depth perception
Summary
Depth perception is the ability to see the world in three dimensions and judge distance, even though each retina receives a flat image. The brain uses binocular cues (retinal disparity, convergence) and monocular cues (such as linear perspective and relative size).
Detail
Meaning: Each retina receives a two-dimensional image, so the brain infers distance from cues. Binocular cues need both eyes. Retinal (binocular) disparity is the difference between the left and right retinal images, and it is larger for nearby objects. Convergence is the inward turning of the eyes, which is stronger for nearby objects. Monocular cues work with one eye: relative size, interposition (overlap), linear perspective, texture gradient, and motion parallax, in which near objects seem to sweep across the view faster than far ones.
On the MCAT: Expect a vignette in which you classify a cue as binocular or monocular, or predict which cues remain when one eye is covered. The visual cliff experiment (Gibson and Walk) is the classic design. Infants old enough to crawl usually avoid the deep side, which suggests depth perception is present early in development.
Common confusion: Losing vision in one eye does not remove depth perception. Monocular cues still allow depth judgments, although disparity is lost and precision at close range drops. Also, disparity and convergence are larger for near objects, not far ones, so they help most at short distances.
Sources
- Psychology (Myers)
- Sensation and Perception (Goldstein)
- Psychology (Schacter, Gilbert, Wegner)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.