Abstract: What are the neural correlates of conscious visual awareness? Tackling this question requires contrasting neural correlates of stimulus processing culminating in visual awareness with neural correlates of stimulus processing unaccompanied by awareness. To contrast these two neural states, one must be able to erase an otherwise visible stimulus from awareness. This paper describes and critiques visual phenomena involving dissociation of physical stimulation and conscious awareness: degraded stimulation, visual masking, visual crowding, bistable figures, binocular rivalry, motion-induced blindness, inattentional blindness, change blindness and attentional blink. While no single strategy stands above the others, those producing changing visual awareness despite invariant physical stimulation are clearly preferable

Abstract: 1 INSERM-CEA Unit 562, Cognitive Neuroimaging, Service Hospitalier Fre´de´ric Joliot, Orsay, France, 2 CNRS URA2182 Re´cepteurs and Cognition, Institut Pasteur, Paris, France

Abstract: Tim Crane University College London 1. Introduction P.F. Strawson argued that ‘mature sensible experience (in general) presents itself as … an immediate consciousness of the existence of things outside us’ (1979: 97). He began his defence of this very natural idea by asking how someone might typically give a description of their current visual experience, and offered this example of such a description: ‘I see the red light of the setting sun filtering through the black and thickly clustered branches of the elms; I see the dappled deer grazing in groups on the vivid green grass…’ (1979: 97). In other words, in describing experience, we tend to describe the objects of experience – the things which we experience – and the ways they are when we are experiencing them

Abstract: The Cognitive Neuroscience of Vision begins by introducing the reader to the anatomy of the eye and visual cortex and then proceeds to discuss image and...

Abstract: Our visual system not only mediates information about the visual environment but is capable of generating pictures of nonexistent worlds: afterimages, illusions, phosphenes, etc. We are ''aware'' of these pictures just as we are aware of the images of natural, physical objects. This raises the question: is the neural correlate of consciousness (NCC) of such images the same as that of images of physical objects? Images of natural objects have some properties in common with afterimages (e.g., stability of verticality) but there are also obvious differences (e.g., images maintain size constancy, whereas afterimages follow Emmert's Law: when seen while screens at different distances are observed, an afterimage looks larger, the greater the distance of the screen). The differences can be explained by differences in the retinal extent of images and afterimages, which favors the view that both have the same NCC. It seems reasonable to assume that before neural activity can produce awareness, all the computations necessary for a veridical representation of, e.g., an object, must be completed within the neural substrate and that information characteristic of a particular object must be available within the NCC. Given these assumptions, it can be shown that no retinotopic (in a strict sense) cortical areas can serve as the NCC, although some type of topographic representation is necessary. It seems also to be unlikely that neurons classified as cardinal cells alone can serve as NCC

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

Abstract: Recent developments in psychology and neuroscience suggest away to link the mental phenomenon of visual awareness with specific neural processes. Here, it is argued that the feed-forward activation of cells in any area of the brain is not sufficient to generate awareness, but that recurrent processing, mediated by horizontal and feedback connections is necessary. In linking awareness with its neural mechanisms it is furthermore important to dissociate phenomenal awareness from visual attention or decision processes

Abstract: Logothetis, N.K.: Single units and conscious vision. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences 353, 1801-1818 (1998) Abstract

Abstract: This paper develops an empirically motivated theory of visual consciousness. It begins by outlining neuropsychological support for Jackendoff's (1987) hypothesis that visual consciousness involves mental representations at an intermediate level of processing. It then supplements that hypothesis with the further requirement that attention, which can come under the direction of high level representations, is also necessary for consciousness. The resulting theory is shown to have a number of philosophical consequences. If correct, higher-order thought accounts, the multiple drafts account, and the widely held belief that sensation precedes perception will all be found wanting. The theory will also be used to illustrate and defend a methodology that fills the gulf between functionalists who ignore the brain and neural reductionists who repudiate functionalism

Abstract: It has been shown that visual awareness in the blind hemifield of hemianopic cats that have undergone unilateral ablations of visual cortex can be restored by sectioning the commissure of the superior colliculus or by destroying a portion of the substantia nigra contralateral to the cortical lesion (the Sprague effect). We propose that the visual awareness that is recovered is due to synchronized oscillatory activities in the superior colliculus ipsilateral to the cortical lesion. These oscillatory activities are normally partially suppressed by the inhibitory, GABAergic contralateral nigrotectal projection, and the destruction of the substantia nigra, or the sectioning of the collicular commissure, disinhibits the collicular neurons, causing an increase in the extent of oscillatory activity and/or synchronization between activities at different sites. This increase in the oscillatory and synchronized character is sufficient for the activities to give rise to visual awareness. We argue that in rodents and lower vertebrates, normal visual awareness is partly due to synchronized oscillatory activities in the optic tectum and partly due to similar activities in visual cortex. It is only in carnivores and primates that visual awareness is wholly due to cortical activities. Based on von Baerian recapitulation theory, we propose that, even in humans, there is a period in early infancy when visual awareness is partially due to activities in the superior colliculus, but that this awareness gradually disappears as the nigrotectal projection matures

Abstract: Some patients with a lesion to the striate cortex (V1), when assessed through forced-choice paradigms, are able to detect stimuli presented in the blind field, despite reporting a complete lack of visual experience. This phenomenon, known as blindsight, strongly implicates V1 in visual awareness. However, the view that V1 is indispensable for conscious visual perception is challenged by a recent finding that the blindsight subject GY can be aware of visual qualia in his blind field, implying that V1may not be critical under all circumstances. This apparent contradiction raises the following question: if V1 is not always necessary for phenomenal awareness, why do V1 lesions have such a detrimental effect on conscious perception? It is suggested here that this contradiction can be resolved by considering the impact of V1 lesions on the functioning of the whole visual cortex.

Abstract: Stoerig links blindsight to lesions between the primary visual cortex and the extravisual cortex. A parallel 'blindsight' occurs when input from the primary visual cortex is blocked during eye movements, convergence and blinks. At such moments (i) conscious vision based upon retinal input is blocked, (ii), however, like in blind sight retinal input can be used in motor tasks. The main difference to blindsight is that we are not only blind but cannot even with deliberate attention bring this blindness into awareness. We are doubly unaware: unaware of being blind and unaware that in spite of this that what we can see is created by the posterior parietal cortex substituting output (for that temporarily not coming from the primary visual cortex) for higher areas of the cerebral cortex

Abstract: The visual brain consists of several parallel, functionally specialized processing systems, each having several stages (nodes) which terminate their tasks at different times; consequently, simultaneously presented attributes are perceived at the same time if processed at the same node and at different times if processed by different nodes. Clinical evidence shows that these processing systems can act fairly autonomously. Damage restricted to one system compromises specifically the perception of the attribute that that system is specialized for; damage to a given node of a processing system that leaves earlier nodes intact results in a degraded perceptual capacity for the relevant attribute, which is directly related to the physiological capacities of the cells left intact by the damage. By contrast, a system that is spared when all others are damaged can function more or less normally. Moreover, internally created visual percepts-illusions, afterimages, imagery, and hallucinations-activate specifically the nodes specialized for the attribute perceived. Finally, anatomical evidence shows that there is no final integrator station in the brain, one which receives input from all visual areas; instead, each node has multiple outputs and no node is recipient only. Taken together, the above evidence leads us to propose that each node of a processing-perceptual system creates its own microconsciousness. We propose that, if any binding occurs to give us our integrated image of the visual world, it must be a binding between microconsciousnesses generated at different nodes. Since any two microconsciousnesses generated at any two nodes can be bound together, perceptual integration is not hierarchical, but parallel and postconscious. By contrast, the neural machinery conferring properties on those cells whose activity has a conscious correlate is hierarchical, and we refer to it as generative binding, to distinguish it from the binding that might occur between the microconsciousnesses