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Xiaoli He, Jacob Feldman, Manish Singh; Structure from motion without projective consistency. Journal of Vision 2015;15(12):725. doi: 10.1167/15.12.725.
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© ARVO (1962-2015); The Authors (2016-present)
Structure-from-motion (SFM) studies have shown that people are good at perceiving 3D structure in dynamic dot displays consistent with rigid object rotation. However, observers can still perceive volumetric structure even when image motion is inconsistent with rigid rotation. As an extreme case, in dynamic figure-ground displays containing textural motion, observers perceive the convex/symmetric regions as rotating in 3D, despite constant dot speed everywhere (projectively inconsistent with 3D rotation; Froyen et al. 2013, JOV; Tanrikulu et al., 2013, 2014, VSS). It is unclear, however, to what extent this extreme “tolerance” is due to the figure-ground competition in those displays. Here we examined the case of a single object in isolation, and manipulated the discrepancy of image motion from 3D rigid rotation. We started not with 3D objects, but with a 2D velocity field within a vertically-oriented ellipse. For an ellipsoid rotating about its principal axis, its orthographic-projected speed profile is a cosine function along each orthogonal “rib”. We manipulated the proportion α of cosine motion vs. constant linear motion (range 0-1), and the motion direction θ relative to the orthogonal ribs (range 0-60°). Observers used a 7-point scale to rate the degree to which the display depicted a volumetric object. Volumetric percepts increased significantly with α and decreased significantly with θ, and were surprisingly tolerant to deviations from the projectively correct α=1, θ=0. For α, volumetric ratings increased between 0-0.6 but plateaued beyond 0.6. The effect of θ was surprisingly small, with even θ=45° yielding high volumetric ratings. Thus even with an isolated object, the 3D percept was surprisingly tolerant to discrepancies from projectively correct rigid object motion. These results argue for a more nuanced view of 3D interpretation in which strict projective consistency plays a less prominent role than in conventional SFM accounts.
Meeting abstract presented at VSS 2015
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