Discrete movements in the horizontal plane as a function of their length and direction.

One of the motor reactions commonly involved in the operation of both military and civilian equipment is that of moving a limb (or limbs) as quickly as possible from one position in space to another. Normally, it is desired to terminate the movement at exactly the aimed-for point with a minimum of error and oscillation. The aerial gunner, for example, in tracking a moving target, is often called upon to make quick discrete movements of this sort. Thus when an attacking aircraft is suddenly perceived the guns must be slewed around to the target with the least possible delay. Similarly, during the course of actually tracking the target, observed displacements between the reticle and the target must be quickly and accurately corrected. Previous studies of discrete movements, such as those of Craik (i), Householder (3), and Vince (5), have been oriented rather directly toward the solution of problems arising out of the gunnery tracking situation. In these experiments, the subjects were required to react as quickly as possible, by movements of the hand and arm, to sudden, visually perceived displacements of a target in space. Usually neither the direction in which the movement was to be made nor its