Visual Consciousness Research Articles

Unconscious influences on decision making in blindsight

Newell & Shanks (N&S) argue that an explanation for blindsight need not appeal to unconscious brain processes, citing research indicating that the condition merely reflects degraded visual experience. We reply that other evidence suggests blindsighters' predictive behavior under forced choice reflects cognitive access to low-level visual information that does not correlate with visual consciousness. Therefore, while we grant that visual consciousness may be required for full visual experience, we argue that it may not be needed for decision making and judgment.

Network symmetry and binocular rivalry experiments.

Hugh Wilson has proposed a class of models that treat higher-level decision making as a competition between patterns coded as levels of a set of attributes in an appropriately defined network (Cortical Mechanisms of Vision, pp. 399–417, 2009; The Constitution of Visual Consciousness: Lessons from Binocular Rivalry, pp. 281–304, 2013). In this paper, we propose that symmetry-breaking Hopf bifurcation from fusion states in suitably modified Wilson networks, which we call rivalry networks, can be used in an algorithmic way to explain the surprising percepts that have been observed in a number of binocular rivalry experiments. These rivalry networks modify and extend Wilson networks by permitting different kinds of attributes and different types of coupling. We apply this algorithm to psychophysics experiments discussed by Kovács et al. (Proc. Natl. Acad. Sci. USA 93:15508–15511, 1996), Shevell and Hong (Vis. Neurosci. 23:561–566, 2006; Vis. Neurosci. 25:355–360, 2008), and Suzuki and Grabowecky (Neuron 36:143–157, 2002). We also analyze an experiment with four colored dots (a simplified version of a 24-dot experiment performed by Kovács), and a three-dot analog of the four-dot experiment. Our algorithm predicts surprising differences between the three- and four-dot experiments.

Of the Helmholtz Club, South-Californian seedbed for visual and cognitive neuroscience, and its patron Francis Crick

Taking up the view that semi-institutional gatherings such as clubs, societies, research schools, have been instrumental in creating sheltered spaces from which many a 20th-century project-driven interdisciplinary research programme could develop and become established within the institutions of science, the paper explores the history of one such gathering from its inception in the early 1980s into the 2000s, the Helmholtz Club, which brought together scientists from such various research fields as neuroanatomy, neurophysiology, psychophysics, computer science and engineering, who all had an interest in the study of the visual system and of higher cognitive functions relying on visual perception such as visual consciousness. It argues that British molecular biologist turned South Californian neuroscientist Francis Crick had an early and lasting influence over the Helmholtz Club of which he was a founding pillar, and that from its inception, the club served as a constitutive element in his long-term plans for a neuroscience of vision and of cognition. Further, it argues that in this role, the Helmholtz Club served many purposes, the primary of which was to be a social forum for interdisciplinary discussion, where ‘discussion’ was not mere talk but was imbued with an epistemic value and as such, carefully cultivated. Finally, it questions what counts as ‘doing science’ and in turn, definitions of success and failure—and provides some material evidence towards re-appraising the successfulness of Crick’s contribution to the neurosciences.

Brain-Stimulation Induced Blindsight: Unconscious Vision or Response Bias?

A dissociation between visual awareness and visual discrimination is referred to as “blindsight”. Blindsight results from loss of function of the primary visual cortex (V1) which can occur due to cerebrovascular accidents (i.e. stroke-related lesions). There are also numerous reports of similar, though reversible, effects on vision induced by transcranial Magnetic Stimulation (TMS) to early visual cortex. These effects point to V1 as the “gate” of visual awareness and have strong implications for understanding the neurological underpinnings of consciousness. It has been argued that evidence for the dissociation between awareness of, and responses to, visual stimuli can be a measurement artifact of the use of a high response criterion under yes-no measures of visual awareness when compared with the criterion free forced-choice responses. This difference between yes-no and forced-choice measures suggests that evidence for a dissociation may actually be normal near-threshold conscious vision. Here we describe three experiments that tested visual performance in normal subjects when their visual awareness was suppressed by applying TMS to the occipital pole. The nature of subjects’ performance whilst undergoing occipital TMS was then verified by use of a psychophysical measure (d') that is independent of response criteria. This showed that there was no genuine dissociation in visual sensitivity measured by yes-no and forced-choice responses. These results highlight that evidence for visual sensitivity in the absence of awareness must be analysed using a bias-free psychophysical measure, such as d', In order to confirm whether or not visual performance is truly unconscious.

Blue Light Stimulates Cognitive Brain Activity in Visually Blind Individuals

Light regulates multiple non-image-forming (or nonvisual) circadian, neuroendocrine, and neurobehavioral functions, via outputs from intrinsically photosensitive retinal ganglion cells (ipRGCs). Exposure to light directly enhances alertness and performance, so light is an important regulator of wakefulness and cognition. The roles of rods, cones, and ipRGCs in the impact of light on cognitive brain functions remain unclear, however. A small percentage of blind individuals retain non-image-forming photoreception and offer a unique opportunity to investigate light impacts in the absence of conscious vision, presumably through ipRGCs. Here, we show that three such patients were able to choose nonrandomly about the presence of light despite their complete lack of sight. Furthermore, 2 sec of blue light modified EEG activity when administered simultaneously to auditory stimulations. fMRI further showed that, during an auditory working memory task, less than a minute of blue light triggered the recruitment of supplemental prefrontal and thalamic brain regions involved in alertness and cognition regulation as well as key areas of the default mode network. These results, which have to be considered as a proof of concept, show that non-image-forming photoreception triggers some awareness for light and can have a more rapid impact on human cognition than previously understood, if brain processing is actively engaged. Furthermore, light stimulates higher cognitive brain activity, independently of vision, and engages supplemental brain areas to perform an ongoing cognitive process. To our knowledge, our results constitute the first indication that ipRGC signaling may rapidly affect fundamental cerebral organization, so that it could potentially participate to the regulation of numerous aspects of human brain function.

Predicting visual consciousness electrophysiologically from intermittent binocular rivalry.

PurposeWe sought brain activity that predicts visual consciousness.MethodsWe used electroencephalography (EEG) to measure brain activity to a 1000-ms display of sine-wave gratings, oriented vertically in one eye and horizontally in the other. This display yields binocular rivalry: irregular alternations in visual consciousness between the images viewed by the eyes. We replaced both gratings with 200 ms of darkness, the gap, before showing a second display of the same rival gratings for another 1000 ms. We followed this by a 1000-ms mask then a 2000-ms inter-trial interval (ITI). Eleven participants pressed keys after the second display in numerous trials to say whether the orientation of the visible grating changed from before to after the gap or not. Each participant also responded to numerous non-rivalry trials in which the gratings had identical orientations for the two eyes and for which the orientation of both either changed physically after the gap or did not.ResultsWe found that greater activity from lateral occipital-parietal-temporal areas about 180 ms after initial onset of rival stimuli predicted a change in visual consciousness more than 1000 ms later, on re-presentation of the rival stimuli. We also found that less activity from parietal, central, and frontal electrodes about 400 ms after initial onset of rival stimuli predicted a change in visual consciousness about 800 ms later, on re-presentation of the rival stimuli. There was no such predictive activity when the change in visual consciousness occurred because the stimuli changed physically.ConclusionWe found early EEG activity that predicted later visual consciousness. Predictive activity 180 ms after onset of the first display may reflect adaption of the neurons mediating visual consciousness in our displays. Predictive activity 400 ms after onset of the first display may reflect a less-reliable brain state mediating visual consciousness.

Overlapping activity periods in early visual cortex and posterior intraparietal area in conscious visual shape perception: A TMS study

Parietal cortex is often activated in brain imaging studies on conscious visual processing, but its causal role and timing in conscious and nonconscious perception are poorly understood. We studied the role of posterior intraparietal sulcus (IPS) and early visual areas (V1/V2) in conscious and nonconscious vision by interfering with their functioning with MRI-guided transcranial magnetic stimulation (TMS). The observers made binary forced-choice decisions concerning the shape or color of the metacontrast masked targets and rated the quality of their conscious perception. TMS was applied 30, 60, 90, or 120ms after stimulus-onset. In the shape discrimination task, TMS of V1/V2 impaired conscious perception at 60, 90, and 120ms and nonconscious perception at 90ms. TMS of IPS impaired only conscious shape perception, also around 90ms. Conscious color perception was facilitated or suppressed depending on the strength of the TMS-induced electric field in V1/V2 at 90ms. The results suggest that simultaneous activity in V1/V2 and IPS around 90ms is necessary for visual awareness of shape but not for nonconscious perception. The overlapping activity periods of IPS and V1/V2 may reflect recurrent interaction between parietal cortex and V1 in conscious shape perception.

Unconscious Priming Requires Early Visual Cortex at Specific Temporal Phases of Processing

Although examples of unconscious shape priming have been well documented, whether such priming requires early visual cortex (V1/V2) has not been established. In the current study, we used TMS of V1/V2 at varying temporal intervals to suppress the visibility of preceding shape primes while the interval between primes and targets was kept constant. Our results show that, although conscious perception requires V1/V2, unconscious priming can occur without V1/V2 at an intermediate temporal interval but not at early (5-25 msec) or later (65-125 msec) stages of processing. Because the later time window of unconscious priming suppression has been proposed to interfere with feedback processing, our results further suggest that feedback processing is also essential for unconscious priming and may not be a sufficient condition for conscious vision.

Smiles may go unseen in generalized social anxiety disorder: Evidence from binocular rivalry for reduced visual consciousness of positive facial expressions

Research has demonstrated increased attention to negative social cues and reduced attention to positive social cues in generalized social anxiety disorder (GSAD), but little is known about whether GSAD also involves differences in lower levels of visual processing. This study explored visual experience in GSAD compared to participants with generalized anxiety disorder (GAD) and healthy controls using binocular rivalry. Participants were presented with dissimilar images to each eye, and the two images competed for perceptual dominance. Consistent with the hypothesis that GSAD involves a reduced visual salience for positive social cues, we found that smiling faces were dominant for significantly shorter durations in GSAD compared to GAD and controls. Contrasting with our hypothesis of greater visual salience of negative social cues, we found no difference in negative stimuli salience. These findings are consistent with the broader view that a perceiver's affective state directly influences the content of visual consciousness.

Perception-action dissociations depend on the luminance contrast of the stimuli

The observation that near-threshold low-contrast visual distractors can equally influence perceptual state and goal-directed motor responses was recently taken as an argument against a sharp separation between a conscious vision for perception and an unconscious vision for action. However, data supporting the dual visual system theory have principally involved high-contrast stimuli. In the present study, we assessed the effect of varying the contrast of a near-threshold visual distractor while keeping its visibility constant with backward noise masks. Eight participants performed fast manual reaching movements toward a highly visible target while subsequently reporting the presence/absence of a near-threshold distractor appearing at the opposite location with respect to the body midline. For all distractor contrasts, hand trajectory deviations toward the distractor were observed when the distractor was present and detected. When the distractor remained undetected deviations also occurred, but for higher contrasts. The subliminal motor effect traditionally observed in visual masking studies may therefore primarily depend on the luminance contrast of the interfering stimuli. These results suggest that dissociations between perceptual and motor responses can be explained by a single-signal model involving differential thresholds for perception and action that are specifically modulated as a function of both the requirements of the task and the contrast level of the stimuli. Such modulation is compatible with neurophysiological accounts of visual masking in which feedforward activation to--and feedback activation from--higher visual areas are correlated with the actual presence of the stimulation and its conscious perception, respectively.

Being confident without seeing: What subjective measures of visual consciousness are about

Can observers be confident about the accuracy of a discrimination response without a visual experience of the stimulus? In a series of five experiments, observers performed a masked orientation discrimination task, a masked shape discrimination task, or a random-dot motion discrimination task, followed by two subjective ratings after each trial, in which participants reported either their visual experience of the stimulus or their confidence in being correct. We observed that the threshold for ratings of the perception of the stimulus was above the threshold for ratings of a decision, that decision ratings outperformed stimulus ratings in predicting trial accuracy, and that different decision-related scales were more strongly associated with other decision-related scales than with ratings of stimulus clarity. We propose a taxonomy of subjective measures of consciousness that differentiates between subjective measures relating to the percept of the stimulus and measures relating to a discrimination decision and discuss the relation to type II blindsight.

Amygdala Activation for Eye Contact Despite Complete Cortical Blindness

Cortical blindness refers to the loss of vision that occurs after destruction of the primary visual cortex. Although there is no sensory cortex and hence no conscious vision, some cortically blind patients show amygdala activation in response to facial or bodily expressions of emotion. Here we investigated whether direction of gaze could also be processed in the absence of any functional visual cortex. A well-known patient with bilateral destruction of his visual cortex and subsequent cortical blindness was investigated in an fMRI paradigm during which blocks of faces were presented either with their gaze directed toward or away from the viewer. Increased right amygdala activation was found in response to directed compared with averted gaze. Activity in this region was further found to be functionally connected to a larger network associated with face and gaze processing. The present study demonstrates that, in human subjects, the amygdala response to eye contact does not require an intact primary visual cortex.

Posing for awareness: Proprioception modulates access to visual consciousness in a continuous flash suppression task

The rules governing the selection of which sensory information reaches consciousness are yet unknown. Of our senses, vision is often considered to be the dominant sense, and the effects of bodily senses, such as proprioception, on visual consciousness are frequently overlooked. Here, we demonstrate that the position of the body influences visual consciousness. We induced perceptual suppression by using continuous flash suppression. Participants had to judge the orientation a target stimulus embedded in a task-irrelevant picture of a hand. The picture of the hand could either be congruent or incongruent with the participants' actual hand position. When the viewed and the real hand positions were congruent, perceptual suppression was broken more rapidly than during incongruent trials. Our findings provide the first evidence of a proprioceptive bias in visual consciousness, suggesting that proprioception not only influences the perception of one's own body and self-consciousness, but also visual consciousness.

Subjective Characteristics of TMS-Induced Phosphenes Originating in Human V1 and V2

One way to study the neural correlates of visual consciousness is to localize the cortical areas whose stimulation generates subjective visual sensations, called phosphenes. While there is support for the view that the stimulation of several different visual areas in the occipital lobe may produce phosphenes, it is not clear what the contribution of each area is. Here, we studied the roles of the primary visual cortex (V1) and the adjacent area V2 in eliciting phosphenes by using functional magnetic resonance imaging-guided transcranial magnetic stimulation (TMS) combined with spherical modeling of the TMS-induced electric field. Reports of the subjective visual features of phosphenes were systematically collected and analyzed. We found that selective stimulation of V1 and V2 are equally capable of generating phosphenes, as demonstrated by comparable phosphene thresholds and similar characteristics of phosphene shape, color, and texture. However, the phosphenes induced by V1 stimulation were systematically perceived as brighter than the phosphenes induced by the stimulation of V2. Thus, these results suggest that V1 and V2 have a similar capability to produce conscious percepts. Nevertheless, V1 and V2 contribute differently to brightness: neural activation originating in V1 generates a more intense sensation of brightness than similar activation originating in V2.

A Neural Marker of Perceptual Consciousness in Infants

Infants have a sophisticated behavioral and cognitive repertoire suggestive of a capacity for conscious reflection. Yet, demonstrating conscious access in infants remains challenging, mainly because they cannot report their thoughts. Here, to circumvent this problem, we studied whether an electrophysiological signature of consciousness found in adults, corresponding to a late nonlinear cortical response [~300 milliseconds (ms)] to brief pictures, already exists in infants. We recorded event-related potentials while 5-, 12-, and 15-month-old infants (N = 80) viewed masked faces at various levels of visibility. In all age groups, we found a late slow wave showing a nonlinear profile at the expected perceptual thresholds. However, this late component shifted from a weak and delayed response in 5-month-olds (starting around 900 ms) to a more sustained and faster response in older infants (around 750 ms). These results reveal that the brain mechanisms underlying the threshold for conscious perception are already present in infancy but undergo a slow acceleration during development.

Prefrontal lesion evidence against higher-order theories of consciousness

According to higher-order theories of consciousness, a mental state is conscious only when represented by another mental state. Higher-order theories must predict there to be some brain areas (or networks of areas) such that, because they produce (the right kind of) higher-order states, the disabling of them brings about deficits in consciousness. It is commonly thought that the prefrontal cortex produces these kinds of higher-order states. In this paper, I first argue that this is likely correct, meaning that, if some higher-order theory is true, prefrontal lesions should produce dramatic deficits in visual consciousness. I then survey prefrontal lesion data, looking for evidence of such deficits. I argue that no such deficits are to be found, and that this presents a compelling case against higher-order theories.

Visual Consciousness and The Phenomenology of Perception

AbstractIdeally, psychological and phenomenological studies of visual experience should be mutually informative. In that spirit, this article outlines parts of Maurice Merleau‐Ponty's phenomenological view of visual experience as a kind of independently active opaque bodily synthesis, and uses those views to (a) help ground and extend Alva Noë's rejection of the “snapshot” theory of visual experience in favor of a more enactive view of visual content, (b) critique a failing of Noë's account, and (c) show how the assumptions underlying more internalist and Cartesian views of visual experience can illegitimately creep in even when they are being carefully criticized.

The Case for Zombie Agency

Recent empirical work suggests that unconscious vision guides and controls much of our bodily actions. We are accordingly zombie agents (Koch and Crick 2001). While many have been willing to accept this zombie picture as part of accepting David Milner and Melvyn Goodale’s (1995) influential account of the human visual system, Christopher Mole (2009) has trenchantly argued against it by questioning a common interpretation of the empirical evidence. Here I respond to Mole’s case. I argue that we must separate two issues: (1) whether Milner and Goodale’s functional account of human vision is correct and (2) whether there are zombie actions. While I agree with Mole that the empirical case for Milner and Goodale’s account is more contentious than philosophers acknowledge, I argue that a case can be made for zombie agency. The empirical evidence at issue is dissociation evidence showing that a subject deploys information p to control behavior, yet when queried explicitly in some way whether p, the subject denies it or assents to incompatible information. Goodale and Milner (1995) draw on this and other evidence to argue for a specific hypothesis about the function of the two anatomically separate cortical visual streams in humans: the dorsal stream directly guides action, the ventral stream generates conscious vision. The

Posing for awareness: Proprioception modulates access to visual consciousness in a continuous flash suppression task

Posing for awareness: Proprioception modulates access to visual consciousness in a continuous flash suppression task

Does the oblique effect influence early neural correlates of visual consciousness during binocular rivalry?

Does the oblique effect influence early neural correlates of visual consciousness during binocular rivalry?