Identity and Delay Functions of Meaningful Stimuli: Enhanced Equivalence Class Formation

The inclusion of a meaningful stimulus in a set of abstract stimuli enhances the likelihood of forming an equivalence class with the set. Class enhancement effects can be due to the discriminative, conditional discriminative, and class-based behavioral functions served by the meaningful stimulus. This experiment determined whether acquisition of an identity conditional discriminative function by an abstract stimulus enhances the formation of an equivalence class of which it is a member along with other abstract stimuli. Forty adults attempted to form 3 three-node five-member equivalence classes (A → B → C → D → E) using the simultaneous protocol. In the PIC group, the C stimuli were pictures and the A, B, D, and E stimuli were abstract shapes. In the ABS group, all of the stimuli were abstract shapes. In the Id-S-MTS (identity simultaneous matching-to-sample) and Id-6sD-MTS (identity 6 s delayed matching-to-sample) groups, prior to class formation, identity conditional discriminations were formed with the C stimuli using simultaneous or 6 s delayed matching-to-sample procedures, respectively. Classes were formed by 80 and 60 % of participants in the PIC and delayed identity groups, and by 0 and 10 % of participants with no prior training (ABS group) or after forming identity relations on a simultaneous basis. These outcomes were confirmed with post class formation sorting tests. Thus, a portion of the class enhancing effects of meaningful stimuli can be attributed to their presumed delayed identity conditional discriminative function. Adventitious coding or mediating behavior during identity training might have influenced acquisition of baseline relations and likelihood of class formation.