title: Crossing the line: estimations of line length in the Oppel-Kundt illusion.
abstract: In the Oppel-Kundt illusion, one of the oldest and least understood geometrical visual illusions, a line subdivided by a series of short orthogonal ticks appears longer than an identical line without these. Paradoxically, bisecting a long line with a single tick leads to perceived shortening of the line. We have systematically investigated the effects of adding 1 to 12 ticks on perceived line length and results suggest that at least three mechanisms must be at work: (a) bisection, which reduces perceived length; (b) a filled extent effect, which is also apparent in the von Helmholtz illusion, though no satisfactory explanation for it exists; and (c) a local contour repulsion effect of the penultimate tick upon the perceived position of the end tick, but this effect, though significant, is too small to explain the Oppel-Kundt illusion in its entirety.
authors: Department of Psychology, University of York, UK.
authors: Kyriaki
authors: K
authors: Mikellidou
authors: Department of Psychology, University of York, UK.
authors: Peter
authors: P
authors: Thompson
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D012858:Size Perception / Q000502:physiology*; D055815:Young Adult
keywords: Oppel-Kundt; bisection; illusion; lateral inhibition; line length