On the robustness of Fitts' Law


Fitts' Law (Fitts, 1954: J Exp Psychol) discovered the logarithmic relation between the ratio of distance and target width with movement time, such that T = a + b Log2 (2D/W). In the present paper I explore the ramifications of Fitts Law. First, the classic paper by Carlton (1994: J Mot Behav) shows that Fitts' Law behaviour is not related to the linear speed-accuracy trade-off (Schmidt, et al. 1979: Psychol Rev). We then present two new experiments that show that individual differences in Fitts' Law performance are correlated. Finally, it is demonstrated that linear speed accuracy trade-off performance is related to Fitts' Law performance. Thus, although these two relations are mathematically distinct, a common principle relates the two tasks. Possible explanatory mechanisms are discussed.