Smeets, P. M., Barnes-Holmes, Y., Akpinar, D., & Barnes-Holmes, D. (2003). Reversal of equivalence relations. The Psychological Record, 53, 91-120.
The authors, researchers at the National University of Ireland and University of Leiden, concurred that previous research has demonstrated that equivalence relations are difficult to reverse. This study sought to determine if this difficulty is related to particular features of the training tasks. This procedure requires the subjects to make novel choices during all training tasks. Almost all subjects showed reversal of equivalence relations irrespective of the training protocol. Experiments 2-7 examined if this finding could be related to the subject's age and mental ability. Other important factors were the response topography, the identity and location of the experimenter, specific features of the training and testing program.