MacDonall, J. S. (1999).
A local model of concurrent performance.
Journal of the Experimental Analysis of Behavior,
71, 57-74.
Concurrent procedures may
be conceptualized as consisting of two pairs of schedules with only one pair operating at
a time. One schedule of each pair arranges reinforcers for staying in the current
alternative, and the other schedule arranges reinforcers for switching to the other
alternative. These pairs alternate operation as the animal switches between choices. This
analysis of the contingencies suggests that variables operating within an alternative
produce behavior that conforms to the generalized matching law. Rats were exposed to
one pair of stay and switch schedules in each condition, and the probabilities of
reinforcement varied across conditions. Both run length and visit duration were power
functions of the ratio of the probabilities of reinforcement for staying and switching. The
local model, a model of performance on concurrent procedures, was derived from this
power function. Performance on concurrent schedules was synthesized from the
performances on the separate pairs. Both the generalized matching law and the local
model fitted the synthesized concurrent performances. These results are consistent with
the view that the contingencies in the alternative, the probability of stay and switch
reinforcement, are responsible for performance consistent with the generalized matching
law. These results are compatible with momentary maximizing and molar maximizing
accounts of concurrent performance. Models of concurrent performance that posit
comparisons among the alternatives are not easily applied to these results.
Key words: concurrent schedules, probability of reinforcement, local models,
stay schedules, switch schedules, lever press, rats