DO MOVEMENT DIRECTION AND ARM CONFIGURATION AFFECT THE SPEED AND ACCURACY OF SINGLE JOINT MOVEMENTS?

Abstract

INTRODUCTION Models of speed-accuracy trade-offs assume that movement distance and target width are the controlled variables. Performance measures of multi-joint arm movements -spatial accuracy of the end-point (Gordonet al., 1995), movement time (Bassile and Karninski, 1991), and the shape of hand paths (Flash, 1987; Haggard & Richardson, 1996) - vary for movements made in different directions or in different parts of the workspace however, even for a given distance and target width. This study investigates whether the origin of these performance differences can be traced to biomechanical constraints peculiar to the observed joint motion. METHODS Several performance measures, including the slope of a Fitts' Law regression, are used to compare conditions which impose different biomechanical constraints. Four subjects are tested under all combinations of three factors: a) movement direction - flexion vs. extension; b) joint - wrist vs.elbow; and c) configuration of the nonfocal joints in the arm (i.e. various elbow and shoulder angles are used when testing wrist movements). RESULTS Within subject analyses showed significant differences in movement time, spatial accuracy, Fitts' Law regression parameters, as well as in certain kinematic variables across conditions. DISCUSSION Results suggest that detailed predictions of performance must account for biomechanical characteristics of joint motion, rather than relying solely on distance and target width. Additional work is planned to investigate whether these single-joint effects contribute to performance differences seen in multi-joint movements (Gordon et al., 1995; States, 1994). REFERENCES Bassile, C.A. and Kaminski, T. (1991). Speed-accuracy tradeoff must take into account the biomechanics of the movement. Society for Neuroscience Abstracts, 17(2), #629.12. Flash, T. (1987). The control of hand equilibrium trajectories in multi-joint arm movements.Bio1ogical Cybernetics, 57,257-274. Gordon, J., Ghilardi, M.F., Cooper, S. and Ghez, C. (1995). Accuracy of planar reachingmovements. 11. Systematic errors resulting from inertial anisotropy. Experimental Brain Research, 99, 112-130. Haggard, P. and Richardson, J. (1996). Spatial patterns in the control of human armmovement. Journal of Experimental Psychology: Human Perception and Performance, 22,42-62. States, R.A. (1994). Resolving indeterminacy associated with joint-level motor equivalence in planar aimed arm movements. Dissertation Abstracts International, 55(06), 2425. (University Microfilms No.AAC 9427 143).