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Diane Beck, Ana Torralbo; Perceptual load-induced selection as a consequence of spatial interactions in visual cortex. Journal of Vision 2008;8(6):993. doi: https://doi.org/10.1167/8.6.993.
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Perceptual load has been proposed as a determining factor in the degree to which unattended information is processed. Although there is considerable support for this theory, there is currently no a priori definition of what constitutes high or low perceptual load. Last year, we suggested that local competitive interactions in visual cortex underlie perceptual load: stimuli that induce strong competitive interactions among items should require a strong top-down bias in order to overcome the competition and select the target, and can thus be characterized as high perceptual load. Accordingly, we showed that increasing display density, which should also increase competitive interactions in visual cortex, resulted in reduced distractor processing. This year we test an even more surprising prediction of our theory. If perceptual load is determined by local interactions in early or intermediate visual areas (in which the representation of a hemifield is confined to a hemisphere), then placing multiple items within the same hemifield should result in greater perceptual load and reduced distractor processing than when the target item appears alone within a hemifield. In half of the trials the search array was positioned such that target appeared alone in the hemifield (with the non-targets in the opposite hemifield). In the other half of the trials, the target shared a hemifield with the two non-target items. The distractor was located at fixation. As predicted, we found that trials in which the target appeared in a different hemifield than the non-targets produced greater distractor effects than trials in which the target appeared in the same hemifield as the non-targets. These results not only support the hypothesis that local suppressive interactions among the target set dictate the extent to which a distractor can be ignored, but they also suggest that the attentional bias is determined independently in the two hemispheres.
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