Development of conditional and equivalence relations without differential consequences

Two experiments were conducted to establish conditional stimulus relations without differential consequences and to test for the emergence of other relations. In Experiment 1, 3 adults responded to match-to-sample displays in which sample-comparison pairs were constant while the second comparison presented with each pair changed periodically across trials. No differential consequences followed any comparison selections. All subjects learned conditional relations between constant samples and comparisons, but results of tests for transitivity in those relations were equivocal. In Experiment 2, 4 children were given unreinforced training and testing similar to that provided to the adults in Experiment 1, with procedural refinements. One child learned conditional relations and demonstrated emergent relations that confirmed the development of two four-member equivalence classes. Another child learned the conditional relations but did not demonstrate any emergent relations reliably. A 3rd child, after reinforced training on two conditional relations, learned four new conditional relations without differential consequences and demonstrated symmetry but not equivalence in the trained relations. The 4th child did not learn the conditional relations. These findings emphasize the importance of careful construction of tests for stimulus equivalence and suggest a need for critical analyses of the apparent emergence of untrained stimulus relations on unreinforced tests that has been observed in several stimulus equivalence studies.     

Naming in conditional discrimination and stimulus equivalence.

Using a matching-to-sample procedure, McIntire, Cleary, and Thompson (1987) taught monkeys the conditional relations A1-R1-A1-R1, A2-R2-A2-R2, A1-R1-B1-R1, A2-R2-B2-R2, B1-R1-C1-R1, and B2-R2-C2-R2, where the first and third terms in each relation refer to the sample and comparison stimuli, respectively, and the second and last terms refer to the emission of a distinctive pattern of responding. The subjects were then tested for the emergent relations A-C, C-A, B-A, C-B, and B-B, with the differential response produced by a given stimulus during training also emitted on test trials (e.g., A1-R1-C1-R1). The performances of both subjects were as accurate on the tested relations as they had been on the trained relations. The new relations were characterized as demonstrations of stimulus equivalence. However, the conditional discrimination literature shows that such training procedures generate control of comparison selection by the differential response patterns. Therefore, no emergent relations were demonstrated because all of the trained response-stimulus relations were preserved on test trials. This paper suggests that these procedures do not provide an appropriate analogy for the kind of emergent stimulus-stimulus relations exhibited by human subjects in equivalence studies and outlines a paradigm for assessing the relative influence of stimulus-stimulus and response-stimulus relations.     

Development and crossmodal transfer of contextual control of emergent stimulus relations

Six normally capable adults first learned three conditional relations in each of two prospective equivalence classes via match-to-sample training with figures as conditional (sample) and discriminative (comparison) stimuli. Then one trained conditional relation in each prospective class was brought under the control of contextual stimuli, two dictated nonsense syllables. Test performances indicated the emergence of untrained conditional relations, and therefore two equivalence classes, that were conditional on the contextual stimuli. These tests involved untrained combinations of contextual stimuli and stimuli in conditional relations, suggesting that the contextual stimuli functioned independently to control conditional relations rather than forming compound stimuli with samples and comparisons in training. Next, two novel figures were made equivalent to each of the original dictated contextual stimuli by match-to-sample training and testing. On subsequent tests, all subjects demonstrated transfer of conditional control of untrained conditional relations from the original auditory contextual stimuli to equivalent visual stimuli. These outcomes further supported the conclusion that the contextual stimuli exerted true conditional control over conditional relations in the equivalence classes and were not merely elements of compound stimuli.     

Go/no‐go procedure with compound stimuli with children with autism

The go/no‐go with compound stimuli is an alternative to matching‐to‐sample to produce conditional and emergent relations in adults. The aim of this study was to evaluate the effectiveness of this procedure with two children diagnosed with autism. We trained and tested participants to respond to conditional relations among arbitrary stimuli using the go/no‐go procedure. Both learned all the trained conditional relations without developing response bias or responding to no‐go trials. Participants demonstrated performance consistent with symmetry, but not equivalence.     

The development of functional and equivalence classes in high-functioning autistic children: the role of naming.

The development of functional and equivalence classes was studied in four high-functioning, preschool-aged autistic children. Initially, all subjects failed to demonstrate match-to-sample relations indicative of stimulus equivalence among two three-member classes of visual stimuli. Then, 2 subjects showed emergence of those relations after they were taught to assign the same name to all members in each class. Next, subjects were taught names for new stimuli outside the match-to-sample format. On subsequent match-to-sample tests, 2 subjects demonstrated untrained conditional relations among the stimuli given a common name. New, unnamed stimuli were then related via match-to-sample training to stimuli from sets of named stimuli. Tests for emergent conditional relations between the new unnamed stimuli and the named stimuli yielded positive results for 1 subject and somewhat mixed results for 3 subjects. Finally, without naming, 2 subjects developed stimulus equivalence among two new three-member classes of visual stimuli. These data suggest that naming may remediate failures to develop untrained conditional relations, some of which are indicative of stimulus equivalence.     

Transfer of a conditional ordering response through conditional equivalence classes

Eight adult humans were taught conditional discriminations in a matching-to-sample format that led to the formation of two four-member equivalence classes. When subjects were taught to select one comparison stimulus from each class in a set order, they then ordered all other members of the equivalence classes without explicit training. When the ordering response itself was brought under conditional control, conditional sequencing also transferred to all other members of the two equivalence classes. When the conditional discriminations in the matching-to-sample task were brought under higher order conditional control, the eight stimulus members were arranged into four conditional equivalence classes. Both ordering and conditional ordering transferred to all members of the four conditional equivalence classes; for some subjects this occurred without a typical test for equivalence. One hundred twenty untrained sequences emerged from eight trained sequences for all subjects. Transfer of functions through equivalence classes may contribute to a behavior-analytic approach to semantics and generative grammar.     

The merger and development of equivalence classes by unreinforced conditional selection of comparison stimuli

Three experiments assessed the likelihood that subjects with histories of equivalence class development would respond conditionally on new discriminations in the absence of differential consequences for responses. In the first two experiments, two groups of subjects with different experimental histories, but whose performances showed four equivalence classes, responded on trials without explicit reinforcement involving samples from two of the classes and comparisons from the other two classes, in a two-choice matching-to-sample format. Subjects consistently selected a particular comparison in the presence of a particular sample. Subsequent tests showed the emergence of equivalence relations between stimuli from classes linked by the unreinforced conditional selections. Subsequently, in Experiment II, the subjects' responses in the conditional selection trials were reinforced if the selection was reversed from that made previously. Although reversed selection was maintained, 2 of the 3 subjects continued to perform on equivalence relation trials according to their original unreinforced selections. In the third experiment, these 2 subjects responded on a series of conditional discriminations involving three new pairs of sample stimuli and one new pair of comparison stimuli. No explicit reinforcement followed responses on any trial in this experiment. Subsequent tests for equivalence between sample stimuli revealed the development of two equivalence classes.     

Class-consistent Differential Reinforcement And Stimulus Class Formation In Pigeons

Match-to-sample training clusters of A1 (sample): B1/B2 (comparisons), A2: B2/B1, B1: A1/A2, B2: A2/A1, B1: C1/C2, B2: C2/C1, C1: B1/B2, and C2: B2/B1 were presented to pigeons with class-consistent differential reinforcement using two dissimilar types of food reinforcers. Distinctive class-consistent response patterns occurred to the samples during the fixed-ratio 5 sample observing response requirement. Subsequent tests, modeled from the equivalence class paradigm demonstrated the emergence (80% class consistent) of the transitive-like A-C and C-A relations for 4 and 2 of 12 pigeons, respectively, and a strong trend (over 70%) for 7 and 6 others, respectively; the emergence of the reflexive-like identity relation when the nonidentical comparison was from the other class; and the disruption of the trained within-class relation with the addition of a reflexive comparison. After directional training of C1: D1/D2 and C2: D2/D1, tests indicated no emergence of the symmetric-like D-C relation or the composite D-B and D-A relations, but the B-D and A-D transitive-like relation occurred with some pigeons. Off-baseline training with class-consistent differential reinforcement contingent on responding to the D stimuli alone produced distinctive responding and, in turn, a trend to D-C symmetric-like control in 4 of 12 pigeons, as well as a shift toward class-consistent control on D-B and D-A test trials. Class-consistent differential reinforcement that produced distinctive sample behavior promoted stimulus control relations like those that circumscribe equivalence class formation. Respondent—operant interactions permit an analysis of the possible enrollment of stimulus values of distinctive responding to the discriminative stimuli forming the stimulus classes via processes corresponding to naming in humans.     

Formation of new stimulus equivalence classes by exclusion

This study presents three experiments that aimed to show the formation of stimulus equivalence relations among stimuli that had been previously related only by exclusion. In Experiment 1, participants were trained on baseline conditional discriminations to establish two 3‐member equivalence classes. Then, they were exposed to exclusion trials, without feedback, in which undefined stimuli had to be matched by rejecting the defined baseline stimuli. Finally, participants responded to test trials evaluating the emergence of symmetry and transitivity among the undefined stimuli from the exclusion trials. For half of the participants, the stimuli related by exclusion were introduced as S‐ stimuli in the baseline trials, whereas for the other half they were not. Further, half of the participants were assessed for emergent relations with stimuli from all the classes, whereas the other half was assessed for emergent relations with only the stimuli related by exclusion. In Experiment 2, the S‐ comparisons in the emergent relations test trials with stimuli only related by exclusion were stimuli from a null class. In Experiment 3, the number of exclusion trials was doubled. Across experiments, most participants showed emergence of equivalence relations among the stimuli related by exclusion. Some conditions of stimulus control associated with exclusion learning and the emergence of equivalence relations are discussed.     

Naming and equivalence: Response latencies for emergent relations

In an attempt to distinguish between associative network and verbal mediation accounts of equivalence formation, three experiments were carried out in which conditional stimulus relations were established and response latencies assessed during tests for emergent relations. In Experiment 1, three groups of adults were trained with six three-member classes of visual stimuli, using different kinds of stimuli for each group: readily nameable pictograms, which were “preassociated” (Group 1); equally nameable but “non-associated” pictograms (Group 2); or non-associated “abstract” stimuli, designed to discourage the use of verbal mediators (Group 3). For those trained with pictograms, equal response latencies were observed on all tested relations, viz. trained associations, symmetry, transitivity, and transitivity with symmetry, but for subjects given abstract stimuli response latencies were greater on tests requiring transitivity. In Experiment 2 this result was replicated with methodological refinements, using only groups trained with preassociated pictograms or abstract stimuli. In Experiment 3 subjects were pretrained to label abstract stimuli with either individual names or class names. Latencies were longer for tests involving transitivity in the case of those subjects using individual names, but equal response latencies were observed on all four types of test for those using class names. The results suggest that equivalence classesMaybe supported by either an associative network or by verbal mediation, depending on stimulus conditions and the subsequent strategies employed by subjects.     

Relations among equivalence, naming, and conflicting baseline control

Three studies were conducted with different groups of 6 students each to explore the effects of training class-inconsistent relations and naming on demonstrations of emergent arbitrary stimulus relations. In all studies, two three-member equivalence classes of Greek symbols (A1B1C1 and A2B2C2) emerged as a result of training in conditional discriminations. Two new symbols were introduced (X and Y), and additional conditional discriminations were trained, whereby X was designated as the positive discriminative stimulus (S+) and Y was designated as the negative discriminative stimulus (S-) for A1 and B2. Conversely, Y was designated as the S+ and X as the S- for B1 and A2. This introduced conflicting sources of control within and between classes. In Study 1, subjects were not provided with names for the stimuli. In Study 2, the experimenter provided common names for the stimuli within each class. In Study 3, the subjects were required to use the common names during conditional discrimination training and test-trial blocks. In all experiments, equivalence responding with respect to the original classes was disrupted for some subjects subsequent to learning the new relations. Furthermore, in Studies 2 and 3, there were frequent examples of noncorrespondence between observed (listener or speaker) naming patterns and derived relations. These results support the view that demonstrations of equivalence are subject to control from a variety of sources rather than being fundamentally dependent on naming.     

Equivalence relations, contextual control, and naming

This paper reports two experiments that investigated the role of verbal behavior in the emergence and generalization of contextually controlled equivalence classes. During both experiments, participants were trained with two different combinations of the same easily nameable, yet formally unrelated, pictorial stimuli. Match-to-sample baselines for eight four-member classes were established under the contextual control of two colors. In the presence of one color, conditional relations were established between stimuli whose normative names rhymed. In the presence of the other color, conditional relations were established between stimuli whose normative names did not rhyme. Although, during Experiment 1, all participants demonstrated equivalence classes involving rhyming stimuli, none demonstrated the formation of nonrhyme equivalence classes. To investigate this finding, Experiment 2 evaluated whether participants would demonstrate both rhyme and nonrhyme equivalence classes given more extensive exposure to the experimental contingencies. All participants demonstrated contextually controlled rhyme and nonrhyme equivalence classes, although rhyme classes were demonstrated with greater facility than nonrhyme classes. Results indicate that visual stimuli are named, that verbal bases for stimulus classification can affect the emergence of contextually controlled equivalence classes, and that untrained contextually controlled conditional discriminations involving novel stimuli can emerge on the basis of participants' verbal behavior.     

Emergent equivalence relations between interoceptive (drug) and exteroceptive (visual) stimuli.

Conditional "if-then" relations between drug (interoceptive) stimuli and visual (exteroceptive) stimuli were taught to 4 normal humans. Interoceptive stimuli were the effects produced by 0.32 mg/70 kg triazolam (a prototypical benzodiazepine) and placebo (lactose-filled capsules); exteroceptive stimuli were black symbols on white flash cards. Following the training of the prerequisite conditional relations, tests of emergent relations were conducted between exteroceptive stimuli and between interoceptive and exteroceptive stimuli. Equivalence relations emerged immediately without explicit training for all 4 subjects. Accuracy of responding during the interoceptive-exteroceptive equivalence tests and subjects' self-reports showed consistent discrimination between the drug effects of triazolam and placebo. Finally, a generalization test assessed whether a novel visual stimulus presented in the context of the placebo (i.e., no drug) would generalize to visual stimuli belonging to the placebo stimulus class. All 3 subjects who completed this test reliably chose the visual stimuli belonging to the placebo class and not the visual stimuli belonging to the triazolam stimulus class. The development of equivalence relations between interoceptive and exteroceptive stimuli demonstrates that private and public stimulus events can emerge as members of the same equivalence class. Theoretical and clinical implications are discussed.     

Nodal structure and stimulus relatedness in equivalence classes: post-class formation preference tests

Three experiments used postclass formation within-class preference test performances to evaluate the effects of nodal distance on the relatedness of stimuli in equivalence classes. In Experiment 1, two 2-node four-member equivalence classes were established using the simultaneous protocol in which all of the baseline relations were trained together, after which all emergent relations probes were presented together. All training and testing was done using match-to-sample trials that contained two comparisons. After class formation, the effects of nodal distance were evaluated using within-class preference tests that contained samples and both comparisons from the same class. These tests yielded inconsistent performances for most participants. Experiment 2 replicated Experiment 1, but a third null comparison was used on all trials during class formation. Thereafter, virtually all of the within-class probes, for all participants, evoked performances that were consistent with the predicted effects of nodal distance, that is, the selection of comparisons that were nodally closer to the samples. It appears, then, that the establishment of the equivalence classes with a third null comparison induced control by nodal structure of the classes. Experiment 3 demonstrated the generality of these findings with larger classes that contained more nodal separations, that is, three-node five-member classes. Emergent-relations tests conducted immediately after the within-class tests showed the classes to be intact. Thus, the differential relatedness of stimuli in a class or their interchangeability depended on the content of a test trial: within-class probes occasioned responding indicative of differential strength among the stimuli in the class, while cross-class tests occasioned responding indicative of interchangeability of stimuli in the same class.     

Symmetry training in pigeons can produce functional equivalences

Functional stimulus equivalence has been demonstrated using a transfer of training design with matching-to-sample training in which two sample stimuli are associated with the same comparison stimulus (A-B, C-B; many-to-one matching). Equivalence is shown by training a new association (A-D) and demonstrating the presence of an emergent relation (C-D). In the present experiment, we show that symmetry training, in which a bidirectional association is trained between two stimuli (A-B, B-A, using successive stimulus presentations followed by reinforcement), can also produce functional equivalence using a transfer of training design (i.e., train B-C, test A-C). The results suggest that training pigeons in the substitutability of two stimuli may be sufficient to produce functional stimulus equivalence between them. The results also have implications for the development of an emergent transitive relation, because training on A-B and B-C relations results in the emergence of an untrained A-C relation, if B-A training also is provided.     

Resurgence of derived stimulus relations.

Resurgence has been shown in human and nonhuman operant behavior, but not in derived relational responses. The present study examined this issue. Twenty-three undergraduates were trained to make conditional discriminations in a three-choice matching-to-sample paradigm. The training resulted in three equivalence classes, each consisting of four arbitrarily configured visual stimuli. The same 12 stimuli were then reorganized, and the conditional discrimination training was repeated such that three new classes were possible. In a subsequent test of derived relations, most subjects showed response patterns that were consistent with the altered conditional discriminations. Subjects were then exposed to conditional discrimination trials under extinction. Most subjects continued to respond consistently with the most recently reinforced conditional discrimination trials. During the next phase, subjects were exposed to symmetry and equivalence trials. Responses consistent with the most recent training produced feedback saying that the responses were incorrect, whereas other responses produced no feedback. Most subjects showed a resurgence of responding that was consistent with their earlier training. Finally, subjects were exposed to conditional discrimination trials carried out in extinction. Most subjects continued to show a resurgence of responding that was consistent with their early training.     

New knowledge derived from learned knowledge: functional-anatomic correlates of stimulus equivalence

Forming new knowledge based on knowledge established through prior learning is a central feature of higher cognition that is captured in research on stimulus equivalence (SE). Numerous SE investigations show that reinforcing behavior under control of distinct sets of arbitrary conditional relations gives rise to stimulus control by new, derived relations. This investigation examined whether frontal-subcortical and frontal-parietal networks known to support reinforced conditional relations also support derived conditional relations. Twelve adult subjects completed matching-to-sample (MTS) training with correct/wrong feedback to establish four trained conditional relations within two distinct, three-member stimulus classes: (1) A1-->B1, B1-->C1 and (2) A2-->B2, B2-->C2. Afterwards, functional neuroimaging was performed when MTS trials were presented involving matching two identical circles (a sensorimotor control condition), trained relations (A-->B, B-->C), and derived relations: symmetry (B-->A, C-->B), transitivity (A-->C), and equivalence (C-->A). Conditional responding to trained and derived relations was similarly correlated with bilateral activation in the targeted networks. Comparing trained to derived relations, however, highlighted greater activation in several prefrontal regions, the caudate, thalamus, and putamen, which may represent the effects of extended training or feedback present during imaging. Each derived relation also evidenced a unique activation pattern. Collectively, the findings extend the role of frontal-subcortical and frontal-parietal networks to derived conditional relations and suggest that regional involvement varies with the type of derived conditional relation.     

Emergent, untrained stimulus relations in many-to-one matching-to-sample discriminations in rats

The present experiment investigated whether rats formed emergent, untrained stimulus relations in many-to-one matching-to-sample discriminations. In Phase 1, rats were trained to match two samples (triangle and horizontal stripes) to a common comparison (horizontal stripes) and two additional samples (circle or vertical stripes) to another comparison (vertical stripes). Then, in Phase 2, the rats were trained to match the one sample (triangle) to a new comparison (black) and the other sample (circle) to another comparison (white). In the Phase 3 test, half the rats (consistent group) were given two new tasks in which the sample-correct comparison relation was consistent with any emergent stimulus relations that previously may have been learned. The remaining 6 rats (inconsistent group) were given two new tasks in which the sample-correct comparison relation was not consistent with any previously learned emergent stimulus relations. Rats in the consistent group showed more accurate performance at the start of Phase 3, and faster learning to criterion in this phase, as compared with rats in the inconsistent group. This finding suggests that rats may form emergent, untrained stimulus relations between the discriminative stimuli in many-to-one matching-to-sample discriminations.     

Training intraverbal naming to establish equivalence class performances

The purpose of this three‐experiment study was to evaluate whether performance consistent with the formation of equivalence classes could be established after training adults to tact and intraverbally relate the names of visual stimuli. Fourteen participants were exposed to tact training, listener testing, and intraverbal training (A'B’ and B'C’) prior to matching‐to‐sample (MTS) and intraverbal posttests presented in different sequences across experiments. All participants demonstrated emergent MTS and intraverbal relations consistent with equivalence class formation. More importantly, all participants emitted experimentally defined or self‐generated tacts or intraverbally named the correct sample‐comparison pairs at some point during posttests. These results are consistent with the intraverbal naming account (Horne & Lowe, 1996) in that participants who passed novel relations MTS tests also demonstrated emergence of corresponding intraverbal relations. However, verbal reports and latency data suggest that participants did not necessarily have to use intraverbal naming as a problem solving strategy continuously throughout MTS posttests. These results extended previous research by showing that verbal behavior training of baseline relations (A'B’ and B'C’) is sufficient to establish novel conditional relations consistent with equivalence class formation.     

Some tests of response membership in acquired equivalence classes

Pigeons were trained on many-to-one matching in which pairs of samples, each consisting of a visual stimulus and a distinctive pattern of center-key responding, occasioned the same reinforced comparison choice. Acquired equivalence between the visual and response samples then was evaluated by reinforcing new comparison choices to one set of samples, and examining generalization of these choices to the other samples. Three separate experiments found no evidence of such generalization, as indexed by performance on class-consistent versus class-inconsistent tests. Other tests showed that the pigeons' center-key response patterns during training had indeed served as a conditional cue for choice. These results do not support the hypothesis that different defined responses can become members of acquired equivalence classes.