「第3問」は背景画像と50%明度の円形画像の透過重ね合わせ画像の 部分は左右で共通、背景は左右で明度反転画像としてあります。
「第4問」は左右とも単調な塗りつぶし画像で共通、背景は左右で明度反転画像としてあります。
「第5問」は、円形の部分を90度だけ回転している以外は「第3問」と同じです。 背景と境界が連続していないので、「第4問」よりは難しいものの、「第3問」よりは 同じ明るさであることが容易に分かります。
http://www.nature.com/nature/journal/v434/n7029/abs/nature03271_fs.html
Nature 434, 79 - 83 (03 March 2005); doi:10.1038/nature03271Image segmentation and lightness perception
BARTON L. ANDERSON1 AND JONATHAN WINAWER2
1 University of New South Wales, School of Psychology, Sydney, New South Wales 2052, Australia 2 Massachusetts Institute of Technology, Brain and Cognitive Sciences, Cambridge, Massachusetts 02139, USA
Correspondence and requests for materials should be addressed to B.L.A. (bart.a@unsw.edu.au).
The perception of surface albedo (lightness) is one of the most basic aspects of visual awareness. It is well known that the apparent lightness of a target depends on the context in which it is embedded, but there is extensive debate about the computations and representations underlying perceived lightness. One view asserts that the visual system explicitly separates surface reflectance from the prevailing illumination and atmospheric conditions in which it is embedded, generating layered image representations. Some recent theory has challenged this view and asserted that the human visual system derives surface lightness without explicitly segmenting images into multiple layers. Here we present new lightness illusionsﾑthe largest reported to dateﾑthat unequivocally demonstrate the effect that layered image representations can have in lightness perception. We show that the computations that underlie the decomposition of luminance into multiple layers under conditions of transparency can induce dramatic lightness illusions, causing identical texture patches to appear either black or white. These results indicate that mechanisms involved in decomposing images into layered representations can play a decisive role in the perception of surface lightness.