Are the obtuse angles the key components of the Poggendorff illusion?
An experiment is reported which confirms and extends a previous finding that amputations of the Poggendorff figure do not necessarily result in large positive effects with obtuse-angle stimuli, and small or even negative effects with acute-angle stimuli. Indeed, the acute-angle effects found were significantly greater than the obtuse-angle effects, and the full Poggendorff error was not explicable in terms of the linear summation of the component-angle effects. An 'alignment displacement effect' reported earlier by Hotopf and Obonai was shown to occur, but could not be an important component of the Poggendorff illusion.
D000293:Adolescent; D000328:Adult; D004215:Distance Perception; D005260:Female; D005556:Form Perception; D006801:Humans; D007088:Illusions; D008297:Male; D009903:Optical Illusions; D009949:Orientation; D010469:Perceptual Distortion