title: Determining whether a ball will land behind or in front of you: not just a combination of expansion and angular velocity.
abstract: We propose and evaluate a source of information that ball catchers may use to determine whether a ball will land behind or in front of them. It combines estimates for the ball's horizontal and vertical speed. These estimates are based, respectively, on the rate of angular expansion and vertical velocity. Our variable could account for ball catchers' data of Oudejans et al. [The effects of baseball experience on movement initiation in catching fly balls. Journal of Sports Sciences, 15, 587-595], but those data could also be explained by the use of angular expansion alone. We therefore conducted additional experiments in which we asked subjects where simulated balls would land under conditions in which both angular expansion and vertical velocity must be combined for obtaining a correct response. Subjects made systematic errors. We found evidence for the use of angular velocity but hardly any indication for the use of angular expansion. Thus, if catchers use a strategy that involves combining vertical and horizontal estimates of the ball's speed, they do not obtain their estimates of the horizontal component from the rate of expansion alone.
authors.affiliation: Max Planck Institute for Biological Cybernetics, Department Bülthoff, P.O. Box 2169, 72012 Tübingen, Germany. abrouwer@cvs.rochester.edu
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Brouwer
authors.forename: Joan
authors.initials: J
authors.lastname: López-Moliner
authors.forename: Eli
authors.initials: E
authors.lastname: Brenner
authors.forename: Jeroen B J
authors.initials: JB
authors.lastname: Smeets
mesh_terms: D001288:Attention; D003196:Computer Graphics; D003463:Cues; D006801:Humans; D007600:Judgment; D009039:Motion Perception / Q000502:physiology*; D011434:Proprioception; D011581:Psychological Tests; D011601:Psychophysics; D013028:Space Perception / Q000502:physiology