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Dima Amso, Jonathan A. Slemmer, Scott P. Johnson; Visual attention mechanisms are sensitive to manner of occlusion. Journal of Vision 2002;2(7):182. doi: 10.1167/2.7.182.
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We investigated the differences in visual attention mechanisms involved in tracking a moving object when it becomes occluded behind a luminance-defined versus a virtual (illusory) occluder. Previous research suggests that the existence of a virtual occluder does not impair the tracking of moving objects (Scholl & Pylyshyn, 1999). We were interested in subjects' interaction with an object as it moves behind an occluder and then is unexpectedly stopped before re-emerging along its predictable trajectory. We recorded eye movements from adult subjects as they watched a ball move along a predictable trajectory and behind two distinct occluders. In one condition, the two occluders were illusory, whereas in the other they were blue rectangular boxes. In both conditions, subjects tracked the ball's motion which was interrupted at random intervals for two seconds behind one of the occluders. We found that subjects readily tracked the ball as it moved behind both the virtual and luminance-defined occluders. When the ball was stopped behind the luminance-defined occluder, subjects looked for an equal amount of time within the occluder (where the ball was located) and in the anticipation zone (where the ball would emerge). However, when the occluder was virtual, we found that subjects looked significantly longer in the anticipation zone than within the occluder. This finding suggests that manner of occlusion affects the tracking of a moving object and will be discussed in light of divided visual attention between the occluder and the moving object.
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