Panum Phenomenoneffect

Panum's limiting case = Wheatstone-Panum limiting case. In 1858, the Danish physician/ physiologist Peter Ludvig Panum (1820-1885) described this visual sensation concerning three-dimensional depth that occurs when two lines - one to each of the person's eyes - are given at positions that permit binocular fusion to occur. Then, at the same time, a third line is presented to one of the person's eyes at a different position. This stimulus-condition results in a perception where the fused line appears nearer than the single line. The effect is called a limiting case because it is similar to the stimulus pattern that occurs when two stimulus objects at different distances are viewed from an angle such that one of the objects is hidden behind the other one from the vantage point of one eye (whereas the other eye sees both of the objects). The effects described in the Panum phenomenon were discovered initially by the English inventor/physicist Sir Charles Wheatstone (1802-1875) in 1838, a year in which he described, also, his famous "stereoscope," a prism device used even today in psychological experiments to study three-dimensional perception ("stereopsis"). Another term Panum's fusion area, also named in honor of Peter Panum, refers to an area or volume of space (relative to the horopter - the curved surface of points in space that, for a given degree of ocular convergence, are pro jected on to corresponding retinal points, and where all points on the horopter are perceived as the same distance away as the point being fixated) within which different points projected onto the right and left retinas result in binocular fusion and produce a sensation of visual depth. Points far from the horopter -outside Panum's fusion area - do not result in binocular fusion, but produce double images in a condition of double-vision called "diplo-pia." See also CYCLOPEAN EYE; HOROP-TER THEORY; PERCEPTION (I. GENERAL), THEORIES OF. REFERENCES

Panum, P. L. (1858). Physioloogische untersuchungen uber das sehen mit zwei augen. Leipzig: Breitkopf, Hartel. Wade, N. J. (Ed.) (1983). Brewster and Wheatstone on vision. London: Academic Press.

PANUM'S LIMITING CASE. See PANUM PHENOMENON/EFFECT.

PAPER TIGER EFFECT. See INOCULATION THEORY.

PAPEZ-MacLEAN THEORIES. See EMOTIONS, THEORIES/LAWS OF.

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