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Depth perception - Definition and Overview |
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Depth perception is the visual ability to perceive the world in three dimensions. It is a trait common to many higher animals. Depth perception allows the beholder to accurately gauge the distance to an object.
Depth perception is achieved through a variety of mechanisms:
- Binocular vision - By using two images of the same scene taken from slightly different angles, it is possible to triangulate the distance to an object with a high degree of accuracy. This is the major mechanism for depth perception. It is taken advantage of to trick people into thinking they perceive depth when viewing Magic Eyes, 3D movies and sterioscopic photos.
- Motion parallax - The apparent relative motion of several stationary objects against a background when the observer moves gives hints about their relative distance. This effect can be seen clearly when driving in a car, nearby things pass quickly, while far off objects appear stationary. Some animals that lack binocular vision due to wide placement of the eyes employ parallax for depth cueing (e.g. some types of birds, which bob their heads to achieve motion parallax, and squirrels, which move in lines orthogonal to an object of interest to do the same).1
- Color vision - Correct interpretation of color, and especially lighting cues, allows the beholder to determine the shape of objects.
- Perspective - The property of parallel lines converging at infinity allows us to reconstruct the relative distance of two parts of an object, or of landscape features.
- Relative size - An automobile that is close to us seems larger than one that is far away; our visual system exploits the relative size of similar (or familiar) objects to judge distance.
- Distance fog - Due to light scattering, objects that are a great distance away seem hazier to the eye; the visual system is attuned to this effect.
- Occlusion - Occlusion (blocking the sight) of objects by other objects is a clue, albeit a weak one, for judging relative distance. It only allows the beholder to create a "ranking" of nearness, and does not give any insight as to actual distances. In the absence of color vision (as at night) or binocular vision (as with one-eyed creatures - test it!) occlusion often serves as the method of last resort for providing rudimentary depth perception.
These functions are carried out automatically by the visual cortex; however, they are still a sort of guesswork by the brain, and so the beholder may fall victim to optical illusions that result in mistakes in depth perception.
Trained artists are keenly aware of the above mentioned methods for perceiving depth (Color vision, Distance fog, Perspective and relative sizes). They often take advantage of them to make their works appear real.
Notes
1 The term 'parallax vision' is often used as a synonym for binocular vision, and should not be confused with motion parallax. The former allows far more accurate gauging of depth than the latter.
External Links
See also: visual perception
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