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Kinematic rules for upper and lower arm contributions to grasp orientation
J J Marotta1, W P Medendorp, J D Crawford
1Canadian Institutes of Health Research Group for Action and Perception, Department of Psychology, Centre for Vision Research, York University, Toronto, Ontario M3J-1P3, Canada. marotta@yorku.ca
Journal of Neurophysiology
|August 22, 2003
Summary
The study found that both upper and lower arm movements coordinate to achieve grasp orientation, challenging the idea of separate control for reaching and grasping. This coordinated motion helps maintain Donders' Law for the upper arm.
Area of Science:
- Neuroscience
- Biomechanics
- Human Motor Control
Background:
- Understanding arm movement coordination is crucial for grasping.
- Donders' Law describes a constraint on upper arm rotation during reaching.
Purpose of the Study:
- To investigate the contribution of upper and lower arm torsion to grasp orientation.
- To examine how the visuomotor system manages conflicting demands of arm torsion and Donders' Law.
Main Methods:
- Subjects reached and grasped target blocks with varying orientations and positions.
- Experiment 1 used 19 target orientations; Experiment 2 used 9 positions.
Main Results:
- Both upper (9%) and lower arm (42%) showed significant clockwise torsional rotation with increasing grasp orientation.
- A linear relationship between upper and lower arm torsion indicated coordinated rotation.
- Donders' "surfaces" remained invariant in shape across grasp orientations.
Conclusions:
- The entire arm-hand system contributes to grasp orientation, not just the lower arm.
- The reach/grasp distinction is better understood through coordinated orienting rules and location-dependent kinematics, rather than separate proximal-distal control.