A Review of Backward Higher-Order Conditioning: Implications for a Pavlovian Conditioning Analysis of Stimulus Equivalence.

Stimulus equivalence (SE) is demonstrated when participants exposed to conditional discrimination training pass tests for reflexivity, symmetry, transitivity, and equivalence (symmetry combined with transitivity). Most theorists attribute the origin of SE to operant processes, but some argue that it results from Pavlovian conditioning. Symmetry is problematic for the latter hypothesis because it seems to require excitatory backward conditioning. However, equivalence tests resemble backward sensory preconditioning (BSP) and backward second-order conditioning (BSOC), two well-established processes. A review of associationistic theories of BSP and BSOC showed that the temporal coding hypothesis (TCH) explains outcomes that other associationistic theories cannot explain (i.e., BSOC and BSP effects after first-order conditioning with delay vs. trace conditioning and forward vs. backward conditioning). The TCH assumes that organisms encode the temporal attributes of stimulus events (e.g., order and interval duration) and this temporal information is integrated across separate phases of training. The TCH seems compatible with a behavioral analysis if direct stimulus control replaces the notion of temporal maps. The TCH perspective does not seem applicable to SE because SE tests are not predictive tasks. This suggests that SE is fundamentally different from BSP and BSOC and a Pavlovian conditioning analysis of SE is inadequate. This conclusion is consistent with previous criticism of a Pavlovian account of SE according to which Pavlovian conditioning cannot be interpreted as stimulus substitution.

The Problem of Class Breakdown in Sidman's (1994, 2000) Theory about the Origin of Stimulus Equivalence.

Sidman (1994, 2000) hypothesized that equivalence relations are a direct outcome of reinforcement contingencies. This theory is problematic because contingencies do not always result in equivalence. Sidman proposed that equivalence relations may conflict with analytic units, the other outcome of contingencies (e.g., in conditional discriminations with common responses/reinforcers). This conflict may result in a generalized class breakdown and a failure to pass equivalence tests. This is more likely in nonhumans, very young humans, etc. The conflict can also result in a selective class breakdown and success in equivalence tests. This occurs after experience shows the organism the necessity and utility of this process. The nature of that experience and the class breakdown processes were not described by Sidman. I explored the implications of the following hypotheses for Sidman's theory. First, conditional discriminations with a common response/reinforcer result in a generalized class breakdown when participants fail to discriminate emergent relations incompatible with contingencies from those compatible. Second, learning to discriminate between the two requires a history of multiple exemplar training (MET). This implies that equivalence class breakdown is a common response to exemplars that have nothing in common except their relations. This, however, contradicts Sidman's views about the impossibility of such process in the absence of a complex verbal repertoire. If that type of learning from MET is possible, then the possibility that MET results in the selective formation of equivalence classes must be admitted, and the utility of hypothesizing that equivalence is a direct outcome of reinforcement contingencies can be questioned.

Rate matching, probability matching, and optimization in concurrent ratio schedules.

Much research has documented rate matching in concurrent variable-interval schedules, but comparatively little research has examined performance in concurrent variable-ratio schedules, except in discrete-trials procedures that sometimes produce probability matching. One should expect that the two types of schedule would result in different performances, because ratio schedules cannot improve with time the way interval schedules do; ratio schedules lack the temporal dynamics of interval schedules. The present experiment exposed rats to concurrent variable-ratio schedules. Seven unsignaled components were presented in random order within each daily session, with probability ratios ranging from 1:8 to 8:1. Three conditions were studied that varied the overall probability of food while leaving probability ratios the same. Choice appeared to conform to probability matching, because sensitivities in the rate-matching relation were close to 0.5, whereas sensitivities to probability ratio were close to 1.0. The sensitivities alone, however, could not confirm probability matching, because undermatching to rate occurs often. Analyses at smaller time scales supported the interpretation of probability matching. In particular, control by food deliveries was highly local in concurrent variable-ratio schedules, in contrast with concurrent variable-interval schedules, in which control is extended. Activity continued to switch between alternatives throughout components, contradicting optimal sampling theory.

Equivalence class analysis of responding consistent with the relational frame of opposition.

We replicated and extended studies showing that contextual cues for matching stimuli from 2 separate equivalence classes control the same derived relations as contextual cues for opposition frames in RFT studies. We conducted 2 experiments with 6 college students. In Phase 1, they received training in a conditional discrimination AB. Then, they received training for maintaining AB with X1 as context, and for reversing the sample-comparison relations of AB, with X2. In Phase 2, X1 functioned as context for matching same-class stimuli, and X2 functioned as context for matching separate-class stimuli. In Phase 3, X2 controlled the same derived arbitrary relations as cues for opposition frames in RFT studies. This functional equivalence may suggest that X2 functioned as a cue for opposition frames. In Phase 4, participants matched different stimuli with X2 as context, instead of matching most different (opposite) stimuli. In addition, Different, a cue for matching different stimuli, controlled the same derived arbitrary relations as X2. These results are incompatible with X2 being a cue for opposition frames. Contextual control over equivalence and responding by exclusion can explain these outcomes. The implications of these findings for RFT studies on opposition frames are discussed.

Spontaneously hypertensive (SHR) rats choose more impulsively than Wistar-Kyoto (WKY) rats on a delay discounting task.

Indications of Attention Deficit Hyperactivity Disorder (ADHD) in the spontaneously hypertensive rat (SHR) are not consistent across different tests of impulsivity, questioning the SHR's validity as a rodent model of ADHD. This study used a concurrent-chains procedure to examine possible differences in impulsive choice between SHRs and control-normotensive Wistar Kyoto (WKY) rats. The aim was to extend the generality of findings showing regularities between the hyperbolic-decay model and the generalized matching law fitting delay discounting data from nonhuman animals. The objectives were to: (1) examine differences in impulsive choice between SHRs and WKYs; (2) add evidence suggesting that the SHR is a suitable model of ADHD; (3) demonstrate that concurrent-chains procedures requiring locomotion detect differences in impulsive choice between SHRs and WKYs; (4) support the idea that impulsivity in nonhuman animals increases with training. The initial link used two non-independent random interval schedules arranging entries to the terminal links, where one fixed-time (FT) schedule delayed 1-food pellet and the other FT 4-food pellets. The FT delaying the former was kept constant at 0.1s and that delaying the latter changed after every 10 food deliveries, defining six delay components (0.1, 5, 10, 20, 40, and 80s) presented in random order each session. Results showed that the SHRs choose more impulsively than the WKYs, adding to the body of evidence suggesting that the SHR may be a suitable model of ADHD. Both models of choice fitted the impulsive choices of the SHRs and WKYs well; positive correlations between estimates of parameters k and s suggested compatibility between models of choice showing that impulsivity increases with training.

Analysis of apparent demonstrations of responding in accordance with relational frames of sameness and opposition.

We evaluated whether contextual control over equivalence and nonequivalence and responding by exclusion can explain the outcomes of relational frame theory (RFT) studies on sameness and opposition relations. We trained nine college students to maintain and reverse conditional discriminations with X1 and X2 as contextual stimuli. In Experiment 1, X1 and X2 controlled derived stimulus relations (DSR) analogous to those controlled by Same and Opposite in RFT studies. These results can be explained by at least two hypotheses: X1 and X2 were cues for equivalence and nonequivalence and responding by exclusion, or for sameness and opposition. In Experiment 2, X1 and X2 controlled DSR predicted by the hypothesis that they were cues for equivalence and nonequivalence and responding by exclusion, and not predicted by the hypothesis that they were cues for sameness and opposition. The results of Experiment 2 and the functional equivalence of X1 and X2 with Same and Opposite in Experiment 1 suggest that Same and Opposite were cues for equivalence and nonequivalence and responding by exclusion in RFT studies.

Contextual control over equivalence and nonequivalence explains apparent arbitrary applicable relational responding in accordance with sameness and opposition.

We evaluated whether contextual control over equivalence and nonequivalence (i.e., selecting comparisons equivalent to the samples in the presence of a contextual cue, and excluding the selection of comparisons equivalent to the samples in the presence of another contextual cue) can account for apparent arbitrarily applicable relational responding (AARR) in accordance with the frames of sameness and opposition, as defined in relational frame theory (RFT). Three college students were trained to maintain previously established conditional discriminations in the presence of a contextual cue X1, and to reverse them in the presence of another contextual cue X2 (e.g., X1-A1B1, X1-A2B2, X2-A1B2, X2-A2B1). Subsequent tests demonstrated that X1 and X2 functioned as cues for equivalence and nonequivalence. Later on, X1 and X2 were demonstrated to be functionally equivalent to supposed contextual cues for the frames of sameness and opposition employed in RFT studies (i.e., SAME and OPPOSITE cues), in tests for arbitrary and nonarbitrary derived stimulus relations. The functional equivalence of X2 and OPPOSITE suggests that OPPOSITE worked as a cue for nonequivalence. Thus, the results in RFT studies with SAME and OPPOSITE can be explained just by contextual control over equivalence and nonequivalence. Therefore, the explanation that they actually demonstrated AARR in accordance with the frames of sameness and opposition can be questioned and replaced by a more parsimonious explanation, based on a few simple learning principles. We discuss the implications of this conclusion for the debate among competing theories about the origin of stimulus equivalence and other derived stimulus-stimulus relations.

A long-term study of the impulsive choices of Lewis and Fischer 344 rats.

Contemporary analyses of choice were implemented to analyze the acquisition and maintenance of response allocation in Lewis (LEW) and Fischer 344 (F344) rats. A concurrent-chains procedure varied the delay to the larger reinforcer (0.1, 5, 10, 20, 40, and 80 s). Delays were presented within sessions in ascending, descending, and random orders. Each condition lasted 105 days, and the entire data set was analyzed to obtain discounting functions for each block of 15 sessions and each food delivery across delay components. Both a hyperbolic-decay model and the generalized matching law described well the choices of LEW and F344 rats. Estimates of discounting rate and sensitivity to the immediacy of reinforcement correlated positively. The slope of the discounting function changed with presentation orders of the delays to the larger reinforcer. Extended training reduced differences between the LEW and F344 rats in discounting rates, sensitivity to the immediacy of reinforcement, and estimates of the area under the curve. We concluded that impulsive choice can change as a function of learning and is not a static property of behavior that is mainly determined by genetic and neurochemical mechanisms. Choosing impulsively may be an advantage for organisms searching for food in rapidly changing environments.

Derived control by compound and single stimuli in a matching-to-sample task in children / Control derivado ejercido por estímulos compuestos y simples en una tarea de igualación a la muestra en niños

A matching-to-sample procedure was used to investigate whether 9-year-old children would demonstrate the emergence of a derived compound-sample conditional discrimination following training in four interrelated single-sample conditional discriminations and vice versa, as adults did in previous studies. In Experiment 1, three out of three children demonstrated the emergence of a compound-sample conditional discrimination following training in four single-sample conditional discriminations. In Experiment 2, two out of three children acquired a compound-sample conditional discrimination and they demonstrated the emergence of four single-sample conditional discriminations; one of them did so only after being exposed to a remediation training and testing procedure. Training variables that facilitated discrimination emergence in both directions are discussed. In general, results showed that the sophisticated learning skills that are supposedly possessed by adults are not required to demonstrate the two types of derived control under study (AU)

Se empleó un procedimiento de igualación a la muestra para investigar si niños de 9 años mostrarían la emergencia de una discriminación condicional de muestra compuesta a partir del entrenamiento de cuatro discriminaciones condicionales de muestra simple interrelacionadas, y viceversa, tal como hicieron participantes adultos en investigaciones previas. En el Experimento 1, tres de tres niños mostraron la emergencia de una discriminación condicional de muestra compuesta tras ser entrenados en cuatro discriminaciones condicionales de muestra simple. En el Experimento 2, dos de tres niños adquirieron una discriminación condicional de muestra compuesta y a continuación ambos mostraron la emergencia de cuatro discriminaciones condicionales de muestra simple; uno de ellos solo lo hizo tras haber sido expuesto a un procedimiento de entrenamiento y prueba específicamente diseñado para ello. Las características del entrenamiento que facilitaron la emergencia de discriminaciones en ambas direcciones son discutidas. En general, los resultados demostraron que las sofisticadas habilidades de aprendizaje que supuestamente poseen los adultos no son necesarias para mostrar el tipo de control de estímulos derivado que se estudió (AU)

Derived control by compound and single stimuli in a matching-to-sample task in children.

A matching-to-sample procedure was used to investigate whether 9-year-old children would demonstrate the emergence of a derived compound-sample conditional discrimination following training in four interrelated single-sample conditional discriminations and vice versa, as adults did in previous studies. In Experiment 1, three out of three children demonstrated the emergence of a compound-sample conditional discrimination following training in four single-sample conditional discriminations. In Experiment 2, two out of three children acquired a compound-sample conditional discrimination and they demonstrated the emergence of four single-sample conditional discriminations; one of them did so only after being exposed to a remediation training and testing procedure. Training variables that facilitated discrimination emergence in both directions are discussed. In general, results showed that the sophisticated learning skills that are supposedly possessed by adults are not required to demonstrate the two types of derived control under study.

Common control by compound samples in conditional discriminations.

We tested whether teaching control by single stimulus samples in conditional discriminations would result in common control of two-stimuli compound samples, and vice versa. In Experiment 1, 5 participants were first taught four single-sample conditional discriminations. The first conditional discrimination was as follows: given sample stimulus P1, select comparison stimulus A1 and not A2; given sample P2 select comparison A2 and not A1. The second conditional discrimination was as follows: given sample P1 select comparison B1 and not B2; given sample P2 select B2 and not B1. Different sample stimuli (Q1 and Q2) were used in the third and fourth conditional discriminations. Moreover, A1 and B1 were presented together as comparisons, such that, if Q1 was presented as the sample, A1 was correct and B1 was incorrect; and if Q2 was presented as the sample, B1 was correct and A1 was incorrect. A2 and B2 were also presented as comparisons. When Q1 was presented, A2 was correct and when Q2 was presented B2 was correct. After training with these four single stimulus sample discriminations, participants were tested with compound PQ samples presented with A1, A2, B1, and B2 as comparisons. If common control were established by the PQ stimuli, a participant would select A1 when P1Q1 was presented, A2 when P2Q1 was presented, B1 when P1Q2 was presented, and B2 when P2Q2 was presented. Such common control by PQ samples occurred in 4 of 5 participants. In Experiment 2, 4 participants were given reverse training. They were first taught to select the A1, A2, B1, and B2 stimuli in response to the appropriate PQ combinations and then probed on the single stimulus sample discriminations. All 4 participants were successful on this probe. Experiments 3 and 4 investigated the effects of teaching additional conditional discriminations with novel stimuli on subsequent transfer from the single-sample discriminations to performance on the compound-sample conditional discrimination.