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.

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.

Teaching relational discrimination to individuals with mental retardation: some problems and possible solutions.

The problem of teaching relational discriminations to people with mental retardation was examined. The limitations of several commonly used teaching procedures were discussed and alternative approaches that derive from studies of simple-discrimination learning were described. Results of two preliminary studies were summarized that demonstrate the feasibility of these approaches and suggest new methods for teaching relational discriminations to individuals with developmental limitations.

Stimulus class formation and functional equivalence in moderately retarded individuals' conditional discrimination.

Three mentally retarded humans first acquired a simple discrimination: Simultaneously displayed visual stimuli A1 and A2 functioned as S+ and S-, respectively. The subjects also acquired a conditional discrimination, learning to select visual stimuli B1 and B2 conditionally upon A1 and A2, respectively. Then, B1 and B2 were displayed without A1 or A2. Subjects selected B1, an emergent discrimination that showed that B1 and B2 had become functionally equivalent to A1 and A2, respectively. Two subjects next learned to select C1 and C2 conditionally upon B1 and B2, respectively. They also learned to select B1 and B2 conditionally upon D1 and D2, respectively. Subsequent simple discrimination probe trials displayed (a) C1 and C2 and (b) D1 and D2. On the former, the subjects nearly always selected C1. On the latter, they initially selected D1 and D2 about equally often. Thus, the emergence of simple discrimination appears to depend on a specific experimental history.

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.

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.

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.

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.

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.

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.

Stimulus class membership established via stimulus-reinforcer relations.

In an arbitrary matching-to-sample procedure, two mentally retarded subjects learned conditional discriminations with two sets of stimuli. Each set included a spoken name (N1 or N2), an object (O1 or O2), and a printed symbol (S1 or S2). One subject selected conditionally (a) O1 upon N1, and O2 upon N2, and (b) S1 upon O1, and S2 upon O2. The other subject selected conditionally (a) S1 upon N1, and S2 upon N2, and (b) O1 upon S1, and O2 upon S2. For both subjects, selections of O1 and S1 produced one type of food, F1; selections of O2 and S2 produced a different type of food, F2. Both subjects also learned identity-matching performances, selecting O1, O2, S1, S2, F1, and F2 conditionally upon those stimuli as samples; F1 followed selections of O1, S1, and F1; F2 followed selections of O2, S2, and F2. Matching performances consistent with stimulus class formation involving the names, objects, symbols, and foods were demonstrated on probe trials, even though these performances had not been taught explicitly. Next, new objects, X1 and X2, were presented on identity-matching trials, producing F1 and F2, respectively. Without further training, X1 was selected conditionally upon N1, S1, and O1, and X2 was selected upon N2, S2, and O2. When the contingencies were changed so that selections of X1 and X2 were now followed by F2 and F1, respectively, X2 was selected conditionally upon N1, S1, and O1, and X1 was selected upon N2, S2, and O2. Class membership of X1 and X2 had apparently changed. This study provides evidence that reinforcers may become members of stimulus classes, and that new stimuli may become class members through relations with reinforcers.

Emergent simple discrimination established by indirect relation to differential consequences.

Three experiments examined a discrimination training sequence that led to emergent simple discrimination in human subjects. The experiments differed primarily in their subject populations. Normally capable adults served in the first experiment, preschool children in the second, and mentally retarded adults in the third. In all experiments, subjects learned a simple simultaneous discrimination: When visual stimuli A1 and A2 were displayed together, reinforcers followed selections of A1, the S+, but not A2, the S-. The subjects also learned a conditional discrimination taught with an arbitrary visual-visual matching-to-sample procedure. Comparisons were two additional visual stimuli, B1 and B2, and samples were A1 and A2. Reinforcers followed selections of B1 in the presence of A1 and of B2 in the presence of A2. After the simple-discrimination and conditional-discrimination baselines had been acquired, B1 and B2 were displayed alone (without a sample) on probe trials. Subjects had never been taught explicitly how to respond to such displays. Nonetheless, they almost always selected B1, which was involved in a conditional relation with A1, the stimulus that served as S+ on the simple-discrimination trials. This outcome suggested the formation of stimulus classes during conditional-discrimination training. Through class formation, B1 and B2 had apparently acquired stimulus functions similar to those shown by A1 and A2 on simple-discrimination trials, thereby leading to emergent selections of B1 on the probes.

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.

Controlling relations in conditional discrimination and matching by exclusion.

Normally capable adults learned two-choice identity matching of three-digit numerals and arbitrary matching of physically dissimilar nonsense syllables. The stimuli were displayed on a computer terminal, and responses consisted of typing on the terminal's keyboard. In Experiment 1, every trial displayed a sample numeral, a comparison numeral, and three equal signs (= = =). The comparison stimulus was to be selected if it was identical with the sample; otherwise the equal sign was to be selected. This "single comparison" method was then used to show that arbitrary matching could be based upon either sample-S+ or sample-S- relations. In Experiment 2, a series of probe trials displayed a novel sample, a comparison stimulus from the arbitrary matching baseline, and = = =. Subjects typically selected = = =; they apparently were excluding the baseline comparison stimulus. Experiments 3 through 5 investigated which variables in training would lead to the selection of baseline comparison stimuli in response to novel samples. Behavior was usually unchanged when baseline training included relating comparison stimuli to as many as four different samples. Punishment contingencies were effective, but performance did not generalize unless those contingencies were applied in relation to more than one baseline comparison stimulus.

Establishing control by spoken words with profoundly mentally retarded individuals.

Five low-functioning mentally retarded subjects were taught initially to insert tokens in a slot only when an auditory-visual complex stimulus was presented. The auditory component was a spoken reinforcer name (e.g., "Food"), and the visual component was a flashing red light in the slot opening. Later, the name was presented without the light on probe trials. Three subjects did not respond, suggesting that their token insertions had been controlled by the visual but not by the auditory component of the auditory-visual complex. These subjects then received a fading program designed to establish auditory stimulus control. The program was successful with two subjects. The third subject required post-program remedial teaching, but ultimately demonstrated exclusive control by the spoken name. The results suggest methods for establishing auditory stimulus control with this population and highlight variables that may influence the reliability of such control in some subjects.

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.

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.

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 money skills through stimulus class formation, exclusion, and component matching methods: three case studies.

This paper describes novel methodology for teaching monetary skills to mentally retarded individuals. The goal of the methodology is to generate such skills with relatively little explicit training. To do so, the procedures were designed to produce emergent new behavior through stimulus class formation, exclusion, and matching of stimulus components. Three case studies demonstrate the methods and provide illustrative supporting data.