Oral self-administration of pentobarbital by rhesus monkeys: maintenance of behavior by different concurrently available volumes of drug solution.
Bigger reinforcers win choice battles, even when the reinforcer is a drug.
01Research in Context
What this study did
Scientists let rhesus monkeys drink two liquids at the same time. One spout held plain water. The other held pentobarbital, a barbiturate, mixed at 1 mg per mL.
Both spouts sat on fixed-ratio schedules. The monkey had to press a lever several times to earn a sip. The team varied how much drug solution each press delivered. They watched which spout the monkey chose.
What they found
Monkeys almost always picked the drug spout. When the drug portion grew larger, they pressed even more for that spout. Their choice tracked the size of the reinforcer, just like food or water would.
How this fits with other research
Rusch et al. (1981) ran a similar test with heroin versus food. Heroin doses changed, and monkeys shifted choice the same orderly way. The 1989 drug-volume study extends that pattern to oral barbiturates.
Ploog (2001) later showed pigeons also pick the key that leads to a bigger food pile. Across species and reinforcer type, magnitude drives choice.
Duker et al. (1991) swapped drug for electric shock and still saw clean preference. Together these papers say, "It’s not the drug—it’s the schedule." Larger, less frequent, or simply better payoff wins every time.
Why it matters
You can trust the basic matching law with unusual reinforcers. If a client keeps choosing a problem behavior, check what size payoff it produces. Increase the payoff for the replacement skill, decrease the payoff for the problem response, and watch choice shift—just like the monkeys did.
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02At a glance
03Original abstract
For 4 rhesus monkeys, mouth-contact responses with either of two brass spouts were reinforced according to fixed-ratio schedules by 0.65-mL liquid deliveries during daily 3-hr sessions. Three experiments were conducted. In each experiment, independent fixed-ratio schedules were concurrently in effect at the two spouts. Following completion of each fixed ratio on a spout, a specified number of liquid deliveries were available from that spout under a continuous-reinforcement schedule. The number of such deliveries available at each spout was manipulated independently. In Experiment 1, a 1-mg/mL pentobarbital solution was simultaneously available with water (the drug vehicle) under concurrent fixed-ratio schedules of 32 responses for 3 subjects and 64 responses for the remaining subject. The number (N) of liquid deliveries that were available after completion of each fixed ratio was varied in the following order: 8, 4, 2, 1, and 8 (retest). For each subject at each condition, drug maintained more responding than water. The number of drug deliveries obtained per session was directly related to the amount of drug available per fixed ratio (i.e., to N), whereas the number of fixed ratios completed per session generally was inversely related to the value of N. In Experiment 2, fixed-ratio size was the same for each subject as in Experiment 1, but deliveries of a 1-mg/mL pentobarbital solution were available at both spouts. The number of drug deliveries available under one fixed-ratio schedule (Ns, the "standard" reinforcer amount) was held at eight, and the number of drug deliveries available under the second schedule (Nc, the "comparison" reinforcer amount) was changed across blocks of six sessions of stable responding in the following order: 1, 2, 4, 8, 4, 2, and 1. The identical series of comparison reinforcer amounts (Nc) was then tested twice more, but with the standard reinforcer (Ns) held first at four and then at two deliveries. Across the three choice series, reinforcing effects were directly related to reinforcer magnitude. In Experiment 3, deliveries of a 1-mg/mL pentobarbital solution again were available at both spouts. However, the two reinforcer amounts were held constant at N = 8 deliveries under one schedule and N = 4 deliveries under the second schedule, and fixed-ratio size was systematically varied. Across the range of fixed-ratio sizes from low to high, the degree to which behavior was better maintained by the larger of the two drug quantities was an inverted U-shaped function of fixed-ratio size.(ABSTRACT TRUNCATED AT 400 WORDS)
Journal of the experimental analysis of behavior, 1989 · doi:10.1901/jeab.1989.52-111