title: The functional subdivision of the visual brain: Is there a real illusion effect on action? A multi-lab replication study.
abstract: It has often been suggested that visual illusions affect perception but not actions such as grasping, as predicted by the "two-visual-systems" hypothesis of Milner and Goodale (1995, The Visual Brain in Action, Oxford University press). However, at least for the Ebbinghaus illusion, relevant studies seem to reveal a consistent illusion effect on grasping (Franz & Gegenfurtner, 2008. Grasping visual illusions: consistent data and no dissociation. Cognitive Neuropsychology). Two interpretations are possible: either grasping is not immune to illusions (arguing against dissociable processing mechanisms for vision-for-perception and vision-for-action), or some other factors modulate grasping in ways that mimic a vision-for perception effect in actions. It has been suggested that one such factor may be obstacle avoidance (Haffenden Schiff & Goodale, 2001. The dissociation between perception and action in the Ebbinghaus illusion: nonillusory effects of pictorial cues on grasp. Current Biology, 11, 177-181). In four different labs (total N = 144), we conducted an exact replication of previous studies suggesting obstacle avoidance mechanisms, implementing conditions that tested grasping as well as multiple perceptual tasks. This replication was supplemented by additional conditions to obtain more conclusive results. Our results confirm that grasping is affected by the Ebbinghaus illusion and demonstrate that this effect cannot be explained by obstacle avoidance.
authors.affiliation: University of Hamburg, Department of Psychology, Hamburg, Germany; Center for Neuroscience and Cognitive Systems@UniTn, Istituto Italiano di Tecnologia (IIT), Rovereto, TN, Italy. Electronic address: karl.kopiske@iit.it.
authors.forename: Karl K
authors.initials: KK
authors.lastname: Kopiske
authors.affiliation: Dipartimento di Neuroscienze, Università di Parma, Unità di Psicologia, Parma, Italy. Electronic address: nicola.bruno@unipr.it.
authors.forename: Nicola
authors.initials: N
authors.lastname: Bruno
authors.affiliation: University of Aberdeen, School of Psychology, Kings College, Old Aberdeen, United Kingdom. Electronic address: c.hesse@abdn.ac.uk.
authors.forename: Constanze
authors.initials: C
authors.lastname: Hesse
authors.affiliation: Ludwig-Maximilians Universität München, Department of ​Psychology, Munich, Germany. Electronic address: thomas.schenk@psy.lmu.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schenk
authors.affiliation: University of Hamburg, Department of Psychology, Hamburg, Germany; University of Tübingen, Department of Computer Science, Experimental Cognitive Science, Tübingen, Germany. Electronic address: volker.franz@uni-tuebingen.de.
authors.forename: Volker H
authors.initials: VH
authors.lastname: Franz
mesh_terms: D018737:Hand Strength / Q000502:physiology; D006801:Humans; D009903:Optical Illusions / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D014785:Vision, Ocular / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
keywords: Action perception; Grasping; Illusions; Manual size estimation; Visual processing