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Nicolas Burra, Dirk Kerzel; Is attentional capture modulated by task difficulty? An N2pc study with visual search of repeated and changing targets. Journal of Vision 2011;11(11):82. doi: 10.1167/11.11.82.
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Attention may be guided by intentions in a top_down fashion or may be driven by salient stimuli in a bottom-up fashion. Using event-related potentials (ERPs), Hickey et al. (2006) demonstrated that salient colour singletons catch attention without any intention to attend to colour, supporting the notion of bottom-up control. However, using similar displays, by Schubo (2009) did not observe that irrelevant colour singletons capture attention. We tested the idea that this discrepancy was due to the difference in task difficulty between the two studies. As in the previous studies, we measured ERPs and focused on the N2pc component as a measure of attentional deployment. Similar to Hickey et al. (2006), our subjects searched for a shape singleton whose identity varied unpredictably from trial to trial (mixed target condition). Additionally, we ran a condition similar to Schubo (2009) in which target identity remained constant in a block of trials (same target condition). Our behavioural results showed that the same target condition was performed significantly faster than the mixed target condition, confirming a difference in task difficulty. Additionally, responses were slowed by the presence of an irrelevant colour singleton in mixed and same target conditions, but interference was larger in the mixed than in the same target condition (consistent with Pinto et al., 2005). Further, we did not replicate an N2pc to the colour singleton that was reported by Hickey et al. However, we found a significant enhancement of the N2pc component in the same target condition compared to the mixed target condition. The N2pc enhancement was observed for different positions of the colour singleton (same side, opposite side or vertical). Based on these findings, we conclude that the N2pc may index mechanisms involved in identifying and localizing relevant stimuli through enhancement of their features.
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