor recall and organisation at the delayed tests among all of the LoP groups, suggesting that deep processing may not produce highly accessible memories over very long delays.     

Tracking the processes behind conscious perception: a review of event-related potential correlates of visual consciousness

Event-related potential (ERP) studies have attempted to discover the processes that underlie conscious visual perception by contrasting ERPs produced by stimuli that are consciously perceived with those that are not. Variability of the proposed ERP correlates of consciousness is considerable: the earliest proposed ERP correlate of consciousness (P1) coincides with sensory processes and the last one (P3) marks postperceptual processes. A negative difference wave called visual awareness negativity (VAN), typically observed around 200 ms after stimulus onset in occipitotemporal sites, gains strong support for reflecting the processes that correlate with, and possibly enable, aware visual perception. Research suggests that the early parts of conscious processing can proceed independently of top-down attention, although top-down attention may modulate visual processing even before consciousness. Evidence implies that the contents of consciousness are provided by interactions in the ventral stream, but indispensable contributions from dorsal regions influence already low-level visual responses.     

On the signals underlying conscious awareness of action

To investigate whether conscious judgments of movement onset are based solely on pre-movement signals (i.e., premotor or efference copy signals) or whether sensory feedback (i.e., reafferent) signals also play a role, participants judged the onset of finger and toe movements that were either active (i.e., self initiated) or passive (i.e., initiated by the experimenter). Conscious judgments were made by reporting the position of a rotating clock hand presented on a computer screen and were then compared to the actual measured time of movement onset. In line with previous studies, judgment errors were found to be anticipatory for both finger and toe movements. There was a significant difference between judgment errors for active and passive movements, with judgments of active movements being more anticipatory than judgments of passive movements. This is consistent with a pre-movement (from here on referred to as an “efferent”) account of action awareness because premotor and efference copy signals are only present in active movements, whereas the main source of movement information in passive movements is sensory feedback which is subject to time delays of conduction (and hence predicts later judgment times for passive movements). However, judgments of active toe movement onset time were less anticipatory than judgments of active finger movement onset time. This pattern of results is not consistent with a pure efferent account of conscious awareness of action onset - as this account predicts more anticipatory judgments for toe movements compared to finger movements. Instead, the data support the idea that conscious judgments of movement onset are based on efferent (i.e., premotor, efference copy) and reafferent (i.e., feedback from the movement) components.     

Inverse zombies, anesthesia awareness, and the hard problem of unconsciousness

Philosophical (p-) zombies are constructs that possess all of the behavioral features and responses of a sentient human being, yet are not conscious. P-zombies are intimately linked to the hard problem of consciousness and have been invoked as arguments against physicalist approaches. But what if we were to invert the characteristics of p-zombies? Such an inverse (i-) zombie would possess all of the behavioral features and responses of an insensate being, yet would nonetheless be conscious. While p-zombies are logically possible but naturally improbable, an approximation of i-zombies actually exists: individuals experiencing what is referred to as "anesthesia awareness." Patients under general anesthesia may be intubated (preventing speech), paralyzed (preventing movement), and narcotized (minimizing response to nociceptive stimuli). Thus, they appear--and typically are--unconscious. In 1-2 cases/1000, however, patients may be aware of intraoperative events, sometimes without any objective indices. Furthermore, a much higher percentage of patients (22% in a recent study) may have the subjective experience of dreaming during general anesthesia. P-zombies confront us with the hard problem of consciousness--how do we explain the presence of qualia? I-zombies present a more practical problem--how do we detect the presence of qualia? The current investigation compares p-zombies to i-zombies and explores the "hard problem" of unconsciousness with a focus on anesthesia awareness.