Motor equivalence and self-motion induced by different movement speeds
- 239 Downloads
This study investigated pointing movements in 3D asking two questions: (1) Is goal-directed reaching accompanied by self-motion, a component of the joint velocity vector that leaves the hand’s movement unaffected? (2) Are differences in the terminal joint configurations among different speeds of reaching motor equivalent (i.e., terminal joint configurations differ more in directions of joint space that do not produce different pointer-tip positions than in directions that do) or non-motor equivalent (i.e., terminal joint configurations differ equally or more in directions of joint space that lead to different pointer-tip positions than in directions that do not affect the pointer-tip position). Subjects reached from an identical starting joint configuration and pointer-tip location to targets at slow, moderate, and fast speeds. Ten degrees of freedom of joint motion of the arm were recorded. The relationship between changes in the joint configuration and the three-dimensional pointer-tip position was expressed by a standard kinematic model, and the range- and null subspaces were computed from the associated Jacobian matrix. (1) The joint velocity vector and (2) the difference vector between terminal joint configurations from pairs of speed conditions were projected into the two subspaces. The relative length of the two components was used to quantify the amount of self-motion and the presence of motor equivalence, respectively. Results revealed that reaches were accompanied by a significant amount of self-motion at all reaching speeds. Self-motion scaled with movement speed. In addition, the difference in the terminal joint configuration between pairs of different reaching speeds revealed motor equivalence. The results are consistent with a control system that takes advantage of motor redundancy, allowing for flexibility in the face of perturbations, here induced by different movement speeds.
KeywordsReaching Motor Control Motor equivalence Movement velocity
This work was supported by NINDS Grant R01-NS050880, awarded to John Scholz.
- Belongie S (1999) Rodrigues’ rotation formula. In: Weisstein EW (ed). MathWorld–A Wolfram Web ResourceGoogle Scholar
- Bernstein N (1967) The co-ordination and regulation of movements. Pergamon Press, OxfordGoogle Scholar
- Gelfand IM, Latash ML (1998) On the problem of adequate language in motor control. Mot Control 2:306–313Google Scholar
- Klein CA, Huang C (1983) Review of pseudoinverse control for use with kinematically redundant manipulators. IEEE Trans Syst Man Cybern 13:245–250Google Scholar
- Latash ML, Scholz JP, Schoner G (2007) Toward a new theory of motor synergies. Mot Control 11:276–308Google Scholar
- Murray R, Li Z, Sastry SS (1994) A mathematical introduction to robotic manipulation. CRC Press, Boca RatonGoogle Scholar
- Rosenbaum DA, Meulenbroek RG, Vaughan J (2001a) Planning reaching and grasping movements: theoretical premises and practical implications. Mot Control 5:99–115Google Scholar
- Rosenbaum DA, Cohen RG, Dawson AM, Jax SA, Meulenbroek RG, van der Wel R, Vaughan J (2009) The posture-based motion planning framework: new findings related to object manipulation, moving around obstacles, moving in three spatial dimensions, and haptic tracking. Adv Exp Med Biol 629:485–497PubMedCrossRefGoogle Scholar
- Tseng Y, Scholz JP (2005) The effect of workspace on the use of motor abundance. Motor Control 9Google Scholar
- Tseng Y, Scholz JP, Schöner G (2002) Goal-equivalent joint coordination in pointing: effect of vision and arm dominance. Mot Control 6:183–207Google Scholar