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Hengqing Chu, Alejandro Lleras; Order effects determine whether irrelevant stimuli are scrutinized in preview and conjunction search. Journal of Vision 2009;9(8):1172. doi: 10.1167/9.8.1172.
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Visual search is facilitated when half of the distractors are previewed before presentation of the full search display. Watson & Humphreys (2005) investigated whether the onset of irrelevant stimuli would disrupt this preview benefit. They found that presenting irrelevant dots between the preview and final displays affected the preview benefit only when the dots shared the same color with the new items. They proposed that this result reflected an anticipatory feature-based set for new stimuli such that stimuli matching this set would be attended. Our study investigated whether attention to irrelevant stimuli that match your attentional set for color is automatic. We found that the answer to this question strongly depended on the order in which participants experience the different search conditions in the experiment. When participants first complete a block of preview trials with irrelevant dots that never match the target color, they learn to ignore these dots and continue to do so throughout the experiment, irrespective of search condition (preview or conjunction search). However, when participants first experience a block of preview trials with irrelevant dots that always match the target color, they learn to attend to these dots and appear to inspect them even in later conjunction search blocks in the experiment. We replicated this result in two experiments. Further, in a third experiment, we found that participants learn to ignore irrelevant dots when the dots color is totally uncorrelated with the color of the target. Congruent with the results of Leber & Egeth (2006), these results suggest that early experience with a set of stimuli determines the attentional fate of these stimuli.
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