van Doorn Andrea J, Koenderink Jan J, Wagemans Johan
Faculty of Industrial Design, Delft University of Technology, Delft, The Netherlands.
J Vis. 2011 Mar 29;11(3):21. doi: 10.1167/11.3.21.
From a theoretical point of view, the use of the shading cue involves estimates of the light field and thus observers need to judge the light field and the shape simultaneously. The conventional stimulus in perceptual experiments, a circular disk filled with a monotonic gradient on a uniform surround, represents a local shading or tonal gradient. In typical scenes, such gradients vary smoothly from point to point over large areas, whereas light fields are globally defined and tend to be invariant over large parts of the scene. Hence, it is hardly surprising that multi-local shape estimates tend to synchronize although previous reports of such synchronies involved uniform, homogeneous light fields. Here, we consider more complicated and more realistic light fields. We present extensive, highly structured, quantitative observations using novel paradigms. Human observers are able to deal with some structured light fields but totally fail in others, even though these may be formally similar (like radial and circular fields). Observers respond very differently in some cases where the light fields differ only by sign, like converging and diverging fields. These results can be qualitatively understood on the basis of a few simple assumptions, mainly global top-down template matching of peripheral local data.
从理论角度来看，使用明暗线索涉及对光场的估计，因此观察者需要同时判断光场和形状。知觉实验中的传统刺激物，即在均匀背景上填充单调梯度的圆盘，代表局部明暗或色调梯度。在典型场景中，这种梯度在大面积区域内逐点平滑变化，而光场是全局定义的，并且在场景的大部分区域往往是不变的。因此，尽管之前关于这种同步性的报道涉及均匀、同质的光场，但多局部形状估计倾向于同步也就不足为奇了。在这里，我们考虑更复杂、更现实的光场。我们使用新颖的范式进行了广泛、高度结构化的定量观察。人类观察者能够处理一些结构化光场，但在其他光场中则完全失败，即使这些光场在形式上可能相似（如径向场和圆形场）。在某些情况下，光场仅符号不同，如汇聚场和发散场，观察者的反应也非常不同。基于一些简单的假设，主要是外围局部数据的全局自上而下模板匹配，可以定性地理解这些结果。
