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Kinematic strategies for upper arm-forearm coordination in three dimensions
W P Medendorp1, J D Crawford, D Y Henriques
1Department of Medical Physics and Biophysics, University of Nijmegen, NL 6525 EZ Nijmegen, The Netherlands.
Journal of Neurophysiology
|November 9, 2000
Summary
The study found that upper arm control strategies adapt to forearm position, with specific rules emerging for different arm configurations. These context-dependent rules govern arm movement, independent of eye gaze.
Area of Science:
- Neuroscience
- Biomechanics
- Human Motor Control
Background:
- Understanding the three-dimensional (3-D) control of the upper arm is crucial for explaining human motor behavior.
- Donders' law describes a constraint on 3-D eye rotations, but its applicability to arm movements is less understood.
- Previous research has not fully elucidated how forearm posture influences upper arm movement strategies.
Purpose of the Study:
- To investigate how the three-dimensional (3-D) control strategy for the upper arm is modulated by forearm position.
- To determine if Donders' law applies to upper arm movements across various static arm configurations.
- To identify context-dependent kinematic rules governing upper arm torsion during pointing tasks.
Main Methods:
- Subjects pointed a laser aligned with the upper arm towards visual targets while maintaining static upper arm-forearm configurations.
- Three-dimensional (3-D) orientations of the upper arm, forearm, and eyes were recorded using 3-D search coils.
- Analysis focused on upper arm torsion as a function of pointing direction, elbow angle, and forearm orientation.
Main Results:
- Donders' law was not universally applied across all pointing tasks, with significant upper arm torsion variation for a single target.
- For static elbow configurations, torsional variance reduced to a Donders-like surface, the shape of which depended on elbow angle and forearm orientation.
- Specific strategies, resembling Listing's law or Fick-like twists, were observed based on arm configuration (e.g., extended vs. flexed in vertical plane), and these were independent of gaze direction.
Conclusions:
- Donders' law is a relevant principle for arm movement control, but its application is context-dependent, manifesting as specific kinematic rules.
- These context-dependent rules implicitly coordinate upper arm torsion with desired forearm posture, likely via neural velocity commands.
- The arm's kinematic rules for orientation control do not appear to directly coordinate with the eye's Listing's law.