Experiments with a target-threshold control theory model for deriving Fitts´ law parameters for human-machine systems

A target-threshold control theory model was developed for predicting human-machine movement time. This allows the previously empirical parameters of Fitts´ speed and accuracy law (1954) to be determined before system construction. Fitts´ law may now serve a role as a predictive design engineering tool for new systems as well as in its traditional role of after-the-fact analysis. The target-threshold model successfully characterized human control movement times, before system construction, in experiments involving camera pointing for a new class of point-and-direct telerobotics. Employing the natural logarithm as the basis for indexing task difficulty, the slope and intercept parameters were found by analysis of calculated step response trajectories at progressively tighter normalized target thresholds corresponding to increasing distances between targets. Tests validated the model for human subjects using the experimental apparatus of the Stanford Point-And-Direct (PAD) Telerobot for which tasks are developed using phrases such as “put that there”. The target-threshold model is a tool for human factors engineers and control system designers that allows fundamental control theory techniques to be used to predict speed of response for new human-machine systems. The technique allows system developers to compare performance of prospective human-machine systems