Color Vision
Theories of Color Vision

Theories of color vision attempt to explain the phenomena of normal and abnormal color vision. The basic experimental facts of each theory must account for the psychophysical aspects of color vision; that is, the ability to match colors. They must account for the physiological aspects of color vision; that is, it must explain the action caused by the radiant energy absorbed within the receptor (cones and rods) of the retina. And finally, every color vision theory must account for the psychological aspects of color vision; that is, it must explain the nerve activities in the cortex (brain) leading to color perception.

There are many different theories attempting to explain some or most of the phenomena of color vision. None of the theories may be considered completely satisfactory, as they all fail to account accurately for all known psychophysical, physiological, and psychological aspects of color vision. The complexity of color vision and the seemingly insurmountable difficulties in experimenting with the human eye and brain have so far prevented the development of a comprehensive and satisfactory theory. However, the mystery of how we see color continues to be a source of interest to may scientists.

Isaac Newton (1643-1727)

Newton was the first to make a major breakthrough in understanding color. When he passed a thin beam of sunlight through a glass prism, he noted the oblong spectrum of colors�red, yellow, green, blue, violet�that formed on the wall opposite. For Newton, these different colors represented particles or corpuscles of light of different sizes. He was careful to point out that light itself had no color; rather, the different particles of light were capable of producing the sensation of various colors. Newton believed that particles of light excited vibrations on the retina that were propagated along the optic nerve to the brain causing the sense of sight. Furthermore, he speculated that particles of light of different sizes would also excite vibrations of different sizes. These vibrations, according to their size, would produce different sensations of color.

Although Newton recognized seven pure colors,: red, orange, yellow, green, blue, indigo, and violet, it is now known that the visible spectrum actually undergo a smooth transition from red through violet. So, in principle, it would be possible to identify literally hundreds of different hues. It is not clear whether Newton regarded his seven basic hues as fundamental or whether these were simply convenient names he gave to major segments of the spectrum. He did recognize that two pure colors, light from different parts of the spectrum, could be mixed to produce a completely different color. For example, green light and red light could be mixed to produce yellow. Likewise, red light and violet light wouldproduce magenta, a hue that cannot be seen in the visible spectrum. Newton also observed that as more hues were added, the resulting color became progressively less saturated and began to resemble white. Presumably, if only one size of vibration were excited on the retina, a pure color was perceived, As the number of kinds of vibrations increased, the perceived hue became progressively whiter or less chromatic.

Newton did not speculate in the exact nature of the structure of the retina, nor on what actually was set to vibrating by the light particles. This question was addressed nearly 100 year later by Thomas Young.