Disentangling relative from absolute amplitude in Fitts' law experiments

Abstract

Target distance (D) and target width (W), traditionally treated as independent variables in Fitts' target acquisition paradigm, are shown to suffer inextricable confounds with task difficulty. Through a simple geometrical analogy, it is shown that relative movement amplitude D/W(which determines difficulty) and absolute movement amplitude D (or scale) are the only two variables that can be manipulated independently in a Fitts' task experiment. Disentangling relative amplitude from absolute amplitude with an appropriate experimental design should help to study target acquisition in graphical user interfaces.