Abstract
When frequent standard, rare target and rare distractor objects are serially presented, neural responses for distractors are increased by discrimination difficulty between the standard and target. This is shown by an enlargement of P3 event-related brain potentials (ERPs). In this study we investigated whether this increase of neural response is associated with the enhancement of attentional capture induced by stimulus salience or the enhancement of cognitive interference in maintenance of the standard/target representation. ERPs were recorded from participants while they performed a visual serial presentation paradigm (70 % standard, 15 % target, 15 % distractor). Four task conditions were defined by a combination of two distractor types (central or bilateral) and two levels of standard/target discrimination difficulty (easy or difficult). In the central condition, the distractor was serially presented at the central location as well as standard and target. In the bilateral condition, distractors were presented on both sides of the centrally presented standard; these flanking distractors appeared abruptly at a previously blank location, and thus they did not interfere with the maintenance of standard/target representation but had high stimulus salience. The results revealed that the P3 elicited by the distractor in the central condition was larger for the difficult task than for the easy task, as in previous studies. In contrast, in the bilateral condition, the distractor elicited large P3s in both the easy and difficult tasks. These results suggest that the increase of neural response by discrimination difficulty is associated with the enhancement of attentional capture induced by stimulus salience, rather than the enhancement of cognitive interference. Serially presented distractor objects may have high stimulus salience in the difficult task since the attentional bias toward the standard/target objects is increased to achieve a cautious discrimination between them, which may make distractor objects more salient within the stimulus context.