Binocular vision

Binocular vision (also called stereoscopic vision) is a type of visual system common in many kinds of animals where both the eyes produce only a single image in the brain. It may be contrasted with monocular vision, where the information from each eye is processed separately. Most humans have binocular vision, unless they are affected by strabismus or a related condition.

In binocular vision, the eyes are forward-facing and cannot move independently of each other. Each eye thus has a slightly different perspective on a scene. This allows the visual cortex of the brain to synthesize the two differing images into one cohesive mental image. These differences in perspective allow the brain to triangulate distance much more accurately, and thus result in vastly improved depth perception. Binocular vision contributes to depth perception at close distances, within 18-20 feet; beyond that, the brain relies on less precise cues, such as shadows and parallax to generate depth information.

Animals in which binocular vision has been disabled (e.g. through accident to one of the eyes) may compensate for the loss through motion of the head; these shifts in perspective provide a rudimentary sort of binocular vision.

Binocular vision is a feature common amongst many hunting animals, but also amongst primates which rely upon it when navigating complex three-dimensional environments.

Binocular vision comes at the expense of a wider field of view, meaning that an animal must rely on other senses to see what is behind it or on the periphery. For many prey species, like cows or horses, the wider field of view given by side-facing eyes and monocular vision is a better adaptation, since it reduces the chance that a predator could sneak up on them.