1. BROWN, J. S. Gradients of approach and avoidance responses and their relation to level of motivation., J. comp. physiol. Psychol., 1948, 41, 450-465.
2. HULL, C. L. A behavior system. New Haven: Yale University Press, 1952.
3. JENKINS, W. O. Studies in spread of effect. The bi-directional gradient in the performance of the white rats on a linea maze. J. comp. Psychol., 1943, 35, 41-56.
4. MILLER, N. E. Experimental studies in conflict. In Hunt, J. McV (Ed), Personality and the behavior disorders. New York: Ronald Press, 1944.
5. MORI, T., & KAJIKAWA, M. The effect of position in a linea maze upon discrimination-learning in the white rats. Ann. anim. Psychol., Tokyo, 1956, 6, 41-48.