Matching as a multivariate power law: Frequency of behavior versus frequency and magnitude of reinforcement

Two groups of food-deprived rats responded for access to liquid reinforcers on a wide range of concurrent variable-interval schedules. During the first part of the experiment, one group chose between two different sucrose solutions; for a second group, the choice involved a sucrose solution and a solution of condensed milk. In the latter part of the experiment, the two groups chose between identical sucrose solutions. A variety of multivariate equations were applied to data obtained from both conditions. The best-fitting equation proved to be a multivariate power function, which is an extension of Herrnstein's basic matching law.