NS-13617. The figures were done gratis by Claudia Carello, to whom the authors are most grateful.
Bernstein N. The coordination and regulation of movement. London: Pergamon Press, 1967.
Fowler C., & Turvey M. T. "Skill acquisition: An event approach with special reference to searching for the optimum of a function of several variables". In G. Stelmach (Ed.), Information processing in motor control and learning. New York: Academic Press, 1978.