Optimality And Concurrent Variable-interval Variable-ratio Schedules.
Brief visits to the leaner alternative on concurrent VI VR schedules can be part of an optimal plan, not a matching error.
01Research in Context
What this study did
Researchers put rats in a chamber with two levers. One lever paid off on a variable-interval (VI) schedule. The other paid on a variable-ratio (VR) schedule.
The team recorded every press and every visit. They then asked: do the rats match their time to the pay rate, or do they optimize?
What they found
Across the whole session, the rats’ time split roughly matched the payoff rates. A closer look told a different story.
Most visits to the VI lever were short. The rats still ended up with the best total payoff. Brief dips into the lean side were part of an overall smart plan, not sloppy matching.
How this fits with other research
Davison et al. (1984) warned that VI VR schedules can fake matching. Their models showed payoff rates can track almost any choice split. The new data agree: global numbers can look like matching even when visit-by-visit choices do not.
Santi (1978) saw clean matching with concurrent VI negative reinforcement in rats. W et al. add VR to the mix and show the picture gets messy. The extra VR schedule lets rats use short VI visits as part of a larger max-out strategy.
Alba et al. (1972) found long changeover delays hurt matching. W et al. zoom in further and show that even without extra delays, visit length—not just switch time—shapes the final allocation.
Why it matters
If you run concurrent schedules in a classroom or clinic, do not trust only the overall time chart. Watch moment-to-moment contact with each option. Short checks on the lean side can be planned, not off-track. Use brief changeover delays and keep data by visit. That micro view tells you if the learner is optimizing or merely drifting.
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02At a glance
03Original abstract
Despite claims to the contrary, all leading theories about operant choice may be seen as models of optimality. Although melioration is often contrasted with global maximization, both make the same core assumptions as other versions of optimality theory, including momentary maximizing, hill climbing, and the various versions of optimal foraging theory. The present experiment aimed to test melioration against more global optimality and to apply the visit‐by‐visit analysis suggested by foraging theory. Rats were exposed to concurrent schedules in which one alternative was always variable‐ratio 10 and the other alternative was a variable‐interval schedule. Although choice relations varied from rat to rat, the overall results roughly confirmed the matching law, a result often taken to support melioration. Pooling the data across sessions and across rats, however, resulted in no increment in unsystematic variance, lending support to the contention by Ziriax and Silberberg (1984) that the choice relation is partly constrained. When the data were analyzed at the level of visits, the results either disconfirmed predictions of melioration or showed regularities about which melioration is silent. Instead, performance tended toward a rough optimization, in which responding favored the variable ratio, but with relatively brief visits to the variable interval. There were no asymmetries in travel or variability that would indicate that different processes were involved in generating visits at the two different schedules. The findings point toward a more global optimality model than melioration and demonstrate the value of per‐visit analysis in the study of concurrent performances.
Journal of the experimental analysis of behavior, 1999 · doi:10.1901/jeab.1999.71-75