Operant variability: procedures and processes.

Barba’s (2012) article deftly weaves three main themes in one argument about operant variability. From general theoretical considerations on operant behavior (Catania, 1973), Barba derives methodological guidelines about response differentiation and applies them to the study of operant variability. In the process, he uncovers unnoticed features of operant variability research (e.g., Neuringer, 2002) and proposes interesting modifications and extensions of current experimental practices. Barba’s article calls for renewed attention to important issues, and we find merit in his proposal to evaluate operant variability by comparing response distributions along a common continuous measure. We are less convinced, however, by the conceptual underpinnings that he brings to the task. Differentiation and operant behavior. First consider Barba’s claim that ‘‘differentiation is the behavioral process that demonstrates an operant relation’’ (p. 000). There is a sense of differentiation in which this claim is trivially true. Operant behavior is demonstrated by choosing a response criterion R, delivering some consequence S for any activity that satisfies R, and noting that the prevalence of R changes as a result (Skinner, 1938). By definition of operant reinforcement, the prevalence of criterial activities (R) must increase during reinforcement, and the prevalence of at least another activity (,R) must decrease because all activities compete for the same total time (Rachlin & Burkhard, 1978). If these changes in the relative prevalence of R and ,R are all that we mean by differentiation, then it is obviously true that reinforcement entails differentiation. In this case, however, there is no need to evaluate probability distributions along a continuous measure (as in Barba’s Figure 2) to demonstrate an operant relation. Any evidence that the prevalence of R increases (or, in the case of punishment, decreases) will do, together with control conditions to show that the observed changes are actually due to the correlation between R and S (Thompson & Iwata, 2005). Alternatively, by response differentiation we may mean something more than the changes of response distribution that are a logical consequence of the definition of reinforcement. Here is how Galbicka (1988) characterizes response differentiation: