title: Reversal of apparent rotation in the Enigma-figure with and without motion adaptation and the effect of T-junctions.
abstract: We studied the time course of apparent rotation and directional reversal in Leviant's Enigma figure. On average, periods of clockwise rotation lasted 5.0 s as opposed to 4.4 for counter-clockwise rotation, resulting in an average reversal frequency of 6.4 within 30 s. At the beginning of a trial, clockwise rotation was perceived almost twice as often as counter-clockwise rotation. This bias could be shifted by previous adaptation to a black-and-white rotating sector disk, suggesting a neural interaction between real motion and illusory motion. We further studied Enigma-type motion on a chromatic bar superimposed onto a black-and-white linear grating. Illusory motion was strongest when the bar was oriented at 90 deg to the grating lines and became progressively weaker with a decrease in angle. This suggests that T-junctions formed by the radial rays impinging onto the colored rings of the Enigma figure are instrumental for eliciting the rotary motion and may rule out a low-level sensory origin of the illusion.
authors.affiliation: Brain Research Unit, Department of Neurology, University Hospital, Breisacher Str. 64, 79106 Freiburg, Germany. simone.gori@unipd.it
authors.forename: Simone
authors.initials: S
authors.lastname: Gori
authors.forename: Kai
authors.initials: K
authors.lastname: Hamburger
authors.forename: Lothar
authors.initials: L
authors.lastname: Spillmann
mesh_terms: D000328:Adult; D003118:Color Perception / Q000502:physiology; D005366:Figural Aftereffect; D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D009903:Optical Illusions; D011601:Psychophysics; D012399:Rotation; D013995:Time