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Ignacio Vallines, En-Ju Lin, Hermann Müller; Cortical control of salient-distracter interference during visual search: Can attentional capture be top-down modulated?. Journal of Vision 2008;8(6):1109. doi: 10.1167/8.6.1109.
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Visual search for a target among homogeneous distracters is notably disrupted by the presence of a salient singleton element in the display. This disrupting effect can be measured as a significant increase in the time needed to respond to the target, and is traditionally explained in terms of a reflexive, involuntary shift of focal attention to the distracter. In this event-related fMRI study, we demonstrate that the magnitude of this interference can be greatly attenuated by exerting top-down control. Observers had to detect and respond to a singleton form target amongst non-target items that could include a salient color singleton distracter, while the frequency of appearance of this distracter (i.e., observers' certainty about the occurrence of a distracter event) was systematically manipulated. The unexpected onset of a color distracter was found to engage areas of the superior parietal and the dorsolateral prefrontal cortex bilaterally. Matching brain activity in the medial frontal gyrus, we observed a significant reduction in the magnitude of interference when observers could anticipate the appearance of the singleton distracter, possibly reflecting active recalibration of dimensional weights (e.g., reducing the weight for color-based feature contrast signals). The small but significant amount of interference that remained even with high stimulus certainty was strongly related to the spatial position of the distracter with respect to the target: the closer the distracter to the target, the stronger the interference. This spatial effect was parametrically reflected in the activity levels of the right dorsolateral prefrontal cortex, which was also significantly engaged by the unexpected onset of the distracter, and seems to be relieved by stimulus certainty. Our data suggests that extra processing costs associated with attentional capture disappear almost completely when observers are allowed to recalibrate dimension-specific weights based on stimulus certainty, and the singleton distracter is spatially distant from the target.
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