MATCHING UNDER NONINDEPENDENT VARIABLE-RATIO SCHEDULES OF DRUG REINFORCEMENT

Response-contingent deliveries of oral pentobarbital maintained respon ding of 3 rhesus monkeys during daily 3-hr sessions. Deliveries of pen tobarbital were arranged under nonindependent concurrent variable-rati o variable-ratio schedules. Responses to either schedule counted towar d completion of both variable-ratio schedule requirements. This schedu le is similar in some respects to conventional concurrent variable-int erval variable-interval schedules, in which passage of time counts tow ard completion of the interval value on both schedules. Restricted non independent concurrent variable-ratio variable-ratio schedules were al so studied. On that schedule, when a drug delivery was assigned to one spout, it had to be collected before responses on the opposite spout again counted toward completion of the schedule requirements. Relative reinforcer magnitude was varied by changing the drug concentration on one schedule while keeping the drug concentration constant on the oth er variable-ratio schedule. Under both types of concurrent variable-ra tio variable-ratio schedules, the relative rate of responding correspo nded to the relative drug intake. Unlike earlier studies of concurrent variable-interval variable-interval intravenous cocaine reinforcement , preference was proportionate to concentration, and exclusive prefere nces did not develop. The relationship between relative rate of respon ding and relative drug intake was well described by the generalized ma tching law.