The role of common stimulus functions in the development of equivalence classes.

College students were exposed to training designed to teach nine simple discriminations, such that sets of three arbitrary visual stimuli acquired common functions. For seven of eight participants, three 3-member contingency classes resulted. When the same stimuli were presented in a match-to-sample procedure under test conditions, four participants demonstrated equivalence-consistent responding, matching all stimuli from the same contingency class. Test performance for two participants was systematically controlled by other variables, and for a final participant was unsystematic. Exposure to a yes/no test yielded equivalence-consistent performance for one participant where the match-to-sample test had not. Implications for the treatment of equivalence as a unified, integrated phenomenon are discussed