To find out whether attentional capture by irrelevant but salient visual objects is an exogenous bottom-up phenomenon, or can be modulated by current task set, two experiments were conducted where the N2pc component was measured as an electrophysiological marker of attentional selection in response to spatially uninformative colour singleton cues that preceded target arrays. When observers had to report the orientation of a uniquely coloured target bar among distractor bars (colour task), behavioural spatial cueing effects were accompanied by an early cue-induced N2pc, indicative of rapid attentional capture by colour singleton cues. In contrast, when they reported the orientation of target bars presented without distractors (onset task), no behavioural cueing effects were found, and no early N2pc was triggered to physically identical cue arrays. Experiment 2 ruled out an alternative interpretation of these N2pc differences in terms of distractor inhibition. These results do not support previous claims that attentional capture is initially unaffected by top-down intention, and demonstrate the central role of task set in involuntary attentional orienting.

The N2pc component has recently become a popular tool in attention research. To investigate whether this component exclusively reflects attentional target selection, or also prior stages in attentional processing (covert orienting, target-unspecific spatial attention), a spatial cueing procedure was combined with a visual search task. In some blocks, informative cues indicated the side of upcoming singleton targets that were present on most trials among uniform distractors. In other blocks, cues were spatially uninformative, and no preparatory shifts of attention were possible. The N2pc in response to targets was unaffected by this manipulation, showing that this component is not associated with attention shifts. Following informative cues, an attenuated N2pc was elicited by uniform non-target arrays, suggesting that the N2pc may also reflect spatially specific processing of stimulus features at task-relevant locations prior to target selection.Over the past thirty years, the brain mechanisms underlying visual-spatial attention have been studied intensively with event-related brain potential (ERP) measures. Different ERP components have been found to be modulated during spatially selective visual processing, and these components have been linked to different underlying sub-processes of spatial attention. The first type of attention-sensitive ERP effect was uncovered in early ERP studies where participants were instructed to direct their attention to a specific location on the left or right side, and keep it focused for an entire experimental block in order to detect target stimuli at that location (cf., Eason, 1981). Visual stimuli presented within the current focus of spatial attention triggered enhanced sensory-specific visual P1 and N1 components at posterior electrodes. Analogous P1 and N1 amplitude modulations were also observed when attention was manipulated in a trial-by-trial fashion by spatial precues that were presented at the start of each trial (cf. Mangun & Hillyard, 1991;Eimer, 1994). Because these P1/N1 enhancements for stimuli at attended locations were present irrespective of whether these stimuli were targets or non-targets (e.g., Mangun & Hillyard, 1987), they are interpreted as reflecting location-specific sensory gating mechanisms in early visual processing that precede the subsequent selection of targets over non-targets. They are assumed to be triggered by top-down signals from higher-order attentional control areas that bias the excitability of visual cortical areas in favour of any sensory input that originates from currently task-relevant locations (cf., Mangun, 1995).Other attention-sensitive ERP modulations found in more recent studies during cued shifts of spatial attention were interpreted as electrophysiological markers of top-down attentional control processes. In these studies, ERP components sensitive to the direction of cued attentional shifts were quantified by comparing ERP waveforms triggered in the interval

We examined visual search for color singleton targets, whose shape was discriminated. Critically, we varied the reward priority of singleton colors (correct fast performance for red singletons was worth more "bonus points" than for green singletons, or vice-versa), while testing whether ERP signatures of visual selection can be affected by distinct reward priorities for different target types, even when every target has to be selected for report. The N2pc component was earlier and larger for high-versus low-reward targets. This reward influence on the N2pc correlated with the subject-by-subject impact of reward level on efficiency of behavioral performance. Later postselection processing was also affected by target reward-level. These results demonstrate that visual selection of task-relevant item is rapidly modulated by reward-related priorities, even when both types of target have to be selected for response.

To study the response profile of the face-selective N170 component, an adaptation procedure was employed where adaptor and test stimuli were presented in rapid succession. Test stimuli came from 4 different face categories (upright, inverted, and eyeless faces and eyes-only images). The same face stimuli, as well as upright and inverted houses, served as adaptors. Strong N170 amplitude reductions indicative of adaptation were found for all types of face test stimuli preceded by face adaptors relative to house adaptors, demonstrating that at a generic level, the N170 reflects the activation of face-selective neurons by full faces and by face parts. The highly specific pattern of N170 adaptation effects for different combinations of adaptor and test stimulus categories suggests additional distinct contributions of eye-selective neurons and of face-sensitive neurons that are tuned to deviations from canonical stimulus orientations to the N170 component. Results demonstrate that the N170 is generated by multiple neural sources at both early and later stages of configural face processing and that rapid adaptation techniques provide a powerful tool to dissociate these sources.

In cross-dimensional visual search tasks, target discrimination is faster when the previous trial contained a target defined in the same visual dimension as the current trial. The 'dimensionweighting' account (DWA; Found & Müller, 1996) explains this intertrial facilitation by assuming that visual dimensions are weighted at an early perceptual stage of processing. Recently, this view has been challenged by models claiming that intertrial facilitation effects are generated at later stages that follow attentional target selection (Mortier et al., 2005). To determine whether intertrial facilitation is generated at a perceptual stage, at the response selection stage, or both, we focused on specific ERP components (directly linkable to perceptual and response-related processing) during a compound search task. Visual dimension repetitions were mirrored by shorter latencies and enhanced amplitudes of the N2pc suggesting a facilitated allocation of attentional resources to the target. Response repetitions and changes systematically modulated the LRP amplitude suggesting a benefit from residual activations of the previous trial biasing the correct response. Overall, the present findings strengthen the DWA indicating a perceptual origin of dimension change costs in visual search.