BruceR. H.An experimental investigation of the thirst drive in rats with especial reference to the goal-gradient hypothesis. J. genet. Psychol., 1937, 17, 49–60.
2.
MaltzmanI.The process need. Psychol. Rev., 1952, 59, 40–48.
3.
TolmanE. C.Principles of purposive behavior. In KochS. (Ed.), Psychology: A study of a science. Vol. 2. General systematic formulations, learning and special processes. New York: McGraw-Hill, 1959. Pp. 92–157.