The Power Model of Fitts' Law Does Not Encompass the Logarithmic Model

Whether Fitts' law, a well-known model of human pointing movement, is a logarithmic law or a power law has remained unclear so far. In two widely cited papers, Meyer et al. have claimed that the power model they derived from their celebrated stochastic optimized-submovement theory encompasses the logarithmic model as a limiting case. We show that Meyer et al.'s theory implies in fact a quasi-logarithmic, rather than quasi-power model, the two models being not equivalent.