Stimulus classes in matching to sample and sequence production: the emergence of numeric relations.

We investigated interrelationships among stimulus classes established in matching-to-sample and sequence-production tasks. The analysis focused on the matching and sequencing of quantities, numerals, and arbitrary forms in two individuals with mental retardation. The basic protocol involved: (a) establishing both matching and sequencing performances with some stimuli, (b) training sequencing with a new set of stimuli and assessing whether new matching performances emerged, and (c) training matching with a new set of stimuli and assessing whether new sequencing emerged. The results showed that sequence training did not readily lead to new matching performances, unlike prior research with college students. In contrast, training in matching to sample yielded emergent sequence production; these data support prior studies involving children and adults without developmental disabilities. The results extend prior stimulus class research and suggest an important role for stimulus control processes in the production of generative numeric performances.

A note on transfer of stimulus control in the delayed-cue procedure: facilitation by an overt differential response.

This case study describes initially unsuccessful attempts to use the delayed-cue procedure to teach conditional discriminations to an individual with moderate mental retardation. The task was matching printed-word comparison stimuli to dictated-name sample stimuli. In three experiments, the subject typically waited for the delayed cue unless differential responses to the dictated samples (repeating the sample names) were required. Hence, the study provides an example of a way to make the delayed-cue method more effective. The stimulus control bases for the results are discussed.

Sequence learning in individuals with behavioural limitations.

The production of sequences by two mentally retarded adults and a normally capable preschooler was assessed after each was trained to touch five physically dissimilar and nonrepresentative forms in an experimenter-specified order (denoted A1-->A2-->A3-->A4-->A5). Performance on the 10 constituent two-term sequences was examined (e.g. A-->A2, A2-->A3, A1-->A3 and A2-->A4). The probe data were largely consistent with the five-term sequence performance trained explicitly and suggest the formation of stimulus relations based on relative position rather than a rote stimulus-response chain. The procedures and results were replicated with a second five-term sequence (B1-->B2-->B3-->B4-->B5). The subjects' performances were also assessed on trials in which mixtures of the two sets of stimuli were presented as either two-term probes (e.g. A2-->B4 and B2-->A4; with all three subjects) or five-term probes (e.g. A1-->B2-->A3-->B4-->A5; with the two adult subjects). Again, the subjects' performances were consistent with their baseline training. The mixed-probe data extend prior research on sequence production and suggest the formation of classes of mutually substitutable sequence stimuli. The overall findings highlight the importance of experiential variables in the formation of ordinal relations in developmentally limited individuals.

Stimulus control analysis of language disorders: A study of substitution between voiced and unvoiced consonants.

This study attempted to analyze defective stimulus control relations underlying persistent substitution between voiced and unvoiced consonants in the speech and writing of two children. A series of 20 tests was administered repeatedly. Some tests consisted of matching-to-sample tasks, with dictated words, printed words, or pictures as samples. Comparison stimuli were arranged in pairs of printed words or pictures, such that the only difference in their corresponding spoken words was the voicing of one consonant phoneme. In other tests, a stimulus (dictated word, printed word, or picture) was presented, and the subject was required to emit an oral response (repeat the dictated word, read the printed word, or name the picture) or a written response (write to dictation, copy the word, or write a picture name). Other tests required the subjects to make a same/different distinction in pairs of dictated words that did or did not differ in the voicing of a single phoneme. Results showed distinct deficit profiles for each subject, consisting of patterns of defective stimulus control relations. The subjects were able, however, to distinguish between voiced and unvoiced sounds and to produce these sounds.

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.

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.

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.

Generalization after intradimensional discrimination training in 2-year-old children.

Two-year-old children received intradimensional discrimination training at initially distant points on a circle-ellipse continuum. This training often did not produce stimulus control by circle-ellipse differences smaller than the original training values. The lack of control did not reflect capacity limitations, however. Good control was established when the children were given further training at nearer points on the continuum. The data confirm results of earlier research on stimulus generalization, extending them to a developing human subject population.

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.

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.

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.

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.

Some observations on control by spoken words in children's conditional discrimination and matching by exclusion.

This study examined matching-to-sample procedures that might result in the emergence of conditional behavior never explicitly taught. Subjects were preschool children. Two pictures were displayed as comparisons on every trial, and samples were spoken words. In baseline training preceding each of three experiments, children learned to select pictures of a dog, a table, and a banana in response to their spoken English names. Thereafter, probe trials displayed novel comparisons with baseline comparisons: one novel comparison was displayed with the dog and another with the table. The three experiments differed primarily in the nature of the samples presented on probe trials. In Experiment 1, probe samples were novel words, "JAIJAI" and "BREEL." On the probes, each of seven subjects reliably selected the novel comparisons, apparently "excluding" the familiar ones. In Experiment 2, probe samples were from the subjects' baseline. On one probe, for example, the sample was "TABLE," and the subject had to choose either the dog or the novel picture. Exclusion was logically possible because the dog had always before been incorrect in the presence of "TABLE." Under these conditions, however, only two of nine children excluded reliably. In Experiment 3, probe samples were words that had never been samples on any matching-to-sample trial, but that had controlled the children's behavior in other settings. On one probe, for example, the sample was "PENCIL," and the subject had to choose either the dog or a novel picture. Subjects virtually always excluded the former and selected the latter. Unreliable exclusion in Experiment 2, therefore, apparently resulted because the probe samples had previously served also as samples on baseline trials. Spontaneous verbalizations recorded during probing provided further data consistent with this interpretation. The study helps to define variables controlling exclusion performances by showing that such performances are more likely to occur if the sample has no prior experimental history.

Fixed-interval and fixed-ratio reinforcement schedules with human subjects.

Operant laboratory studies were conducted as part of the regular activities of a psychiatric research ward. This report includes only some early data obtained from the ward staff, not the patients. A multiple schedule having alternating fixed-ratio and fixed-interval components permitted observations of acquisition and maintenance of behavior at low schedule values, transition to and final performance at greater schedule values, and behavioral changes after a limited-hold contingency was added to the fixed-interval. Prior to the added limited-hold, subjects used watches to time the interval, and usually responded only once before obtaining each fixed-interval reinforcement. Short limited-hold values eliminated clock watching and increased fixed-interval responding. Subjects communicated freely with each other, and it was clear that their performances were controlled both by the contingencies and by instructions. Just as clearly, the instructions themselves were controlled by the contingencies. It was concluded that the kinds of verbal control that were responsible for "nonstandard" fixed-interval performances did not require the postulation of any new behavioral principles.

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.

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.

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.

The use of picture programs in teaching direct care staff.

Direct care staff were taught via picture programs to transfer nonambulatory, severely mentally retarded men between their beds and wheelchairs. Still color photographs illustrated essential details of the complex behavior sequences. Staff transferring performance improved markedly over that shown on a pretest. Study guide questions increased the effectiveness of the programs, perhaps because the questions encouraged accurate observation of the pictures. The procedures may suggest cost effective alternatives to traditional forms of inservice training.

Spoken and signed naming of foods after receptive exclusion training in severe retardation.

Two low-functioning mentally retarded subjects learned to name food items after receptive exclusion training, conducted as follows: The subjects first learned to select a small number of foods in a two-choice matching-to-sample task. For one subject, the samples were dictated names; for the other, the samples were manual signs. They also learned to name these "known" foods, either orally or by signing. On exclusion trials, a known food was displayed with a new food whose corresponding name or sign had not yet been learned, and a novel sample (spoken or signed), corresponding to the new food, was presented. The subjects typically selected the new food immediately, apparently by "excluding" the food related to the known sample. If a known sample was presented, however, the subjects continued to select the known food correctly. Periodically during exclusion training with a number of new foods, the subjects were tested for production of food names or signs. With few exceptions, the subjects produced the food names without direct training, often after only a few receptive exclusion trials. The results suggest strategies for teaching simple receptive and expressive relations to severely mentally retarded individuals.