Listening to subject’s commentaries can be a useful spur to novel scientific departures, as in studies of blindsight. Recently further testing has been possible with subject DB, who was a blindsight patient tested intensively over a period of 10 years and who was the subject of the book, . Essentially his original capacity is the same or somewhat more sensitive. Some further types of discriminations have now been tested that were not possible in the original study. But a new feature (...) was discovered, namely that he describes conscious after-images of a wide range of inducing stimuli of which he is unconscious. The properties of the after-images are briefly described, such as their occurrence following unseen colour patches, luminance changes, shape, spatial frequency, their long durations, showing inter-ocular transfer, as well as their conforming to Emmert’s Law. Various approaches are discussed towards finding the source of their generation, such as the use of after-images of colour mixes of separate inputs to the two eyes . They are also discussed in terms of after-images in normal subjects that are generated by imagination. The discovery offers a rare potential opportunity to compare the brain activity associated with both the conscious and unconscious attributes of the precisely the same stimuli in the same locus in the same subject. (shrink)

Cognitive functions like perception, memory, language, or consciousness are based on highly parallel and distributed information processing by the brain. One of the major unresolved questions is how information can be integrated and how coherent representational states can be established in the distributed neuronal systems subserving these functions. It has been suggested that this so-called ''binding problem'' may be solved in the temporal domain. The hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into (...) cell assemblies and that this process may underlie the selection of perceptually and behaviorally relevant information. As we intend to show here, this temporal binding hypothesis has implications for the search of the neural correlate of consciousness. We review experimental results, mainly obtained in the visual system, which support the notion of temporal binding. In particular, we discuss recent experiments on the neural mechanisms of binocular rivalry which suggest that appropriate synchronization among cortical neurons may be one of the necessary conditions for the buildup of perceptual states and awareness of sensory stimuli. (shrink)

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. (shrink)

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.