title: Second-order motion conveys depth-order information.
abstract: Psychophysical and neurophysiological studies have revealed that the visual system is sensitive to both "first-order" motion, in which moving features are defined by luminance cues, and "second-order" motion, in which motion is defined by nonluminance cues, such as contrast or flicker. Here we show psychophysically that common types of second-order stimuli provide potent cues to depth order. Although motion defined exclusively by nonluminance cues may be relatively rare in natural scenes, the depth-order cues offered by second-order stimuli arise ubiquitously as a result of occlusion of one moving object by another. Our results thus shed new light on the ecological importance of second-order motion. Furthermore, our results imply that visual cortical areas that have been shown to be responsive to second-order motion may be extracting information not just about object motion as has been assumed, but also about the relative depth of objects.
authors.affiliation: The Salk Institute for Biological Studies, La Jolla, CA, USA. jay@salk.edu
authors.forename: Jay
authors.initials: J
authors.lastname: Hegdé
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Albright
authors.forename: Gene R
authors.initials: GR
authors.lastname: Stoner
mesh_terms: D003463:Cues; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009799:Ocular Physiological Phenomena