Teaching Stimulus-Stimulus Relations to Minimally Verbal Individuals: Reflections on Technology and Future Directions.

This paper discusses recent methodological approaches and investigations that are aimed at developing reliable behavioral technology for teaching stimulus-stimulus relations to individuals who are minimally verbal and show protracted difficulty in acquiring such relations. The paper has both empirical and theoretical content. The empirical component presents recent data concerning the possibility of generating rapid relational learning in individuals who do not initially show it. The theoretical component (1) considers decades of methodological investigations with this population and (2) suggests a testable hypothesis concerning some individuals exhibit unusual difficulties in learning. Given this background, we suggest a way forward to better understand and perhaps resolve these learning challenges.

The E.K. Shriver Center at the University of Massachusetts Medical School.

The UMMS Shriver Center promotes an understanding of typical and atypical neurological, cognitive, and behavioral development, emphasizing mental retardation. To accomplish its mission, the Center conducts basic and applied research to determine the biological and environmental factors that influence development and provides training and service programs that directly benefit people with developmental disabilities and their families.

Behavioral momentum in computer-presented discriminations in individuals with severe mental retardation.

Behavioral momentum was examined in 2 individuals with severe mental retardation via within-subject manipulations of obtained reinforcer rates. Subjects performed self-paced discrimination problems presented on a touch screen computer monitor. Two different problems, Tasks A and B, alternated in blocks of 15 trials on a multiple schedule. Reinforcers were snack foods. The reinforcement schedule for Task A was continuous (fixed-ratio 1) and the schedule for Task B was continuous in some conditions and variable ratio in other conditions. Behavioral momentum was assessed in test sessions by prefeeding, presenting response-independent food, and making available alternatives to the tasks. When the obtained reinforcer rate for Task A was at least twice that for Task B, resistance to change was greater for Task A. When both reinforcer rates and response rates were a pproximately equal for the two tasks, resistance to change was approximately equal. These results are consistent with behavioral momentum effects. They extend previous findings with humans by examining momentum in self-initiated discrete-trial discrimination tasks with ratio schedules, and by isolating relative reinforcer rates as a controlling variable via within-subject manipulations.

Equivalence classes in individuals with minimal verbal repertoires.

Studies from two different laboratories tested for equivalence classes in individuals with severe mental retardation and minimal verbal repertoires. In the first study, 3 individuals learned several matching-to-sample performances: matching picture comparison stimuli to dictated-word sample stimuli (AB), matching those same pictures to printed letter samples (CB), and also matching the pictures to nonrepresentative forms (DB). On subsequent tests, all individuals immediately displayed Emergent Relations AC, AD, BC, BD, CD, and DC, together constituting a positive demonstration of equivalence (as defined by Sidman). The second study obtained a positive equivalence test outcome in 1 of 2 individuals with similarly minimal verbal repertoires. Taken together, these studies call into question previous assertions that equivalence classes are demonstrable only in individuals with well-developed language repertoires.

Reduction of stimulus overselectivity with nonverbal differential observing responses.

Three individuals with mental retardation exhibited stimulus overselectivity in a delayed matching-to-sample task in which two sample stimuli were displayed on each trial. Intermediate accuracy scores indicated that participants could match one of the samples but not both of them. Accuracy in a baseline condition was compared to accuracy with a differential observing response procedure. This procedure prompted participants to make simultaneous identity-matching responses that required observation and discrimination of both sample stimuli. These observing responses were never followed by differential consequences. When observing responses were prompted, participants' accuracy scores improved. In a return to the baseline condition, when differential observing responses were no longer prompted, accuracy returned to intermediate levels. The results show that stimulus overselectivity can be greatly reduced by a behavioral intervention that controls observing behavior and verifies discrimination, but that exposure to such procedures alone may be insufficient for lasting benefits.

Blank-comparison assessment of stimulus-stimulus relations in individuals with mental retardation: a methodological note.

Matching to sample is commonly used in research and practice to assess relational learning of persons with mental retardation. However, forced-choice matching tasks are not always appropriate. In this paper we have illustrated blank-comparison matching to sample, a selection-based "yes/no" method requiring no verbal skills. Participants select a comparison stimulus if it is judged to be related to the sample (analogous to "yes") but select a black square (blank) if it is not so judged ("no"). In the first experiment the method was used to explore bases for emergent symbolic "mapping" performances. In the second experiment we assessed similarity judgments between form stimuli. Both experiments confirmed the feasibility and utility of the method for making unambiguous inferences as to whether pairs of stimuli were or were not related.

Blank comparison analysis of emergent symbolic mapping by young children.

Eight typically developing children first learned to select pictures in response to dictated words in a three-choice matching-to-sample format. Next, the matching-to sample baseline was transformed via a stimulus control shaping procedure: Matching trials displayed two pictures and a third stimulus (termed a "blank" comparison). The blank was to be selected if the dictated sample did not match either of the displayed pictures. The blank comparison baseline was then used to evaluate the children's response to matching displays that presented novel sample and comparison stimuli. The blank comparison method permitted the children to indicate whether the novel sample-comparison pair were related (by selecting the picture) or not related (by selecting the blank). The method was used to evaluate emergent symbolic mapping and learning of new word:picture matching relations by the children. This study illustrates new, potentially more informative methods for analyzing symbol mapping in young children. The methods were shown to have considerable promise for advancing theoretical analyses of emergent mapping in both behavior analytic and developmental language research.

Assessing same/different judgments in individuals with severe intellectual disabilities: a status report.

This report summarizes state-of-the-art approaches for assessing visual stimulus same/different judgments in individuals with severe intellectual disabilities. Methods are described that permit one to conduct assessments on a population-wide basis, excluding few if any participants due to failure to acquire necessary baseline performances. Methodological investigations summarized here indicate that one can obtain reliable same/different judgments with a variety of stimuli in virtually anyone for whom a basal score on the Peabody Picture Vocabulary Test can be obtained. This approach includes judgments involving not only familiar, readily nameable stimuli, but also abstract two-dimensional forms of the type commonly used to minimize extraexperimental influences on performance. Taken together, recent findings lead to the conclusion that past studies have significantly under-estimated the capacity of participants with low MA scores to make same/different judgments. They also suggest a more general methodological approach that can potentially lead to more sensitive assessment of other behavioral capacities in this difficult-to-test population.

Reinforcer frequency and restricted stimulus control.

Stimulus control was evaluated in 3 individuals with moderate to severe mental retardation by delayed identity matching-to-sample procedures that presented either one or two discrete forms as sample stimuli on each trial. On pretests, accuracy scores on one-sample trials were uniformly high. On two-sample trials, the correct stimulus (i.e., the one that subsequently appeared in the comparison array) varied unpredictably, and accuracy scores were substantially lower, suggesting that both sample stimuli did not exert stimulus control on every trial. Subjects were then given training sessions with the one-sample task and with a new set of four stimuli. For two of the stimuli, correct matching responses were followed by reinforcers on a variable-ratio schedule that led to a high reinforcer rate. For the other two stimuli, correct responses were followed by reinforcers on a variable-ratio schedule that led to a substantially lower reinforcer rate. Results on two-sample tests that followed showed that (a) on trials in which comparison arrays consisted of one high reinforcer-rate and one low reinforcer-rate stimulus, subjects most often selected the high-rate stimulus; and (b) on trials in which the comparison arrays were either two high reinforcer-rate stimuli or two low reinforcer-rate stimuli and the samples were one high reinforcer- and one low reinforcer-rate stimulus, accuracy was higher on trials with the high-rate comparisons. These results indicate that the frequency of stimulus control by high reinforcer-rate samples was greater than that by low reinforcer-rate samples. Following more training with the one-sample task and reversed reinforcement schedules for all stimuli, the differences in stimulus control frequencies on two-sample tests also reversed. These results demonstrate experimental control by reinforcement contingencies of which of two sample stimuli controlled selections in the two-sample task. The procedures and results may prove to be relevant for understanding restricted stimulus control and stimulus overselectivity.

Auditory discrimination reversal learning and assessment of behavioral teratogenesis in rats.

Qualitative auditory discrimination procedures were used to evaluate discrimination acquisition and reversal learning in rats. Twelve adult rats prenatally exposed to ethanol (ETOH) and 12 unexposed isocaloric controls (CON) were given training with a positively reinforced successive discrimination procedure. Most ETOH subjects were impaired relative to CON subjects on accuracy during early training sessions and the number of sessions required to meet an 80% accuracy criterion. Some ETOH subjects were also impaired on the rate of learning over a series of repeated discrimination reversals. Individual differences in reversal learning rates varied more widely with ETOH subjects than with CON subjects. Our results indicate that the auditory discrimination procedures may find application in assessments of behavioral teratogenesis.

Generalized identity matching to sample of two-dimensional forms in individuals with intellectual disabilities.

An assessment of identity matching to sample with two-dimensional forms was conducted with 44 subjects with moderate and severe intellectual disabilities. Identity matching that did not require conditional discriminative functions was tested first; subjects who passed that test were then tested on a conditional identity matching task. Tests for generalized identity matching were passed by 30 of the 44 subjects. The 14 individuals who did not pass were given a further teaching assessment that sought to teach identity matching directly via standard teaching methods. Some subjects also received training on a series of simple discriminations taught by the same methods. Four additional subjects passed identity matching tests. Overall, generalized identity matching was demonstrated in 34 of 44 subjects, including 7 of 16 individuals with mental age (MA) scores of 3.0 years and below and 14 of 15 individuals with MA scores between 3.0 and 5.0 years. Results with these two groups are much superior to those typically reported for individuals with comparable MA scores. The capacity for generalized performances requiring same/different judgments appears to have been substantially underestimated in this population, perhaps especially when the stimuli are two-dimensional, relatively abstract forms.

Exclusion vs. selection training of auditory-visual conditional relations.

This study was conducted to assess the relative effectiveness of exclusion vs. selection (modified trial-and-error) training in establishing auditory-visual conditional relations. The study was conducted with children who had problems learning in school, but were otherwise normally intellectually capable. Single-subject methodology was used. Each child was exposed to the exclusion and selection conditions twice each in varied order. The exclusion-training procedure proved significantly more effective not only in teaching new auditory-visual conditional relations but also in generating emergent naming of the visual stimuli.

Assessing control by elements of complex stimuli in delayed matching to sample.

A series of six experiments examined delayed identity matching-to-sample performances of subjects with mental retardation. The stimuli were either one or two simultaneously displayed forms. When the reinforcement contingencies required that only one form exert discriminative control, all subjects achieved high accuracy scores. However, accuracy scores were substantially lower when the contingencies required discriminative control by two forms, suggesting restricted stimulus control. The decline in matching accuracy appeared to reflect selective losses of conditional control by sample stimuli and shifts in control to features of the comparison stimulus displays. The experiments suggest improved techniques for assessing control by complex stimuli and for evaluating the effects of procedures that seek to broaden restricted stimulus control. The results challenge interpretations based on stimulus-generalization decrement or shared attention.

Studies of exclusion in individuals with severe mental retardation.

Exclusion performances in matching to sample are demonstrated when subjects select experimentally undefined comparison stimuli in the presence of undefined sample stimuli, apparently by rejecting defined comparison stimuli. Several studies have documented exclusion performances in a small number of individuals with severe mental retardation. These studies also demonstrated the potential of exclusion procedures for establishing prerequisites for emergent naming performances. The present study examined exclusion in a larger cohort of subjects. Initial experiments asked two questions. First, how reliably would exclusion performances be demonstrated? Second, would those performances be followed by emergent naming, and, if so, how reliably? Follow-up experiments examined the stimulus control basis for exclusion performances. Our findings and conclusions can be summarized as follows: First, reliable exclusion was demonstrated in nearly all subjects. Second, naming performances typically emerged. These performances were seen in the context of a recent experimental history of matching to sample and of naming baseline stimuli in the experimental format. Third, apparent exclusion may sometimes result from relating undefined sample and comparison stimuli. Together, our findings suggest potentially effective strategies for teaching people with mental retardation and point to variables that should be considered when designing exclusion-based teaching interventions.

Teaching arbitrary matching via sample stimulus-control shaping to young children and mentally retarded individuals: a methodological note.

Two experiments demonstrated the efficacy of sample stimulus-control shaping programs for teaching arbitrary matching to 4 subjects who did not acquire the performances via standard methods (i.e., differential reinforcement and, in two cases, comparison intensity fading). All 4 had previously demonstrated identity matching with two-dimensional forms. Identity matching performances were then transformed into arbitrary matching by gradually changing the sample stimuli until they no longer resembled the comparison stimuli. Where applicable, these methods may have advantages over others that have been used after the failure of standard techniques.

Generalized oddity performance in preschool children: a bimodal training procedure.

Oddity performance requires relational discriminative responding, which typically is difficult to establish in children with MAs below five. In Experiment 1, a combination intrasubject reversal and multiple baseline across subjects design was used to establish the internal validity of a bimodal intervention in establishing generalized oddity performance. Six of seven children demonstrated oddity responding when presented with stimuli that instantiated the oddity relation in the visual and auditory modalities simultaneously. Oddity performance was evaluated with both reversal assessments and assessments with new sets of stimuli. The newly acquired oddity performance was durable; the six children continued to respond discriminatively when returned to a visual-only task on which they previously had been unsuccessful. Utilizing a reversal assessment more stringent than that of Experiment 1, Experiment 2 replicated this effect. The present studies are the first to demonstrate the utility of bimodal training in establishing oddity performance. The bimodal procedure is discussed with respect to the theoretical positions of Gibson, Dinsmoor, and Dixon.