A discrimination analysis of training-structure effects on stimulus equivalence outcomes

Experiments designed to establish stimulus equivalence classes frequently p roduce differential outcomes that may be attributable to training structure , defined as the order and arrangement of baseline conditional discriminati on training trials. Several possible explanations for these differences hav e been suggested. Here we develop a hypothesis based on an analysis of the simple simultaneous and successive discriminations embedded in conditional discrimination training and testing within each of the training structures that are typically used in stimulus equivalence experiments. Our analysis s hows that only the comparison-as-node (many-to-one) structure presents all the simple discriminations in training that are subsequently required for c onsistently positive outcomes on all tests for the properties of equivalenc e. The sample-as-node tone-to-many) training structure does not present all the simple discriminations required for positive outcomes on either die sy mmetry or combined transitivity and symmetry (equivalence) tests. The linea r-series training structure presents all the simple discriminations require d for consistently positive outcomes on tests for symmetry, but not for sym metry and transitivity combined (equivalence) or transitivity alone. Furthe r, the difference in the number of simple discriminations presented in comp arison-as-node training versus the other training structures is larger when the intended class size is greater than three or the number of classes is larger than two. We discuss the relevance of this analysis to interpretatio ns of stimulus equivalence research, as well as some methodological and the oretical implications.