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A one-dimensional three-state relay control task in which human operators served as the active switching and equalization element was employed to compare performance in three display conditions and to derive measures of performance that might prove useful for further development of models of human tracking behavior. Two displays which provided explicit velocity information in the form of a unidimensional error-velocity vector superimposed on a compensatory error display and two-dimensional phase-plane display of error velocity vs. displacement were shown to enhance learning over that produced by the usual compensatory display of error, but only with the highest value of system gain, 30 cm/second<R>2</R>. An analysis of subjects' initial transient response represented as mean switching points in the phase-plane revealed remarkably little variability and switching performance close to that of an optimal minimum-time controller. Finally, in this and two subsidiary experiments, a measure of time to process visual feedback about the ongoing response process was derived that may provide a first step toward linking discrete reaction-time results to continuous manual-control performance.