Ramachandran V S
University of California, San Diego, La Jolla 92093.
Nature. 1988 Jan 14;331(6152):163-6. doi: 10.1038/331163a0.
The human visual system can rapidly and accurately derive the three-dimensional orientation of surfaces by using variations in image intensity alone. This ability to perceive shape from shading is one of the most important yet poorly understood aspects of human vision. Here we present several findings which may help reveal computational mechanisms underlying this ability. First, we find that perception of shape from shading is a global operation which assumes that there is only one light source illuminating the entire visual image. This implies that if two identical objects are viewed simultaneously and illuminated from different angles, then we would be able to perceive three-dimensional shape accurately in only one of them at a time. Second, three-dimensional shapes that are defined exclusively by shading can provide tokens for the perception of apparent motion, suggesting that the motion mechanism is remarkably versatile in the kinds of inputs it can use. Lastly, the occluding edges which delineate an object from its background can also powerfully influence the perception of three-dimensional shape from shading.
人类视觉系统仅通过利用图像强度的变化就能快速且准确地得出表面的三维方向。这种从阴影中感知形状的能力是人类视觉中最重要但却了解甚少的方面之一。在此，我们展示了几个可能有助于揭示这种能力背后计算机制的发现。首先，我们发现从阴影中感知形状是一种全局操作，它假定只有一个光源照亮整个视觉图像。这意味着，如果同时观察两个相同的物体并从不同角度照亮它们，那么我们一次只能在其中一个物体上准确感知三维形状。其次，仅由阴影定义的三维形状可以为表观运动的感知提供线索，这表明运动机制在其可以使用的输入类型方面具有显著的通用性。最后，将物体与其背景区分开来的遮挡边缘也会对从阴影中感知三维形状产生强大影响。
