Proactive interference between cues trained with a common outcome in first-order Pavlovian conditioning

The nature of interference between cues (X, A) trained apart with a common outcome (O; an unconditioned stimulus) was explored by assessing proactive interference in first-order Pavlovian conditioning (i.e., A-O, X-O, resulting in attenuated responding to X). Three lick-suppression studies were conducted with water-deprived rats. Posttraining extinction of the interfering cue (A) attenuated proactive interference (Experiment 1), which mirrors the observation that extinction of the competing cue can reduce competition between cues trained together (e.g., recovery from overshadowing). Proactive interference was also attenuated with manipulations known to attenuate interference between outcomes trained apart (e.g., counterconditioning), namely reminder cues (Experiment 2) and renewal (Experiment 3). The findings suggest that similar processes underlie interference between cues trained apart, between cues trained together, and between outcomes trained apart.     

Interference between Elementally Trained Stimuli Can Take Place in One Trial

Recent research has shown that the acquisition of a second cue–outcome association can interfere with responding appropriate to a previously acquired association between another cue and the same outcome, even if the two cues had never received compound training (Matute & Pineño, 1998a). This is similar to other results in the paired-associate literature but it is problematic for associative theories of learning because all of them assume that compound training is necessary for cues to interfere with each other. However, given several assumptions, a recent revision of Wagner's (1981) SOP model proposed by Dickinson and Burke (1996) could account for most of the data available on interference between elementally trained cues. According to the modified SOP model, the target cue that is paired with the outcome during Phase 1 could acquire an inhibitory association with the outcome during the Phase 2 trials in which the interfering cue is trained and the target cue is absent. This inhibitory association could be responsible for the weak responding observed to the target cue during testing because it could interfere with the excitatory association acquired during Phase 1. If this is true, interference should be weaker as the number of Phase 2 interfering trials is reduced. However, the three experiments reported here show that interference can occur even when only one interfering trial is given during Phase 2. The results of these experiments, along with other results in the literature, add support to the idea that interference between elementally trained cues occurs during retrieval and that it is not due to the formation of inhibitory associations between an absent cue and the outcome.     

Contrasting reduced overshadowing and blocking

Preexposure of a cue without an outcome (X-) prior to compound pairings with the outcome (XZ-->O) can reduce overshadowing of a target cue (Z). Moreover, pairing a cue with an outcome (X-->O) before compound training can enhance its ability to compete with another cue (i.e., blocking). Four experiments were conducted in a conditioned bar-press suppression preparation with rats to determine whether spacing of the X- or X-->O trials would differentially affect reduced overshadowing and blocking. Experiment 1a showed that reduced overshadowing was larger with massed trials than with spaced trials. Experiment 1b found that blocking was larger with spaced trials than with massed trials. Experiments 2a and 2b indicated that these effects of trial spacing were both mediated by the associative status of the context at test. The results are interpreted in the framework of contemporary learning theories.     

Curved saccade trajectories reveal conflicting predictions in associative learning

We report how the trajectories of saccadic eye movements are affected by memory interference acquired during associative learning. Human participants learned to perform saccadic choice responses based on the presentation of arbitrary central cues A, B, AC, BC, AX, BY, X, and Y that were trained to predict the appearance of a peripheral target stimulus at 1 of 3 possible locations, right (R), mid (M), or left (L), in the upper hemifield. We analyzed as measures of associative learning the frequency, latency, and curvature of saccades elicited by the cues and directed at the trained locations in anticipation of the targets. Participants were trained on two concurrent discrimination problems A+R, AC+R, AX+M, X+M and B+L, BC+L, BY+M, Y+M. From a connectionist perspective, cues were predicted to acquire associative links connecting the cues to the trained outcomes in memory. Model simulations based on the learning rule of the Rescorla and Wagner (1972) model revealed that for some cues, the prediction of the correct target location was challenged by the interfering prediction of an incorrect location. We observed that saccades directed at the correct location in anticipation of the target curved away from the location that was predicted by the interfering association. Furthermore, changes in curvature during training corresponded to predicted changes in associative memory. We propose that this curvature was caused by the inhibition of the incorrect prediction, as previously has been suggested with the concept of distractor inhibition (Sheliga, Riggio, & Rizzolatti, 1994; Tipper, Howard, & Houghton, 2000). The paradigm provides a new method to examine memory interference during associative learning.     

Associative history affects the associative change undergone by both presented and absent cues in human causal learning

R. A. Rescorla (2000) noted that a number of influential theories of associative learning do not take the associative history of cues (i.e., the prior training that they have received) into account when calculating the associative change undergone by those cues. The authors tested this assumption in a human causal learning paradigm and found associative history to be an important determinant of the learning undergone by cues that are presented on a trial. Moreover, associative history was also found to influence the amount of retrospective revaluation undergone by absent cues. These findings conflict with models of causal learning in which the associative change undergone by an element of a cue compound is governed by a summed error term (e.g., R. A. Rescorla & A. R. Wagner, 1972).     

The role of interference produced by conflicting associations in contextual control

In 2 experiments, participants completed a computer task in which they judged the probability of outcomes occurring (e.g., flowers growing, a bug infestation) given cues (e.g., treatment of soil with a fictitious garden product). In each 2-phase experiment, cue X was associated with 1 outcome in Phase 1 and with a 2nd outcome in Phase 2. When the outcome in Phase 1 (e.g., X led to a bug infestation) was replaced in Phase 2 (e.g., X led to flowers growing), contextual control was observed (Experiments 1 and 2). Information learned in each phase was less likely to be retrieved when the cue was tested in a context different from the 1 where training occurred. When the 2nd outcome did not conflict with information acquired in the 1st phase (e.g., X led to flowers and bugs), no contextual control was observed (Experiment 2). Acquiring a 2nd association to X resulted in contextual control only when it conflicted with an association learned earlier. The authors discuss the role of interference produced when conflicting information is acquired in establishing contextual control.     

The basic laws of conditioning differ for elemental cues and cues trained in compound

The cue-duration effect (i.e., longer cues result in less conditioned responding than shorter cues) was examined as a function of whether cues were trained alone or in compound. Compound (AX) or elemental (X) cues of either long or short duration were paired with the unconditioned stimulus. In testing with X alone, the cue-duration effect was observed with elementally trained cues, but not with compound cues. Instead, stronger responding resulted from training with long compound cues relative to short compound cues (i.e., a reversed cue-duration effect). Moreover, an overshadowing effect (i.e., decreased responding due to compound conditioning) was observed when conditioning was conducted with a short cue, but compound conditioning resulted in enhanced responding when it was conducted with a long cue (i.e., reversed overshadowing). These findings are consistent with other recent demonstrations that some laws of learning that apply to elementally trained cues do not similarly apply to cues trained in compound.     

Outcome maximality and additivity training also influence cue competition in causal learning when learning involves many cues and events

Recent evidence shows that outcome maximality (e.g., De Houwer, Beckers, & Glautier, 2002) and additivity training (e.g., Lovibond, Been, Mitchell, Bouton, & Frohard, 2003) have an influence on cue competition in human causal learning. This evidence supports the idea that cue competition is based on controlled reasoning processes rather than on automatic associative processes. Until now, however, all the evidence for controlled reasoning processes comes from studies with rather simple designs that involved only few cues and events. We conducted two experiments with a complex design involving 24 different cues. The results showed that outcome maximality and additivity training had an influence on cue competition but that this influence was more pronounced for forward cue competition than for retrospective cue competition.     

Recovery from blocking between outcomes

Contemporary associative learning research largely focuses on cue competition phenomena that occur when 2 cues are paired with a common outcome. Little research has been conducted to investigate similar phenomena occurring when a single cue is trained with 2 outcomes. Three conditioned lick suppression experiments with rats assessed whether treatments known to alleviate blocking between cues would also attenuate blocking between outcomes. In Experiment 1, conditioned responding recovered from blocking between outcomes when a long retention interval was interposed between training and testing. Experiment 2 obtained recovery from blocking between outcomes when the blocking outcome was extinguished after the blocking treatment. In Experiment 3, a recovery from blocking between outcomes occurred when a reminder stimulus was presented in a novel context prior to testing. Collectively, these studies demonstrate that blocking of outcomes, like blocking of cues, appears to be caused by a deficit in the expression of an acquired association.     

The hide-and-seek of retrospective revaluation: recovery from blocking is context dependent in human causal learning

In a typical blocking procedure, pairings of a compound consisting of 2 stimuli, A and X, with the outcome are preceded by pairings of only A with the outcome (i.e., A+ then AX+). This procedure is known to diminish responding to the target cue (X) relative to a control group that does not receive the preceding training with blocking cue A. We report 2 experiments that investigated the effect of extinguishing a blocking cue on responding to the target cue in a human causal learning paradigm (i.e., A+ and AX+ training followed by A- training). The results indicate that extinguishing a blocking cue increases conditioned responding to the target cue. Moreover, this increase appears to be context dependent, such that increased responding to the target is limited to the context in which extinction of the blocking cue took place. We discuss these findings in the light of associative and propositional learning theories.     

Context-outcome associations mediate context-switch effects in a human predictive learning task

Four experiments explored the role of contexts in information retrieval after different levels of acquisition training in human predictive learning. Participants were trained where cue (X) was followed by an outcome in context A while a different cue (Y) was followed by the absence of the outcome in context B. When 4 training trials with each cue were conducted, testing the stimuli in the alternative contexts decreased predictive judgments to X and increased predictive judgments to Y. These effects disappeared both when training was increased up to 18 trials (Experiments 1a and 1b), and when the outcome was presented in both contexts A and B (Experiments 2 and 4). When the outcome was presented in both contexts, the nonreinforced cue Y, trained in the presumably excitatory context B, became a conditioned inhibitor (Experiment 3). Additional experience with one of the contexts, but not with both, made the context-switch effect reappear (Experiment 4). These results suggest that irrelevant contexts may enter into direct associations with the outcome before prolonged training leads participants to discard them as predictors.     

Backward blocking: The role of within-compound associations and interference between cues trained apart

Most theoretical accounts of backward blocking place heavy stress on the necessity of the target cue having been trained in compound with the competing cue to produce a decrement in responding. Yet, other evidence suggests that a similar reduction in responding to the target cue can be observed when the outcome is later paired with a novel cue never trained in compound with the target cue (interference between cues trained apart). The present experiment shows that pairing another nonassociated cue with the same outcome may be sufficient to produce a decremental effect on the target cue, but the presence of a within-compound association between the target and the competing cue adds to this effect. Thus, both interference between cues trained apart and within-compound associations independently contribute to backward blocking.     

Backward blocking: the role of within-compound associations and interference between cues trained apart

Most theoretical accounts of backward blocking place heavy stress on the necessity of the target cue having been trained in compound with the competing cue to produce a decrement in responding. Yet, other evidence suggests that a similar reduction in responding to the target cue can be observed when the outcome is later paired with a novel cue never trained in compound with the target cue (interference between cues trained apart). The present experiment shows that pairing another nonassociated cue with the same outcome may be sufficient to produce a decremental effect on the target cue, but the presence of a within-compound association between the target and the competing cue adds to this effect. Thus, both interference between cues trained apart and within-compound associations independently contribute to backward blocking.     

Partial reinforcement and context switch effects in human predictive learning

Human participants were trained in a trial-by-trial contingency judgements task in which they had to predict the probability of an outcome (diarrhoea) following different cues (food names) in different contexts (restaurants). Cue P was paired with the outcome on half of the trials (partial reinforcement), while cue C was paired with the outcome on all the trials (continuous reinforcement), both cues in Context A. Test was conducted in both Context A and a different but equally familiar context (B). Context change decreased judgements to C, but not to P (Experiment 1). This effect was found only in the cue trained in the context where a different cue was partially reinforced (Experiment 2). Context switch effects disappeared when different cues received partial reinforcement in both contexts of training (Experiment 3). The implications of these results for an explanation of context switch effects in terms of ambiguity in the meaning of the cues prompting attention to the context (e.g., Bouton, 1997) are discussed.     

A comparison between elemental and compound training of cues in retrospective revaluation

Associative learning theories assume that cue interaction and, specifically, retrospective revaluation occur only when the target cue is previously trained in compound with the to-be-revalued cue. However, there are recent demonstrations of retrospective revaluation in the absence of compound training (e.g., Matute & Pine?o, 1998a, 1998b). Nevertheless, it seems reasonable to assume that cue interaction should be stronger when the cues are trained together than when they are trained apart. In two experiments with humans, we directly compared compound and elemental training of cues. The results showed that retrospective revaluation in the elemental condition can be as strong as and, sometimes, stronger than that in the compound condition. This suggests that within-compound associations are not necessary for retrospective revaluation to occur and that these effects can possibly be best understood in the framework of general interference theory.     

Partial reinforcement and context switch effects in human predictive learning

Human participants were trained in a trial-by-trial contingency judgements task in which they had to predict the probability of an outcome (diarrhoea) following different cues (food names) in different contexts (restaurants). Cue P was paired with the outcome on half of the trials (partial reinforcement), while cue C was paired with the outcome on all the trials (continuous reinforcement), both cues in Context A. Test was conducted in both Context A and a different but equally familiar context (B). Context change decreased judgements to C, but not to P (Experiment 1). This effect was found only in the cue trained in the context where a different cue was partially reinforced (Experiment 2). Context switch effects disappeared when different cues received partial reinforcement in both contexts of training (Experiment 3). The implications of these results for an explanation of context switch effects in terms of ambiguity in the meaning of the cues prompting attention to the context (e.g., Bouton, 1997) are discussed.     

Representation-mediated Inhibitory Learning in the Conditioned-suppression Procedure

In three experiments, rats in group I (for intermixed) were given non-reinforced exposure to two compound stimuli, AX and BX, where A and B represent different auditory cues, and X represents a visual cue. AX and BX were presented in alternation. Group B (blocked) received similar exposure except that subjects experienced a block of AX trials and then a block of BX trials. Subsequent shock reinforcement of A was found to endow B with inhibitory strength in group I, as assessed by retardation (Experiments 1 and 2) and summation tests (Experiment 3). This outcome confirms and extends the results reported by Espinet, Iraola, Bennett, and Mackintosh (1995) and constitutes a further example of mediated learning in which the associative strength of a stimulus is found to be modified as a consequence of training given to some other event with which that stimulus is associated.     

Does the type of judgement required modulate cue competition?

According to the comparator process hypothesis (Matute, Arcediano, & Miller, 1996), cue competition in the learning of between-events relationships arises if the judgement required involves a comparison between the probability of the outcome given the target cue and the probability of the outcome given the competing cue. Alternatively, other associative accounts (the Rescorla-Wagner model: Rescorla &Wagner, 1972) conceive cue competition as a learning deficit affecting the target cue-outcome association. Consequently, the comparator process hypothesis predicts that cue competition occurs in inference judgements but not in contiguity ones, for only the first type of judgement implicitly involves such a comparison. On the other hand, the Rescorla-Wagner model predicts cue competition in both inference and contiguity judgements, because it establishes no relevant role for the type of judgement in producing cue competition. In Experiments 1 and 2 we manipulated the relative validity of cues and the type of question (inference vs. contiguity) in a predictive learning task. In both experiments we found a cue competition effect, but no interaction between the relative validity of cues and the type of question, suggesting that the Rescorla-Wagner theory suffices to explain cue competition.     

Overshadowing in operant conditioning as a function of discriminability

Pigeons were trained in an operant, go/no-go, discrimination by successive presentations of discrete, positive and negative trials. In separate groups, the rate of discriminaion learning based on an auditory cue, on visual cues of different discriminability, and on combined auditory and visual cues was determined. The auditory cue was tone/no-tone, the visual cue was a difference in brightness level on the key. Following discrimination training, stimulus control was tested in extinction by presenting tone or notone at each of four key-brightness levels.Learning was more rapid with two cues than with either cue singly, demonstrating summation. The contribution made by the tone cue to the learning of the discrimination decreased with increasing discriminability of the light cue. The control exerted by the tone cue also decreased (i.e., the tone cue was overshadowed) with increasing discriminability of the light cue. In certain cases, the tone cue decreased control by brightness, showing that in two-cue discriminations each cue may reduce the control exerted by the other.     

Asymmetries in cue competition in forward and backward blocking designs: Further evidence for causal model theory

A hallmark feature of elemental associative learning theories is that multiple cues compete for associative strength when presented with an outcome. Cue competition effects have been observed in humans, both in forward and in backward blocking procedures (e.g., Shanks, 1985) and are often interpreted as evidence for an associative account of human causal learning (e.g., Shanks & Dickinson, 1987). Waldmann and Holyoak (1992), however, demonstrated that cue competition only occurs in predictive, and not diagnostic, learning paradigms. While unexplainable from an associative perspective, this asymmetry readily follows from structural considerations of causal model theory. In this paper, we show that causal models determine the extent of cue competition not only in forward but also in backward blocking designs. Implications for associative and inferential accounts of causal learning are discussed.