The human motor system alters its reaching movement plan for task-irrelevant, positional forces.

Authors

Joshua G A Cashaback, Brain and Mind Institute, Department of Psychology, Western University Canada, London, Ontario, Canada
Heather R McGregor, Brain and Mind Institute, Department of Psychology, Western University Canada, London, Ontario, Canada; Graduate Program in Neuroscience, Western University Canada, London, Ontario, Canada
Paul L Gribble, Brain and Mind Institute, Department of Psychology, Western University Canada, London, Ontario, Canada; Department of Physiology and Pharmacology, Western University Canada, London, Ontario, CanadaFollow

Document Type

Article

Publication Date

4-1-2015

Journal

Journal of neurophysiology

Volume

113

Issue

7

First Page

2137

Last Page

2149

URL with Digital Object Identifier

10.1152/jn.00901.2014

Abstract

The minimum intervention principle and the uncontrolled manifold hypothesis state that our nervous system only responds to force perturbations and sensorimotor noise if they affect task success. This idea has been tested in muscle and joint coordinate frames and more recently using workspace redundancy (e.g., reaching to large targets). However, reaching studies typically involve spatial and or temporal constraints. Constrained reaches represent a small proportion of movements we perform daily and may limit the emergence of natural behavior. Using more relaxed constraints, we conducted two reaching experiments to test the hypothesis that humans respond to task-relevant forces and ignore task-irrelevant forces. We found that participants responded to both task-relevant and -irrelevant forces. Interestingly, participants experiencing a task-irrelevant force, which simply pushed them into a different area of a large target and had no bearing on task success, changed their movement trajectory prior to being perturbed. These movement trajectory changes did not counteract the task-irrelevant perturbations, as shown in previous research, but rather were made into new areas of the workspace. A possible explanation for this behavior change is that participants were engaging in active exploration. Our data have implications for current models and theories on the control of biological motion.