The visibility of contact points influences grasping movements
- 371 Downloads
When humans grasp an object, the thumb habitually contacts the object on the visible part, whereas the index finger makes contact with the object on the occluded part. Considering that the contact points play a critical role in object-oriented actions, we studied if and how the visibility of the points of contact for the thumb and index finger affects grasping movements. We adapted reach-to-point movements (visual feedback displacement: 150 mm in depth) performed with either the thumb or the index finger to measure how a newly learned visuomotor mapping transfers to grasping movements. We found a general transfer of adaptation from reach-to-point to reach-to-grasp movements. However, the transfer of adaptation depended on the visibility of contact points. In the first experiment, in which only the thumb’s contact point was visible during grasping, the transfer of adaptation was larger after thumb than after index finger perturbation. In the second experiment, in which both contact points were equally visible, the transfer of adaptation was of similar magnitude. Furthermore, thumb trajectories were less variable than index trajectories in both experiments weakening the idea that the less variable digit is the digit that guides grasping movements. Our findings suggest that the difficulty in determining the contact points imposes specific constraints that influence how the hand is guided toward the to-be-grasped object.
KeywordsPrehension Reaching Motor control Visuomotor adaptation Digits Human
- Brouwer AM, Franz VH, Gegenfurtner KR (2009) Differences in fixations between grasping and viewing objects. J Vis 9(18):1–24Google Scholar
- Nicolini C, Fantoni C, Mancuso G, Volcic R, Domini F (2014) A framework for the study of vision in active observers. In: Rogowitz BE, Pappas TN, de Ridder H (eds) Human Vision and Electronic Imaging XIX, Proc SPIE, vol 9014, p 901414Google Scholar
- Verheij R, Brenner E, Smeets JBJ (2012) Grasping kinematics from the perspective of the individual digits: a modelling study. PLoS ONE 7(e33):150Google Scholar
- von Helmholtz H (1867) Treatise on physiological optics. Dover Publications, DoverGoogle Scholar