| O'Regan, J.K., Noë, A. A sensorimotor account of vision and visual consciousness Behavioral and Brain Sciences 2001 (24)5 [html] |
| Many current neurophysiological, psychophysical and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The outside world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the governing laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Several lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual "filling in", visual stability despite eye movements, change blindness, sensory substitution, and color perception. |
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| Lutz, A., Lachaux, J.-P. , Martinerie, J., Varela, F.J. Guiding the study of brain dynamics by using first-person data: Synchrony patterns correlate with ongoing conscious states during a simple visual task Proceedings of the National Academy of Sciences USA 2002 (99)3:1586-1591 [pdf] |
| Even during well-calibrated cognitive tasks, successive brain responses to repeated identical stimulations are highly variable. The source of this variability is believed to reside mainly in fluctuations of the subject's cognitive "context" defined by his/her attentive state, spontaneous thought process, strategy to carry out the task, and so on ... As these factors are hard to manipulate precisely, they are usually not controlled, and the variability is discarded by averaging techniques. We combined first-person data and the analysis of neural processes to reduce such noise. We presented the subjects with a three-dimensional illusion and recorded their electrical brain activity and their own report about their cognitive context. Trials were clustered according to these first-person data, and separate dynamical analyses were conducted for each cluster. We found that (i) characteristic patterns of endogenous synchrony appeared in frontal electrodes before stimulation. These patterns depended on the degree of preparation and the immediacy of perception as verbally reported. (ii) These patterns were stable for several recordings. (iii) Preparatory states modulate both the behavioral performance and the evoked and induced synchronous patterns that follow. (iv) These results indicated that first-person data can be used to detect and interpret neural processes. |
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| Life Sciences Computing Facility, Univ. California Santa Barbara [html] |
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| Macaluso, E., Frith, C., Driver, J. Modulation of human visual cortex by crossmodal spatial attention Science 2000 (289):1206-1208 [html] |
| A sudden touch on one hand can improve vision near that hand, revealing crossmodal links in spatial attention. It is often assumed that such links involve only multimodal neural structures, but unimodal brain areas may also be affected. We tested the effect of simultaneous visuo-tactile stimulation on the activity of the human visual cortex. Tactile stimulation enhanced activity in the visual cortex, but only when it was on the same side as a visual target. Analysis of effective connectivity between brain areas suggests that touch influences unimodal visual cortex via back-projections from multimodal parietal areas. This provides a neural explanation for crossmodal links in spatial attention. |
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| Coppola, D., Purves, D. The extraordinarily rapid disappearance of entoptic images Proceedings of the National Academy of Sciences USA 1996 (96):8001-8004 [pdf] |
| It has been known for more than 40 years that images fade from perception when they are kept at the same position on the retina by abrogating eye movements. Although aspects of this phenomenon were described earlier, the use of close-fitting contact lenses in the 1950s made possible a series of detailed observations on eye movements and visual continuity. In the intervening decades, many investigators have studied the role of image motion on visual perception. Although several controversies remain, it is clear that images deteriorate and in some cases disappear following stabilization; eye movements are, therefore, essential to sustained exoptic vision. The time course of image degradation has generally been reported to be a few seconds to a minute or more, depending upon the conditions. Here we show that images of entoptic vascular shadows can disappear in less than 80 msec. The rapid vanishing of these images implies an active mechanism of image erasure and creation as the basis of normal visual processing. |
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| Chichilisky, E., Wandell, B.A. Trichromatic opponent color classification Vision Research 1999 [pdf] |
| Stimuli varying in intensity and chromaticity, presented on numerous backgrounds, were classified into red/green, blue/yellow and white/black opponent color categories. These measurements revealed the shapes of the boundaries that separate opponent colors in three-dimensional color space. Opponent color classification boundaries were generally not planar, but their shapes could be summarized by a piecewise linear model in which increment and decrement color signals are combined with different weights at two stages to produce opponent color sensations. The effect of background light on classification was largely explained by separate gain changes in increment and decrement cone signals. |
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| Feldman, J. What is a visual object ? Trends in Cognitive Sciences 2003 (7)6:252-256 [pdf] |
| The concept of an object plays a central role in cognitive science, particularly in vision, reasoning and conceptual development but it has rarely been given a concrete formal definition. Here I argue that visual objects cannot be defined according to simple physical properties but can instead be understood in terms of the hierarchical organization of visual scene interpretations. Within the tree describing such a hierarchical description, certain nodes make natural candidates as the joints between objects, representing division points between parts of the image that cohere internally but do not perceptually group with one another. Thus each subtree hanging from such a node corresponds to a single perceived object . This formal defi- nition accords with several intuitions about the way objects behave. |
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