Visual Consciousness Research Articles

Brief review of event-related potential correlates of visual consciousness and related studies

Studies of human consciousness (especially visual consciousness) have been increased rapidly during the last decade, including those employ a wide range of paradigms such as masking, binocular rivalry, attentional blink, and change blindness and various methods such as behavior, ERP (event-related potential) and fMRI (functional Magnatic Resonance Imaging). The present paper reviewed the ERP studies that aimed to explore the neural correlates of visual consciousness and briefly introduced the ERP correlates of visual consciousness. Three primary ERP correlates of visual consciousness were introduced: the P1 around 100 ms after stimulus onset, a negativity around 200 ms (visual awareness negativity, VAN), and the late positivity (LP) in the P3 time window. Researches have shown that the amplitudes of ERP evoked by conscious stimuli are significantly larger than that evoked by unconscious stimuli on these three components. Relevant researches were briefly introduced and several research directions and ideas for future studies were proposed from the point of views of the relationship between various attention components and consciousness, the relationship between C1 component and consciousness, the ERP research on high-order consciousness, and the factors affecting the time course of visual consciousness.

Los dioses tienen sed: reflexión sobre Proyecto Ruanda de Alfredo Jaar

The following article focuses on the iconic procedures used by Alfredo Jaar (Santiago, 1956) in his huge artpiece The Rwanda Project, a work-in-progress exhibited since 1994, which states the disaster of heartless violence in Rwanda’s genocide. Our objective is to understand the rethoric processes in Jaar’s work, its functions and how they are adressed to the visual consciousness of the audience by means of total or partial concealing of images, using sequential narratives or scenographic appeal on great scale installations, or by evocation of literary memories.

Causal Contributions of the Left Frontal Eye Field to Conscious Perception

The quest for the neural correlates of consciousness has led to controversial results. When contrasting consciously seen versus unseen stimuli, some authors have proposed that consciousness is related to activity in visual areas along the ventral cortical visual stream, while others propose the implication of parietal and frontal regions ( Dehaene and Changeux 2011). When invisibility is caused by neglect or inattention, high levels of activity recorded in early visual areas ( Vuilleumier et al. 2001) suggest that further activity in fronto-parietal regions might be necessary for conscious perception. Recent functional magnetic resonance imaging evidence ( Chica, Paz-Alonso, et al. 2012) suggested a key role for the left frontal eye field (FEF) in the attentional modulation of visual consciousness. Here, we used the high temporal resolution and causal power of event-related transcranial magnetic stimulation to explore the causal contributions of the left FEF on conscious perception and to assess whether or not these effects are mediated by the orienting of spatial attention. Our results provide the first causal evidence on the contribution of the left FEF to conscious visual perception and indicate that such effects are likely to be mediated by its known role on attentional orienting.

S6-5: Visual Consciousness Tracked with Direct Intracranial Recording from Early and High-Level Visual Cortices in Humans and Monkeys

S6-5: Visual Consciousness Tracked with Direct Intracranial Recording from Early and High-Level Visual Cortices in Humans and Monkeys

Manipulation of the extrastriate frontal loop can resolve visual disability in blindsight patients

Patients with blindsight are not consciously aware of visual stimuli in the affected field of vision but retain nonconscious perception. This disability can be resolved if nonconsciously perceived information can be brought to their conscious awareness. It can be accomplished by manipulating neural network of visual awareness. To understand this network, we studied the pattern of cortical activity elicited during processing of visual stimuli with or without conscious awareness. The analysis indicated that a re-entrant signaling loop between the area V3A (located in the extrastriate cortex) and the frontal cortex is critical for processing conscious awareness. The loop is activated by visual signals relayed in the primary visual cortex, which is damaged in blindsight patients. Because of the damage, V3A-frontal loop is not activated and the signals are not processed for conscious awareness. These patients however continue to receive visual signals through the lateral geniculate nucleus. Since these signals do not activate the V3A-frontal loop, the stimuli are not consciously perceived. If visual input from the lateral geniculate nucleus is appropriately manipulated and made to activate the V3A-frontal loop, blindsight patients can regain conscious vision.

AD 5 The illusion of seeing

J Kevin O9Regan, Laboratoire Psychologie de la Perception, Centre National de Recherche Scientifique, Institut Paris Descartes de Neurosciences et Cognition, 45, rue des Saints Peres, 75270 Paris cedex 06, France. I am director of the Laboratoire Psychologie de la Perception, which specialises in human visual and auditory perception both in babies and adults. Thanks to my co-directors Jacqueline Fagard and Andrei Gorea, and also thanks to the team leaders and technical and administrative staff, we manage to effectively run our rather large lab: it has about 80 members, of which 25 are permanent researchers, 7 are technical and administrative personnel, plus about 45 doctoral and postdoctoral students and visitors. The lab occupies about 800 m 2 at the Institute of Neuroscience and Cognition of Paris Descartes University, at the Saints Peres Biomedical Center. The lab also has space at the Departement d9Etudes Cognitives of Ecole Normale Superieure. It is co-financed by the Centre National de Recherche Scientifique and Universite Paris Descartes. Change blindness is a much studied phenomenon in experimental psychology where under certain conditions an observer will not see a very large change that occurs in a scene, in an image or in a movie. Inattentional blindness is another phenomenon which is at the root of “looked but failed to see” traffic accidents, where for example a driver is looking directly at a motorcycle driving across his field of view, but still crashes into it. I shall provide demonstrations of these phenomena and show how they can be explained by assuming that our impression of a complete, rich, detailed outside visual world is actually in some sense an “illusion”, caused by the fact that any information we wish to obtain is immediately attainable through a flick of the eye or of attention. Developing this idea further has led me to a theory of visual consciousness, and indeed consciousness in general, that I have described in a recent book (“Why red doesn9t sound like a bell: Understanding the feel of consciousness”, OUP 2011).

Balancing bistable perception during self-motion

In two experiments we investigated whether bistable visual perception is influenced by passive own body displacements due to vestibular stimulation. For this we passively rotated our participants around the vertical (yaw) axis while observing different rotating bistable stimuli (bodily or non-bodily) with different ambiguous motion directions. Based on previous work on multimodal effects on bistable perception, we hypothesized that vestibular stimulation should alter bistable perception and that the effects should differ for bodily versus non-bodily stimuli. In the first experiment, it was found that the rotation bias (i.e., the difference between the percentage of time that a CW or CCW rotation was perceived) was selectively modulated by vestibular stimulation: the perceived duration of the bodily stimuli was longer for the rotation direction congruent with the subject's own body rotation, whereas the opposite was true for the non-bodily stimulus (Necker cube). The results found in the second experiment extend the findings from the first experiment and show that these vestibular effects on bistable perception only occur when the axis of rotation of the bodily stimulus matches the axis of passive own body rotation. These findings indicate that the effect of vestibular stimulation on the rotation bias depends on the stimulus that is presented and the rotation axis of the stimulus. Although most studies on vestibular processing have traditionally focused on multisensory signal integration for posture, balance, and heading direction, the present data show that vestibular self-motion influences the perception of bistable bodily stimuli revealing the importance of vestibular mechanisms for visual consciousness.

Neuronal Discharges and Gamma Oscillations Explicitly Reflect Visual Consciousness in the Lateral Prefrontal Cortex

Neuronal discharges in the primate temporal lobe, but not in the striate and extrastriate cortex, reliably reflect stimulus awareness. However, it is not clear whether visual consciousness should be uniquely localized in the temporal association cortex. Here we used binocular flash suppression to investigate whether visual awareness is also explicitly reflected in feature-selective neural activity of the macaque lateral prefrontal cortex (LPFC), a cortical area reciprocally connected to the temporal lobe. We show that neuronal discharges in the majority of single units and recording sites in the LPFC follow the phenomenal perception of a preferred stimulus. Furthermore, visual awareness is reliably reflected in the power modulation of high-frequency (>50Hz) local field potentials in sites where spiking activity is found to be perceptually modulated. Our results suggest that the activity of neuronal populations in at least two association cortical areas represents the content of conscious visual perception.

Pathways involved in human conscious vision contribute to obstacle‐avoidance behaviour

Human patients with visual field defects following damage to their primary visual cortex (V1) will often misperceive the midpoint of a horizontal line. They tend to shift the midpoint away from the real position towards their blind field. In patients with unilateral neglect, where midpoint shifts can also be observed, these perceptual errors do not lead to errors in an obstacle-avoidance task, which also requires the ability to find the midpoint between two obstacles. This dissociation in neglect patients was taken as evidence that obstacle-avoidance performance is guided by visual information from the dorsal visual stream. Recently it was shown that a patient with hemianopia could avoid an obstacle presented in his blind field. This suggests that obstacle-avoidance behaviour can be guided by subconscious vision alone involving a direct route from extrageniculate structures in the brain to dorsal stream areas. To investigate whether obstacle avoidance relies only on this subconscious route or also uses information from pathways involved in conscious vision, we examined the effect of the hemianopic shift on obstacle-avoidance behaviour. This shift is found in tasks where a conscious visual judgement is required and presumably arises in pathways underlying conscious vision (V1 and ventral stream areas). We compared the performance of six patients with left hemianopia with the performance of six patients with right hemianopia. We found a clear bias in both groups, which also affected obstacle-avoidance performance. It is thus concluded that obstacle avoidance does not bypass the system for conscious vision completely.

Manipulation of Pre-Target Activity on the Right Frontal Eye Field Enhances Conscious Visual Perception in Humans

The right Frontal Eye Field (FEF) is a region of the human brain, which has been consistently involved in visuo-spatial attention and access to consciousness. Nonetheless, the extent of this cortical site’s ability to influence specific aspects of visual performance remains debated. We hereby manipulated pre-target activity on the right FEF and explored its influence on the detection and categorization of low-contrast near-threshold visual stimuli. Our data show that pre-target frontal neurostimulation has the potential when used alone to induce enhancements of conscious visual detection. More interestingly, when FEF stimulation was combined with visuo-spatial cues, improvements remained present only for trials in which the cue correctly predicted the location of the subsequent target. Our data provide evidence for the causal role of the right FEF pre-target activity in the modulation of human conscious vision and reveal the dependence of such neurostimulatory effects on the state of activity set up by cue validity in the dorsal attentional orienting network.

GABAA Agonist Reduces Visual Awareness: A Masking–EEG Experiment

Consciousness can be manipulated in many ways. Here, we seek to understand whether two such ways, visual masking and pharmacological intervention, share a common pathway in manipulating visual consciousness. We recorded EEG from human participants who performed a backward-masking task in which they had to detect a masked figure form its background (masking strength was varied across trials). In a within-subject design, participants received dextromethorphan (a N-methyl-d-aspartate receptor antagonist), lorazepam (LZP; a GABA(A) receptor agonist), scopolamine (a muscarine receptor antagonist), or placebo. The behavioral results show that detection rate decreased with increasing masking strength and that of all the drugs, only LZP induced a further decrease in detection rate. Figure-related ERP signals showed three neural events of interest: (1) an early posterior occipital and temporal generator (94-121 msec) that was not influenced by any pharmacological manipulation nor by masking, (2) a later bilateral perioccipital generator (156-211 msec) that was reduced by masking as well as LZP (but not by any other drugs), and (3) a late bilateral occipital temporal generator (293-387 msec) that was mainly affected by masking. Crucially, only the intermediate neural event correlated with detection performance. In combination with previous findings, these results suggest that LZP and masking both reduce visual awareness by means of modulating late activity in the visual cortex but leave early activation intact. These findings provide the first evidence for a common mechanism for these two distinct ways of manipulating consciousness.

Which image is in awareness during binocular rivalry? Reading perceptual status from eye movements

Binocular rivalry is a useful psychophysical tool to investigate neural correlates of visual consciousness because the alternation between awareness of the left and right eye images occurs without any accompanying change in visual input. The conventional experiments on binocular rivalry require participants to voluntarily report their perceptual state. Obtaining reliable reports from non-human primates about their subjective visual experience, however, requires long-term training, which has made electrophysiological experiments on binocular rivalry quite difficult. Here, we developed a new binocular rivalry stimulus that consists of two different object images that are phase-shifted to move in opposite directions from each other: One eye receives leftward motion while the other eye receives rightward motion, although both eyes' images are perceived to remain at the same position. Experiments on adult human participants showed that eye movements (optokinetic nystagmus, OKN) are involuntarily evoked during the observation of our stimulus. We also found that the evoked OKN can serve as a cue for accurate estimation about which object image was dominant during rivalry, since OKN follows the motion associated with the image in awareness at a given time. This novel visual presentation technique enables us to effectively explore the neural correlates of visual awareness using animal models.

Trans-saccadic priming in hemianopia: Sighted-field sensitivity is boosted by a blind-field prime

We experience visual stability despite shifts of the visual array across the retina produced by eye movements. A process known as remapping is thought to keep track of the spatial locations of objects as they move on the retina. We explored remapping in damaged visual cortex by presenting a stimulus in the blind field of two patients with hemianopia. When they executed a saccadic eye movement that would bring the stimulated location into the sighted field, reported awareness of the stimulus increased, even though the stimulus was removed before the saccade began and so never actually fell in the sighted field. Moreover, when a location was primed by a blind-field stimulus and then brought into the sighted field by a saccade, detection sensitivity for near-threshold targets appearing at this location increased dramatically. The results demonstrate that brain areas supporting conscious vision are not necessary for remapping, and suggest visual stability is maintained for salient objects even when they are not consciously perceived.

Dissociable Neural Activations of Conscious Visibility and Attention

Recent neuroimaging evidence indicates that visual consciousness of objects is reflected by the activation in the lateral occipital cortex as well as in the frontal and parietal cortex. However, most previous studies used behavioral paradigms in which attention raised or enhanced visual consciousness (visibility or recognition performance). This co-occurrence made it difficult to reveal whether an observed cortical activation is related to visual consciousness or attention. The present fMRI study investigated the dissociability of neural activations underlying these two cognitive phenomena. Toward this aim, we used a visual backward masking paradigm in which directing attention could either enhance or reduce the object visibility. The participants' task was to report the level of subjective visibility for a briefly presented target object. The target was presented in the center with four flankers, which was followed by the same number of masks. Behavioral results showed that attention to the flankers enhanced the target visibility, whereas attention to the masks attenuated it. The fMRI results showed that the occipito-temporal sulcus increased activation in the attend flankers condition compared with the attend masks condition, and occipito-temporal sulcus activation levels positively correlated with the target visibility in both attentional conditions. On the other hand, the inferior frontal gyrus and the intraparietal sulcus increased activation in both the attend flankers and attend masks compared with an attend neither condition, and these activation levels were independent of target visibility. Taken together, present results showed a clear dissociation in neural activities between conscious visibility and attention.

Non-visual consciousness and visual images in blindsight

In a recent response paper to Brogaard (2011a), Morten Overgaard and Thor Grünbaum argue that my case for the claim that blindsight subjects are not visually conscious of the stimuli they correctly identify rests on a mistaken necessary criterion for determining whether a conscious experience is visual or non-visual. Here I elaborate on the earlier argument while conceding that the question of whether blindsight subjects are visually conscious of the visual stimuli they correctly identify largely is an empirical question. I conclude by sketching a method for testing whether blindsight subjects have visual consciousness of stimuli presented to them in their blind field.

Asynchrony in Visual Consciousness and the Possible Involvement of Attention

When subjects are asked to perceptually bind rapidly alternating color and motion stimuli, the pairings they report are different from the ones actually occurring in physical reality. A possible explanation for this misbinding is that the time necessary for perception is different for different visual attributes. Such an explanation is in logical harmony with the fact that the visual brain is characterized by different, functionally specialized systems, with different processing times for each; this type of organization naturally leads to different perceptual times for the corresponding attributes. In the present review, the experimental findings supporting perceptual asynchrony are presented, together with the original theoretical explanation behind the phenomenon and its implication for visual consciousness. Alternative theoretical views and additional experimental facts concerning perceptual misbinding are also reviewed, with a particular emphasis given to the role of attention. With few exceptions, most theories converge on the idea that the observed misbinding reflects a difference in perception times, which is in turn due to differences in neuronal processing times for different attributes within the brain. These processing time differences have been attributed to several different factors, attention included, with the possibility of co-existence between them.

Towards a system-level understanding of conscious vision: a study with electrocorticogram (ECoG) recording under continuous flash suppression (CFS).

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Binocular rivalry for beginners.

How to create and use binocular rivalry David Carmel, Michael Arcaro, Sabine Kastner, and Uri Hasson www.jove.com/video/2030/how-to-create-and-use-binocular-rivalry Binocular rivalry is a remarkable phenomenon of vision—two dissimilar images are presented simultaneously to each eye, and perception alternates between them. For example, if the left eye views horizontal lines and the right eye views vertical lines, an observer will report seeing one of the images for a few seconds, then the other, then the first again, and so on for as long as he or she cares to look (Wheatstone, 1838). You can experience this for yourself at www.psy.vanderbilt.edu/faculty/blake/rivalry/BR.html. Binocular rivalry is a popular tool for studying perception and awareness, because perception changes even when the physical stimulus does not. For this reason, rivalry is championed as a useful tool for studying the neural correlates of visual consciousness (Crick & Koch, 1990). However, despite there being a rich literature on rivalry, there are few teaching and learning resources devoted to the subject. Carmel, Arcaro, Kastner, and Hasson (2010) address this in their video: How to create and use binocular rivalry. The video begins with a brief description of binocular rivalry. It then provides a basic tutorial on the importance of stable vergence, because it ensures the two images fall on corresponding locations on the retina, as well as how it can be maintained during a rivalry experiment. For example, vergence can be maintained by surrounding each image with an identical frame of some sort, such as a simple or patterned border, and by placing an identical fixation point or cross in the centre of each image. The video also discusses some of the advantages and disadvantages of different methods to induce binocular rivalry. For example, chromatic (e.g., red-blue, red-green, etc.) goggles are inexpensive (a few dollars) and can be used with fMRI, but are prone to bleed-through and require careful stimulus preparation to ensure that each image can pass through only one of the chromatic filters. The video provides the same level of detail for the mirror stereoscope and prism goggles. Next, the video discusses the appearance of binocular rivalry. In particular, there is a neat demonstration of continuous flash suppression, a form of rivalry where a high-contrast image dominates perception indefinitely, and piecemeal rivalry, when patches of both images are perceived. Finally, the video discusses the distribution of dominance durations where time is plotted on the x-axis of a histogram and frequency is plotted on the y-axis, and that the data can be fitted with a gamma-like function. Overall, the video is professional and easy to use: the descriptions are accurate, the described methods are clear, and the accompanying pictures and demonstrations are crisp. Indeed, the video achieves what its title promises, but it does at the cost of some omission of important features of binocular rivalry. For example, the video mentions shutter and display goggles as methods to induce binocular rivalry, but fails to provide a discussion on the advantages and disadvantages of these techniques, and there is no discussion of the characteristics that affect rivalry. Also, there is no information about how to measure rivalry, such as by pressing one of two keys to report visibility of one of the images. This is especially surprising, because the video gives advice about the statistical tests to be used when analysing such data. Despite these minor omissions, How to create and use binocular rivalry covers a good chunk of material. It is also accompanied by a paper in which some of the video's deficiencies are redressed and in which there is a useful set of references. Although binocular-rivalry enthusiasts will be well-versed in the video's content, it is unlikely that students and newcomers to the field will be, too. For this reason, I strongly endorse Carmel et al.'s (2010) video for teaching and learning purposes. Bradley N. Jack, Discipline of Psychology and Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Southern Cross University, Coffs Harbour, Australia

Eye tracking analysis of minor details in films for audio description

This article focuses on the many instances when minute details found in feature films may have direct implications upon the development of both the visual and plot narratives. The main question we would like to ask examines whether very subtle details which may easily go unnoticed by the viewer should be audio described. To assess the visual consciousness of such minute details, a perception experiment was conducted using eye-tracking technology and questionnaires. Though the result is not conclusive, it shows a clear methodological approach in the field of the audio description of visual details, and does give some indication as to what should be taken into consideration in future studies and analysis. The article concludes by hinting at further tests and analyses which could be undertaken using eye-tracking technology.

Attention and consciousness: related yet different

A recent perceptual imaging experiment uses a rare 2×2 design to dissociate selective visual attention from visual consciousness. Its conclusions support the hypothesis that visual consciousness does not arise from neurons in primary visual cortex and forces a reinterpretation of numerous prior studies.