title: Antigravity hills are visual illusions.
abstract: Antigravity hills, also known as spook hills or magnetic hills, are natural places where cars put into neutral are seen to move uphill on a slightly sloping road, apparently defying the law of gravity. We show that these effects, popularly attributed to gravitational anomalies, are in fact visual illusions. We re-created all the known types of antigravity spots in our laboratory using tabletop models; the number of visible stretches of road, their slant, and the height of the visible horizon were systematically varied in four experiments. We conclude that antigravity-hill effects follow from a misperception of the eye level relative to gravity, caused by the presence of either contextual inclines or a false horizon line.
authors.affiliation: Università di Padova, Padova, Italy. paola.bressan@unipd.it
authors.forename: Paola
authors.initials: P
authors.lastname: Bressan
authors.forename: Luigi
authors.initials: L
authors.lastname: Garlaschelli
authors.forename: Monica
authors.initials: M
authors.lastname: Barracano
mesh_terms: D000328:Adult; D001334:Automobile Driving / Q000523:psychology*; D003867:Depth Perception; D004193:Discrimination Learning; D005260:Female; D006112:Gravitation; D006801:Humans; D008297:Male; D009039:Motion Perception; D009903:Optical Illusions; D009949:Orientation; D010364:Pattern Recognition, Visual; D010469:Perceptual Distortion