Smeets, P. M., Barnes-Holmes, D., & Striefel, S. (2006). Establishing and reversing equivalence relations with precursor to the relational evaluation procedure. The Psychological Record, 56(2), 267-286.
The authors—researchers at the National University of Ireland, Leiden University, and Utah State University—conducted the present study to examined Whether the efficacy of the pREP could be improved while leaving the go/no-go structure intact. The study consists of six experiments. The results indicated that the pREP had one, possibly two weaknesses. First, during testing, it permitted nondifferential responding. Second, during training, the contingencies permitted class ambiguity, that is, class formation based on pressing (Ai-Bi-Ci) or on not pressing (Ai-Bj-Ci). When measures were taken to discourage nondifferential responding (instruction to press on 50% of the trials, using a simple-to-complex test protocol) and to reduce ambiguity (feedback for pressing only), the pREP not only produced equivalence but also equivalence reversal in (almost) all participants.