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Johannes J. Fahrenfort, H. Steven Scholte, Victor A. F. Lamme; Perception correlates with feedback but not with feedforward activity in human visual cortex. Journal of Vision 2007;7(9):388. doi: 10.1167/7.9.388.
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© ARVO (1962-2015); The Authors (2016-present)
Although many experiments have shown that awareness covaries with activity in early visual cortex, the exact spatiotemporal profile of this correlation is still unclear. In this experiment we use EEG to correlate the entire spatiotemporal profile of neural processing in visual cortex with perception. This makes it possible to distinguish between those stages of visual processing that correlate with human perception and those that do not. Subjects had to detect a texture defined square which was degraded by a subsequent pattern mask. We correlated subjects' ability to detect the figure with the corresponding EEG signal through time and space. The results show that extra-striate activity in the 100–160 ms range does not correlate with perception, while more posterior (plausibly striate) activity in the same time frame and beyond correlates strongly with perception. This is consistent with the notion of an unconscious feedforward sweep and feedback processing being necessary for visual awareness. Furthermore, several subsequent stages show an alternating pattern of such bilateral extra-striate (180–230 ms) and more posterior (240–260 ms) activity, all of which correlate with perception. This suggests that multiple reentrant loops are engaged in visual perception.
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