Fitts' law in bivariate pointing on large touch screens: Age-differentiated analysis of motion angle effects on movement times and error rates

Abstract

Fitts' Law is a famous and highly satisfactory model to predict movement times in ergonomic studies. The original Fitts' Law only considers one-dimensional movements. In the field of human-computer interaction however one has to deal with at least two dimensions. Due to inconsistency in previous research concerning the integration of the motion angle into the Fitts' formulation, we investigated the influence of this factor on movement times and errors systematically. 30 subjects, separated in two age groups (younger: 21-36 years, elderly: 58-77 years) were tested in executing a pointing task on a large touch screen. The results reveal that the motion angle has a sinusoidal effect on the movement time for both age groups. Subsequently Fitts' Law was refined by an additional summand which is an explicit sine function of the motion angle. Based on our findings we give practical recommendations where to arrange information elements on large touch screens. © 2011 Springer-Verlag.