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Jocelyn Sy, Barry Giesbrecht; fMRI evidence for top-down influences on perceptual distraction. Journal of Vision 2010;10(7):212. doi: 10.1167/10.7.212.
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Studies of visuospatial attention have demonstrated that the extent to which task-irrelevant information is processed depends on the perceptual demands of processing task-relevant information (e.g., Lavie, 1995). This result has been explained by the load theory of attention that assumes that perceptual resources are allocated automatically and exhaustively (e.g., Lavie et al., 2004). Here, we tested the extent to which the automatic allocation of perceptual resources can be influenced by top-down attentional control systems using behavioral and neural measures. Fourteen observers searched for a target letter (X or N) amongst a homogeneous (low-load) or heterogeneous (high-load) array of distractors. Prior to the search array, a color change at fixation cued the display load (84% valid; 16% invalid). Processing of task-irrelevant information was assessed behaviorally by measuring the interference caused by a task-irrelevant flanker letter. fMRI methods were used to record BOLD responses during the task. The cue+target trials were randomly intermixed with trials in which there was a cue, but no target (cue-only) and trials in which there were no stimuli. The results indicated that behavioral interference was modulated by cue validity, such that on valid trials, there was little interference, but on invalid trials there was greater interference under low than high load. fMRI analyses of the cue-only trials revealed regions of the dorsal frontoparietal network. BOLD responses in subregions of this network (bilateral IPL; left MFG) on cue+target trials were correlated with individual differences in behavioral interference. In visual cortex, areas that represented the task-irrelevant locations (identified by a separate localizer scan) showed larger cue-only responses on low-load trials than on high-load trials. In contrast, areas that represented the task-relevant locations showed larger cue-only responses on high-load trials. These results suggest that top-down expectations influence the allocation of perceptual resources to compensate for anticipated levels of perceptual load.
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