Equivalence relations between visual stimuli: The functional role of naming

The functionality of verbal behavior in equivalence class formation was demonstrated by training 30 verbally able adults using different combinations of the same easily nameable, yet formally unrelated, pictorial stimuli. Match-to-sample baselines for four four-member classes were established sequentially (i.e., AB-BC-CD), with participants in the rhyme condition trained to select comparisons whose normative names rhymed with those of the samples. For the orthogonal condition, class rearrangement was such that on every trial all available comparisons' names rhymed with each other, but not with the name of the sample. In the diagonal condition, stimuli were allocated pseudorandomly as samples and comparisons. Although all participants maintained baseline discriminations prior to emergent testing, equivalence was confined almost exclusively to the rhyme condition, in which it was ubiquitous. These participants also required less training than those in the control conditions, among whom effects of nodal distance were observed most strongly. Subsequent testing presented participants with no-reinforcement trials involving novel pictorial stimuli, in which one of the available comparisons' names always rhymed with that of the sample. All rhyme participants consistently selected these comparisons. Results indicate that visual stimuli are named, that the phonological properties of those names can influence equivalence class formation, and that the emergence of untrained discriminations may, under certain circumstances, be rule governed.