Single-subject withdrawal designs in delayed matching-to-sample procedures

Abstract

In most studies of delayed matching-to-sample (DMTS) and stimulus equivalence, the delay has remained fixed throughout a single experimental condition. We wanted to expand on the DMTS and stimulus equivalence literature by examining the effects of using titrating delays with different starting points during the establishment of conditional discriminations prerequisite for stimulus equivalence. In Experiment 1, a variation of a single-subject withdrawal design was used. Ten adults were exposed to one condition where the delay titrated between 0 and 3000 ms and another condition where the delay varied from 5000 to 8000 ms. Subsequently, participants were re-exposed to the condition they had first experienced. Results show that starting the titration of the delay at 5000 ms may have had a facilitatory effect on stimulus equivalence responding for some participants. For several participants, however, performance was stable throughout the experiment, apparently not affected by either the variations of the starting point of the titrating delay or by previous exposure to stimulus equivalence training and test procedures. In Experiment 2, we examined the effects of being exposed to the same stimulus equivalence procedure three times, again with adults as participants. Results show that such extended exposure had very limited effects on stimulus equivalence responding. This indicates that single-subject withdrawal designs may be an appropriate approach for studying stimulus equivalence