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Xiaoli He, Jacob Feldman, Manish Singh; Projectively inconsistent occluding contours have surprisingly little influence on SFM percepts. Journal of Vision 2016;16(12):651. doi: 10.1167/16.12.651.
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Structure-from-motion (SFM) studies have shown that observers spontaneously perceive 3D structure in dot motion displays that are projectively consistent with a rigid 3D interpretation. However, observers can also perceive 3D structure in displays that are not projectively consistent with a 3D interpretation, such as the "rotating columns" display (Froyen et al., JOV 2013; Tanrikulu et al., VSS 2014, VSS 2015) in which 3D rotation is perceived in alternating image regions despite the constant-speed profile of the image motion. Even in standard SFM displays, the 3D percept is surprisingly robust to deviations of the dot speed profile from projective consistency (He et al., VSS 2015). Here, we extend the study of projective consistency to include the role of occluding contours. We manipulated (i) the degree of symmetry of the occluding contours; and (ii) the speed profile of the dots, varying it from perfectly constant speed to full cosine speed profile (projectively consistent with rigid rotation in depth). Critically, asymmetric contours are grossly inconsistent with a rotating 3D object, because an asymmetric object necessarily changes its silhouette as it rotates, but the contours in our displays do not. For each level of symmetry, we used the method of constant stimuli to obtain psychometric curves for proportion of "volumetric" responses as a function of the proportion of cosine motion. As expected, the proportion of "volumetric" responses increased monotonically with the proportion of cosine motion. However, the degree of shape symmetry had a surprisingly small effect. Although asymmetric displays required a slightly higher proportion of cosine motion to perceive volumetric structure, their psychometric curves were only slightly different than those for symmetric displays. The results show that projective consistency—even of occluding contours—plays a much less prominent role in the perceptual inference of 3D structure than in conventional SFM accounts.
Meeting abstract presented at VSS 2016
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