Formation and Expansion of Stimulus Classes Documented by Sorting Tests

The present experiment studied sorting performance after expansion of class size. Thirty-two participants trained 12 conditional discriminations with a linear series training structure (A->B->C->D->E), which was followed by a CFS testing. Depending on the results of the sorting test, the participants were exposed to two different sequences of training and testing. If the participants sorted correctly (Sequence 1), they were exposed to F->C training to expand class size. Half of the participants were given MTS tests and finally a CFS retest. The other half were given the CFS test, an MTS test, and a final CFS retest. Participants who did not sort correctly on the first CFS (Sequence 2), were trained six baseline conditional relations with new stimuli (G->H->J), given a new sorting test and expanding training (K->H). Half of the participants were given an MTS and then a CFS test, while the other half were given CFS, MTS, and final CFS tests. The main findings were that all participants sorted correctly during tests for class expansion and showed 100% correspondence between sorting and MTS performance. The sorting tests documented the formation and expansion of equivalence classes.