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Brian J. Scholl, Lisa Feigenson; When Out of Sight is Out of Mind: Perceiving Object Persistence Through Occlusion vs. Implosion. Journal of Vision 2004;4(8):26. doi: 10.1167/4.8.26.
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© 2015 Association for Research in Vision and Ophthalmology.
The visual system must not only segment scenes into discrete objects, but also track objects over time, motion, and occlusion as the same persisting individuals. Here we explore how this is accomplished in a multiple-object tracking task where the objects are intermittently invisible. Subjects attentionally tracked 4 target objects as they moved unpredictably for 10 seconds in a field of 4 featurally-identical moving distractors. Previous research (Scholl & Pylyshyn, 1999) demonstrated that tracking is unimpaired by occlusion, but is radically impaired when objects disappear and reappear in ways which do not implicate the presence of an occluding surface (e.g. by imploding and exploding into and out of existence). However, this research never determined whether the impairment was caused by the ‘explosion’ (due to attentional capture from onsetting looming objects) or ‘implosion’ (which signalled that the objects ceased to exist). Here we explored these options in several ways. We first showed that when targets behave in ‘object-consistent’ ways but additional distractors implode and explode, subjects' performance is unimpaired. This suggests that the behavior of the targets, rather than that of the distractors, is critical. A second experiment asked whether impairment was due to target implosion or target explosion by having all objects approach an occluder in one way and depart in a different way. Performance with implosion followed by disocclusion was significantly worse than with occlusion followed by explosion. These results argue against an attentional-capture account, and suggest that implosion cues cause the corresponding ‘object files’ in mid-level vision to be discarded — whereas occlusion cues cause object files to be preserved. Following Gibson, we conclude that the visual system — and attentional tracking in particular — uses occlusion to infer that objects are merely going out of sight, and implosion to infer that objects are going out of existence.
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