1. Annau S, Heffner R, Koob GF (1974) Electrical self-stimulation of single and multiple loci: Long term observations. Physiol Behav 13:281?290
2. Autor SM (1969) The strength of conditioned reinforcers as a function of frequency and probability of reinforcement. In: Hendry DP (ed) Conditioned reinforcement. Dorsey, Homewood, pp 127?191
3. Barrett JE (1976) Effects of alcohol, chlordiazepoxide, cocaine and pentobarbital on responding maintained under fixed-interval schedules of food or shock presentation. J Pharmacol Exp Ther 196:605?616
4. Barrett JE, Katz JL (1981) Drug effects on behavior maintained by different events. In: Thompson T, Dews PB (eds) Advances in behavioral pharmacology, vol 3. Academic, New York, pp 119?168
5. Branch MN (1979) Consequent events as determinants of drug effects on schedule-controlled behavior: Modification of effects of cocaine and d-amphetamine following chronic amphetamine administration. J Pharmacol Exp Ther 210:354?360