STIMULUS EQUIVALENCE: TESTING SIDMAN'S (2000) THEORY

Sidman's (2000) theory regarding the origin of equivalence relations predicts that a reinforcing stimulus common to distinct equivalence classes must drop out of the equivalence relations. This prediction was tested in the present study by arranging class‐specific reinforcers, R1 and R2, following correct responding on the prerequisite conditional discriminations (Ax—Bx, Cx—Bx) for two stimulus classes, A1B1C1 and A2B2C2. A class‐common reinforcer, R3, was presented following correct responding on the prerequisite conditional discriminations for a further two stimulus classes, A3B3C3 and A4B4C4. Sidman's theory predicts reinforcer inclusion within Classes 1 and 2 only, given this training arrangement. Experiment 1 tested for the emergence of four equivalence classes and of stimulus—reinforcer and reinforcer—stimulus relations in each class. Four of the 6 subjects demonstrated the reinforcer‐based relations in all four equivalence classes, rather than in only those classes with a class‐specific reinforcer, as Sidman's theory predicts. One of the remaining 2 subjects showed the reinforcer‐based relations in three of the four classes. Experiment 2 extended these findings to document the emergence of interclass matching relations based on the common reinforcer R3, in 5 of 6 subjects, such that a Class 3 sample occasioned the selection of a Class 4 sample when the Class 3 comparison was absent, and similarly, a Class 4 sample occasioned the selection of a Class 3 comparison when the Class 4 comparison was absent. These interclass relations emerged despite the simultaneous maintenance of Class 3 and 4 baseline conditional discriminations, so that the Class 3 and 4 stimuli and reinforcer simultaneously were, and were not, part of a single larger equivalence class. These data are irreconcilable with Sidman's theory, and question the utility of the application of the equivalence relation in describing derived stimulus relations.