Jain Anshul, Zaidi Qasim
Graduate Center for Vision Research, SUNY College of Optometry, New York, NY, USA.
J Vis. 2013 Jan 16;13(1):18. doi: 10.1167/13.1.18.
Most living things and many nonliving things deform as they move, requiring observers to separate object motions from object deformations. When the object is partially occluded, the task becomes more difficult because it is not possible to use two-dimensional (2-D) contour correlations (Cohen, Jain, & Zaidi, 2010). That leaves dynamic depth matching across the unoccluded views as the main possibility. We examined the role of stereo cues in extracting motion of partially occluded and deforming three-dimensional (3-D) objects, simulated by disk-shaped random-dot stereograms set at randomly assigned depths and placed uniformly around a circle. The stereo-disparities of the disks were temporally oscillated to simulate clockwise or counterclockwise rotation of the global shape. To dynamically deform the global shape, random disparity perturbation was added to each disk's depth on each stimulus frame. At low perturbation, observers reported rotation directions consistent with the global shape, even against local motion cues, but performance deteriorated at high perturbation. Using 3-D global shape correlations, we formulated an optimal Bayesian discriminator for rotation direction. Based on rotation discrimination thresholds, human observers were 75% as efficient as the optimal model, demonstrating that global shapes derived from stereo cues facilitate inferences of object motions. To complement reports of stereo and motion integration in extrastriate cortex, our results suggest the possibilities that disparity selectivity and feature tracking are linked, or that global motion selective neurons can be driven purely from disparity cues.
大多数生物和许多非生物在移动时都会变形，这就要求观察者将物体的运动与物体的变形区分开来。当物体被部分遮挡时，这项任务就变得更加困难，因为无法使用二维（2-D）轮廓相关性（科恩、贾恩和扎伊迪，2010年）。这使得跨未遮挡视图的动态深度匹配成为主要可能性。我们研究了立体线索在提取部分遮挡和变形的三维（3-D）物体运动中的作用，这些物体由设置在随机分配深度并均匀分布在一个圆圈周围的圆盘形随机点立体图模拟。圆盘的立体视差在时间上振荡，以模拟整体形状的顺时针或逆时针旋转。为了使整体形状动态变形，在每个刺激帧上给每个圆盘的深度添加随机视差扰动。在低扰动下，观察者报告的旋转方向与整体形状一致，即使与局部运动线索相悖，但在高扰动下性能会下降。利用三维整体形状相关性，我们制定了一个用于旋转方向的最优贝叶斯判别器。根据旋转辨别阈值，人类观察者的效率是最优模型的75%，这表明从立体线索中得出的整体形状有助于物体运动的推断。为了补充关于纹外皮层中立体和运动整合的报告，我们的结果表明了视差选择性和特征跟踪相关联的可能性，或者全局运动选择性神经元可以完全由视差线索驱动。
