Extraordinary Color Vision

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Science  24 Jan 2014:
Vol. 343, Issue 6169, pp. 381-382
DOI: 10.1126/science.1249614

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How do animals see color? We may never know how another animal experiences red or blue, but we do know that sensitivity to ultraviolet light allows bees to see patterns on flowers where we see plain yellow or white. In fact, bee and human color vision are much alike. Both have three spectral types of photoreceptor whose signals are compared by neural “opponent” mechanisms, which are sensitive to the relative amounts of light at different wavelengths, allowing the animal to distinguish the spectrum of a light source from its brightness. Thomas Young (1) recognized in 1802 that having multiple receptors each with a different spectral sensitivity at each point in the image is essential for color vision, but inevitably impairs spatial resolution. He proposed three spectral receptors as the likely compromise. In fact, theory predicts that two to four receptor types are optimal for discriminating the spectra of natural materials and maximizing the number of objects that could be distinguished by color (2). The eyes of many animals seem to follow these principles, with a retina containing two to four spectral receptors combined with a neural mechanism to compare the responses of different receptor types (the color opponent process). It is therefore fascinating to find an animal that sees color in a fundamentally different way, as reported by Thoen et al. on page 411 of this issue (3).