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The curved surface of points in space that, for a given degree of ocular convergence, are projected on to corresponding retinal points, all points on the horopter being perceived as the same distance away as the point being fixated. Points close to the horopter within Panum's fusion area give rise to binocular disparity and produce sensations of three-dimensional depth, and points far from the horopter outside Panum's fusion area fail to result in binocular fusion and produce double images or diplopia. See also correspondence problem, stereopsis. [From Greek horos boundary + optos seen, from ops an eye]

Subjects: Psychology.

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