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Anshul Jain, Qasim Zaidi; Efficiency of object motion extraction using disparity signals. Journal of Vision 2012;12(9):153. doi: 10.1167/12.9.153.
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© ARVO (1962-2015); The Authors (2016-present)
Many objects deform when moving and are often partially occluded, requiring observers to integrate disparate local motion signals into coherent object motion. To test whether stereo information can help do this task, we measured the efficiency of extracting purely stereo-driven object motion by comparing tolerance of deformation noise by human observers to an optimal observer. We also compared the efficacy of global shape defined by stereo-disparities to the efficacy of local motion signals by presenting them in opposition.
Stimuli consisted of 3-D shapes defined by disk-shaped random-dot stereograms uniformly arranged around a circle, varying randomly in stereoscopic depth. The disparities were oscillated to simulate clockwise or counterclockwise rotation of the 3-D shape. Observers performed a 2AFC direction discrimination task. The mean shape on a trial was constructed by assigning random depths to the disks (Shape Amplitude). The shape was dynamically deformed on every frame by independent random depth perturbations of each disk (Jitter Amplitude).
Observers’ percent-correct discrimination declined monotonically as a function of Jitter Amplitude, but improved with Shape Amplitude. Observers were roughly 80% as efficient as the optimal shape-matching Bayesian decoder. Next, on each frame, we rotated the shape by 80% of the inter-disk angle, resulting in 2-D local motions opposite to the global object motion direction. Observers’ performances were largely unaffected at small dynamic distortions, but favored local motion signals at large dynamic distortions.
Our original stimuli were devoid of monocular motion information, hence observers had to extract stereo-defined 3-D shapes in order to perform the task. These stimuli simulate disparity signals from both 3-D solid shapes and transverse-waves viewed through fixed multiple windows. Thus, our results provide strong evidence for the general role of 3-D shape inferences on object-motion perception. The cue-conflict stimuli reveal a trade-off between local motion and global depth cues based on cue-reliability.
Meeting abstract presented at VSS 2012
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