Concurrent nonindependent fixed‐ratio schedules of alcohol self‐administration: Effects of schedule size on choice
Bigger ratio requirements can make a strong reinforcer lose to a weak one, so schedule size alone can flip choice.
01Research in Context
What this study did
Meisch et al. (2016) let rats drink two ethanol solutions at the same time.
Each drink cost a fixed number of lever presses. The cost changed across days.
Scientists watched which drink the rats picked when the price went up or down.
What they found
When the cheaper cup gave weaker booze, rats still picked it.
Once the cheaper cup asked for many more presses, rats flipped to the stronger booze.
Preference reversed as the schedule size grew, even though the stronger reinforcer never changed.
How this fits with other research
Zimmerman (1969) first showed that bigger food rewards shorten the pause after a ratio. Meisch adds the twist: under concurrent schedules, bigger rewards can lose the race if the price is high.
Baer et al. (1984) saw the same shield in rhesus monkeys. Higher pentobarbital concentration protected responding against large ratios. Meisch repeats the pattern with ethanol, confirming the rule crosses drugs and species.
Landon et al. (2002) tracked both snap choices after a reinforcer and long-term shifts. Their pigeons also flipped when extreme ratios stacked the deck, showing the effect is not limited to ethanol or rats.
Why it matters
Your client may pick a low-quality reinforcer if it is easy to get. Raise the response cost and the same client may switch to a higher-quality item.
Use this when you thin schedules or increase task length. Start with the rich reinforcer at a low ratio, then gradually enlarge the ratio for the rich option while keeping the lean option cheap. Watch for the flip point; it tells you the true value difference.
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02At a glance
03Original abstract
Choice behavior was studied under concurrent nonindependent fixed‐ratio fixed‐ratio (nFR) schedules of reinforcement, as these schedules result in frequent changeover responses. With these schedules, responses on either operandum count toward the completion of the ratio requirements of both schedules. Five monkeys were subjects, and two pairs of liquid reinforcers were concurrently available: 16% (w/v) and 0% ethanol or 16% and 8% ethanol. For each pair of reinforcers, the nFR sizes were systematically altered across sessions while keeping the schedule size equal for both liquids. Responding varied as a function of reinforcer pair and nFR size. With the 16% and 0% pair, higher response rates were maintained by 16% and were an inverted U‐shape function of nFR size. With 16% and 8%, a greater number of responses initially occurred on the schedule that delivered 8% ethanol. However, as nFR size increased, preference reversed such that responses that delivered 16% ethanol were greater. When the nFR size was subsequently decreased, preference reverted back to 8%. Number of responses emitted per delivery was a dependent variable and, in behavioral economic terms, was the price paid for each liquid delivery. With 16% and 0%, changeover responses initially increased and then decreased as schedule size became larger. In contrast, with the 16% and 8% pair, changeover responses increased directly with schedule size. Responding under nFR schedules is sensitive to differences in reinforcer magnitude and demonstrates that relative reinforcing effects can change as a function of schedule size.
Journal of the Experimental Analysis of Behavior, 2016 · doi:10.1002/jeab.215