title: Illusion of length in acute- and obtuse-angle figures.
abstract: The apparent expansion and contraction of the length of the arms of an obtuse (160 degrees) and an acute (20 degrees) angle were measured as a function of the relative lengths of the arms. 20 subjects reproduced the apparent length of the fixed-length (50-mm) horizontal lower arm of the angle. The length of the oblique arm was varied from 10 to 90 mm in 20-mm steps. The expansion of the obtuse-angle horizontal arm and the contraction of the acute-angle horizontal arm decreased as a function of the length of the oblique arm. The acute-angle illusion did not reverse from apparent contraction to apparent expansion for the longer oblique arms. These results are relevant to assimilation theories of visual-length distortions; they suggest that the assimilatory processes mediating the angle-length illusion are confined mainly to spatial regions near the vertex of the angle.
authors.affiliation: Department of Psychology, University of Sydney, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Predebon
mesh_terms: D000328:Adult; D001288:Attention; D004193:Discrimination Learning; D005260:Female; D006801:Humans; D008297:Male; D009903:Optical Illusions; D009949:Orientation; D010364:Pattern Recognition, Visual; D011597:Psychomotor Performance; D012858:Size Perception