In visual search tasks, negative features provide information about stimuli that can be excluded from search. It has been shown that these negative features help participants to locate the target, possibly by attentional suppression of stimuli sharing the negative feature. Attentional suppression is assumed to be reflected in an event-related potential, the P D component. To provide a further test of these assumptions, we presented the color of the distractor at the start of a trial and asked participants to find the other colored stimulus in the subsequent search display. Consistent with attentional suppression, we observed a P D to a lateral distractor shown with a vertical target. However, the P D occurred in this condition only when target and distractor could also be on opposite sides of fixation. The effect of trial context on the P D suggests that the P D reflects a search strategy whereby participants select stimuli opposite to the distractor when trials with opposite placements occur during the experiment. Therefore, the P D to the distractor may in fact be an N2pc to the opposite stimulus, indicating that the distractor is not suppressed, but avoided by redirecting attentional selection to the opposite side.

The biased competition account claims that competition between two stimuli increases when they are close together compared with when they are far apart. The reason is that nearby stimuli are more likely to be represented in the same receptive fields, requiring top–down or bottom–up biases to resolve the ambiguity. Consistent with biased competition, previous research showed that an index of attentional enhancement, the N2pc component, was attenuated when two targets were close together. In contrast, it is unclear whether distractor processing would also be attenuated when the distractor is close to the target. To answer this question, we used the additional singleton paradigm where a target is sometimes accompanied by a more salient, but entirely irrelevant, distractor. In the conditions of interest, the distance between the target and the distractor was systematically manipulated whereas the eccentricity to central fixation was always the same. The results showed that two indices of attentional suppression, the positivity posterior contralateral and distractor positivity components, were attenuated when the distractor was close to the target. Consistent with biased competition, attentional suppression of distractors was inhibited when the distance between target and distractor was short. The reduced attentional suppression of distractors with nearby targets may contribute to the increased behavioral interference with close distractors.

In visual search, the internal representation of the target feature is referred to as the attentional template. The attentional template can be broad or precise depending on the task requirements. In singleton search, the attentional template is broad because the target is the only colored element in the display. In feature search, a precise attentional template is required because the target is in a specific color in an array of varied colors. To measure the precision of the attentional template, we used a cue-target paradigm where cueing benefits decrease when the cue color differs from the target color. Consistent with broad and precise attentional templates, the decrease of cueing effects was stronger in feature than in singleton search. Measurements of ERPs showed that the N2pc elicited by the cue decreased with increasing color difference, suggesting that attention was more strongly captured by cues that were similar to the target. However, the cue-elicited N2pc did not differ between feature and singleton search, making it unlikely to reflect the mechanism underlying attentional template precision. Furthermore, there was no evidence for attentional suppression as there was no cue-elicited P D , even in conditions where the cueing benefit turned into a same-location cost. However, an index of signal enhancement, the contralateral positivity, reflected attention template precision. In general, there was sensory enhancement of the stimulus appearing at the cued location in the search display. With broad attentional templates, any stimulus at the cued location was enhanced, whereas enhancement was restricted to target-matching colors with precise attentional templates.