What do animals see? (speculation)

An interesting, and highly speculative question is, what do animals see? There are several aspects to this question, such as how their eyes work, how they behave in experiments, and what photo-pigments are in their eyes.

What do animals see?

Many animals can see things that we cannot. For example, cats can see at night when it is too dark for us. However, we do not know what animals actually perceive. There is an important difference between merely having light illuminate our retina, and actually understanding what we are seeing.

The role of color vision in an animal's perception, behavior, and ecological setting, and its underlying retina and neuronal mechanisms vary enormously in different groups of animals. Although color as a perceptual category with cognitive significance obviously plays a great role in human life, there is, with the exception of hymenopterous insects, still little evidence about the roles of color perception in nonhuman animals, especially nonprimates. Current research finds that color vision in non-primate mammals is very limited, and probably bears little resemblance to humans'. Nevertheless, it is proven that animals see some form of color vision, as in the following examples.

	Experiments in 1969 trained dogs to choose between different colored dog dishes, and in more recent experiments, dogs were able to differentiate colored circles.		This Costa Rican red-eyed treefrog has a very limited visual pathway; its neural behavior and jumping reflex suggest it only "sees" its prey if it is moving.



			Comparison of wavelengths visible to humans and bees. The range of vision for the bee and butterfly extends into the ultraviolet. The leaves of the flowers they pollinate have special ultraviolet patterns which guide the insects deep into the flower.
	Eyespots on the Tanzanian caterpillar. Head coloring and fake eyes resemble those of a snake, warning off predators. Real eyes are small, barely visible, located near the snout. Earthworms and caterpillars have "eye spots," and see only light and dark, helping them stay out of the hot sun.

Some simple animals have very different eyes. Sea stars and crablike copepods have "eye cups," with light-sensitive cells inside the tip of each arm. Nautilus see through a pinhole. Scallops have 50-100 mirror-eyes, which bounce light to photoreceptors in the middle of the eye. Some animals which exceed human senses, and see many more colors than we do, such as mantis shrimp (at least 12 different photoreceptors) or pigeons (6 photoreceptors).

In the honeybee, four of the visual cells in each ommatidium respond best to yellow-green light (530 nm); two respond maximally to blue light (430 nm); and the remaining two respond best to ultraviolet light (340 nm), allowing the honeybee to distinguish colors (except red).