The degree of convergence decreases with an increase in distance of the object. (ii) Convergence: When the eyes converge inward to bring the image on the fovea of each eye, a group of muscles sends messages to the brain which are interpreted as cues to the perception of depth. Large retinal disparity means a close object and small retinal disparity means a distant object. The difference in the images formed by the eyes is due to the retinal disparity. (i) Retinal or Binocular disparity: It occurs when the two eyes have different locations in the head and are separated horizontally with a difference of 6.5 centimetres. Their role in the perception of depth is as follows: The binocular cues of depth perception are provided by both the eyes in three-dimensional spaces. Important monocular cues are relative size and height, interposition, linear and aerial perspective, light and shade, texture gradient, and motion parallax. They are also known as pictorial cues as they are used by artists to induce depth in two-dimensional paintings. George H.The monocular cues of depth perception induce depth in objects when viewed through a single eye. Princeton, NJ: Princeton University Press. Spatial orientation: The spatial control of behavior in animals and man (C. Ed.), Stevens' handbook of experimental psychology: Vol. Listening in the dark: The acoustic orientation of bats and men. Sensation and perception in the history of experimental psychology. Additional auditory cues for depth are amount of reverberation, spectral characteristics (atmospheric absorption is greater for higher frequencies), motion parallax, and relative loudness of known sounds.ĭepth cues provided by other senses include proximity detection because of the strength of a familiar odor, thermal detection in pit vipers, and the electric field sensitivity found in some fish. Echolocation in bats and cetaceans represents an elaboration of this capability. ![]() This region, when viewed with a stereoscope, appears to stand above or below the rest of the pattern.Īuditory depth cues are used by blind people who can approach and stop before colliding with a wall by (unconsciously) attending to reflected sounds. A later development has been Bela Julesz's invention (1971) of random-dot stereograms: computergenerated patterns of random dots with pattern pairs that are identical except for a laterally displaced region. Three-ĭimensional perception can be provided by the stereoscope, which presents two nearly identical views separately to the two eyes. The visual cliff (a platform device with a glass floor extending out over an apparently deep side and shallow side) can be used to test depth perception in human and nonhuman subjects by ascertaining the amount of preference for the shallow side. One approach is to have the subject (under binocular or monocular conditions) adjust a rod or needle such that it is equally distant relative to a standard. Visual depth perception is studied in several ways. It is difficult experimentally to identify which cues are operating at a given time. Several of these cues may be simultaneously operating, each one corroborating the others. Pupillary constriction occurs as an associated third response with the increased depth of field possibly serving as an additional depth cue. Both of these provide kinesthetic feedback indicating depth. Asecond physiologically linked response is that of accommodation (mentioned previously as a monocular cue). This is the binocular cue of convergence. Specifically, as the distance to an object is reduced, each eye rotates inward through the activation (mainly) of the medial rectus and inhibition of the lateral rectus extraocular muscles of the eye. when the two eyes are directed toward and become focused upon objects at varying distances, several changes occur. In human visual development this cue becomes effective (on average) at an age of 4 months (although in cases where there is a failure of the eyes to work together, as in uncorrected strabismus, the child may, if not functionally blind in one eye, nevertheless become stereoblind). ![]() These different views form slightly different images on the separate retinas of the eyes and serve as the basis for the cue of retinal disparity. Two eyes separated in space receive different views of the visual field.
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