Summary
Highlights
Light enters the eye and is focused on the retina, which contains specialized cells called rods and cones. Rods function in dim light providing grayscale vision, while cones are responsible for color vision in bright light. Each photoreceptor contains retinal, which absorbs light, and an opsin protein that determines the color of light it is sensitive to.
With no cones, a 'rod monochromat' experiences grayscale vision with poor acuity, unable to function well in bright light. With only one cone type, a 'cone monochromat' also sees in grayscale, only discerning differences in brightness. Animals like deep-sea fish, owl monkeys, whales, dolphins, and seals exhibit this single-cone vision.
A 'dichromat' has two types of cones. For humans, this is considered a deficit, often resulting in red-green color blindness where colors are seen on a blue-yellow palette due to the color opponent process. However, this is standard for most mammals like dogs, cats, pigs, cows, horses, and elephants. Behavioral and analytical methods are used to understand animal color perception, revealing neutral points where colors are indistinguishable from white.
Humans typically possess three cone types, leading to rich, trichromatic color vision. This is common in some primates, fish in shallow waters, and most insects (though insects perceive ultraviolet, blue, and green). The advantage of three-color vision, especially for primates, is the ability to distinguish ripe fruit (red/orange) from unripe fruit, aiding in foraging and seed dispersal.
Some fish and birds, as well as some women, exhibit four cone pigments, theoretically enabling tetrachromatic vision. While the neural processing for this extra information in humans is unclear, proven examples of functional four-color vision exist in goldfish, chickens, and pigeons. The video concludes by hinting at the complex and varied color vision found in primates, which will be the subject of the next discussion.