Baum, W. M. & C. F. Aparicio (1999).
Optimality and concurrent variable-interval variable-ratio schedules
Journal of the Experimental Analysis of Behavior,
71, 75-89.
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.
Key words: concurrent schedules, concurrent variable interval variable ratio,
optimality, foraging theory, per-visit analysis, lever press, rats