Plummer D J, Ramachandran V S
Psychology Department, University of California at San Diego, La Jolla 92093-0109.
Spat Vis. 1993;7(2):113-23. doi: 10.1163/156856893x00315.
If two neutral density (ND) filters overlap partially, the luminance of the overlapping region is given by a multiplicative relationship (e.g., if the filters have 50% transmittance then on a 100 cd m-2 background, the luminance of each filter would be 50 cd m-2 but the luminance of the overlapping region would be 50% of 50 cd m-2, i.e. 25 cd m-2). Does the visual system respect this relationship? Two grey rectangles were overlapped to form a 'cross' and the luminance of the intersection was randomly varied. Naive subjects' ratings of transparency showed a surprising consistency with physics. A similar relationship is seen if two moving square-wave gratings are superimposed. When the intersection luminances were close to the multiplicative (25 cd m-2) case, component motion was seen, and values less than 25 cd m-2 and higher than 50 cd m-2 caused a decline in perceived component motion. Two interpretations are offered. (a) The visual system has access to 'tacit knowledge' of transparency and shadows. (b) If you assume a log signal compression in the retina, then by multiplying the luminances you would null the Fourier energy from the 'blobs' (i.e. regions of overlap between the two gratings). This would prevent 'blob tracking' and lead to the perception of coherent motion. Since most researchers in the field had simply added the gratings linearly they would have inadvertently introduced extra Fourier energy in the blobs and this might account for all previous instances of coherent motion observed in such displays. Whatever the ultimate interpretation, the present results provide the first clear evidence that even the processing of certain primitive visual dimensions--such as motion--can be powerfully constrained by the perception of transparency (Ramachandran V. S. (1990) in: AI and the Eye, Wiley, Chichester; Stoner, G., Albright, T. and Ramachandran, V. S. (1990) Nature 344, 153-155). This is well in line with other recent results demonstrating that transparency can also constrain the processing of stereopsis (Nakayama, K., Shimojo, S. and Ramachandran, V. S. (1991) Perception 19, 497-513) and perceptual grouping (Ramachandran, V. S. (1990) in: AI and the Eye, Wiley, Chichester).
如果两个中性密度（ND）滤光片部分重叠，重叠区域的亮度由乘法关系给出（例如，如果滤光片的透光率为50%，那么在100坎德拉每平方米的背景下，每个滤光片的亮度将为50坎德拉每平方米，但重叠区域的亮度将是50坎德拉每平方米的50%，即25坎德拉每平方米）。视觉系统是否遵循这种关系呢？将两个灰色矩形重叠形成一个“十字”，交叉点的亮度随机变化。未经过训练的受试者对透明度的评分与物理学表现出惊人的一致性。如果将两个移动的方波光栅叠加，也会看到类似的关系。当交叉点亮度接近乘法（25坎德拉每平方米）情况时，会看到成分运动，而小于25坎德拉每平方米和高于50坎德拉每平方米的值会导致感知到的成分运动下降。文中提供了两种解释。（a）视觉系统拥有关于透明度和阴影的“隐性知识”。（b）如果你假设视网膜中存在对数信号压缩，那么通过将亮度相乘，你将消除来自“斑点”（即两个光栅之间的重叠区域）的傅里叶能量。这将阻止“斑点跟踪”并导致连贯运动的感知。由于该领域的大多数研究人员只是简单地将光栅线性相加，他们可能无意中在斑点中引入了额外的傅里叶能量，这可能解释了此前在此类显示中观察到的所有连贯运动实例。无论最终的解释是什么，目前的结果提供了首个明确证据，即即使是某些原始视觉维度（如运动）的处理，也可能受到透明度感知的强烈限制（拉马钱德兰V.S.（1990年），载于《人工智能与眼睛》，威利出版社，奇切斯特；斯托纳，G.，奥尔布赖特，T.和拉马钱德兰，V.S.（1990年），《自然》344卷，第153 - 155页）。这与最近的其他结果非常一致，这些结果表明透明度也可以限制立体视觉的处理（中山，K.，下条，S.和拉马钱德兰，V.S.（1991年），《感知》19卷，第497 - 513页）以及感知分组（拉马钱德兰，V.S.（1990年），载于《人工智能与眼睛》，威利出版社，奇切斯特）。
