Expansion of Sidman's theory: The inclusion of prompt stimuli in equivalence classes.

Stimulus equivalence is defined as the ability to relate stimuli in novel ways after training in which not all of the stimuli had been directly linked to one another. Sidman (2000) suggested all elements of conditional discrimination training contingencies that result in equivalence potentially become class members. Research has demonstrated the inclusion of samples, comparisons, responses, and reinforcers in equivalence classes. Given the evidence that all elements of a conditional discrimination become part of the class, the purpose of this study was to determine if class-specific prompts would also enter into their relevant equivalence classes. Experiment 1 investigated the inclusion of prompts in an equivalence class using abstract stimuli with neurotypical students enrolled in higher education courses. Experiment 2 systematically replicated Experiment 1 using meaningful stimuli and individuals diagnosed with autism spectrum disorder. The results of both experiments demonstrated that class-specific prompts became part of equivalence classes with the other positive elements of the contingency. The results are discussed in terms of class expansion and the potential impact on equivalence-based instruction.

Another Perspective on Research as a Measure of High-Quality Practitioner Training: a Response to Dixon, Reed, Smith, Belisle, and Jackson.

Dixon et al. (Behavior Analysis in Practice 8:7-15, 2015) argued that the research productivity of behavior analytic graduate programs may be a reasonable criterion to evaluate training program quality. They reviewed the cumulative publications of graduate programs. From this analysis, they generated a top ten list of graduate programs with the greatest number of faculty publications and, because of the number of these publications, inferred that they may be better training programs than those not on the list. We countered that the quality of graduate training programs is evident in the behavior of those who are trained, and thus, our field's interest should focus on determining the degree to which individual program graduates-and not their faculty-have mastered the research process. Thus, we proposed including student authors' work as an alternative to Dixon et al.'s analysis.

Delayed matching to complex samples and the formation of stimulus classes in children.

In two experiments (ns = 3 plus a previously tested child, and 2, respectively), children learned delayed matching with complex samples, each consisting of a form and a printed nonsense word. Forms or printed words were comparison stimuli. For form comparisons, selecting the form identical to that in the preceding sample was reinforced. For printed word comparisons, selecting the word identical to that in the preceding sample was reinforced. During testing, the children then matched the forms and printed words to one another. In subsequent training, the samples were (a) old forms combined with new words or (b) old words combined with new forms. Novel matching performances among forms and words appeared across these training phases. Word-form contiguity in a matching-to-sample context may contribute to the formation of classes of stimuli that may be equivalent.

Matching to complex samples and stimulus class formation in adults with autism and young children.

Adults with autism and young children first learned to match one-element comparison stimuli to two-element sample stimuli. Test conditions then examined whether each of the individual sample elements (a) controlled selections of the comparison stimuli to which they were related during training, (b) were interchangeable with one another as either sample or comparison stimuli, and (c) were interchangeable with the original comparison stimuli. Test data were positive and suggested the formation of three-member stimulus classes. Subsequent experiments demonstrated the formation of four-member classes by (a) adding novel stimuli by training outside the original context; (b) adding novel stimulus elements to the two-element samples used during baseline training; and (c) training with three-element rather than two-element sample stimuli from the outset. Results suggest that acquisition of stimulus classes may be one of the benefits of broad rather than restricted attention to the components of complex stimuli.

Functional classes and equivalence relations.

Three adult subjects were taught a set of two-choice simultaneous discriminations, with three positive and three negative stimuli; all possible combinations of positive and negative stimuli yielded nine different pairs. The discriminations were repeatedly reversed and rereversed, the former positive stimuli becoming negative and the former negative stimuli becoming positive. With all subjects, a reversal of the contingencies for one pair of stimuli became sufficient to change their responses to all of the other pairs. The reversals had produced functional stimulus classes. Then, all subjects showed conditional discriminations emerging between members of a functional class; given a sample from one class and comparisons from both classes, they selected the comparison that was in the same class as the sample. Next, 2 of the subjects showed that the within-class conditional relations possessed the symmetric and transitive properties of equivalence relations; after having been taught to relate new stimuli to existing class members, the subjects then matched other class members to the new stimuli. Subsequent tests of two-choice discriminations showed that the conditional discriminations had transferred functional class membership to the new stimuli. The 3rd subject, who did not show equivalence relations among functional class members, was also found to have lost the within-class conditional relations after the equivalence tests.

Stimulus class formation and stimulus-reinforcer relations.

This study examined stimulus class membership established via stimulus-reinforcer relations. Mentally retarded subjects learned conditional discriminations with four two-member sets of visual stimuli (A, B, C, and D). On arbitrary-matching trials, they selected comparison stimuli B1 and B2 conditionally upon samples A1 and A2, respectively, and C1 and C2 conditionally upon B1 and B2, respectively. On identity-matching trials, they selected all stimuli as comparisons conditionally upon identical stimuli as samples. Throughout training, correct selections of A1, B1, C1, and D1 were followed by one reinforcer, R1, and those of A2, B2, C2, and D2 were followed by another, R2. Subsequent tests documented the formation of two four-member stimulus classes, A1-B1-C1-D1 and A2-B2-C2-D2. The class membership of the A, B, and C stimuli could have been based on equivalence relations that resulted from the arbitrary-matching training. D1 and D2 had never appeared on arbitrary-matching trials, however. Their class membership must have been based on relations with R1 and R2, respectively. Results thus confirm a previous finding that stimulus classes can be expanded via stimulus-reinforcer relations. They also define more precisely the potential nature of those classes and the conditions under which class membership can be established.