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Jonathan I. Flombaum, Brian J. Scholl, Zenon W. Pylyshyn; Attentional high-beams in tracking through occlusion. Journal of Vision 2006;6(6):765. doi: 10.1167/6.6.765.
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A considerable amount of research has uncovered several heuristics that the visual system employs to keep track of objects through frequent periods of occlusion. Relatively little work, by comparison, has investigated the on-line mechanisms that implement and support these heuristics. We explored how attention is distributed throughout a display when featurally identical objects become momentarily occluded during multiple object tracking (MOT). Observers tracked three targets among three distractors as they moved haphazardly during 10 second trials. All objects periodically became occluded when they passed behind two visible static ‘walls’. During tracking, observers also had to detect small probes that appeared sporadically on targets, distractors, occluders, or empty space. Though occlusion did not impair MOT, probe detection rates for these categories confirmed the earlier finding that detection on nontargets was worse than on targets or in empty space and also revealed two novel effects. First, probe detection on an occluder's surface was much greater when either a target or distractor was currently occluded in that location, compared to when no object was behind that occluder. Thus object-based attention can still be active in a display even when the attended object is not visible. Second, and more surprisingly, probe detection was always better when objects were occluded (vs. unoccluded) for both targets and distractors. This attentional high-beams effect indicates that the apparently effortless ability to track through occlusion actually requires the active allocation of additional resources, and the current experiments demonstrate a new way that such effects can be discovered and quantified.
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