Abstract
The identification of a target in a rapid visual stream of non-target letters is impaired by the abrupt onset of a task-irrelevant peripheral distractor. This impairment, known as attentional capture, is thought to occur because the attentional focus is diverted spatially from the central stream to the distractor. This study examined the hypothesis that attentional capture consists of attentional diversion to the distractor and re-orienting from the distractor to the target by manipulating the duration of the peripheral distractor. We predicted that if the offset does not capture attention, the identification accuracy would improve when the distractor disappears briefly. This is because it would be easier to disengage attention from a stimulus when it disappears than when it remains visible. However, if the offset also captures attention, the abrupt offset of the distractor would impair the accuracy. Observers identified a colored oddball letter (the target) embedded in a rapid stream of grey non-target letters. Peripheral distractors appeared 200 ms before the onset of the target. The duration of the distractor was 50 ms in the Short condition or 200 ms in the Long condition. The target identification accuracy was greater in the Long condition than in the Short condition. The same pattern of results was obtained when the distractors remained until the end of the stream presentation in the Long condition. The result suggests that attentional re-orienting from the distractor to the target is disrupted by offset of the distractor if it occurs immediately after its onset. We conclude that attentional capture is caused by two events: the abrupt onset and offset of the distractor.