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Tatiana Aloi Emmanouil, Philip Avigan, Marjan Persuh, Tony Ro; Saliency affects feedforward more than feedback processing in primary visual cortex. Journal of Vision 2011;11(11):151. doi: 10.1167/11.11.151.
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Visual cortex activity is influenced by both top-down attention and bottom-up saliency effects. We used transcranial magnetic stimulation (TMS) over primary visual cortex to investigate how different feature tasks and saliencies influence the timing of visual processing. Participants performed color or orientation judgments on stimuli of the same luminance but different color saliency. A TMS pulse was applied at varying SOAs after stimulus presentation to assess the timecourse of visual suppression. The results showed similar suppression for color and orientation tasks, but differences based upon feature saliency: the more salient stimuli were more resistant to TMS-induced visual suppression than the less salient stimuli, especially at the early SOAs. These results indicate a stronger initial representation of more salient stimuli in primary visual cortex and suggest that different forms of processing may be occurring during early (i.e., feedforward) and late (i.e., feedback) stages of processing.
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