The conditional control of equivalence has received much attention in the analysis of verbal behavior. While previous research identified conditional control of relational responding and conditional control of equivalence class formation, this study investigated the possibility of conditional control of members of an equivalence class. Following baseline conditional discrimination training and equivalence testing, subjects were taught to select a particular member in the presence of a Green background screen and another member in the presence of a Red background screen.

In recent years, there has been an increasing interest in the study of human operant behavior. One area of study reflecting this interest is the study of the formation of equivalent classes of stimuli by human subjects. The focus of the present research was the study of the conditions under which classes of equivalent stimuli can be inferred to be under conditional control. In Experiment 1-A, three college students were trained to respond to a balanced five-term contingency via a visual-visual simultaneous matching-to-sample task with two choices of comparison stimuli. Probe tests showed that subjects' behavior could be described as being controlled by positive and negative stimulus relations. When the second-order stimulus was removed during subsequent probes, none of the three subjects demonstrated strong correct responses to the four-term unit relations. Also, none of the three subjects demonstrated the expected transitive relations when the second-order (five-term) stimulus was removed. In Experiment 1-B--with the same three subjects--explicit training of the four-term unit relations showed the expected transitive relations in the absence of the second-order stimulus. In Experiments 2 through 5--using a matching-to-sample task similar to that used in Experiments 1-A and 1-B--five subjects were trained to respond to comparison stimuli C and E in the presence of sample A and second-order stimulus X and to comparison stimuli Band Fin the presence of sample D and second-order stimulus X. Likewise, the subjects were trained to respond to comparison stimuli Band Fin the presence of sample A and second-order stimulus Y and to comparison stimuli C and E in the presence of sample D and second-order stimulus Y. Probe tests for transitive relations showed that four of the five subjects eventually demonstrated four three-member classes of equivalent stimuli that functioned separately under the control of the second-order stimuli. The four subjects demonstrating the classes of equivalent stimuli either a) demonstrated the transitive relations immediately orb) demonstrated the transitive relations after explict retraining of the underlying four-term unit relations. The results of all experiments together indicated that the composition of classes of equivalent stimuli can be conditionally controlled by either a) removing the second-order stimulus orb) training subjects to respond to classes of equivalent stimuli under the control of other explicit visual second-order stimuli. The results are discussed in terms of verbal behavior, emergent behavior, and conceptual development.