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Sung Jun Joo, Scott O. Murray; Contextual effects in human visual cortex depend on surface structure. Journal of Vision 2013;13(9):817. doi: 10.1167/13.9.817.
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© ARVO (1962-2015); The Authors (2016-present)
The neural response to a stimulus inside the receptive field of a V1 neuron ("target") is suppressed when it is surrounded by iso-oriented compared to orthogonal stimuli ("flankers"). Despite the importance of orientation-specific surround suppression in potentially mediating a number of important perceptual effects including saliency, contour integration, and orientation discrimination, the underlying neural mechanisms remain unknown. Here we show using measurements of event-related potentials (ERPs) in humans that surround suppression depends on the surface structure in an image. In Experiment 1, we established the basic surround suppression effect using stimulus configurations where the target was surrounded by "nearby" flankers. P1 amplitude in our ERP data was suppressed when the flankers matched the target orientation (same condition) compared to when the flankers were orthogonal to the target orientation (orthogonal condition). In Experiment 2, we increased the distance between the target and flankers by doubling the flanker-target distance used in Experiment 1. Perceptually, the stimuli now appeared to be 3 isolated stimuli rather than a single array of stimuli. We found no difference in P1 amplitude between the same and orthogonal conditions. In Experiment 3, we used the distant-flanker configuration of Experiment 2 but made the target and flankers appear to be grouped on a common surface that was distinct from the background. P1 amplitude was suppressed in the same condition compared to the orthogonal condition. In Experiment 4, we used the same spatial parameters of Experiment 1—where we observed strong surround suppression—but moved the flankers to different surfaces than the target. Although the flankers were displayed in the near proximity of the target, we found no evidence of surround suppression in the P1 amplitude. Our results demonstrate a surprising role of high-level, global processes in determining when contextual effects occur in early visual cortex.
Meeting abstract presented at VSS 2013
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