The psychology of learning has been dominated by the concept of associationism, with its explanatory principle of contiguity, and by the concepts of animal learning with its explanatory principle of the conditioned reflex. Ebbinghaus, 11 who is the father of experimental investigations of learning as well of the higher thought processes, accepted the concepts of associationism and worked out his experiments on their foundation. For him learning was essentially an activity of memorizing descrete units of verbal material. The process of imprinting was repetition; and the combining principle, contiguity. Under his influence an immense impetus was given to the investigation of numerous quantitative factors influencing the learning and retaining of meaningless material, such as the number of readings, the number of units, the distribution of the readings in time, the distribution of the readings in space, order and position of the units, rhythmic presentation, rate of presentation, sensory mode, retroactive inhibition, proactive inhibition, length of interval between learning and relearning, organic state of the learner, attitude and motivation of the learner, physical and other environmental conditions, and age, sex and ability of the learner.Before these investigations had gone very far, similar problems began to be studied in motor learning in humans and in animals. The pioneer investigations of Bryan and Harter 8 and of Thorndike 38 gave a special impetus to the study of learning curves and of the numerous factors that influence their shape. In these studies the maze became the most important psychological instrument. It is the motor parallel of a row of nonsense syllables. It is meaningless, quantitatively variable, and a collection of descrete units. The learning of it requires the association of these units into a certain order, it iB mastered primarily by repetition, and the combining principle is contiguity. The maze, first used in animal experiments, is now used with almost equal frequency in problems of human learning. Like a row of nonsense syllables, it makes much of the learning process objectively observable, makes the control of variables and of experimental condi-• An address delivered before the Psychological Division of the A.A.A.8 .