Reproduction of simple movements as a function of factors influencing proprioceptive feedback.

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Abstract
This study tested the hypotheses that elasticity added to a control should lead to improved spatial accuracy of movements, while damping and mass added to a control should lead to improved temporal accuracy of movement. These hypotheses are derived from the fact that the physical parameters of spring stiffness, damping, and mass characterizing a control determine proportionality relations between applied torque and changes in the position, rate of motion, and acceleration, respectively, of the control. This proportionality provides a basis for learning to associate a given torque with a given characteristic of the movement. To test these hypotheses subjects (Ss) performed simple circular and triangular control motions with a joystick when the control was loaded with various degrees of spring stiffness, or damping, or mass. Three levels of each control parameter were equated originally by means of a psychophysical procedure so that movements opposed by each of the 3 physical factors were judged by Ss to involve equal "effort." In each control loading condition the movements were first practiced for 3 trials with the help of a visual guide and paced by means of a metronome. Visual and auditory guides were then removed, and Ss were instructed to reproduce the motions as accurately as possible. Photographic records of all motions were measured for accuracy of temporal and spatial reproductions. An increase of viscous damping or of inertia of the control resulted in greater uniformity of speed within individual motions, and also in greater uniformity of speed in successive reproductions of the same motion. In the case of the triangular motions increased mass and increased damping led to greater uniformity of peak velocity on each side of the triangle on successive trials. Increased damping and mass also led to slightly lower average velocities of motion, but an analysis of covariance on Score 1 indicated that the reduction in temporal variability was still significant when the effect of movement time was controlled. These results support the hypotheses regarding the utilization of proprioceptive information. The effect of spring loading upon spatial accuracy of the reproduced motion was in general not significant. It is suggested that extended practice with knowledge of results are needed for effective utilization of cues provided by spring loading. The beneficial effects of mass and viscosity might, of course, also increase with extended train ing.
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