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 narrow as it goes off in 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.
See lectures on depth perception: