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Clayton Hickey, Jan Theeuwes; ERP correlates of inter-trial effects in visual search. Journal of Vision 2008;8(6):377. doi: 10.1167/8.6.377.
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Visual search for a singleton target is slowed by the presence of a singleton distractor, and this interference effect is exacerbated when target and distractor identities are uncertain. For example, search for a uniquely shaped target is slowed more by the presence of a uniquely colored distractor when the defining characteristics of these objects change from trial to trial than when these characteristics remain the same over experimental blocks. This has been interpreted as evidence that endogenous attentional control can minimize the interference of salient-yet-irrelevant distractor stimuli. However, recent results have tied the cost of target and distractor uncertainty to inter-trial priming rather than top-down set. According to this perspective salient distractor stimuli capture attention when the characteristic that defines the distractor on trial n has changed from trial n-1. We used the event-related potential (ERP) technique to investigate the how target and distractor uncertainty affect visual search. The results were consistent with the idea that inter-trial priming underlies uncertainty effects in visual search. Furthermore, it appears that inter-trial priming has discrete influences on attentive and post-perceptual processing stages, but not on early sensory and perceptual activity. These results are consistent with models of selection and visual search in which stimulus-driven factors play an important role.
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