This latter finding is important as it suggests that the N2pc is created in cortex that is responsible for representing the target, and thus does not reflect modulation of the distractor representation itself.1 A more recent study has demonstrated that N2pc amplitude does not vary as a function of the need for distractor suppression, and that the component

can be elicited under circumstances where distractor suppression would presumably be counter-productive (Mazza et al., 2009). Results like these have led to the recent proposal that the N2pc may index ambiguity resolution through the action of multiple mechanisms, some acting on brain areas responsible for representing the distractor and others acting on brain areas responsible for check details representing the target itself (Hickey et al., 2009). This last perspective is the one adopted in the current study: we believe that the N2pc indexes more than one attentional mechanism, as suggested by Hickey et al. (2009), but that the core purpose of these operations is the resolution and disambiguation of visual input, as suggested by Luck et al., 1997a and Luck et al., 1997b. In the context

of feature priming, this motivates the possibility that the type of perceptual ambiguity resolved by the N2pc may be similar in nature to the type of perceptual Leukotriene-A4 hydrolase ambiguity that Meeter and Olivers,

2006 and Olivers and Meeter, 2006) suggest causes feature priming. A prediction can be generated from this idea, namely that manipulations of perceptual Tacrolimus datasheet ambiguity that increase intertrial priming–such as the inclusion of a salient distractor in a display–should create a larger target-elicited N2pc. In order to test this hypothesis we recorded ERPs while participants completed a task based on the additional singleton paradigm of Theeuwes (1991). Participants searched for a shape singleton and responded based on the orientation of a line contained within this object. There were two important manipulations in the experimental design. First, display ambiguity was varied by replacing one of the non-targets in the search display with a task-irrelevant singleton defined by unique color. This is known to slow reaction time (RT) and increase error in this task, reflecting increased competition for selection ( Theeuwes, 1991). Second, in order to measure intertrial priming, the colors that defined the target and distractor in any one trial could remain the same in the next trial or could swap. Given this design we generated three predictions. First, the amplitude of target-elicited N2pc should be larger when displays contain a salient distractor and attention is deployed to the target.