Hegedüs Ramón, Horváth Gábor
Biooptics Laboratory, Department of Biological Physics, Loránd Eötvös University, Pázmány Péter Sétány 1, H-1117 Budapest, Hungary.
Vision Res. 2004;44(20):2337-48. doi: 10.1016/j.visres.2004.05.004.
It was hypothesized that egg-laying Papilio butterflies could use polarizational colours as a cue to detect leaf orientation and to discriminate between shiny and matt leaves. These hypotheses would be supported if the following general questions were answered positively: (1) Can surface orientation be unambiguously coded by the polarizational colours perceived by polarization-sensitive colour vision systems? (2) Are the changes in the polarizational colours due to retinal rotation significantly different between shiny and matt surfaces? Using video polarimetry, we measured the reflection-polarizational characteristics of a shiny green hemisphere in the red, green and blue spectral ranges for different solar elevations and directions of view with respect to the solar azimuth as well as for sunlit and shady circumstances under clear skies. The continuously curving hemisphere models numerous differently oriented surfaces. Using the polarization- and colour-sensitive retina model developed earlier, we computed the polarizational colours of the hemisphere, and investigated the correlation between colours and local surface orientation. We also calculated the maximal changes of the polarizational colours of shiny and matt hemispheres induced by rotation of the retina. We found that a surface with any orientation can possess almost any polarizational colour under any illumination condition. Consequently, polarizational colours cannot unambiguously code surface orientation. Polarization sensitivity is even disadvantageous for the detection of surface orientation by means of colours. On the other hand, the colour changes due to retinal rotation can be significantly larger for shiny surfaces than for matt ones. Thus, polarizational colours could help discrimination between shiny and matt surfaces. The physical and perceptional reasons for these findings are explained in detail. Our results and conclusions are of general importance for polarization-dependent colour vision systems.
据推测，产卵的凤蝶可能会利用偏振色作为线索来检测叶片方向，并区分有光泽和无光泽的叶片。如果以下一般问题得到肯定回答，这些假设将得到支持：（1）表面方向能否由偏振敏感颜色视觉系统感知的偏振色明确编码？（2）有光泽和无光泽表面之间，由于视网膜旋转导致的偏振色变化是否存在显著差异？我们使用视频偏振测量法，在不同太阳高度、相对于太阳方位的不同观察方向以及晴朗天空下的阳光照射和阴影环境中，测量了一个有光泽的绿色半球在红、绿和蓝光谱范围内的反射偏振特性。连续弯曲的半球模拟了许多不同方向的表面。使用先前开发的偏振和颜色敏感视网膜模型，我们计算了半球的偏振色，并研究了颜色与局部表面方向之间的相关性。我们还计算了视网膜旋转引起的有光泽和无光泽半球偏振色的最大变化。我们发现，在任何光照条件下，任何方向的表面都可能具有几乎任何偏振色。因此，偏振色不能明确编码表面方向。偏振敏感度甚至不利于通过颜色检测表面方向。另一方面，有光泽表面由于视网膜旋转引起的颜色变化可能比无光泽表面大得多。因此，偏振色有助于区分有光泽和无光泽的表面。我们详细解释了这些发现的物理和感知原因。我们的结果和结论对于依赖偏振的颜色视觉系统具有普遍重要性。
