Depth perception is the visual ability to perceive the world in three dimensions, enabling judgements of distance. Depth perception arises from a variety of depth cues, which are typically classified into monocular and binocular cues.
Monocular cues can provide depth information when viewing a scene with one eye, and include:
– Motion parallax: this effect can be seen clearly when driving in a car. Nearby things pass quickly, while far off objects appear stationary.
– Perspective: an example would be standing on a straight road, looking down the road, and seeing the road narrows as it goes off into the distance.
– Aerial perspective: images seem blurrier the farther away they are.
– Overlap or interposition: if one object partially blocks the view of another object, it is perceived as being closer.
– Texture gradient: the texture of an object can be seen clearly when close by, but becomes less and less apparent the farther away the object is.
Binocular cues provide depth information when viewing a scene with both eyes, and include:
– Stereopsis or retinal disparity: By using two images of the same scene obtained from slightly different angles (right and left eyes), the brain can calculate depth in the visual scene providing a major means of depth perception.
– Convergence: This is the simultaneous inward movement of both eyes toward each other when viewing an object, stretching the eye muscles and helping in depth/distance perception.