Shading and Stereo in Early Perception of Shape and Reflectance
Shading and Stereo in Early Perception of Shape and Reflectance
复制标题
形状和反射率早期感知中的阴影和立体
作者：
Jennifer Sun;P. Perona
最近关于阴影2-D刺激的实验表明，早期视觉机制能够从阴影中解释3-D形状。特别是，目标辨别任务表明，当背景干扰物(而不是目标)可以被解释为凸起并从上方或左上角照明时，目标会“弹出”。由于从阴影中提取3D形状的问题本质上是模糊的，早期的视觉可能需要做出凸度和左上角照明的双重假设，以限制该问题。当3D形状可以被其他线索明确定义时，比如立体视差，这些假设会被认为是不必要的，从而被抛弃吗？在目标辨别实验中采用2AFC刺激起始的掩蔽异步化范式。研究人员比较了五名天真受试者在只有阴影线索的任务中的表现，以及在涉及阴影以及明确定义形状的立体线索的任务中的表现。结果表明，虽然早期视觉3-D机制融合了立体视差信息，但它并不能推翻默认的光照和形状假设。立体信息是在左上角照明的框架内解释的，并且一致地偏爱凸面而不是凹面。
Recent experiments involving shaded 2-D stimuli have shown that early-vision mechanisms are capable of interpreting 3-D shape from shading. In particular, target discrimination tasks suggest that a target ‘pops out’ when background distractors, but not the target, can be interpreted as convex and lit from above or top-left. Since the problem of extracting 3-D shape from shading is intrinsically ill-defined, early vision may need to make these twin assumptions of convexity and top-left lighting in order to constrain the problem. Would these assumptions be recognized as unnecessary and consequently discarded when 3-D shape could be unambiguously defined by some other cue, like stereo disparity? A 2AFC stimulus onset asynchrony paradigm with masking was used in target discrimination experiments. The performance of five naive subjects on tasks where only shading cues were present was compared with that on tasks involving shading as well as stereo cues that define shape unambiguously. The results show that although stereo disparity information is incorporated by early-vision 3-D mechanisms, it is not used to overturn the default assumptions of lighting and shape. Stereo information is interpreted within the framework of top-left lighting, and a consistent preference for convexity is seen over concavity.