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Sung-Ho Kim, Manish Singh, Jacob Feldman; Curved apparent motion induced by amodal completion and the launching effect. Journal of Vision 2010;10(7):798. doi: 10.1167/10.7.798.
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© ARVO (1962-2015); The Authors (2016-present)
Many aspects of amodal completion in static scenes have been studied, but relatively little is known about how completion interacts with moving structures in dynamic scenes. We examined whether amodal completion can bias an apparent motion path towards longer curved paths behind an occluder, which would violate the well-established principle that apparent motion follows the shortest possible path. In a series of experiments, observers viewed motion sequences of two alternating rectangular targets positioned at the ends of a semicircular “tube,” with varying inter-stimulus intervals (ISI: 100-500 ms). With short ISIs, observers tended to report simple straight path motion, i.e. outside the tube. But with longer ISIs, they became increasingly likely to report a curved motion path occluded by the tube. Subjects also reported that at longer ISIs straight motion became jerker while curved motion became smoother. In the next experiment, we varied the shape of the occluder, and found similar results with no effect of occluder shape. Other experiments investigated whether the motion path could be influenced by a Michotte-style “launch” at the initiation of motion. We added two more small objects which appeared to collide with the motion tokens at offset, in the direction of either the straight path or the curved path. Subjects in these experiments almost exclusively perceived a motion path in the direction of the launch, regardless of ISI, suggesting a very strong bias in the direction of perceived momentum. In sum, our results suggest that (1) The amodal representation of a fully hidden object behind an occluder can bridge the gap between two token locations via a curved motion trajectory, (2) amodal completion in space-time can make curved motion appear relatively smooth and continuous, and (3) the launching effect strongly induces a motion path in the direction of launching.
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