Grasping trajectories in a virtual environment adhere to Weber’s law
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Virtual-reality and telerobotic devices simulate local motor control of virtual objects within computerized environments. Here, we explored grasping kinematics within a virtual environment and tested whether, as in normal 3D grasping, trajectories in the virtual environment are performed analytically, violating Weber’s law with respect to object’s size. Participants were asked to grasp a series of 2D objects using a haptic system, which projected their movements to a virtual space presented on a computer screen. The apparatus also provided object-specific haptic information upon “touching” the edges of the virtual targets. The results showed that grasping movements performed within the virtual environment did not produce the typical analytical trajectory pattern obtained during 3D grasping. Unlike as in 3D grasping, grasping trajectories in the virtual environment adhered to Weber’s law, which indicates relative resolution in size processing. In addition, the trajectory patterns differed from typical trajectories obtained during 3D grasping, with longer times to complete the movement, and with maximum grip apertures appearing relatively early in the movement. The results suggest that grasping movements within a virtual environment could differ from those performed in real space, and are subjected to irrelevant effects of perceptual information. Such atypical pattern of visuomotor control may be mediated by the lack of complete transparency between the interface and the virtual environment in terms of the provided visual and haptic feedback. Possible implications of the findings to movement control within robotic and virtual environments are further discussed.
KeywordsGrasping Perception and action Weber’s law 2D grasping Virtual environment Object perception.
This study was supported by an Israel Science Foundation (ISF) Grant 274/15 to Tzvi Ganel and to Daniel Algom and by the Helmsley Charitable Trust through the Agricultural, Biological and Cognitive Robotics Center of Ben-Gurion University of the Negev.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Bingham G, Coats R, Mon-Williams M (2007) Natural prehension in trials without haptic feedback but only when calibration is allowed. Neuropsychologia 45(2):288–294. https://doi.org/10.1016/j.neuropsychologia.2006.07.011 CrossRefPubMedGoogle Scholar
- Gonzalez CLR, Ganel T, Whitwell RL, Morrissey B, Goodale MA (2008) Practice makes perfect, but only with the right hand: sensitivity to perceptual illusions with awkward grasps decreases with practice in the right but not the left hand. Neuropsychologia 46(2):624–631. https://doi.org/10.1016/j.neuropsychologia.2007.09.006 CrossRefPubMedGoogle Scholar
- Johansson RS, Flanagan JR (2009b) Sensory control of object manipulation. In: Hermsdorfer J, Nowak DA (eds) Sensorimotor control of grasping: physiology and pathophysiology. Cambridge Univ. Press, Cambridge, UKGoogle Scholar
- Magdalon EC, Michaelsen SM, Quevedo AA, Levin MF (2011) Comparison of grasping movements made by healthy subjects in a 3-dimensional immersive virtual versus physical environment. Acta Physiol (Oxf) 138(1):126–134Google Scholar
- Milner AD, Goodale MA (2008) Two visual systems re-viewed. Neuropsychologia 46(3):774–785. https://doi.org/10.1016/j.neuropsychologia.2007.10.005 CrossRefPubMedGoogle Scholar
- Whitwell RL, Ganel T, Byrne CM, Goodale MA (2015) Real-time vision, tactile cues, and visual form agnosia: removing haptic feedback from a “natural” grasping task induces pantomime-like grasps. Front Hum Neurosci 9:216. https://doi.org/10.3389/fnhum.2015.00216 CrossRefPubMedPubMedCentralGoogle Scholar