EMERGENT RELATIONS IN THE FORMATION OF STIMULUS CLASSES BY PIGEONS

A defining feature of a stimulus class is the presence of untrained (emergent) relations among its members. Three types of emergent relations that define formal stimulus equivalence are reflexivity, symmetry, and transitivity. We find that pigeons can demonstrate all three types of emergent relations. Reflexivity is demonstrated by showing the transfer of identity-matching to new stimuli. Symmetry is demonstrated by showing that positive transfer results when differential food versus no food outcomes (associated with correct responding to comparison stimuli in a conditional discrimination) are substituted for conditional stimuli in a matching task. Transitivity is demonstrated when training with a simple successive hue discrimination is followed by training on a symbolic matching task involving food and no-food samples and line-orientation comparisons, and positive transfer is found when the hues are substituted for the food and no-food events. Finally, pigeons can demonstrate simultaneous evidence for symmetry and transitivity relations. For example, two samples are first associated with a common comparison in many-to-one delayed matching-to-sample. When one of those samples is then associated with a new comparison, evidence for an emergent relation between the remaining sample and the new comparison is found. Overall, the pigeon data provide strong evidence for emergent relations using procedures that result in stimulus class formation.