26 Optics & Photonics News n January 2001 1047-6938/01/01/0026/8-$0015.00 ' Optical Society of America Almost Reason Enough for Having Eyes

I t is a commonly held misconception that dogs are color blind. The truth is that a dog’s ability to seecolors is similar to that of most other mammals,1 although different from that of humans with nor-mal vision. Cross-species comparisons of differences in color vision have helped us appreciate our own ability to see colors, as well as to understand the underlying mechanisms of color vision. Among humans with normal color vision, there are differences in color perception that can also help us under-stand the fundamental processes of color vision.2,3 Over the past decade, comparisons and contrasts made at the cellular and molecular level among different color vision systems have brought us to a new under-standing of color vision, one that differs in many unexpected ways from the tenets of conventional wisdom. With this understanding comes a new appreciation of the fact that wavelength sensing, in the form of color discrimination, is a fundamental visual capacity that serves to greatly expand the eye’s information-gathering power. Color vision has played an important role in how the biological machinery for seeing has developed over the course of evolution. when the white light from the star stimu-lates the photoreceptors. Activation of this labeled line is responsible for the percep-tion of white. Another line, the labeled line for “blackness, ” carries output collecte