Abstract
Purpose: :
Nowadays many authors invoke Hering's Opponent-Process Theory (OPT) to explain negative and complementary afterimages. However, the fact is that the colors exhibited in afterimages are complementary to their original ones - not the opponent colors (particularly, the Red-Green pair) assumed in OPT. Here I demonstrate that OPT is an incorrect (or incomplete at best) explanation for afterimages in specific and many other color phenomena in general.
Methods: :
The phenomenon used in this study is the so-called "Flight-Of-Colors" (FOC): If one looks at an intense bright light for a short duration and then closes eyes, one will experience an afterimage consisting of a sequence of colors and lasting up to several minutes. Would the colors manifested in this phenomenon turn out to be every possible hues? or just the 4 unique hues subsumed in OPT? or in other ways? Many investigators had described the colors in FOC, but it appears that they had used color names rather inconsistently - for instance, some authors had used the term "Greenish-Blue" or just "Blue" for the color that nowadays we would call "Cyan". Therefore I have made many observations staring directly and briefly (< 1 second) at Northern California's bright sun and then closing or opening eyes to experience FOC.
Results: :
(1) The FOC afterimage usually consists of one or two rings surrounding an inner disk; (2) With closed eyes the predominant colors occurring in FOC are Cyan, Magenta, and Yellow; (3) With open eyes and projecting FOC to a white background the colors would immediately change to their complementary ones - this is possibly the reason why Helmholtz described the colors in FOC as Red, Green, and Blue; (4) Other colors also occur in FOC but they mainly result from color filling-in and mixing in parts of the afterimage - for example, Magenta from a surrounding ring would intrude into the central disk of Yellow to produce an orange color.
Conclusions: :
(1) The results are clearly more consistent with Young-Helmholtz's Trichromatic Theory than with OPT; (2) The fact of hue reversal implies that FOC occurs at a neural level instead of as some photochemical bleaching process; (3) Thus I suggest that there is a cortical, tetra-channel, complementary color system consisting of three chromatic pairs (Red-Cyan, Green-Magenta, and Yellow-Blue) and one achromatic pair (Black-White); (4) As afterimages are normally monocular, mapping onto the anatomical organization of human visual system, I suggest that layer 4C in primary visual cortex (V1) is the neural substrate for FOC in specific and afterimages in general; (5) I further propose, tentatively, that this neural substrate holds the mechanisms for color mixing, color filling-in, color transparency, and color complementarity observed in many color (including brightness) perceptual phenomena.
Keywords: color vision • color appearance/constancy • visual cortex