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Xiaoli He, Manish Singh, Jacob Feldman; Violation of projective consistency in structure-from-motion: a role for skin motion?. Journal of Vision 2018;18(10):298. doi: https://doi.org/10.1167/18.10.298.
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SFM studies have shown that observers can have vivid 3D percepts in dynamic dot displays that are projectively consistent with 3D rotation. However, under certain conditions, observers can also perceive 3D structures that are not projectively consistent with image motion (Ramachandran et al. 1988; Froyen et al., JOV2013; Tanrikulu et al., JOV2016). In previous work (He et al., VSS, 2015, 2016, 2017), we have investigated the violation of projective consistency in SFM in terms of both dot motion and occluding contour geometry. We found that observers perceive 3D shape despite the lack of projective consistency. One alternative explanation of this apparent violation is that, in the projectively-inconsistent cases, observers perceive 3D structure, but the dots are seen as sliding along the 3D surface, rather than rigidly attached to it. Under this account, percepts of skin motion should increase systematically with the degree of projective inconsistency. Stimulus shapes consisted of two vertically oriented sine curves with different relative phases, generating a transition from symmetric to parallel. The occluding contour remained fixed, so that only the symmetric shape could be projectively consistent with 3D rotation. Dots moved horizontally, with speed profiles varying from cosine motion (projectively consistent with rotation in depth) to constant speed. Observers judged whether each display looked three-dimensional and, if so, whether the dots looked like they were sliding along the 3D surface. The pattern of 3D responses replicated our previous findings: 3D percepts were reported > 75% with only 40% cosine motion and this pattern was barely different for symmetric vs. asymmetric shapes. However, no consistent pattern could be discerned across observers regarding the skin-motion percept. While skin motion is an interesting and largely ignored percept that deserves to be investigated on its own, it seems unlikely to provide a viable account of the violation of the projective-consistency constraint.
Meeting abstract presented at VSS 2018
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