Do animals see like you?
The perception and ability to distinguish different colours is mediated by a variety of mechanisms in the eye retina (see Did you know ?) as well as the brain. It is possible to determine anatomic structures of the anterior segment of animal eyes, but what colour does the animal see? Vision, like all of our senses, is processed in the brain. Without being able to get into the head of an animal, it is only possible to know what colors can be detected and not how they “look” to the animal.
The ability of vertebrates to distinguish colours relates to the number of cone photopigments in the retina. Tetrachromacy includes four cone cell types for ultraviolet, blue, green and red wavelengths. It seems restricted to few animal species such as fishes, insects and birds. The latter rely on their excellent colour vision to select food, dazzle mates, escape predators and navigate diverse terrain. Wavelengths <400 nm are undetectable to the human eye:
Humans cannot see the fantastic range of colours on fish scales and bird feathers: primates are trichromatic (blue, green, red). In humans, daltonism or colour blindness is usually caused by faulty cone cells. Most of mammalian species have only two classes (blue, green) of cone photopigments. Like cats and dogs, pigs are dichromatic; for them, senses of smell and hearing are more important than a clear vision. Neither cows do not see red light frequencies. Bulls see red capes as yellowish-gray: it is the threatening, waving motion of the matador’s muleta that enrages the animal.