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Sung Jun Joo, Geoffrey Boynton, Scott Murray; Long-range, pattern-dependent contextual effects in early visual cortex. Journal of Vision 2011;11(11):1089. doi: 10.1167/11.11.1089.
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A stimulus that deviates from a pattern can be readily detected, indicating an enhanced representation of this stimulus in the visual system. We demonstrate that neural activity in early visual cortex may mediate global, pattern-dependent saliency. We manipulated the saliency of an oriented target Gabor using both adjacent and remote flankers. For example, a vertically (V) oriented target can be considered a part of a pattern when surrounded by flankers of the same orientation (same condition: V-V-V or V-V-V-V-V). The identical target becomes salient when it deviates from the orientation of adjacent horizontal (H) flankers (orthogonal condition: H-V-H or H-H-V-H-H). However, the saliency of the target can be reduced by remote flankers by forming a global, repeating pattern (pattern condition: V-H-V-H-V). Critically, in the pattern condition, the local configuration (e.g., H-V-H) is the same as the orthogonal condition thus any changes in response to the target result from long-range processes.
We assessed the response to the target as a function of pattern-dependent saliency using: (1) contrast adaptation, (2) reaction time (RT), and (3) fMRI. The target produced greater adaptation in the orthogonal condition than in the same condition, suggesting higher neural activity for a salient target. Critically, the amount of adaptation decreased in the pattern condition compared to the orthogonal condition, even though the local configuration remained equivalent. We found that RTs were faster for detecting the target in the orthogonal relative to the same and pattern conditions. An fMRI experiment also demonstrated higher responses to the target in V1-V3 in the orthogonal compared to the same and pattern conditions. Overall, these converging findings suggest that global pattern information is encoded in early visual cortex and that neural responses are modulated by both adjacent and remote stimuli.
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