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Shlomit Yuval-Greenberg, David J. Heeger; Continuous Flash Suppression Modulates Cortical Activity in Early Visual Cortex . Journal of Vision 2014;14(10):379. doi: 10.1167/14.10.379.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A salient visual stimulus can be rendered invisible by presenting it to one eye while flashing a mask to the other eye. This procedure, called continuous flash suppression (CFS), has been proposed as an ideal way of studying awareness as it can make a stimulus imperceptible for extended periods of time without changing its physical properties. CFS has been extensively used to study visual awareness using behavioral measurements, functional magnetic resonance imaging (fMRI) , and electrophysiology. Previous studies reported robust suppression of activity in higher visual areas during CFS , but the role of primary visual cortex (V1) is controversial. Here, we resolve this controversy on the role of V1 in CFS, and offer an explanation of the computational processes underlying CFS. Methods: We measured activity in human V1 using fMRI while subjects viewed CFS stimuli composed of a mask and a target (low, medium or high contrast), presented to the same eye (always visible) or to different eyes (invisible for the low contrast). Each subject participated in multiple fMRI scanning sessions to ensure sufficient statistical power. Results: Functional MRI responses in early visual cortex were smaller when target and mask were in different eyes compared to the same eye, not only for the lowest contrast target rendered invisible by CFS, but also for higher contrast targets which were visible even when presented to the eye opposite the mask. Conclusions: Our results suggest that CFS is a form of perceptual masking, for which the presence of a mask suppresses activity evoked by the target , and that the suppression is stronger when mask and target are presented to different eyes. We propose that CFS impacts awareness by modulating the gain of neural responses to the target, at an early stage of visual processing, akin to reducing target contrast.
Meeting abstract presented at VSS 2014
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