It has been reported in the literature that the smoothness of human subjects' arm/hand movements vanishes as the movements become slower. Intermittencies in the movement are observed as distinct peaks in the speed profile.
Doeringer and Hogan (1998) proposed two possibilities for the origin of intermittency in slow movements: (1) noise in neuromuscular circuitry, and (2) a movement planner that can only construct simple movements. They showed that the intermittency can not be due to noise or delays in visual feedback.
We designed an experiment to evaluate the two propositions. We used a Vicon 3D motion capture system to record trajectories of fingertip, wrist, elbow and shoulder as five participants completed a simple manual circular tracking task at various constant speed levels. Statistical analyses indicated that movement intermittency, quantified by a number of peaks metric, increased in distal direction. When the movement execution is thought as a serial process where more noise gets introduced at every joint or muscle involved in the movement, this finding supports the neuromuscular noise model for origins of intermittency. Additionally, movement speed was determined to have a significant effect on intermittency, while orientation of the task plane showed no significance.
Preliminary findings were presented in the workshop "Understanding the Human Hand for Advancing Robotic Manipulation" at RSS 2009 (see publications below), and will appear in the proceedings of IEEE IROS 2009. We have captured data from additional five participants and now a journal manuscript is in preparation.
This project is in collaboration with Dr. Zhigang Deng and Qin (Eric) Gu from the Department of Computer Science at University of Houston (Computer Graphics and Interactive Media Lab - CGIM).
Reference:
J. A. Doeringer and N. Hogan, “Intermittency in preplanned elbow movements persists in the absence of visual feedback,” J Neurophysiol, vol. 80, no. 4, pp. 1787–1799, 1998.