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. (shrink)

Philosophers concerned with issues of mind have been turning to the neurosciences, especially neuropsychology, for empirical guidance. While I endorse this emphasis, I find that one important neuropsychological phenomenon, blindsight appears to have been misused by some prominent philosophers. In this paper, I examine this alleged misuse by spelling out the accounts of blindsight given by Daniel Dennett and Ned Block. I attempt to show that both Dennett and Block have ignored many complications surrounding blindsight including subjects' reports of visual (...) sensations. This neglect has serious ramifications for their respective models of human consciousness which I also try to explicate. Further, by misrepresenting blindsight, these accounts serve to hamper scientific and philosophical understanding of the phenomenon and of consciousness. I conclude by sketching a model of blindsight that acknowledges these neglected details. (shrink)

A key element of the distinction between explicit and implicit cognitive functioning is the presence or absence of conscious awareness. In this review, we consider the proposal that neuropsychological disorders can best be considered in terms of a decoupling between preserved implicit or unconscious processing and impaired explicit or conscious processing. Evidence for dissociations between implicit and explicit processes in blindsight, amnesia, object agnosia, prosopagnosia, hemi-neglect, and aphasia is examined. The implications of these findings for a) our understanding of a (...) variety of neuropsychological disorders, b) the conceptualization of normal cognitive functioning, c) the neural basis of consciousness, and d) the clinical rehabilitation of brain-injured individuals are also discussed. (shrink)