Smeets, P. M., van Wijngaarden, M., Barnes-Holmes, D., & Cullinan, V. (2004). Assessing stimulus equivalence with a precursor to the relational evaluation procedure. Behavioural Processes, 65, 241-251.
Most human adults respond in accordance with symmetry (B-A, C-B) and equivalence (C-A) when measured with MTS tests and with a precursor to the Relational Evaluation Procedure (pREP). The present study was an effort to replicate these findings. Very few subjects evidenced pREP symmetry and equivalence unless they had (a) already demonstrated symmetry and equivalence in a MTS test before, or (b) received pREP pretraining with unrelated stimulus pairs and symmetry was tested before equivalence. Failures to show symmetry were always associated with pressing at or close to 50% of these trials. Failures to show equivalence were associated with pressing or not pressing on (almost) all trials. Current findings are similar to those obtained in equivalence studies involving MTS probes permitting the subjects not to respond to the designated comparison.