STIMULUS EQUIVALENCE - EFFECTS OF A DEFAULT-RESPONSE OPTION ON EMERGENCE OF UNTRAINED STIMULUS RELATIONS

Default-response options, intended to measure uncertainty, sometimes a re included in discrete-choice measurement in an attempt to clarify st imulus control of remaining response options. Recent experiments have used a default-response procedure to investigate emergent stimulus rel ations, but no study to date has compared effects of different default -response procedures on emergence of the untrained relations that defi ne stimulus equivalence. Five groups of college undergraduates (each n = 16) completed a conditional discrimination training procedure to in state the stimulus relations prerequisite to three three-member equiva lence classes; a training review intermingling all of the explicitly t rained relations; and tests for emergent relations. The groups differe d in terms of (a) presence versus absence of a ''none'' option during emergent relations tests and (b) the amount of experience with ''catch trials'' in which ''none'' was the correct selection. Stimulus equiva lence was demonstrated in 94% of subjects in a control group who were trained and tested without the ''none'' response option and without ca tch trials and in 41% of subjects in the ''none'' groups. Among subjec ts in the ''none'' groups who failed to demonstrate equivalence initia lly, 95% did so when retested under control-group conditions. Across ' 'none'' groups, probability of equivalence class formation was positiv ely correlated with amount of experimental experience with catch trial s in preliminary training and equivalence testing. Among the emergent relations defining stimulus equivalence, reflexivity was most often pr ecluded by the ''none'' option, although there was evidence of group d ifferences in relation specificity. These results suggest that a defau lt-response option can interfere with the formation of emergent relati ons, and that the effects are contextually sensitive. Although there m ay be advantages to employing default-response procedures in studies o f emergent stimulus relations, the responses they control should be vi ewed as behavior under specific stimulus control rather than a generic expression of uncertainty.