Localization and globalization in conscious vision

Self-Regulation of the Posterior-Frontal Brain Activity with Real-Time fMRI Neurofeedback to Influence Perceptual Discrimination

The Global Neuronal Workspace (GNW) hypothesis states that the visual percept is available to conscious awareness only if recurrent long-distance interactions among distributed brain regions activate neural circuitry extending from the posterior areas to prefrontal regions above a certain excitation threshold. To directly test this hypothesis, we trained 14 human participants to increase blood oxygenation level-dependent (BOLD) signals with real-time functional magnetic resonance imaging (rtfMRI)-based neurofeedback simultaneously in four specific regions of the occipital, temporal, insular and prefrontal parts of the brain. Specifically, we hypothesized that the up-regulation of the mean BOLD activity in the posterior-frontal brain regions lowers the perceptual threshold for visual stimuli, while down-regulation raises the threshold. Our results showed that participants could perform up-regulation (Wilcoxon test, session 1: p = 0.022; session 4: p = 0.041) of the posterior-frontal brain activity, but not down-regulation. Furthermore, the up-regulation training led to a significant reduction in the visual perceptual threshold, but no substantial change in perceptual threshold was observed after the down-regulation training. These findings show that the up-regulation of the posterior-frontal regions improves the perceptual discrimination of the stimuli. However, further questions as to whether the posterior-frontal regions can be down-regulated at all, and whether down-regulation raises the perceptual threshold, remain unanswered.

Online control of rapid target-directed aiming using blurred visual feedback

The accuracy and precision of target-directed aiming is contingent upon the availability of online visual feedback. The present study aimed to examine the visual regulation of aiming with blurred vision. The aiming task was executed using a stylus on a graphics digitizing board, which was translated onto a screen in the form of a cursor (representing the moving limb) and target. The vision conditions involved the complete disappearance or blur of the cursor alone, target alone, and cursor+target. These conditions involved leaving the screen uncovered or covering with a diffusing sheet to induce blur. The distance between the screen and sheet was increased to make the blur progressively more severe (0 cm, 3 cm). Results showed significantly less radial and variable error under blurred compared to no vision of the cursor and cursor+target. These findings were corroborated by the movement kinematics including a shorter proportion of time to peak velocity, more negative within-participant correlation between the distances travelled to and after peak velocity, and lower spatial variability from peak velocity to the end of the movement under blurred vision. The superior accuracy and precision under the blurred compared to no vision conditions is consistent with functioning visual regulation of aiming, which is primarily contingent upon the online visual feedback of the moving limb. This outcome may be attributed to the processing of low spatial-high temporal frequencies. Potential implications for low vision diagnostics are discussed.

From non-conscious processing to conscious events: a minimalist approach

The minimalist approach that we develop here is a framework that allows to appreciate how non-conscious processing and conscious contents shape human cognition, broadly defined. It is composed of three simple principles. First, cognitive processes are inherently non-conscious, while their inputs and (interim) outputs may be consciously experienced. Second, non-conscious processes and elements of the cognitive architecture prioritize information for conscious experiences. Third, conscious events are composed of series of conscious contents and non-conscious processes, with increased duration leading to more opportunity for processing. The narrowness of conscious experiences is conceptualized here as a solution to the problem of channeling the plethora of non-conscious processes into action and communication processes that are largely serial. The framework highlights the importance of prioritization for consciousness, and we provide an illustrative review of three main factors that shape prioritization-stimulus strength, motivational relevance and mental accessibility. We further discuss when and how this framework (i) is compatible with previous theories, (ii) enables new understandings of established findings and models, and (iii) generates new predictions and understandings.

Subjectivity as an Emergent Property of Information Processing by Neuronal Networks

Here, we examine subjectivity and consciousness as emergent properties of the computational complexity of information processing by the brain, rather than metaphysical phenomena. While Psychology concentrates on the emergent properties and Neurobiology examines the properties of the biological substrate, Neurophysiology and Cognitive Neuroscience link the two levels by investigating the mechanisms and processes by which the functions of the brain emerge from the anatomical, cellular and network properties of the nervous system. Our purpose here is not to locate the neural structures that sustain subjectivity or other psychic functions; rather, we examine the operating modes of neurons and neural circuits: they reveal an intrinsically relational quality; sensory elaboration itself proves to be relational and self-centred, necessarily associated with the vital, hedonic, emotional relevance of each experience and external cue, and intrinsically oriented to a behavioral interaction with the latter. The hippocampus adds to this self-centred relational perspective the capability of transforming the identification and the spatial location of objects into a contextualized representation of reality. Since the hippocampus is strongly interconnected with the archaic structures that evaluate vital and hedonic relevance and generate emotional responses, the contextualized information, emotionally colored, is transformed into a comprehensive individual experience. This way, a subjective, self-centred, affectively colored perspective arises in animals due to the intrinsic properties of neuronal circuits in the brain. We conclude that neuronal network processing is strongly characterized per se by a relational and self-centred (subjective) and emotionally colored, motivationally oriented (personal) perspective. The properties and features of neural processing discussed here constitute well-established knowledge in the neuroscientific community. Yet, from a layman’s perception, subjectivity still mysteriously arises in our brain due to the action of consciousness, and in epistemological and philosophical debates, the question often arises as to how consciousness may add the subjective and personal perspective to neural elaboration. The answer appears to be simple: it does not; subjectivity is already there, present ab initio in neuronal processing and not added a posteriori by some other “consciousness” function of unclear neural basis.

Imaging the Visual Network in the Migraine Spectrum

The involvement of the visual network in migraine pathophysiology has been well-known for more than a century. Not only is the aura phenomenon linked to cortical alterations primarily localized in the visual cortex; but also migraine without aura has shown distinct dysfunction of visual processing in several studies in the past. Further, the study of photophobia, a hallmark migraine symptom, has allowed unraveling of distinct connections that link retinal pathways to the trigeminovascular system. Finally, visual snow, a recently recognized neurological disorder characterized by a continuous visual disturbance, is highly comorbid with migraine and possibly shares with it some common pathophysiological mechanisms. Here, we review the most relevant neuroimaging literature to date, considering studies that have either attempted to investigate the visual network or have indirectly shown visual processing dysfunctions in migraine. We do this by taking into account the broader spectrum of migrainous biology, thus analyzing migraine both with and without aura, focusing on light sensitivity as the most relevant visual symptom in migraine, and finally analyzing the visual snow syndrome. We also present possible hypotheses on the underlying pathophysiology of visual snow, for which very little is currently known.

Understanding the Higher-Order Approach to Consciousness

The higher-order theory (HOT) of consciousness has often been misunderstood by critics. Here, we clarify its position on several issues, and distinguish it from other views, such as the global workspace theory (GWT) and early sensory models (e.g., first-order local recurrency theories). For example, HOT has been criticized for overintellectualizing consciousness. We show that, while higher-order states are cognitively assembled, the requirements are in fact considerably less than often presumed. In this sense, HOT may be viewed as an intermediate position between GWT and early sensory views. We also clarify that most proponents of HOT do not stipulate consciousness as equivalent to metacognition or confidence. Furthermore, compared with other existing theories, HOT can arguably account better for complex everyday experiences, such as emotions and episodic memories. This makes HOT particularly useful as a framework for conceptualizing pathological mental states.

The function of connectomes in encoding sensory stimuli

The enormous number of neurons and the massive sum of connecting fibers linking them make the neural processes of encoding sensory signals extraordinarily complex, and this challenge is far from being elucidated. Simply stated, for the present paper, the question is - how does the brain encode complex images? Our proposal argues that modulation of strengths of functional relationships between firing neurons in relation to an input results in the formation of stimulus-salient functional connectomes. This type of connection/coupling strength is computed by performing cross correlograms (CCG) of spike trains between simultaneously firing cells. Significantly, the strength is dependent upon stimuli characteristics, inferring that cells may join or leave particular ensembles, thus creating signature emergent connectomes for different images, thereby, allowing their discrimination. We observed in an ensemble that functionally connected cells exhibited synergistic excitatory activity, increased coherence, and augmented gamma oscillations within a window-of-opportunity contrasting with unconnected neighboring neuronal companions. We suggest that investigating and revealing such stimulus-salient emergent connectomes is a realistic and promising pursuit toward answering how the brain processes complex images.

Sensory Processing Across Conscious and Nonconscious Brain States: From Single Neurons to Distributed Networks for Inferential Representation

Neuronal activity is markedly different across brain states: it varies from desynchronized activity during wakefulness to the synchronous alternation between active and silent states characteristic of deep sleep. Surprisingly, limited attention has been paid to investigating how brain states affect sensory processing. While it was long assumed that the brain was mostly disconnected from external stimuli during sleep, an increasing number of studies indicates that sensory stimuli continue to be processed across all brain states-albeit differently. In this review article, we first discuss what constitutes a brain state. We argue that-next to global, behavioral states such as wakefulness and sleep-there is a concomitant need to distinguish bouts of oscillatory dynamics with specific global/local activity patterns and lasting for a few hundreds of milliseconds, as these can lead to the same sensory stimulus being either perceived or not. We define these short-lasting bouts as micro-states. We proceed to characterize how sensory-evoked neural responses vary between conscious and nonconscious states. We focus on two complementary aspects: neuronal ensembles and inter-areal communication. First, we review which features of ensemble activity are conducive to perception, and how these features vary across brain states. Properties such as heterogeneity, sparsity and synchronicity in neuronal ensembles will especially be considered as essential correlates of conscious processing. Second, we discuss how inter-areal communication varies across brain states and how this may affect brain operations and sensory processing. Finally, we discuss predictive coding (PC) and the concept of multi-level representations as a key framework for understanding conscious sensory processing. In this framework the brain implements conscious representations as inferences about world states across multiple representational levels. In this representational hierarchy, low-level inference may be carried out nonconsciously, whereas high levels integrate across different sensory modalities and larger spatial scales, correlating with conscious processing. This inferential framework is used to interpret several cellular and population-level findings in the context of brain states, and we briefly compare its implications to two other theories of consciousness. In conclusion, this review article, provides foundations to guide future studies aiming to uncover the mechanisms of sensory processing and perception across brain states.

Long-Term Visuo-Gustatory Appetitive and Aversive Conditioning Potentiate Human Visual Evoked Potentials

Human recognition of foods and beverages are often based on visual cues associated with flavors. The dynamics of neurophysiological plasticity related to acquisition of such long-term associations has only recently become the target of investigation. In the present work, the effects of appetitive and aversive visuo-gustatory conditioning were studied with high density EEG-recordings focusing on late components in the visual evoked potentials (VEPs), specifically the N2-P3 waves. Unfamiliar images were paired with either a pleasant or an unpleasant juice and VEPs evoked by the images were compared before and 1 day after the pairings. In electrodes located over posterior visual cortex areas, the following changes were observed after conditioning: the amplitude from the N2-peak to the P3-peak increased and the N2 peak delay was reduced. The percentage increase of N2-to-P3 amplitudes was asymmetrically distributed over the posterior hemispheres despite the fact that the images were bilaterally symmetrical across the two visual hemifields. The percentage increases of N2-to-P3 amplitudes in each experimental subject correlated with the subject's evaluation of positive or negative hedonic valences of the two juices. The results from 118 scalp electrodes gave surface maps of theta power distributions showing increased power over posterior visual areas after the pairings. Source current distributions calculated from swLORETA revealed that visual evoked currents rose as a result of conditioning in five cortical regions-from primary visual areas and into the inferior temporal gyrus (ITG). These learning-induced changes were seen after both appetitive and aversive training while a sham trained control group showed no changes. It is concluded that long-term visuo-gustatory conditioning potentiated the N2-P3 complex, and it is suggested that the changes are regulated by the perceived hedonic valence of the US.

The Merit of Synesthesia for Consciousness Research

Synesthesia is a phenomenon in which additional perceptual experiences are elicited by sensory stimuli or cognitive concepts. Synesthetes possess a unique type of phenomenal experiences not directly triggered by sensory stimulation. Therefore, for better understanding of consciousness it is relevant to identify the mental and physiological processes that subserve synesthetic experience. In the present work we suggest several reasons why synesthesia has merit for research on consciousness. We first review the research on the dynamic and rapidly growing field of the studies of synesthesia. We particularly draw attention to the role of semantics in synesthesia, which is important for establishing synesthetic associations in the brain. We then propose that the interplay between semantics and sensory input in synesthesia can be helpful for the study of the neural correlates of consciousness, especially when making use of ambiguous stimuli for inducing synesthesia. Finally, synesthesia-related alterations of brain networks and functional connectivity can be of merit for the study of consciousness.

Target sites for transcallosal fibers in human visual cortex - A combined diffusion and polarized light imaging study

Transcallosal fibers of the visual system have preferential target sites within the occipital cortex of monkeys. These target sites coincide with vertical meridian representations of the visual field at borders of retinotopically defined visual areas. The existence of preferential target sites of transcallosal fibers in the human brain at the borders of early visual areas was claimed, but controversially discussed. Hence, we studied the distribution of transcallosal fibers in human visual cortex, searching for an organizational principle across early and higher visual areas. In-vivo high angular resolution diffusion imaging data of 28 subjects were used for probabilistic fiber tracking using a constrained spherical deconvolution approach. The fiber architecture within the target sites was analyzed at microscopic resolution using 3D polarized light imaging in a post-mortem human hemisphere. Fibers through a seed in the splenium of the corpus callosum reached the occipital cortex via the forceps major and the tapetum. We found target sites of these transcallosal fibers at borders of cytoarchitectonically defined occipital areas not only between early visual areas V1 and V2, V3d and V3A, and V3v and V4, but also between higher extrastriate areas, namely V4 (ventral) and posterior fusiform area FG1 as well as posterior fusiform area FG2 and lateral occipital cortex. In early visual areas, the target sites coincided with the vertical meridian representations of retinotopic maps. The spatial arrangement of the fibers in the 'border tuft' region at the V1/V2 border was found to be more complex than previously observed in myeloarchitectonic studies. In higher visual areas, our results provided additional evidence for a hemi-field representation in human area V4. The fiber topography in posterior fusiform gyrus indicated that additional retinotopic areas might exist, located between the recently identified retinotopic representations phPITv/phPITd and PHC-1/PHC-2 in lateral occipital cortex and parahippocampal gyrus.

Maintenance of non-consciously presented information engages the prefrontal cortex

Conscious processing is generally seen as required for flexible and willful actions, as well as for tasks that require durable information maintenance. Here we present research that questions the assumption that only consciously perceived information is durable (>500 ms). Using the attentional blink (AB) phenomenon, we rendered otherwise relatively clearly perceived letters non-conscious. In a first experiment we systematically manipulated the delay between stimulus presentation and response, for the purpose of estimating the durability of non-conscious perceptual representations. For items reported not seen, we found that behavioral performance was better than chance across intervals up to 15 s. In a second experiment we used fMRI to investigate the neural correlates underlying the maintenance of non-conscious perceptual representations. Critically, the relatively long delay period demonstrated in experiment 1 enabled isolation of the signal change specifically related to the maintenance period, separate from stimulus presentation and response. We found sustained BOLD signal change in the right mid-lateral prefrontal cortex, orbitofrontal cortex, and crus II of the cerebellum during maintenance of non-consciously perceived information. These findings are consistent with the controversial claim that working-memory mechanisms are involved in the short-term maintenance of non-conscious perceptual representations.

Investigating ongoing brain oscillations and their influence on conscious perception - network states and the window to consciousness

In cognitive neuroscience, prerequisites of consciousness are of high interest. Within recent years it has become more commonly understood that ongoing brain activity, mainly measured with electrophysiology, can predict whether an upcoming stimulus is consciously perceived. One approach to investigate the relationship between ongoing brain activity and conscious perception is to conduct near-threshold (NT) experiments and focus on the pre-stimulus period. The current review will, in the first part, summarize main findings of pre-stimulus research from NT experiments, mainly focusing on the alpha band (8–14 Hz). It is probable that the most prominent finding is that local (mostly sensory) areas show enhanced excitatory states prior to detection of upcoming NT stimuli, as putatively reflected by decreased alpha band power. However, the view of a solely local excitability change seems to be too narrow. In a recent paper, using a somatosensory NT task, Weisz et al. (2014) replicated the common alpha finding and, furthermore, conceptually embedded this finding into a more global framework called “Windows to Consciousness” (Win2Con). In this review, we want to further elaborate on the crucial assumption of “open windows” to conscious perception, determined by pre-established pathways connecting sensory and higher order areas. Methodologically, connectivity and graph theoretical analyses are applied to source-imaging magnetoencephalographic data to uncover brain regions with strong network integration as well as their connection patterns. Sensory regions with stronger network integration will more likely distribute information when confronted with weak NT stimuli, favoring its subsequent conscious perception. First experimental evidence confirms our aforementioned “open window” hypothesis. We therefore emphasize that future research on prerequisites of consciousness needs to move on from investigating solely local excitability to a more global view of network connectivity.

Substituting objects from consciousness: a review of object substitution masking

Object substitution masking (OSM) occurs when a sparse (e.g., four-dot), temporally trailing mask obscures the visibility of a briefly presented target. Here, we review theories of OSM: those that propose that OSM reflects the interplay between feedforward and feedback/reentrant neural processes, those that predict that feedforward processing alone gives rise to the phenomenon, and theories that focus on cognitive explanations, such as object updating. We discuss how each of these theories accommodates key findings from the OSM literature. In addition, we examine the relationship between OSM and other visual-cognitive phenomena, including object correspondence through occlusion, change blindness, metacontrast masking, backward masking, and visual short-term memory. Finally, we examine the level of processing at which OSM impairs target perception. Collectively, OSM appears to reflect the conditions under which the brain confuses two visual events for one when they are encoded with low spatiotemporal resolution, due to processing resources being otherwise occupied.

Physical integration: a causal account for consciousness

The issue of integration in neural networks is intimately connected with that of consciousness. In this paper, integration as an effective level of physical organization is contrasted with a methodological integrative approach. Understanding how consciousness arises out of neural processes requires a model of integration in just causal physical terms. Based on a set of feasible criteria (physical grounding, causal efficacy, no circularity and scaling), a causal account of physical integration for consciousness centered on joint causation is outlined.

Subjective rating of weak tactile stimuli is parametrically encoded in event-related potentials

Neural signatures of somatosensory awareness have often been studied by examining EEG responses to hardly detectable stimuli. Previous reports consistently showed that event-related potentials (ERPs) measured over early somatosensory cortex diverge for detected and missed perithreshold stimuli at 80-100 ms after stimulus onset. So far, however, all previous studies have operationalized somatosensory awareness as binary stimulus detection. Here, we investigated whether ERP components attributed to neuronal activity in early somatosensory cortices would parametrically reflect subjective ratings of stimulus awareness. EEG (64 channel) was recorded in human participants (N = 20), with perithreshold electrical stimulation applied to the left median nerve. Participants indicated perceptibility on a continuous visual rating scale, and stimulation intensity was readjusted in each block to a perithreshold level. The aim of the analysis was to investigate which brain areas reflect the subsequent perceptual awareness ratings parametrically, and how early such parametric effects occur. Parametric ERP effects were found as early as 86 ms after stimulus onset. This parametric modulation of ERP amplitude was source localized to secondary somatosensory cortex, and attributed to feedforward processing between primary and secondary somatosensory cortex by means of dynamic causal modeling (DCM). Furthermore, later in the analysis window, the subjective rating of stimuli correlated with the amplitude of the N140 component and with a broadly distributed P300 component. By DCM modeling, these late effects were explained in terms of recurrent processing within the network of somatosensory and premotor cortices. Our results indicate that early neural activity in the somatosensory cortex can reflect the subjective quality of tactile perception.

Global workspace dynamics: cortical "binding and propagation" enables conscious contents

A global workspace (GW) is a functional hub of binding and propagation in a population of loosely coupled signaling elements. In computational applications, GW architectures recruit many distributed, specialized agents to cooperate in resolving focal ambiguities. In the brain, conscious experiences may reflect a GW function. For animals, the natural world is full of unpredictable dangers and opportunities, suggesting a general adaptive pressure for brains to resolve focal ambiguities quickly and accurately. GW theory aims to understand the differences between conscious and unconscious brain events. In humans and related species the cortico-thalamic (C-T) core is believed to underlie conscious aspects of perception, thinking, learning, feelings of knowing (FOK), felt emotions, visual imagery, working memory, and executive control. Alternative theoretical perspectives are also discussed. The C-T core has many anatomical hubs, but conscious percepts are unitary and internally consistent at any given moment. Over time, conscious contents constitute a very large, open set. This suggests that a brain-based GW capacity cannot be localized in a single anatomical hub. Rather, it should be sought in a functional hub - a dynamic capacity for binding and propagation of neural signals over multiple task-related networks, a kind of neuronal cloud computing. In this view, conscious contents can arise in any region of the C-T core when multiple input streams settle on a winner-take-all equilibrium. The resulting conscious gestalt may ignite an any-to-many broadcast, lasting ∼100-200 ms, and trigger widespread adaptation in previously established networks. To account for the great range of conscious contents over time, the theory suggests an open repertoire of binding coalitions that can broadcast via theta/gamma or alpha/gamma phase coupling, like radio channels competing for a narrow frequency band. Conscious moments are thought to hold only 1-4 unrelated items; this small focal capacity may be the biological price to pay for global access. Visuotopic maps in cortex specialize in features like color, retinal size, motion, object identity, and egocentric/allocentric framing, so that a binding coalition for the sight of a rolling billiard ball in nearby space may resonate among activity maps of LGN, V1-V4, MT, IT, as well as the dorsal stream. Spatiotopic activity maps can bind into coherent gestalts using adaptive resonance (reentry). Single neurons can join a dominant coalition by phase tuning to regional oscillations in the 4-12 Hz range. Sensory percepts may bind and broadcast from posterior cortex, while non-sensory FOKs may involve prefrontal and frontotemporal areas. The anatomy and physiology of the hippocampal complex suggest a GW architecture as well. In the intact brain the hippocampal complex may support conscious event organization as well as episodic memory storage.

Qualia could arise from information processing in local cortical networks

Re-entrant feedback, either within sensory cortex or arising from prefrontal areas, has been strongly linked to the emergence of consciousness, both in theoretical and experimental work. This idea, together with evidence for local micro-consciousness, suggests the generation of qualia could in some way result from local network activity under re-entrant activation. This paper explores the possibility by examining the processing of information by local cortical networks. It highlights the difference between the information structure (how the information is physically embodied), and the information message (what the information is about). It focuses on the network’s ability to recognize information structures amongst its inputs under conditions of extensive local feedback, and to then assign information messages to those structures. It is shown that if the re-entrant feedback enables the network to achieve an attractor state, then the message assigned in any given pass of information through the network is a representation of the message assigned in the previous pass-through of information. Based on this ability the paper argues that as information is repeatedly cycled through the network, the information message that is assigned evolves from a recognition of what the input structure is, to what it is like, to how it appears, to how it seems. It could enable individual networks to be the site of qualia generation. The paper goes on to show networks in cortical layers 2/3 and 5a have the connectivity required for the behavior proposed, and reviews some evidence for a link between such local cortical cyclic activity and conscious percepts. It concludes with some predictions based on the theory discussed.

Local category-specific gamma band responses in the visual cortex do not reflect conscious perception

Which neural processes underlie our conscious experience? One theoretical view argues that the neural correlates of consciousness (NCC) reside in local activity in sensory cortices. Accordingly, local category-specific gamma band responses in visual cortex correlate with conscious perception. However, as most studies manipulated conscious perception by altering the amount of sensory evidence, it is possible that they reflect prerequisites or consequences of consciousness rather than the actual NCC. Here we directly address this issue by developing a new experimental paradigm in which conscious perception is modulated either by sensory evidence or by previous exposure of the images while recording intracranial EEG from the higher-order visual cortex of human epilepsy patients. A clear prediction is that neural processes directly reflecting conscious perception should be present regardless of how it comes about. In contrast, we observed that although subjective reports were modulated both by sensory evidence and by previous exposure, gamma band responses solely reflected sensory evidence. This result contradicts the proposal that local gamma band responses in the higher-order visual cortex reflect conscious perception.

Cytoarchitectonical analysis and probabilistic mapping of two extrastriate areas of the human posterior fusiform gyrus

The human extrastriate visual cortex comprises numerous functionally defined areas, which are not identified in the widely used cytoarchitectonical map of Brodmann. The ventral part of the extrastriate cortex is particularly devoted to the identification of visual objects, faces and word forms. We analyzed the region immediately antero-lateral to hOc4v in serially sectioned (20 μm) and cell body-stained human brains using a quantitative observer-independent cytoarchitectonical approach to further identify the anatomical organization of the extrastriate cortex. Two novel cytoarchitectonical areas, FG1 and FG2, were identified on the posterior fusiform gyrus. The results of ten postmortem brains were then registered to their MRI volumes (acquired before histological processing), 3D reconstructed, and spatially normalized to the Montreal Neurological Institute reference brain. Finally, probabilistic maps were generated for each cytoarchitectonical area by superimposing the areas of the individual brains in the reference space. Comparison with recent functional imaging studies yielded that both areas are located within the object-related visual cortex. FG1 fills the gap between the retinotopically mapped area VO-1 and a posterior fusiform face patch. FG2 is probably the correlate of this face patch.

Keep your eyes on development: the behavioral and neurophysiological development of visual mechanisms underlying form processing

Visual form perception is essential for correct interpretation of, and interaction with, our environment. Form perception depends on visual acuity and processing of specific form characteristics, such as luminance contrast, spatial frequency, color, orientation, depth, and even motion information. As other cognitive processes, form perception matures with age. This paper aims at providing a concise overview of our current understanding of the typical development, from birth to adulthood, of form-characteristic processing, as measured both behaviorally and neurophysiologically. Two main conclusions can be drawn. First, the current literature conveys that for most reviewed characteristics a developmental pattern is apparent. These trajectories are discussed in relation to the organization of the visual system. The second conclusion is that significant gaps in the literature exist for several age-ranges. To complete our understanding of the typical and, by consequence, atypical development of visual mechanisms underlying form processing, future research should uncover these missing segments.

Distilling the neural correlates of consciousness

Solving the problem of consciousness remains one of the biggest challenges in modern science. One key step towards understanding consciousness is to empirically narrow down neural processes associated with the subjective experience of a particular content. To unravel these neural correlates of consciousness (NCC) a common scientific strategy is to compare perceptual conditions in which consciousness of a particular content is present with those in which it is absent, and to determine differences in measures of brain activity (the so called "contrastive analysis"). However, this comparison appears not to reveal exclusively the NCC, as the NCC proper can be confounded with prerequisites for and consequences of conscious processing of the particular content. This implies that previous results cannot be unequivocally interpreted as reflecting the neural correlates of conscious experience. Here we review evidence supporting this conjecture and suggest experimental strategies to untangle the NCC from the prerequisites and consequences of conscious experience in order to further develop the otherwise valid and valuable contrastive methodology.

Consciousness cannot be separated from function

Numerous theories of consciousness hold that there are separate neural correlates of conscious experience and cognitive function, aligning with the assumption that there are 'hard' and 'easy' problems of consciousness. Here, we argue that any neurobiological theory based on an experience/function division cannot be empirically confirmed or falsified and is thus outside the scope of science. A 'perfect experiment' illustrates this point, highlighting the unbreachable boundaries of the scientific study of consciousness. We describe a more nuanced notion of cognitive access that captures personal experience without positing the existence of inaccessible conscious states. Finally, we discuss the criteria necessary for forming and testing a falsifiable theory of consciousness.

Visual cognition

Visual cognition, high-level vision, mid-level vision and top-down processing all refer to decision-based scene analyses that combine prior knowledge with retinal input to generate representations. The label "visual cognition" is little used at present, but research and experiments on mid- and high-level, inference-based vision have flourished, becoming in the 21st century a significant, if often understated part, of current vision research. How does visual cognition work? What are its moving parts? This paper reviews the origins and architecture of visual cognition and briefly describes some work in the areas of routines, attention, surfaces, objects, and events (motion, causality, and agency). Most vision scientists avoid being too explicit when presenting concepts about visual cognition, having learned that explicit models invite easy criticism. What we see in the literature is ample evidence for visual cognition, but few or only cautious attempts to detail how it might work. This is the great unfinished business of vision research: at some point we will be done with characterizing how the visual system measures the world and we will have to return to the question of how vision constructs models of objects, surfaces, scenes, and events.

Delayed perceptual awareness in rapid perceptual decisions

The flourishing of studies on the neural correlates of decision-making calls for an appraisal of the relation between perceptual decisions and conscious perception. By exploiting the long integration time of noisy motion stimuli, and by forcing human observers to make difficult speeded decisions – sometimes a blind guess – about stimulus direction, we traced the temporal buildup of motion discrimination capability and perceptual awareness, as assessed trial by trial through direct rating. We found that both increased gradually with motion coherence and viewing time, but discrimination was systematically leading awareness, reaching a plateau much earlier. Sensitivity and criterion changes contributed jointly to the slow buildup of perceptual awareness. It made no difference whether motion discrimination was accomplished by saccades or verbal responses. These findings suggest that perceptual awareness emerges on the top of a developing or even mature perceptual decision. We argue that the middle temporal (MT) cortical region does not confer us the full phenomenic depth of motion perception, although it may represent a precursor stage in building our subjective sense of visual motion.

Perceptual learning beyond retinotopic reference frame

Repetitive experience with the same visual stimulus and task can remarkably improve behavioral performance on the task. This well-known perceptual-learning phenomenon is usually specific to the trained retinal- or visual-field location, which is taken as an indication of plastic changes in retinotopic visual areas. In previous studies of perceptual learning, however, a change in stimulus location on the retina is accompanied by positional changes of the stimulus in nonretinotopic frames of reference, such as relative to the head and other objects. It is unclear, therefore, whether the putative location specificity is exclusively retinotopic or if it could also depend on nonretinotopic representation of the stimulus, which is particularly important for multisensory and sensorimotor integration as well as for maintenance of stable visual percepts. Here, by manipulating subjects' gaze direction to control spatial and retinal locations of stimuli independently, we found that, when the stimulated retinal regions were held constant, the improvement with training in motion-direction discrimination of two successively displayed stimuli was restricted to the relative spatial position of the stimuli but independent of their absolute locations in head- and world-centered frame. These findings indicate location specificity of perceptual learning beyond retinotopic frame of reference, suggesting a pliable spatiotopic mechanism that can be specifically shaped by experience for better spatiotemporal integration of the learned stimuli.

Equal degrees of object selectivity for upper and lower visual field stimuli

Functional MRI (fMRI) studies of the human object recognition system commonly identify object-selective cortical regions by comparing blood oxygen level-dependent (BOLD) responses to objects versus those to scrambled objects. Object selectivity distinguishes human lateral occipital cortex (LO) from earlier visual areas. Recent studies suggest that, in addition to being object selective, LO is retinotopically organized; LO represents both object and location information. Although LO responses to objects have been shown to depend on location, it is not known whether responses to scrambled objects vary similarly. This is important because it would suggest that the degree of object selectivity in LO does not vary with retinal stimulus position. We used a conventional functional localizer to identify human visual area LO by comparing BOLD responses to objects versus scrambled objects presented to either the upper (UVF) or lower (LVF) visual field. In agreement with recent findings, we found evidence of position-dependent responses to objects. However, we observed the same degree of position dependence for scrambled objects and thus object selectivity did not differ for UVF and LVF stimuli. We conclude that, in terms of BOLD response, LO discriminates objects from non-objects equally well in either visual field location, despite stronger responses to objects in the LVF.

Perceptual qualia and local network behavior in the cerebral cortex

This paper explores the implications of a recently published theory that relates the experience of qualia to the attractor activity in networks of pyramidal cells in the cerebral cortex. The paper builds on this theory, and aims to link activity in different networks to the nature of the qualia experienced. Some basic links between network activity and qualia experiences are initially presented, showing the importance of learning, and the paper then proceeds to relate these mechanisms to the qualia experienced during sensory perception. The paper argues that attractor behavior in networks of layer 2/3 pyramidal neurons could underpin the vivid sensory qualia of perception, and attractor behavior in networks of layer 5A pyramidal neurons could have a role in the more understanding kind of perceptual qualia. Communication between these networks is explored to suggest their involvement in putting incoming sensory information into the context of all prior experience, and the understanding that could result.

Cueless blindsight

The term blindsight describes the non-reflexive visual functions that remain or recover in fields of absolute cortical blindness. As visual stimuli confined to such fields are subjectively invisible, they are customarily announced by visible or audible cues that inform the patients when to respond. The pervasive use of cueing has spawned the widely held assumption that sight and blindsight differ in that only blindsight requires cueing. To test this assumption, we measured detection of auditorily cued and un-cued stimuli in three hemianopic patients. Stimuli fell onto the photosensitive retina of the subjectively blind field, onto the objectively blind optic disc, and, in one patient, into a region where they evoked impoverished conscious sight. Regardless of whether cues were given, performance was highly significant in the latter region of poor sight, clearly above chance in the subjectively blind field, and random in the optic disc control condition. Moreover, cues enhanced detection only in the relatively blind field. Showing that blindsight performance persists when cues are omitted, the results imply that non-reflexive responses can be initiated in the absence of both stimulus awareness and perceptible cues.

Visuell-räumliches Arbeitsgedächtnis

Zusammenfassung. In der Multikomponentenkonzeption des Arbeitsgedächtnisses wird explizit eine separate visuelle Teilkomponente postuliert, die in einen Speicher für statische visuelle Informationen (Visual Cache) und einen dynamischen (räumlichen) Wiederholungsprozess (Inner Scribe) unterteilt wird. In der vorliegenden Arbeit wird argumentiert, dass eine solche Aufteilung begrifflich unscharf und nicht geeignet ist, die empirischen Befunde angemessen zu erklären. Die Unterscheidung statisch versus dynamisch trifft nicht die richtige Dimension. Stattdessen sprechen neurowissenschaftliche Befunde eher für eine Trennung zwischen räumlich und visuell, wobei die räumliche Komponente zum Teil supramodal ist, während die visuelle Komponente eine Binnendifferenzierung entlang den repräsentierten Inhalten aufweist. Es wird die These aufgestellt, dass kein separater Speicher postuliert werden muss, um die in der Literatur dokumentierten Phänomene zu erklären. Die Annahme von temporär im visuellen Wahrnehmungsprozess entstehenden Repräsentationen reicht aus, um kurzzeitiges Erinnern zu erklären. Folglich wird das Arbeitsgedächtnis im gleichen verteilten neuronalen Netzwerk realisiert, das die visuelle Informationsverarbeitung in der Wahrnehmung leistet.

The Geometry of Visual Perception: Retinotopic and Non-retinotopic Representations in the Human Visual System

Geometry is closely linked to visual perception; yet, very little is known about the geometry of visual processing beyond early retinotopic organization. We present a variety of perceptual phenomena showing that a retinotopic representation is neither sufficient nor necessary to support form perception. We discuss the popular "object files" concept as a candidate for non-retinotopic representations and, based on its shortcomings, suggest future directions for research using local manifold representations. We suggest that these manifolds are created by the emergence of dynamic reference-frames that result from motion segmentation. We also suggest that the metric of these manifolds is based on relative motion vectors.

Learning as a possible sign of non-reflective consciousness in persons with a diagnosis of vegetative state and pervasive motor impairment

A diagnosis of vegetative state represents a serious predicament, which basically precludes/minimizes rehabilitation perspectives. Reliability of the assessment approach in these situations is of paramount importance, but not easy to achieve. In recent studies, a learning assessment procedure has been suggested as a supplement in the diagnostic process and assessed with eight patients. The procedure involves an ABABCB sequence in which A represents baseline phases with no stimulation available, B intervention phases with stimuli delivered contingently on target responses, and C a control condition. This condition involves stimulation presented non-contingently. The patients' ability to associate responding with environmental stimuli and thus increase such responding during the B phases, and reduce it during the A and C phases, may be considered a sign of learning. Learning might be viewed as representative of forms of concrete knowledge and presumably basic levels of consciousness. Preliminary results indicate that (a) signs of learning may appear in patients with a previous diagnosis of vegetative state and (b) the presence of those signs may require a revision of their diagnostic label and a reappraisal of their rehabilitation perspectives.

3D surface perception from motion involves a temporal-parietal network

Previous research has suggested that three-dimensional (3D) structure-from-motion (SFM) perception in humans involves several motion-sensitive occipital and parietal brain areas. By contrast, SFM perception in nonhuman primates seems to involve the temporal lobe including areas MT, MST and FST. The present functional magnetic resonance imaging study compared several motion-sensitive regions of interest including the superior temporal sulcus (STS) while human observers viewed horizontally moving dots that defined either a 3D corrugated surface or a 3D random volume. Low-level stimulus features such as dot density and velocity vectors as well as attention were tightly controlled. Consistent with previous research we found that 3D corrugated surfaces elicited stronger responses than random motion in occipital and parietal brain areas including area V3A, the ventral and dorsal intraparietal sulcus, the lateral occipital sulcus and the fusiform gyrus. Additionally, 3D corrugated surfaces elicited stronger activity in area MT and the STS but not in area MST. Brain activity in the STS but not in area MT correlated with interindividual differences in 3D surface perception. Our findings suggest that area MT is involved in the analysis of optic flow patterns such as speed gradients and that the STS in humans plays a greater role in the analysis of 3D SFM than previously thought.

Minding time in an amodal representational space

How long did it take you to read this sentence? Chances are your response is a ball park estimate and its value depends on how fast you have scanned the text, how prepared you have been for this question, perhaps your mood or how much attention you have paid to these words. Time perception is here addressed in three sections. The first section summarizes theoretical difficulties in time perception research, specifically those pertaining to the representation of time and temporal processing. The second section reviews non-exhaustively temporal effects in multisensory perception. Sensory modalities interact in temporal judgement tasks, suggesting that (i) at some level of sensory analysis, the temporal properties across senses can be integrated in building a time percept and (ii) the representational format across senses is compatible for establishing such a percept. In the last section, a two-step analysis of temporal properties is sketched out. In the first step, it is proposed that temporal properties are automatically encoded at early stages of sensory analysis, thus providing the raw material for the building of a time percept; in the second step, time representations become available to perception through attentional gating of the raw temporal representations and via re-encoding into abstract representations.

A theory of moving form perception: Synergy between masking, perceptual grouping, and motion computation in retinotopic and non-retinotopic representations

Because object and self-motion are ubiquitous in natural viewing conditions, understanding how the human visual system achieves a relatively clear perception for moving objects is a fundamental problem in visual perception. Several studies have shown that the visible persistence of a briefly presented stationary stimulus is approximately 120 ms under normal viewing conditions. Based on this duration of visible persistence, we would expect moving objects to appear highly blurred. However, in human vision, objects in motion typically appear relatively sharp and clear. We suggest that clarity of form in dynamic viewing is achieved by a synergy between masking, perceptual grouping, and motion computation across retinotopic and non-retinotopic representations. We also argue that dissociations observed in masking are essential to create and maintain this synergy.

Consciousness, accessibility, and the mesh between psychology and neuroscience

How can we disentangle the neural basis of phenomenal consciousness from the neural machinery of the cognitive access that underlies reports of phenomenal consciousness? We see the problem in stark form if we ask how we can tell whether representations inside a Fodorian module are phenomenally conscious. The methodology would seem straightforward: Find the neural natural kinds that are the basis of phenomenal consciousness in clear cases--when subjects are completely confident and we have no reason to doubt their authority--and look to see whether those neural natural kinds exist within Fodorian modules. But a puzzle arises: Do we include the machinery underlying reportability within the neural natural kinds of the clear cases? If the answer is "Yes," then there can be no phenomenally conscious representations in Fodorian modules. But how can we know if the answer is "Yes"? The suggested methodology requires an answer to the question it was supposed to answer! This target article argues for an abstract solution to the problem and exhibits a source of empirical data that is relevant, data that show that in a certain sense phenomenal consciousness overflows cognitive accessibility. I argue that we can find a neural realizer of this overflow if we assume that the neural basis of phenomenal consciousness does not include the neural basis of cognitive accessibility and that this assumption is justified (other things being equal) by the explanations it allows.

The contribution of synaptic plasticity in the basal ganglia to the processing of visual information

A mechanism for the involvement of the basal ganglia in the processing of visual information, based on dopamine-dependent modulation of the efficiency of synaptic transmission in interconnected parallel associative and limbic cortex-basal ganglia-thalamus-cortex circuits, is proposed. Each circuit consists of a visual or prefrontal area of the cortex connected with the thalamic nucleus and the corresponding areas in different nuclei of the basal ganglia. The circulation of activity in these circuits is supported by the recurrent arrival of information in the thalamus and cortex. Dopamine released in response to a visual stimulus modulates the efficiencies of "strong" and "weak" corticostriatal inputs in different directions, and the subsequent reorganization of activity in the circuit leads to disinhibition (inhibition) of the activity of those cortical neurons which are "strongly" ("weakly") excited by the visual stimulus simultaneously with dopaminergic cells. The pattern in each cortical area is the neuronal reflection of the properties of the visual stimulus processed by this area. Excitation of dopaminergic cells by the visual stimulus via the superior colliculi requires parallel activation of the disinhibitory input to the superior colliculi via the thalamus and the "direct" pathway" in the basal ganglia. The prefrontal cortex, excited by the visual stimulus via the mediodorsal nucleus of the thalamus, mediates the descending influence on the activity of dopaminergic cells, simultaneously controlling dopamine release in different areas of the striatum and thus facilitating the mutual selection of neural reflections of the individual properties of the visual stimulus and their binding into an integral image.