title: Motion-induced position shifts are influenced by global motion, but dominated by component motion.
abstract: Object motion and position have long been thought to involve largely independent visual computations. However, the motion-induced position shift (Eagleman & Sejnowski, 2007) shows that the perceived position of a briefly presented static object can be influenced by nearby moving contours. Here we combine a particularly strong example of this illusion with a bistable global motion stimulus to compare the relative effects of global and component motion on the shift in perceived position. We used a horizontally oscillating diamond (Lorenceau & Shiffrar, 1992) that produces two possible global directions (left and right when fully visible versus up and down when vertices are occluded by vertical bars) as well as the oblique component motion orthogonal to each contour. To measure the motion-induced shift we flashed a test dot on the contour as the diamond reversed direction (Cavanagh & Anstis, 2013). Although the global motion had a highly significant influence on the direction and size of the motion-induced position shift, the perceived displacement of the probe was closer to the direction of the component motion. These findings show that while global motion can clearly influence position shifts, it is the component motion that dominates in setting the position shift. This is true even though the perceived motion is in the global direction and the component motion is not consciously experienced. This suggests that perceived position is influenced by motion signals that arise earlier in time or earlier in processing compared to the stage at which the conscious experience of motion is determined.
authors.affiliation: Department of Psychology, Stanford University, 450 Serra Mall, Stanford, CA 94305, United States. Electronic address: pjkohler@stanford.edu.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Kohler
authors.affiliation: Laboratoire Psychologie de la Perception, Université Paris Descartes, Sorbonne Paris Cité, and CNRS UMR 8242, 75006 Paris, France. Electronic address: patrick.cavanagh@parisdescartes.fr.
authors.forename: Patrick
authors.initials: P
authors.lastname: Cavanagh
authors.affiliation: Department of Psychological & Brain Sciences, Dartmouth College, 6207 Moore Hall, Hanover, NH 03755, United States. Electronic address: peter.u.tse@dartmouth.edu.
authors.forename: Peter U
authors.initials: PU
authors.lastname: Tse
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D005133:Eye Movements / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D055815:Young Adult
keywords: Component motion; Global motion; Motion-induced position shifts