Attentional set and explicit expectations of perceptual load determine flanker interference.

Task-irrelevant stimuli often capture our attention despite our best efforts to ignore them.It has been noted that tasks involving perceptually complex displays can lead to reduced interference from distractors.The mechanism behind this effect is debated, with some accounts emphasising the 'perceptual load' of the stimuli themselves, and others emphasising the role of proactive control.Here, in three experiments, we investigated the roles of perceptual load, proactive control, and reward motivation in determining distractor interference.Participants performed a visual search task of high, low, or intermediate-load, with flanking task-irrelevant distractors.Each trial was preceded by a cue indicating the level of perceptual load (Experiments 1-3) as well as the potential reward that could be earned (Experiments 2-3).In all three experiments, the attentional set induced by preceding trial and cued proactive expectation of perceptual load interacted to determine flanker interference, which was significant for all trial types except trials cued as high-load which were also preceded by high-load.These effects were not modulated by reward motivation, although in the final experiment reward did significantly improve performance overall.Thus, successful distractor exclusion does not depend upon motivation or load per se but does require an expectation of high load. Significance statementWe all experience distraction by irrelevant stimuli which can impair our performance of tasks, even when we are motivated to ignore them.There has been considerable debate as to which factors determine whether or not a distractor will capture our attention.We investigated several factors, including the prospect of obtaining a reward and proactive preparation based on the expected task difficulty.Our results suggest that both the expectation of a difficult task, and the recent experience, combine to allow us to effectively and proactively ignore distractors.In contrast, rewards could improve performance overall, but did not affect the extent to which distractors captured attention.