Abstract The primary purpose was to study how the expansion of equivalence classes is documented by sorting tests. In two experiments with 40 adult participants, there were three phases of training and testing of emergent relations. In the first phase, the participants were trained on 12 conditional discriminations arranged as a linear series training structure (A➔B➔C➔D➔E) followed by a sorting test. The second phase included simple discrimination training of C stimuli. The training comprised different numbers of key presses, and these numbers were used as F stimuli in the expansion test of the existing classes. The final phase contained sorting and matching‐to‐sample (MTS) tests. The two experiments differed in the number of key presses in the simple discrimination training and stimuli used as F stimuli in Phase 2 and the order of sorting and MTS tests in Phase 3. The main findings of the two experiments were that 100% of the participants sorted the stimuli correctly in the first phase, 83% (25 of 30) of the participants showed expansion and sorted the stimuli in the second phase, and finally, 90% (36 of 40) of the participants responded correctly on the MTS test in the third phase.
Arntzen et al. (Tue,) studied this question.