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Tetsuko Kasai, Takatsune Kumada; Effects of occlusion on within-object shift of attention. Journal of Vision 2002;2(7):688. doi: 10.1167/2.7.688.
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In accordance with object-based account of attention, one-object advantage has been shown in attentional shift of locations, even when the object was occluded (Moore, Yantis, & Vaughan, 1998). It is unknown, however, whether attention equally operates on occluded and non-occluded objects. The purpose of this study is to explore the substance of “object” on which attention operates. Experiment 1 compared attentional shift of locations on a single perceptual object between across and along an occluded region. Stimuli were generated by random-dot stereograms, in which a square was overridden by a bar having crossed or uncrossed disparity relative to the square, so that the square was perceived as two segmented rectangles or an occluded square. As a cue, a corner of the square was flashed. After 300 ms of the cue onset, participants detected the diminishment of dots at the cued (valid trial) or uncued location (invalid trial). RTs on valid trials were faster than those on invalid trials. In the segmented display, RTs on invalid trials were faster for cued rectangles than uncued ones, replicating one-object advantage of attentional shift. In the occluded display, however, RTs on invalid trials were slower for a cued region compared to an uncued region, suggesting faster attentional shift across than along an occluded region of a single object. Experiment 2 compared within-object shift of attention on occluding and occluded surfaces using a central arrow cue. The same two slanted surfaces were placed adjacently, so that one was perceived to occlude the other and the border between them was owned by the occluding surface. RTs on invalid cued-surface trials were faster for an occluding surface, showing that attentional shift along the border was facilitated for the surface having the border. Results of both experiments support an involuntary tracing operation of attention in direction of boundary and surface formation of 3D objects.
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