Unusual hand postures but not familiar tools show motor equivalence with precision grasping.

Authors

Rixin Tang, The Department of Psychology, Nanjing University, Nanjing 210046, People's Republic of ChinaFollow
Robert L Whitwell, Department of Psychology, The University of British Columbia, Vancouver, British Columbia, Canada; The Brain and Mind Institute, The University of Western Ontario, London, Ontario, Canada
Melvyn A Goodale, The Brain and Mind Institute, The University of Western Ontario, London, Ontario, Canada; The Department of Psychology, The University of Western Ontario, London, Ontario, Canada; The Graduate Program in Neuroscience, The University of Western Ontario, London, Ontario, Canada; The Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, CanadaFollow

Document Type

Article

Publication Date

6-1-2016

Journal

Cognition

Volume

151

First Page

28

Last Page

36

URL with Digital Object Identifier

10.1016/j.cognition.2016.02.013

Abstract

A central question in sensorimotor control is whether or not actions performed with the hands and corresponding actions performed with tools share a common underlying motor plan, even though different muscles and effectors are engaged. There is certainly evidence that tools used to extend the reach of the limb can be incorporated into the body schema after training. But even so, it is not clear whether or not actions such as grasping with tools and grasping with the fingers share the same programming network, i.e. show 'motor equivalence'. Here we first show that feedback-appropriate motor programming for grasps with atypical hand postures readily transfers to stereotypical precision grasps. In stark contrast, however, we find no evidence for an analogous transfer of the programming for grasps using tools to the same stereotypical precision grasps. These findings have important implications for our understanding of body schema. Although the extension of the limb that is afforded by tool use may be incorporated into the body schema, the programming of a grasping movement made with tools appears to resist such incorporation. It could be the case that the proprioceptive signals from the limb can be easily updated to reflect the end of a tool held in the hand, but the motor programs and sensory signals associated with grasping with the thumb and finger cannot be easily adapted to control the opening and closing of a tool. Instead, new but well-practiced motor programs are put in place for tool use that do not exhibit motor equivalence with manual grasping.