title: Illusory smoke and dazzling fog.
abstract: It is well known that a flat ellipse rotating in the frontoparallel plane appears, after brief inspection, as a rigid circular disc tilting back and forth in a 3-D space. We here report that rotation of a grey-shaded ellipse on a white or on a black background produces the compelling illusion of a dark smoke or a dazzling fog (depending on the conditions of the background) moving in front of a completely white or completely black tilting disc. The fog effect disappears when there is a luminance contrast all along the perimeter of the ellipse. An experiment is reported showing that the effect can be experienced in static conditions only to a limited extent and mostly in the 'dazzling' version, and that relative movement between the contours of the figure and the shaded area is crucial to the occurrence of the effect, while the occurrence of a depth effect is not.
authors.affiliation: Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy. ltommasi@psico.unipd.it
authors.forename: L
authors.initials: L
authors.lastname: Tommasi
authors.forename: D
authors.initials: D
authors.lastname: Zavagno
authors.forename: G
authors.initials: G
authors.lastname: Vallortigara
mesh_terms: D006801:Humans; D008027:Light; D009039:Motion Perception / Q000502:physiology; D009903:Optical Illusions; D014796:Visual Perception / Q000502:physiology*