Stimulus equivalence, the ability to categorize stimuli on the basis of relations shared through associative contingencies and not physical features, may be a necessary prerequisite for symbolic Functioning and language development. Monkeys, chimpanzees, and sea lions can form some of the emergent relations that determine empirically the existence of equivalence classification: reflexivity, symmetry, and transitivity. Of these criteria, transitivity is the most difficult to ascertain because it is the most behaviorally complex; it is the ability to infer a relation between two stimuli given that both are related to a third stimulus. A positive outcome on transitivity tests may indicate the potential for symbolic functioning in the absence of language, a theoretical position with profound implications for understanding how cognition relates to the development of communicative behavior. A scant number of studies have suggested that rats also are capable of transitivity; however, certain methodological issues limit interpretation of these findings. We have developed a paradigm for rats to circumvent these issues so that a practical laboratory animal model of transitivity can be established and elaborated for future research: Rats will be trained in an automated nose poke apparatus to develop two arbitrary stimulus classes. A matching-to-sample task using six olfactory Stimuli will be used to teach explicitly some of the possible stimulus pairs within a class; e.g., match to B and then B to C. If rats have developed emergent transitivity, then they should show high curacy on probe trials for matching A to C, the untaught stimulus pair. Rats are expected to display transitive behavior. If they do, some specific studies for future research will be suggested that would proceed logically from such results. Ultimately, this rat model will lead to advances in the assessment of non-language based symbolic behavior, and to applications in the fields of behavioral toxicology and animal models of developmental disabilities.
