Department of Psychology, Vanderbilt University, Nashville, Tennessee 37203, USA.
J Neurosci. 2010 Jan 20;30(3):838-48. doi: 10.1523/JNEUROSCI.3116-09.2010.
Recent computational models of biological motion perception operate on ambiguous two-dimensional representations of the body (e.g., snapshots, posture templates) and contain no explicit means for disambiguating the three-dimensional orientation of a perceived human figure. Are there neural mechanisms in the visual system that represent a moving human figure's orientation in three dimensions? To isolate and characterize the neural mechanisms mediating perception of biological motion, we used an adaptation paradigm together with bistable point-light (PL) animations whose perceived direction of heading fluctuates over time. After exposure to a PL walker with a particular stereoscopically defined heading direction, observers experienced a consistent aftereffect: a bistable PL walker, which could be perceived in the adapted orientation or reversed in depth, was perceived predominantly reversed in depth. A phase-scrambled adaptor produced no aftereffect, yet when adapting and test walkers differed in size or appeared on opposite sides of fixation aftereffects did occur. Thus, this heading direction aftereffect cannot be explained by local, disparity-specific motion adaptation, and the properties of scale and position invariance imply higher-level origins of neural adaptation. Nor is disparity essential for producing adaptation: when suspended on top of a stereoscopically defined, rotating globe, a context-disambiguated "globetrotter" was sufficient to bias the bistable walker's direction, as were full-body adaptors. In sum, these results imply that the neural signals supporting biomotion perception integrate information on the form, motion, and three-dimensional depth orientation of the moving human figure. Models of biomotion perception should incorporate mechanisms to disambiguate depth ambiguities in two-dimensional body representations.
近期有关生物运动知觉的计算模型都是以身体的二维（例如，快照、姿势模板）表示为基础的，并且没有明确的方法来消除感知到的人体三维方向的歧义。在视觉系统中是否存在代表运动中的人体方向的三维的神经机制？为了分离和描述介导生物运动知觉的神经机制，我们使用了适应范式以及双稳态点光（PL）动画，这些动画的朝向感知方向随时间波动。在暴露于具有特定立体定义朝向的 PL 步行者之后，观察者经历了一致的后效：双稳态 PL 步行者可以在适应的方向或深度反转中被感知，主要被感知为深度反转。相位混淆的适应器没有产生后效，但是当适应和测试步行者在大小上不同或在注视后出现在相反侧时，确实会发生后效。因此，这种朝向后效不能用局部的、视差特定的运动适应来解释，并且尺度和位置不变性的特性意味着神经适应的更高层次起源。对于产生适应，视差也不是必需的：当悬浮在立体定义的旋转球体上方时，上下文消除歧义的“环球旅行者”足以偏向双稳态步行者的方向，全身适应器也是如此。总之，这些结果表明，支持生物运动知觉的神经信号整合了运动人体的形式、运动和三维深度方向的信息。生物运动知觉模型应该包含用于消除二维身体表示中深度歧义的机制。
