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The human motor system alters its reaching movement plan for task-irrelevant, positional forces.
Joshua G A Cashaback1, Heather R McGregor2, Paul L Gribble3
1Brain and Mind Institute, Department of Psychology, Western University Canada, London, Ontario, Canada;
Journal of Neurophysiology
|January 16, 2015
Summary
The human nervous system may actively explore its environment, responding to both relevant and irrelevant forces during reaching movements. This challenges the idea that responses only occur when task success is threatened.
Area of Science:
- Neuroscience
- Motor Control
- Human Movement Science
Background:
- The minimum intervention principle and uncontrolled manifold hypothesis suggest the nervous system reacts to perturbations only if they impact task success.
- Previous research tested these principles using muscle/joint frames and workspace redundancy, often with spatial/temporal constraints.
- Constrained movements are rare in daily life and may not reflect natural motor behavior.
Purpose of the Study:
- To investigate whether humans respond to task-relevant and task-irrelevant forces during reaching movements under relaxed constraints.
- To test the hypothesis that the nervous system ignores forces not affecting task success.
Main Methods:
- Two reaching experiments were conducted using relaxed task constraints.
- Participants performed reaching movements while experiencing task-relevant and task-irrelevant force perturbations.
- Movement trajectories were analyzed to assess responses to different force types.
Main Results:
- Participants responded to both task-relevant and task-irrelevant forces.
- Notably, participants altered their movement trajectories *before* experiencing task-irrelevant forces.
- These trajectory changes aimed at new workspace areas, not to counteract the irrelevant perturbations.
Conclusions:
- The findings challenge existing models of motor control by demonstrating responses to task-irrelevant forces.
- Active exploration may explain the observed proactive changes in movement trajectories.
- This research has significant implications for understanding biological motion control and sensorimotor adaptation.
