Purpose. For most natural surfaces, the illumination consists of at least two distinct parts: the direct illumination, from a primary source, and the indirect or mutual illumination, created by light reflected from surfaces onto each other. Can the visual system discount the color of mutual illumination? Methods. A colored version of the Mach Card was created, with one side made of red card and the other of white card. The Mach Card was folded so that the crease joining the red and white sides was concave. The red side cast a reddish light on the white side, thereby contributing an indirect component to its illumination. Observers were asked to view the colored Mach Card with and without a pseudoscope. The pseudoscope reversed the stereo disparity making the colored Mach Card appear convex. Results. When the Mach Card was seen as concave, observers reported the white face to be white to slightly pink; but when the Mach Card was seen as convex, its white face appeared pink. Conclusions. Our result is consistent with a Bayesian analysis of generic properties in which the visual system seeks image interpretations which, in our case, are robust over varying color and position of the light source. For a convex geometry in which the red card does not face the white one, red and pink surface colors are less accidental than red and white surface colors. For the concave geometry, the visual system appears to use its knowledge of the relationship of shape and mutual illumination to discount the reddish indirect light and to recover correctly the surface color of the white paper.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|