Rats show no preference between free and earned water in an advance-response procedure

Although an arbitrarily specified instrumental response may persist when free reinforcers are concurrently available, the interpretation that earned reinforcers are preferred is tenuous. The present advance-response procedure used both time allocation and advance response rates as indices of preference between free and earned water in rats. When multiple schedule components were two response-dependent schedules with different overall reinforcement rates, higher rates of reinforcement were preferred. However, when the multiple schedule consisted of response-dependent and response-independent components equated for overall rates of reinforcement, no consistent preference for free or earned reinforcers was evident. That a preference for free reinforcers was not obtained is difficult to reconcile with concepts of least effort.