Merger and expansion of equivalence classes via meaningful stimuli

The present experiments evaluated the effect of meaningful stimuli on the inclusion of a set of extra-experimental meaningful pictures into equivalence classes using within- and between-subjects designs. There were 35 adult participants in total (N_EXP1 = 22; N_EXP2 = 13). In both experiments, participants were first trained on six baseline relations with abstract stimuli (A, B, and C) and assessed on the emergence of three 3-member equivalence classes. Next, they were trained on DA relations and assessed on the inclusion of the D stimuli and a set of meaningful pictures in the equivalence classes. In Experiment 1, D1 and D2 were meaningful written words and D3 was a written pseudoword. In Experiment 2, for 2 groups, D1, D2, and D3 were meaningful words; for another group, D1, D2, and D3 were pseudowords. In both experiments, participants formed the ABC classes and included the D stimuli in the classes. When D was a meaningful word, participants also included a set of pictures potentially related to the word in the ABC class established experimentally. The results have implications for the definition of meaningfulness and contribute to discussions on the impact of test arrangements on emergent responding.