Illusory Color & the Brain

Some believe that color is purely based on specific wavelengths of light reflected from objects. But, if this were true, color would change dramatically throughout the day. It is the patterns of activity in the brain that give an object it’s relatively stable color. Some also believe that color is not needed at all but, as we see through this article, color helps us see the world more accurately. Through the study of illusory colors (colors that the brain is tricked into seeing) researchers have found that the processing of color occurs hand in hand with shape and boundary and other boundaries.
First it is important to understand how the brain processes color. Photons (packets of energy) are absorbed by the cones and rods in the retina. The cone photoreceptor’s response is transmitted to on and off ganglion cells. Ganglion cells sharpen the brain’s response to edges and borders. Then signals are relayed to the lateral geniculate nucleus in the center of the brain. From the lateral geniculate nucleus signals are sent to the visual cortex. In the visual cortex neurons are organized into maps that represent the visual field. Then visual signals are sent to more that thirty different areas. Each of these areas has a special function, such as processing color or motion. All this information is combined into a perception of an object.
The first of the experiments involving illusory color is the watercolor effect. In the watercolor effect researchers were surprised to find that when an uncolored area is enclosed by two differently colored boundary contours (the inner contour being lighter than the outer) there is a tint from the lighter colored contour which spread across the entire area. This figure also appears dense and slightly elevated. When the colors of the contour are reversed the interior region appears to be a cold white and slightly recessed. This effect reveals that color defines what becomes figure and what becomes background. One possible explanation for this effect is that the combination of lighter and darker contours stimulates neurons to only respond to the contour color on the inside.
The radial line illusion also gives evidence in support of the role color plays in distinguishing figure from background. Ehrenstein, a German psychologist, found that a bright circular patch, which appears to be slightly in front, fills the central gap between a series of radial lines. When a black ring is added to the center of the radial lines the illusion disappears and the middle does not look any brighter than the background. But if the ring in the center is colored, the center looks even brighter than if it had no circle at all. When a gray disk is put into the center gap, the central disk appears to be shimmering, a phenomenon call scintillating. This illusion may be the result of competition between on and off systems (line-induced brightness is competing with the dark gray of the disk). Another variation is a black surrounding and a black disk with a colored ring. This figure’s illusion is a very dark central disk, almost like a black hole. And the last variation is black radial lines with a colored ring and a gray central disk. The disk in this figure appears to be tinted with the complementary color of the ring and appears to flash or scintillate. These illusions all show that color has some role in the distinguishing of figure from background.

I think it is very interesting that with all the knowledge that we have today we still do not fully understand our bodies, especially our sight. This article said several times that we still do not fully understand the details of how certain aspects of sight come about and that we cannot explain why some of the above illusions take place. This article made me think about how complex our God is and how miraculous sight is. I never really thought about how color effects our perceptions and how important it is.