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Helen Payne, Harriet Allen; Active ignoring in early visual cortex. Journal of Vision 2009;9(8):88. doi: 10.1167/9.8.88.
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The time taken to find a search target amongst distractors can be reduced if half the distractors are previewed before the remainder of the distractors (and target) are added to the display. Participants behave as if they are excluding the previewed items from their search. Previous studies suggest that this “preview benefit” results from active ignoring of search items presented in the preview display. These studies also reveal enhanced neural activation in posterior parietal cortex in response to preview trials. Here we investigated, using event-related fMRI, whether changes in neural activity during active ignoring can be found in early visual cortex.
Whilst maintaining central fixation, participants searched for a sideward T amongst a set of L-shaped distractors. In the Preview condition an initial display of distractors was previewed and remained on the screen when the new distractor items and target appeared. In the Full Set condition the initial distractor display was uninformative and disappeared upon arrival of the new distractors and target. The number of distractor items in the second display was identical in the two conditions. Crucially, on a minority of trials (Preview-display only and Full Set-first-display only trials) the second display was not presented. These trials were visually identical between conditions, only the expectation of the participant differed. This allowed us to measure preparatory activity associated with ignoring the previewed distractors.
We found higher activation in early visual cortex in the Preview-display only trials compared to the Full Set-first-display only trials during blocks of trials where participants benefited from the preview display. This is consistent with increased attention to the successfully previewed items. We also found that this activation was modulated by the amount of preview benefit. Our results suggest that active ignoring of previewed distractors leads to signal changes even in the earliest visual areas.
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