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Jaeeun Lee, Yoonsang Lee, Sung-Ho Kim; Objects with salient parts break apart easily: The influence of object shape in the perceptual organization of a dynamic event and its causal structure. Journal of Vision 2019;19(10):94b. doi: https://doi.org/10.1167/19.10.94b.
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© ARVO (1962-2015); The Authors (2016-present)
Unlike previous studies of part-based shape representations which mostly investigated static images, we explored how geometric cues to part boundaries affect the perception of ambiguous dynamic events involving globally inconsistent kinetic occlusion. When an object moved horizontally across another stationary object with either its upper or lower half occluded by the other object (and the other half occluding the stationary object), observers perceived one object to be split into halves by the other. In Experiments 1–2, we manipulated an object’s part structure by introducing concave or convex cusps along its contour where we found that concave objects were more likely perceived as being split than convex objects and that this tendency grew as concavity increased. Experiment 3 examined the interaction between the geometric shape cues and the stereoscopic depth cues in object-split perception. The relative stereoscopic depth of the moving object’s two halves was manipulated such that the half occluded by the stationary object could be placed in either the same depth plane as, or a slightly farther depth than the other half occluding the stationary object. Throughout this event, the horizontal midline of the whole display was occluded by a thin belt to hide the depth discontinuity between the two halves. We found that the actual stereoscopically-split moving object was likely to be seen as splitting the stationary object as long as its shape is convex, suggesting that shape representation can override metric depth information in object-split perception. Overall, our study suggests that salient parts are not only represented as independent units but also likely seen as separated in a physical sense, which in turn alters the perception of a motion event and its causal structure. It provides a new insight into spatiotemporal perceptual organization, integrating seemingly separate processes of perceptual unit formation and event perception.
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