title: Accurate visuomotor control below the perceptual threshold of size discrimination.
abstract: BACKGROUND
  Human resolution for object size is typically determined by psychophysical methods that are based on conscious perception. In contrast, grasping of the same objects might be less conscious. It is suggested that grasping is mediated by mechanisms other than those mediating conscious perception. In this study, we compared the visual resolution for object size of the visuomotor and the perceptual system.
  
  
  RESULTS
  In Experiment 1, participants discriminated the size of pairs of objects once through perceptual judgments and once by grasping movements toward the objects. Notably, the actual size differences were set below the Just Noticeable Difference (JND). We found that grasping trajectories reflected the actual size differences between the objects regardless of the JND. This pattern was observed even in trials in which the perceptual judgments were erroneous. The results of an additional control experiment showed that these findings were not confounded by task demands. Participants were not aware, therefore, that their size discrimination via grasp was veridical.
  
  
  CONCLUSIONS
  We conclude that human resolution is not fully tapped by perceptually determined thresholds. Grasping likely exhibits greater resolving power than people usually realize.
authors.affiliation: Department of Psychology and Zlotowski Center for Neuroscience, Ben-Gurion University of Negev, Beer-Sheva, Israel. tganel@bgu.ac.il
authors.forename: Tzvi
authors.initials: T
authors.lastname: Ganel
authors.forename: Erez
authors.initials: E
authors.lastname: Freud
authors.forename: Eran
authors.initials: E
authors.lastname: Chajut
authors.forename: Daniel
authors.initials: D
authors.lastname: Algom
mesh_terms: D004192:Discrimination, Psychological / Q000502:physiology*; D006801:Humans; D009068:Movement / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*