1. Amsel, A.: Partial reinforcement effects on vigor and persistence: Advances in frustration theory derived from a variety of withinsubjects experiments. In: The psychology of learning and motivation: Advances in research and theory, vol. 1, K. W. Spence, J. T. Spence, eds., pp. 1?65. New York: Academic 1967
2. Baltzer, V., Weiskrantz, L.: Negative and positive behavioral contrast in the same animals. Nature 228, 581?582 (1970)
3. Barnett, S. A.: The rat: A study in behavior. Chicago: Aldin 1963
4. Bower, G. H.: A contrast effect in differential conditioning. J. Exp. Psychol. 62, 196?199 (1961)
5. Brimer, C. J.: Disinhibition of an operant response. In: Inhibition and learing, R. A. Boakes, M. S. Halliday, eds., pp. 205?227. London: Academic 1972