Hypothesis of the equilibrium point and variability of the amplitude, speed and time of single-joint movement

The problems of variability in single-joint fast movements are analyzed within the framework of the equilibrium point hypothesis (λ-model). Control of the movement is described with the aid of three central parameters associated with the amplitude, speed and time. It is shown that such a description leads to the natural advent of three strategies of movement, only one of them leads to the appearance of the traditional dependence of the point of movement on speed described by Fitts' law. Experiments have been run to verify one of the implications of the model: the subjects performed identical series of single-joint fast movements in the elbow joint with the eyes open and closed. It was established that movements with the eyes closed are characterized by higher peak speeds with no change in variability of the final position; this contradicts Fitts' law and corresponds to the model.