Perceptual judgement, grasp point selection and object symmetry

• Published in: Experimental brain research Vol. 152; no. 2; pp. 156 - 165
• Main Authors: Lederman, Susan J., Wing, Alan M.
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.09.2003; Springer Nature B.V
• Subjects: Adult; Biological and medical sciences; Cues; Female; Form Perception - physiology; Friction; Fundamental and applied biological sciences. Psychology; Geometry; Hand - physiology; Humans; Judgment; Male; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Psychomotor Performance - physiology; Symmetry; Vertebrates: nervous system and sense organs; Visual Perception - physiology; Human; Gripping; Thumb; Motor control; Grasp; Manual task; Sensorimotor coordination; Grasp-axis orientation; Perceived object symmetry; Visual cue; Vision; Visually-guided action; Body movement; Perception; Object symmetry; Symmetry
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-003-1522-5

Object symmetry is a visual attribute that may contribute to perceptual judgement and to action. We evaluated the effects of varying the physical symmetry of planar objects (presence versus absence) on both aspects. In Experiment 1, subjects estimated the magnitude of visually perceived symmetry of the objects. The results confirmed the influence of physical symmetry on perceived symmetry, and supported our binary categorisation of stimulus objects in terms of presence versus absence of physical symmetry. In Experiment 2, participants used a precision grip to grasp and stably lift the same planar objects varying in degree of symmetry. Choice of grasp points was unrestricted. Participants selected a grasp axis (between thumb and middle finger) that limited the perpendicular distance from CM (i.e., grasp-axis error) to just a few millimetres. Moreover, they took advantage of visual cues to object symmetry to better determine CM, thus reducing their grasp-axis error for symmetric (vs. asymmetric) objects by 31%. We interpret these findings in terms of user and object-geometry constraints on grasp-point selection.