HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 92/2/1199    most recent 00519.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (24) Citing Articles via Google Scholar Google Scholar Articles by Osu, R. Articles by Kawato, M. Search for Related Content PubMed PubMed Citation Articles by Osu, R. Articles by Kawato, M.

Optimal Impedance Control for Task Achievement in the Presence of Signal-Dependent Noise

¹ATR Computational Neuroscience and ³Human Information Processing Research Laboratories, Kyoto 619-0288; ²Nagaoka University of Technology, Niigata 940-2188, Japan; and ⁴Institute of Neuroscience, University of Plymouth, Plymouth PL4 8AA, United Kingdom

Submitted 30 May 2003; accepted in final form 16 March 2004

There is an infinity of impedance parameter values, and thus different co-contraction levels, that can produce similar movement kinematics from which the CNS must select one. Although signal-dependent noise (SDN) predicts larger motor-command variability during higher co-contraction, the relationship between impedance and task performance is not theoretically obvious and thus was examined here. Subjects made goal-directed, single-joint elbow movements to either move naturally to different target sizes or voluntarily co-contract at different levels. Stiffness was estimated as the weighted summation of rectified EMG signals through the index of muscle co-contraction around the joint (IMCJ) proposed previously. When subjects made movements to targets of different sizes, IMCJ increased with the accuracy requirements, leading to reduced endpoint deviations. Therefore without the need for great accuracy, subjects accepted worse performance with lower co-contraction. When subjects were asked to increase co-contraction, the variability of EMG and torque both increased, suggesting that noise in the neuromotor command increased with muscle activation. In contrast, the final positional error was smallest for the highest IMCJ level. Although co-contraction increases the motor-command noise, the effect of this noise on the task performance is reduced. Subjects were able to regulate their impedance and control endpoint variance as the task requirements changed, and they did not voluntarily select the high impedance that generated the minimum endpoint error. These data contradict predictions of the SDN-based theory, which postulates minimization of only endpoint variance and thus require its revision.

This article has been cited by other articles:

				R. Laboissiere, D. R. Lametti, and D. J. Ostry Impedance Control and Its Relation to Precision in Orofacial Movement J Neurophysiol, July 1, 2009; 102(1): 523 - 531. [Abstract] [Full Text] [PDF]

				J. Wong, E. T. Wilson, N. Malfait, and P. L. Gribble Limb Stiffness Is Modulated With Spatial Accuracy Requirements During Movement in the Absence of Destabilizing Forces J Neurophysiol, March 1, 2009; 101(3): 1542 - 1549. [Abstract] [Full Text] [PDF]

				J. Wong, E. T. Wilson, N. Malfait, and P. L. Gribble The Influence of Visual Perturbations on the Neural Control of Limb Stiffness J Neurophysiol, January 1, 2009; 101(1): 246 - 257. [Abstract] [Full Text] [PDF]

				D. W. Franklin, G. Liaw, T. E. Milner, R. Osu, E. Burdet, and M. Kawato Endpoint Stiffness of the Arm Is Directionally Tuned to Instability in the Environment J. Neurosci., July 18, 2007; 27(29): 7705 - 7716. [Abstract] [Full Text] [PDF]

				E. Trainin, R. Meir, and A. Karniel Explaining Patterns of Neural Activity in the Primary Motor Cortex Using Spinal Cord and Limb Biomechanics Models J Neurophysiol, May 1, 2007; 97(5): 3736 - 3750. [Abstract] [Full Text] [PDF]

				E. A. Christou, B. Poston, J. A. Enoka, and R. M. Enoka Different Neural Adjustments Improve Endpoint Accuracy With Practice in Young and Old Adults J Neurophysiol, May 1, 2007; 97(5): 3340 - 3350. [Abstract] [Full Text] [PDF]

				L. P. J. Selen, J. H. van Dieen, and P. J. Beek Impedance Modulation and Feedback Corrections in Tracking Targets of Variable Size and Frequency J Neurophysiol, November 1, 2006; 96(5): 2750 - 2759. [Abstract] [Full Text] [PDF]

				D. W. Franklin, U. So, M. Kawato, and T. E. Milner Impedance Control Balances Stability With Metabolically Costly Muscle Activation J Neurophysiol, November 1, 2004; 92(5): 3097 - 3105. [Abstract] [Full Text] [PDF]