Matching under nonindependent variable-ratio schedules of drug reinforcement.
Monkeys divide their work between two drug levers the same way they divide food lever presses—straight matching.
01Research in Context
What this study did
Scientists gave monkeys two levers. Pressing either lever delivered drug shots on variable-ratio schedules.
The team watched which lever each monkey picked. They checked if the animals matched response rates to the drug amounts received.
What they found
Monkeys spread their lever presses in the same ratio as the drug they got. The old matching law held true even when the reinforcer was a drug.
Choice stayed steady even though the schedules were not independent.
How this fits with other research
Wearden (1983) had already shown that small bursts of pressing can make choice look off, but the law still works. Farrant et al. (1998) now prove the law also holds when drugs, not food, keep the behavior going.
MacDonall (2009) later built the stay/switch model and said it beats the matching law. Their data came from food setups, not drug setups, so the two papers do not truly clash.
Avellaneda (2025) keeps the matching idea but adds a smart Markov model for when animals hop between levers. The 1998 drug data still fit inside this bigger picture.
Why it matters
If you run concurrent schedules in the lab, expect matching whether the payoff is juice, tokens, or a drug. When choice looks odd, first check reinforcer rates, not the reinforcer type. This keeps your analysis simple and your graphs clean.
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02At a glance
03Original abstract
Response-contingent deliveries of oral pentobarbital maintained responding of 3 rhesus monkeys during daily 3-hr sessions. Deliveries of pentobarbital were arranged under nonindependent concurrent variable-ratio variable-ratio schedules. Responses to either schedule counted toward completion of both variable-ratio schedule requirements. This schedule is similar in some respects to conventional concurrent variable-interval variable-interval schedules, in which passage of time counts toward completion of the interval value on both schedules. Restricted nonindependent concurrent variable-ratio variable-ratio schedules were also 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 other variable-ratio schedule. Under both types of concurrent variable-ratio schedules, the relative rate of responding corresponded to the relative drug intake. Unlike earlier studies of concurrent variable-interval variable-interval intravenous cocaine reinforcement, preference was proportionate to concentration, and exclusive preferences did not develop. The relationship between relative rate of responding and relative drug intake was well described by the generalized matching law.
Journal of the experimental analysis of behavior, 1998 · doi:10.1901/jeab.1998.70-23