Three-dimensional head and upper arm orientations during kinematically redundant movements and at rest

• Published in: Experimental brain research Vol. 142; no. 2; pp. 181 - 192
• Main Authors: ADMIRAAL, M. A, MEDENDORP, W. P, GIELEN, C. C. A. M
• Format: Journal Article
• Language: English
• Published: Berlin Springer 2002; Springer Nature B.V
• Subjects: Adult; Arm - physiology; Biological and medical sciences; Biomechanical Phenomena; Fundamental and applied biological sciences. Psychology; Head Movements - physiology; Humans; Middle Aged; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Orientation - physiology; Posture - physiology; Psychomotor Performance - physiology; Rotation; Vertebrates: nervous system and sense organs; Human; Head; Coordination; Proprioception; Goal directed movement; Spatial orientation; Three dimensional space; Motor control; Pointing task; Kinematics; Body movement; Upper limb; Trajectory
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-001-0897-4

The three rotational degrees of freedom of the head and the upper arm exceed the number needed in a two-dimensional (2-D) facing or pointing task, respectively. Previous studies reported a reduction of the number of degrees of freedom from three to two, with one degree of freedom being a unique function of the other two (Donders' law). This study investigated whether three-dimensional (3-D) orientations of the head and arm are the same at rest and during movement for corresponding pointing or facing directions. Two separate experiments were performed: one focused on head orientations, the other focused on upper arm orientations. We instructed subjects to direct the nose or to point the extended arm in the direction of targets, which appeared in a quasi-random order at 2-s intervals. The head and upper arm orientations at rest were described by a 2-D surface with a scatter less than 3 or 4 degrees, respectively. Both for the arm and the head, orientations started and ended near the 2-D surface, but for a number of the target pairs, the orientations deviated from those predicted by the 2-D surface during movement in a way that was consistent and reproducible for movements between each target pair. For upper arm movements, we often found that deviations of arm orientations from the 2-D surface increased with increasing movement velocity. Such a positive correlation between deviation and movement velocity was not found for head movements. These results clearly indicate violations of Donders' law during movement and argue against several models for movement control found in the literature.