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Lee A. Gilroy, Randolph Blake; Cognitive Factors Influence the Perception of 3D Structure-From-Motion. Journal of Vision 2004;4(8):474. doi: 10.1167/4.8.474.
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Background. Devoid of additional depth cues, a 3D structure-from-motion (SFM) stimulus can be ambiguous with regard to its direction of rotation and ordering of surfaces in depth. In this study, we provide evidence for the influence of high-level (top-down) factors on the disambiguation of 3D-SFM. Methods/Results. In one set of experiments, we measured rotational coupling between two horizontally-aligned SFM spheres. One sphere in the pair was ambiguous while the other was made to rotate unambiguously CW or CCW. Consistent with previous studies, observers predominantly perceived co-rotation if the spheres were spatially separated. In contrast, when the edges of the two spheres appeared to touch, observers predominantly perceived them rotating in opposite directions (counter-rotation). We attribute this perception of counter-rotation to observer's intuitive knowledge regarding physical interactions among objects implying friction. Importantly, this “friction effect” is not due to lateral inhibition/facilitation as the effect disappeared once the two spheres were slightly separated. Also, when the spheres were spatially contiguous and counter-rotating, instigating a physical reversal in rotation for the unambiguous sphere produced a concomitant perceptual reversal in rotation for the ambiguous sphere, thus maintaining the perception of counter-rotation. In another set of experiments, we found that differentially allocating attention to a particular surface or direction of motion influenced the disambiguation of a single SFM sphere. For example, attention involuntarily directed to the elements comprising the back surface of the sphere promoted those elements to the front and the sphere's direction of rotation reversed (attention directed to the elements on the front surface of the sphere did not cause a reversal). Conclusion. The perception of 3D-SFM is amenable to high-level (top-down) influences not accounted for by current neural and computational models of SFM.
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