Equal response rates maintained by concurrent drug and nondrug reinforcers: a design for treatment evaluation

During daily 3-h sessions, four rhesus monkeys had concurrent access to 16% alcohol (w/v) and saccharin. A response occurred when a monkey made mouth contact with the metal spout and thereby completed a drinkometer circuit. The liquids were available under concurrent nonindependent fixed-ratio 32 schedules. With these schedules, responses on the right spout decremented both the right and left fixed-ratio counters and vice versa. Responding was well maintained by both alcohol and saccharin. Increases in saccharin concentration produced increases in saccharin responding to the point that saccharin responding exceeded alcohol responding. Responses per saccharin delivery were also a direct function of the saccharin concentration. In contrast, responses per alcohol delivery generally decreased as the saccharin concentration became greater. Changeover or switching responses were also a direct function of the saccharin concentration. Relative reinforcing effects of each combination of liquid pairs were measured for each monkey. For all monkeys, it was possible to establish equal rates of responding for both reinforcers and frequent switching between reinforcers. The balanced responding can serve as a baseline for the evaluation of potential treatments that may alter relative reinforcing effects.