The Search for Stimulus Equivalence in Nonverbal Organisms

A currently unresolved issue in stimulus equivalence research is the relation of equivalence and language competence. The current consensus is that equivalence according to widely adopted criteria proposed by Sidman has not yet been demonstrated in nonverbal experimental subjects. This judgment rests primarily on the failure of nonhuman subjects to display the equivalence outcome under conditions comparable to those used with human subjects. We discuss theoretical and methodological issues that arise in research seeking to delineate the "lower limits" of equivalence phenomena in studies with laboratory animals or nonverbal humans. We propose a behavior-analytic approach to the question, examine the relationship between functional stimulus classes and equivalence classes, and describe some preliminary studies.