title: Perceptual compression of space through position integration.
abstract: The mechanism of positional localization has recently been debated due to interest in the flash-lag effect, which occurs when a briefly flashed stationary stimulus is perceived to lag behind a spatially aligned moving stimulus. Here we report positional localization observed at motion offsets as well as at onsets. In the 'flash-lead' effect, a moving object is perceived to be behind a spatially concurrent stationary flash before the two disappear. With 'reverse-repmo', subjects mis-localize the final position of a moving bar in the direction opposite to the trajectory of motion. Finally, we demonstrate that simultaneous onset and offset effects lead to a perceived compression of visual space. By characterizing illusory effects observed at motion offsets as well as at onsets, we provide evidence that the perceived position of a moving object is the result of an averaging process over a short time period, weighted towards the most recent positions. Our account explains a variety of motion illusions, including the compression of moving shapes when viewed through apertures.
authors.affiliation: Department of Anatomy and Developmental Biology, University College London, London WC1E 6BT, UK. b.roulston@ucl.ac.uk
authors.forename: Barrie W
authors.initials: BW
authors.lastname: Roulston
authors.forename: Matt W
authors.initials: MW
authors.lastname: Self
authors.forename: Semir
authors.initials: S
authors.lastname: Zeki
mesh_terms: D003463:Cues; D006801:Humans; D009039:Motion Perception; D009903:Optical Illusions; D013028:Space Perception; D013997:Time Factors