Neural Correlates Of Visual Awareness Research Articles

Neural Correlates of Motion-induced Blindness in the Human Brain

Motion-induced blindness (MIB) is a visual phenomenon in which highly salient visual targets spontaneously disappear from visual awareness (and subsequently reappear) when superimposed on a moving background of distracters. Such fluctuations in awareness of the targets, although they remain physically present, provide an ideal paradigm to study the neural correlates of visual awareness. Existing behavioral data on MIB are consistent both with a role for structures early in visual processing and with involvement of high-level visual processes. To further investigate this issue, we used high field functional MRI to investigate signals in human low-level visual cortex and motion-sensitive area V5/MT while participants reported disappearance and reappearance of an MIB target. Surprisingly, perceptual invisibility of the target was coupled to an increase in activity in low-level visual cortex plus area V5/MT compared with when the target was visible. This increase was largest in retinotopic regions representing the target location. One possibility is that our findings result from an active process of completion of the field of distracters that acts locally in the visual cortex, coupled to a more global process that facilitates invisibility in general visual cortex. Our findings show that the earliest anatomical stages of human visual cortical processing are implicated in MIB, as with other forms of bistable perception.

Neural correlates of motion-induced blindness in the human brain

Motion-induced blindness (MIB) is a visual phenomenon in which highly salient visual targets spontaneously disappear from visual awareness (and subsequently reappear) when superimposed on a moving background of distracters. Such fluctuations in awareness of the targets, although they remain physically present, provide an ideal paradigm to study the neural correlates of visual awareness. Existing behavioral data on MIB are consistent both with a role for structures early in visual processing and with involvement of high-level visual processes. To further investigate this issue, we used high field functional MRI to investigate signals in human low-level visual cortex and motion-sensitive area V5/MT while participants reported disappearance and reappearance of an MIB target. Surprisingly, perceptual invisibility of the target was coupled to an increase in activity in low-level visual cortex plus area V5/MT compared with when the target was visible. This increase was largest in retinotopic regions representing the target location. One possibility is that our findings result from an active process of completion of the field of distracters that acts locally in the visual cortex, coupled to a more global process that facilitates invisibility in general visual cortex. Our findings show that the earliest anatomical stages of human visual cortical processing are implicated in MIB, as with other forms of bistable perception.

Neural correlate of visual awareness in the superior colliculus of the animal model of blindsight

Neural correlate of visual awareness in the superior colliculus of the animal model of blindsight

Neural dissociation between visual awareness and spatial attention

To what extent does what we consciously see depend on where we attend to? Psychologists have long stressed the tight relationship between visual awareness and spatial attention at the behavioral level. However, the amount of overlap between their neural correlates remains a matter of debate. We recorded magnetoencephalographic signals while human subjects attended toward or away from faint stimuli that were reported as consciously seen only half of the time. Visually identical stimuli could thus be attended or not and consciously seen or not. Although attended stimuli were consciously seen slightly more often than unattended ones, the factorial analysis of stimulus-induced oscillatory brain activity revealed distinct and independent neural correlates of visual awareness and spatial attention at different frequencies in the gamma range (30-150 Hz). Whether attended or not, consciously seen stimuli induced increased mid-frequency gamma-band activity over the contralateral visual cortex, whereas spatial attention modulated high-frequency gamma-band activity in response to both consciously seen and unseen stimuli. A parametric analysis of the data at the single-trial level confirmed that the awareness-related mid-frequency activity drove the seen-unseen decision but also revealed a small influence of the attention-related high-frequency activity on the decision. These results suggest that subjective visual experience is shaped by the cumulative contribution of two processes operating independently at the neural level, one reflecting visual awareness per se and the other reflecting spatial attention.

Covert spatial attention in search for the location of a color-afterimage patch speeds up its decay from awareness: Introducing a method useful for the study of neural correlates of visual awareness

Previous research has reported that attention to color afterimages speeds up their decay. However, the inducing stimuli in these studies have been overlapping, thereby implying that they involved overlapping receptive fields of the responsible neurons. As a result it is difficult to interpret the effect of focusing attention on a phenomenally projected target-afterimage. Here, we present a method free from these shortcomings. In searching for a target-afterimage patch among spatially separate alternatives the target fades from awareness before its competitors. This offers a good means to study neural correlates of visual awareness unconfounded with attention and enabling a temporally extended pure phenomenal experience free from simultaneous inflow of sensory transients.

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.

The N2pc as an Electrophysiological Correlate of Attention in Change Blindness

Changes between two successively presented pictures are hard to detect when their presentation is interrupted by a blank (change blindness). This task is well established for investigating the neural correlates of visual awareness. It allows the comparison of electrophysiological activity evoked by physically identical trials in which the change was detected versus trials in which the change remained unnoticed. One possible correlate of aware processing is the N2pc component, an increased negative activity, contralateral to a processed stimulus between 200–300 ms after stimulus onset. However, this component has been also assigned to the allocation of attention. In two experiments, an N2pc was observed for detected changes. This component was markedly reduced for undetected changes and even more if participants reported a change that was not present (imagined change). These results suggest that the N2pc rather reflects attentional processing of stimuli in visual cortical areas than the actual aware representation.

Neural correlates of visual awareness following binocular rivalry start at different times for different stimulus dimensions

Event Abstract Back to Event Neural correlates of visual awareness following binocular rivalry start at different times for different stimulus dimensions Sandra Veser1* and U. Roeber1 1 University of Leipzig, Germany During binocular rivalry, a supra-threshold stimulus presented to one eye intermittently disappears for several seconds. In order to explore the fate of such an invisible stimulus, we investigated neural activity following transitions from binocular rivalry stimuli to binocular fusion stimuli by changing the stimulus viewed by one eye. Depending on the prevailing percept, these changes either elicited a change in perception or did not. This procedure allowed for time-locked event-related potential analyses to physically identical events differing in their perceptual consequences. When a stimulus changed without awareness, similar but attenuated neural responses were found compared to when a stimulus changed with awareness. The onset of the attenuation, however, differed depending on the specific stimulus dimension that was changed: with changes in stimulus orientation or shape awareness-dependent modulations began at about 100 ms (P1), with changes in color at about 200 ms (N1), and with changes in motion at about 220 ms (P2). Despite the differences in onset times, source activity correlated with perception for all changes was in similar ventro-lateral occipito-temporal networks. This suggests that visual awareness is mediated by dimension-unspecific superior cortical areas but its effects follow a dimension-specific time-course. This research was supported by the German Research Foundation (DFG grant no. RO 3061/1-2). Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Oral Presentation Topic: Symposium 11: Visual consciousness at different levels of the brain Citation: Veser S and Roeber U (2008). Neural correlates of visual awareness following binocular rivalry start at different times for different stimulus dimensions. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.050 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Nov 2008; Published Online: 27 Nov 2008. * Correspondence: Sandra Veser, University of Leipzig, Leipzig, Germany, urte@uni-leipzig.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Sandra Veser U. Roeber Google Sandra Veser U. Roeber Google Scholar Sandra Veser U. Roeber PubMed Sandra Veser U. Roeber Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Visual Cortex Allows Prediction of Perceptual States during Ambiguous Structure-From-Motion

We investigated the role of retinotopic visual cortex and motion-sensitive areas in representing the content of visual awareness during ambiguous structure-from-motion (SFM), using functional magnetic resonance imaging (fMRI) and multivariate statistics (support vector machines). Our results indicate that prediction of perceptual states can be very accurate for data taken from dorsal visual areas V3A, V4D, V7, and MT+ and for parietal areas responsive to SFM, but to a lesser extent for other visual areas. Generalization of prediction was possible, because prediction accuracy was significantly better than chance for both an unambiguous stimulus and a different experimental design. Detailed analysis of eye movements revealed that strategic and even encouraged beneficial eye movements were not the cause of the prediction accuracy based on cortical activation. We conclude that during perceptual rivalry, neural correlates of visual awareness can be found in retinotopic visual cortex, MT+, and parietal cortex. We argue that the organization of specific motion-sensitive neurons creates detectable biases in the preferred direction selectivity of voxels, allowing prediction of perceptual states. During perceptual rivalry, retinotopic visual cortex, in particular higher-tier dorsal areas like V3A and V7, actively represents the content the visual awareness.

Decoding Near-Threshold Perception of Fear from Distributed Single-Trial Brain Activation

Instead of contrasting functional magnetic resonance imaging (fMRI) signals associated with 2 conditions, as customarily done in neuroimaging, we reversed the direction of analysis and probed whether brain signals could be used to "predict" perceptual states. We probed the neural correlates of perceptual decisions by "decoding" brain states during near-threshold fear detection. Decoding was attempted by using support vector machines and other related techniques. Although previous decoding studies have employed relatively "blocked" data, our objective was to probe how the "moment-to-moment" fluctuation in fMRI signals across a population of voxels reflected the participant's perceptual decision. Accuracy increased from when 1 region was considered (approximately 64%) to when 10 regions were used (approximately 78%). When the best classifications per subject were averaged, accuracy levels ranged between 74% and 86% correct. An information theoretic analysis revealed that the information carried by pairs of regions reliably exceeded the sum of the information carried by individual regions, suggesting that information was combined "synergistically" across regions. Our results indicate that the representation of behavioral choice is "distributed" across several brain regions. Such distributed encoding may help prepare the organism to appropriately handle emotional stimuli and regulate the associated emotional response upon the conscious decision that a fearful face is present. In addition, the results show that challenging brain states can be decoded with high accuracy even when "single-trial" data are employed and suggest that multivariate analysis strategies have considerable potential in helping to elucidate the neural correlates of visual awareness and the encoding of perceptual decisions.

Precuneus–Prefrontal Activity during Awareness of Visual Verbal Stimuli

Awareness is a personal experience, which is only accessible to the rest of world through interpretation. We set out to identify a neural correlate of visual awareness, using brief subliminal and supraliminal verbal stimuli while measuring cerebral blood flow distribution with H215O PET. Awareness of visual verbal stimuli differentially activated medial parietal association cortex (precuneus), which is a polymodal sensory cortex, and dorsolateral prefrontal cortex, which is thought to be primarily executive. Our results suggest participation of these higher order perceptual and executive cortical structures in visual verbal awareness.

The role of primary visual cortex (V1) in visual awareness

In the search for the neural correlate of visual awareness, much controversy exists about the role of primary visual cortex. Here, the neurophysiological data from V1 recordings in awake monkeys are examined in light of two general classes of models of visual awareness. In the first model type, visual awareness is seen as being mediated either by a particular set of areas or pathways, or alternatively by a specific set of neurons. In these models, the role of V1 seems rather limited, as the mere activity of V1 cells seems insufficient to mediate awareness. In the second model type, awareness is hypothesized to be mediated by a global mechanism, i.e. a specific kind of activity not linked to a particular area or cell type. Two separate versions of global models are discussed, synchronous oscillations and spike rate modulations. It is shown that V1 synchrony does not reflect perception but rather the horizontal connections between neurons, indicating that V1 synchrony cannot be a direct neural correlate of conscious percepts. However, the rate of spike discharges of V1 neurons is strongly modulated by perceptual context, and these modulations correlate very well with aspects of perceptual organization, visual awareness, and attention. If these modulations serve as a neural correlate of visual awareness, then V1 contributes to that neural correlate. Whether V1 plays a role in the neural correlate of visual awareness thus strongly depends on the way visual awareness is hypothesized to be implemented in the brain.

Alpha-band oscillations in visual cortex: part of the neural correlate of visual awareness?

It was originally proposed that synchronized gamma-band oscillations in neurons of the visual cortex constitute the neural correlate of visual awareness. Two hypotheses are presented in this article: (a) both alpha-band and gamma-band oscillatory activity correspond to visual awareness; and (b) alpha-band activity occurs in the parvocellular processing pathway and gamma-band activity occurs in the magnocellular pathway, and the two modes of oscillation are correlated. It is further proposed that the frequency of the gamma-band oscillation in a group of neurons representing a particular visual scene segment is three times that of the alpha-band oscillation in the neurons representing the same segment. These hypotheses are discussed in relation to recent neurophysiological and psychophysiological experiments.

Rival ideas about binocular rivalry

Binocular rivalry has been used to investigate neural correlates of visual awareness. For this investigation to succeed, however, it is necessary to know what rivals during binocular rivalry. Recent work has raised questions about whether rivalry is between eyes or between stimuli. We find that stimulus rivalry occurs only within a limited range of spatial and temporal parameters—otherwise eye rivalry dominates.

On the neural correlates of visual perception.

Neurological findings suggest that the human striate cortex (V1) is an indispensable component of a neural substratum subserving static achromatic form perception in its own right and not simply as a central distributor of retinally derived information to extrastriate visual areas. This view is further supported by physiological evidence in primates that the finest-grained conjoined representation of spatial detail and retinotopic localization that underlies phenomenal visual experience for local brightness discriminations is selectively represented at cortical levels by the activity of certain neurons in V1. However, at first glance, support for these ideas would appear to be undermined by incontrovertible neurological evidence (visual hemineglect and the simultanagnosias) and recent psychophysical results on 'crowding' that confirm that activation of neurons in V1 may, at times, be insufficient to generate a percept. Moreover, a recent proposal suggests that neural correlates of visual awareness must project directly to those in executive space, thus automatically excluding V1 from a related perceptual space because V1 lacks such direct projections. Both sets of concerns are, however, resolved within the context of adaptive resonance theories. Recursive loops, linking the dorsal lateral geniculate nucleus (LGN) through successive cortical visual areas to the temporal lobe by means of a series of ascending and descending pathways, provide a neuronal substratum at each level within a modular framework for mutually consistent descriptions of sensory data. At steady state, such networks obviate the necessity that neural correlates of visual experience project directly to those in executive space because a neural phenomenal perceptual space subserving form vision is continuously updated by information from an object recognition space equivalent to that destined to reach executive space. Within this framework, activity in V1 may engender percepts that accompany figure-ground segregations only when dynamic incongruities are resolved both within and between ascending and descending streams. Synchronous neuronal activity on a short timescale within and across cortical areas, proposed and sometimes observed as perceptual correlates, may also serve as a marker that a steady state has been achieved, which, in turn, may be a requirement for the longer time constants that accompany the emergence and stability of perceptual states compared to the faster dynamics of adapting networks and the still faster dynamics of individual action potentials. Finally, the same consensus of neuronal activity across ascending and descending pathways linking multiple cortical areas that in anatomic sequence subserve phenomenal visual experiences and object recognition may underlie the normal unity of conscious experience.

Vision comes to mind.

An overview is presented in which visual awareness is regarded as the epitome of the general mind-body problem. An experimental solution of the problem is considered first, followed by a philosophical outlook. It is argued that the scientific approach may eventually discover the neural correlate of visual awareness, but visual perceptions, even simple qualia like 'brightness' or 'color', occur in the mind of a conscious observer and are not reducible to observable activity of a specific set of neurons in the brain.