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Carmel Mevorach, Glyn Humphreys, Lilach Shalev; Reflexive and preparatory selection and suppression of salient information in the right and left posterior parietal cortex. Journal of Vision 2008;8(6):394. doi: 10.1167/8.6.394.
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Attentional cues can trigger activity in the parietal cortex in anticipation of visual displays, and this activity may in turn induce changes in other areas of the visual cortex, hence implementing attentional selection. In a recent TMS study (Mevorach, Humphreys & Shalev, 2006) it was shown that the parietal cortex can utilize the relative saliency (a non-spatial property) of a target and distractor to bias visual selection. Furthermore, selection was lateralised so that the right PPC is engaged when salient information must be selected and the left PPC when the salient information must be ignored. However, it is not clear how PPC implements these complementary forms of selection. Here we used online triple-pulse TMS over the right or left PPC prior to or after the onset of Global/Local displays. When delivered after the onset of the display, TMS to right PPC disrupted the selection of the more salient aspect of the hierarchical letter. In contrast, left PPC activity delivered prior to the onset of the stimulus disrupted responses to the lower saliency stimulus. These findings suggest that selection and suppression of saliency, rather than being ‘two sides of the same coin’ are fundamentally different processes. Selection of saliency seems to operate reflexively whereas suppression of saliency relies on a preparatory phase that ‘sets-up’ the system in order to effectively ignore saliency.
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