Depth perception is the ability to see the world in three dimensions and to judge the distance of objects. It turns the flat images on the two retinas into a coherent sense of space.

Binocular cues rely on the slightly different views each eye receives. Retinal disparity—the difference between the two images—is computed by the brain to yield precise depth information for nearby objects. Convergence, the inward turning of the eyes, supplies an additional signal at close range. Monocular cues work with one eye alone and become more important at greater distances: relative size, interposition, linear perspective, texture gradient, and motion parallax all contribute.

Infants show sensitivity to depth within the first few months of life, as demonstrated by the visual cliff experiments. Experience refines the system; people who grow up in environments with few right angles may be less susceptible to certain perspective illusions. Depth perception can be disrupted by strabismus or by loss of vision in one eye, forcing greater reliance on monocular information.

Without depth perception the world would remain a flat collage. With it, we reach, navigate, and avoid obstacles with confidence.