Abstract
The present paper develops the argument that an effective evaluation of performance under time-sharing conditions requires a joint manipulation of tasks difficulty and operator's resources allocation. An experiment is presented in which each of the dimensions in a two dimensional pursuit tracking task was manipulated and controlled seperately. Single and dual task conditions were created by presenting one dimension or two dimensions simultaneously. Time-sharing efficiency was assessed under a joint manipulation of tracking difficulty on each dimension and their relative priorities. Subjects' tracking ability was individually calibrated by adaptive procedures. Regression equations and performance functions were obtained to describe the joint effects of the experimental variables. Results are discussed in terms of their implications to the problem of measuring capacity, and their contribution to the understanding of tracking behavior.
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