The performance of human operators acting within closed-loop control systems is investigated in a classic tracking task. The dependence of the control error (tracking error) on the parameters display gain, k_display, and input signal frequency bandwidth, f_g, which alter task difficulty and presumably the control delay, is studied with the aim of functionally specifying it via a model.

The human operator as an element of a cascaded human–machine control system (e.g., car driving or piloting an airplane) codetermines the overall system performance. Control performance of humans in continuous tracking has been described in earlier studies.

Using a handheld joystick, 10 participants tracked continuous random input signals. The parameters f_g and k_display were altered between experiments.

Increased task difficulty promoted lengthened control delay and, consequently, increased control error. Tracking performance degraded profoundly with target deflection components above 1 Hz, confirming earlier reports.

The control error is composed of a delay-induced component, a demand-based component, and a novel component: a human tracking limit. Accordingly, a new model that allows concepts of the observed control error to be split into these three components is suggested.

To achieve optimal performance in control systems that include a human operator (e.g., vehicles, remote controlled rovers, crane control), (a) tasks should be kept as simple as possible to achieve shortest control delays, and (b) task components requiring higher-frequency (>1 Hz) tracking actions should be avoided or automated by technical systems.