Formation of Stimulus Equivalence Relations by Exclusion: Evidence using the Blank Comparison Stimulus Procedure

Abstract

Emergence of equivalence relations among stimuli previously related by exclusion was assessed by using the blank-comparison-stimulus procedure throughout baseline and test trials, in order to avoid problems involved in testing emergent relations with either baseline or novel stimuli as S– comparisons. In Experiment 1, participants were exposed to pretraining phases in order to learn to respond to a blank comparison stimulus as the correct one when the other comparison stimuli were incorrect. Then, they learned a baseline of conditional relations for the emergence of stimulus Classes 1 and 2. Thereafter, they were exposed to exclusion trials, in which stimuli from the preexperimentally defined Class 3 were introduced as undefined stimuli, whereas baseline stimuli were defined. They were then presented with symmetry and transitivity trials for all three classes (Group 1), or only Class 3 (Group 2), in three-choice matching trials. Most participants in Group 2 related stimuli previously related by exclusion as if they were in an equivalence relation, but most participants in Group 1 did not. In Experiment 2, most participants of a single group (Group 3) showed emergence of equivalence by exclusion and transfer of stimuli functions when exposition to exclusion trials occurred after demonstration of equivalence of the baseline classes, and assessment of equivalence was conducted for the three classes in two-choice matching trials. Conditions under which the emergence of equivalence by exclusion occurs are discussed.