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Doug Bemis, Steven Franconeri, George Alvarez; It takes attention to capture attention. Journal of Vision 2005;5(8):510. doi: 10.1167/5.8.510.
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We intuitively believe that a sudden movement or change outside the focus of attention will attract our attention. Indeed, numerous studies of stimulus-driven attention show that sudden changes to a display capture attention, even when subjects know that they are irrelevant to the primary task. This mechanism may exist to automatically allocate visual attention to potentially important changes in the world, even when attention is focused elsewhere. In contrast, we present evidence that a sudden change to the stimulus (the abrupt onset of a new search item) attracts attention in easy search tasks, but not in difficult search tasks, suggesting that important changes to the world are more likely to be missed when we are focused on a difficult task.
In three experiments, we systematically manipulated the difficulty of a letter search task. In Experiments 1 & 2 we varied the set of distractor letters, and in Experiment 3 we rotated all stimuli by 90 degrees. In each experiment, the size of the transient created by the abrupt onset was identical - only the difficulty of the search varied. Across these three experiments, and a meta analysis of several published experiments, the degree of search priority for an abrupt onset letter decreased systematically with task difficulty (r2 = .94); the more difficult the search, the weaker the capture effect.
Past evidence suggests that more difficult identification tasks require a ‘smaller spotlight’ of attention (e.g., Castiello & Umilta 1990). Thus, transients may only capture attention in easy search tasks, where subjects use a wide spotlight over large portions of a display, but not in difficult search tasks, where target identification might require a tighter spotlight around smaller sets of search items. Surprisingly, sudden changes to the world may only attract attention if they occur within the spotlight of attention.
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