Relatedness of Equivalence Class Members: Combined Effects of Nodality and Relational Type

Abstract

In equivalence classes, stimulus relatedness is an inverse function of the nodal number for the same type of derived relation. Also, transitive relations are preferred to equivalence relations when the nodal number is held constant. The current study evaluated the combined effects of nodal number and relational type on relatedness of stimuli within equivalence classes. After eight college students formed two 7-node, 9-member equivalence classes, participants were presented with trials during within-class relational preference tests that pitted 1-node equivalence relations against 1- to 5-node transitive relations. Consistent with prior research, 1-node transitive relations were always preferred to 1-node equivalence relations. For the six participants who formed classes rapidly, preference for the 1-node equivalence relation increased as a direct function of increases in the number of nodes in the competing transitive relation. In addition, the 1-node equivalence relation was equally preferred to an approximately 2-node transitive relation. Because equivalence classes remained intact after preference testing, performances documented the coexistence of equal and differential relatedness of class members. Two participants formed the classes on a delayed basis and produced inverted U-shaped preference functions instead of monotonic preference functions. Because the preference functions differed in terms of speed of emergence, the same nominal equivalence classes were not functionally equivalent to each other with regard to stimulus relatedness.