The suggestion has been made (2, 3, 4, 10) that man's control of precise hand and arm movements is analogous to the operation of a servo system. The response of a continuously-following servo involves the comparison, at all times, between the input and the output with the discrepancy between the two utilized as the basis of control. If man acted as a continuously-following servo motor his responses would be guided continually by the degree to which the intended motion had not yet been made.Such a mode of control would require that continuous information be furnished concerning where the body member is and where it should be. The position of the hand or arm in space might be derived from visual or kinesthetic stimulation (or feedback, as it is called by engineers).

Position and acceleration dynamics were paired in a 2-coordinate tracking task so that both identical and different dynamics were used with the following display-control configurations: 1-dot display, 1-stick control; 1-dot display, 2-stick control; 2-dot display, 1-stick control; and 2-dot display, 2-stick control. The results showed a striking shift in the order of tracking proficiency for the various display-control configurations with the change from identical to different coordinate dynamics. When the same dynamics are used, the influence of displays predominates. However, when different dynamics are used in each coordinate, controls are the important determiners of accuracy.

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