Further Investigation of Responding Elicited by BC and C After A+, AB-, ABC+ Training

Two experiments with pigeons explored conditioned keypeck responding to new visual targets after visual compound discrimination training. In the first experiment, pigeons were trained with an A+, AB-, ABC+, AD-, ADC+ task, in which stimulus A signalled food, stimulus compounds AB and AD signalled no food, and stimulus compounds ABC and ADC signalled food. According to both an elemental model (Rescorla & Wagner, 1972) and a configural model (Pearce, 1987) of Pavlovian conditioning, test compounds BC and DC should elicit less responding than should C alone. However, the birds responded more to BC and DC than to C. In the second experiment, another set of pigeons was trained with an A+, AB-, ABC+, AD-, ADE+ task, in which stimulus A signalled food, stimulus compounds AB and AD signalled no food, and stimulus compounds ABC and ADE signalled food. Contrary to the prediction of the Rescorla-Wagner model, keypeck responding was not less on BC and DE trials than on C and E trials in testing. However, B and D attenuated responding to E and C, respectively, when presented in compounds BE and DC. The Pearce model was able to accommodate these results.     

Re-assessing causal accounts of learnt behavior in rats

Rats received either a common-cause (i.e., A→B, A→food) or a causal-chain training scenario (i.e., B→A, A→food) before their tendency to approach the food magazine during the presentation of B was assessed as a function of whether it was preceded by a potential alternative cause. Causal model theory predicts that the influence of an alternative cause should be restricted to the common-cause scenario. In Experiment 1, responding to B was reduced when it occurred after pressing a novel lever during the test phase. This effect was not influenced by the type of training scenario. In Experiment 2, rats were familiarized with the lever prior to test by training it as a potential cause of B. After this treatment, the lever now failed to influence test responding to B. In Experiment 3, rats given common-cause training responded more to B when it followed a cue that had previously been trained as a predictor of B, than when it followed another stimulus. This effect was not apparent in rats that received causal-chain training. This pattern of results is the opposite of that predicted by causal model theory. Thus, in three experiments, the presence of an alternative cause failed to influence test responding in manner consistent with causal model theory. These results undermine the application of causal model theory to rats, but are consistent with associative analyses.     

Perceptual learning enhances retrospective revaluation of conditioned flavor preferences in rats

Forward and backward blocking of taste preference learning was compared in rats. In the forward condition, thirsty rats were exposed to a flavor (A) in sucrose solution (+) or in water (-), after which they were exposed to A in compound with another flavor (B) in sucrose solution (i.e., AB+). In the backward condition, these phases were reversed. Consumption of B alone was assessed when rats were food deprived. In the forward condition, rats given A+ consumed less B than rats given A-, providing evidence of forward blocking, whereas in the backward condition, rats given A+ drank more of B than those given A-. Subsequent experiments found that alternating but not blocked preexposure to A and B, when given prior to training, produced blocking of B whether A+ was given before or after AB+, suggesting that prior failures to observe backward blocking reflect failures of discrimination.     

Summation: Further assessment of a configural theory

Rats received Pavlovian conditioning in which food was signalled by a visual stimulus, A+, an auditory stimulus, B+, and a compound composed of different visual and auditory stimuli, CD+. Test trials were then given with the compound AB. Experiments 1 and 2A revealed stronger responding during AB than during CD. In Experiment 2B, there was no evidence of a summation of responding during AB when A+ B+ training was conducted in the absence of CD+ trials. A further failure to observe abnormally strong responding during ABwas found in Experiment 3 for which the training trials with A+ B+ CD+ were accompanied by trials in which C and D were separately paired with food. The results are explained in terms of a configural theory of conditioning, which assumes that responding during a compound is determined by generalization from its components, as well as from other compounds to which it is similar.     

Effect of following an excitatory-inhibitory compound with an intermediate reinforcer

Pavlovian-conditioned inhibition training of the form A++, AB- (where ++ is a strong reinforcer and - is nonreinforcement) was conducted in 3 experiments with rats and 1 with pigeons. Then AB+ training was given (in which + is an effective reinforcer that is weaker than ++). The + reinforcer was achieved by reducing the frequency, lessening the amount, or lengthening the delay with which ++ was delivered. All 4 experiments found the AB+ treatment to enhance responding to both the excitatory A and the inhibitory B in comparison with untreated control stimuli. However, when appropriate assessments were made, the increase was more substantial for the inhibitory B. This pattern of results presents challenges for most current theories of associative learning.     

The role of nonreinforcement in the learning of honeybees

Two series of experiments with honeybees were designed to test the assumption that inhibition is generated by nonreinforcement as a function of the excitatory value of the context. In the first series (Experiments 1-3), summation tests with B were made after A+/C-/AB- as compared to A+/C-/CB- training, with precautions taken to minimize the possibility of a masking effect of excitatory within-compound conditioning on AB trials; responding to B did not vary with training procedure. In the second series (Experiments 4-5), retardation tests rather than summation tests were used, in the belief that they might be more sensitive; after A+/AB-/CD- training, acquisition in a B+/D- problem was found to be no less rapid than in a D+/B- problem. A third series of experiments (Experiments 6-9) was designed to test the more general assumption that the effectiveness of nonreinforcement increases with the excitatory value of the context; response to B was found to be no different after A+/B+/C- training followed by A+/AB- training than after A+/B+/C- training followed by A+/CB- training. The results are compatible with the view that the role of nonreinforcement in honeybees is not to generate inhibition, but only to reduce excitation in a manner independent of the excitatory value of the context.     

Configural associations in discrimination learning

In 4 experiments, Sprague-Dawley rats and homing pigeons received training with an A+ AB0 BC+ discrimination, in which food (+) accompanied trials with A and BC. Food was not presented (0) on trials with the compound AB. Subsequent test trials revealed that responding during C by itself, or the compound ABC, was slower than during either A or BC. Responding during the ABC compound was also found to be slower after training with the A+ AB0 BC+ than an A0 AB+ BC+ discrimination. We argue that these findings demonstrate the importance of configural associations in discrimination learning. Two accounts for the way in which these associations exert their influence are considered.     

Overshadowing and associability change

Three appetitive Pavlovian conditioning experiments with rats examined the associability of stimuli A and B that had a history of compound conditioning (AB+), relative to stimuli X and Y that had a history of conditioning in isolation (X+, Y+). Following this training, Experiment 1 revealed that conditioned responding was higher to X and Y than to A and B (overshadowing). In a subsequent AY+, AX-, BY- test discrimination, the AY/BY discrimination was solved more readily than the AY/AX discrimination. In Experiment 2, following AB+, X+, Y+ training, A and Y were presented as a compound and signaled the availability of reinforcement upon the performance of an instrumental response. Test trials in which A and Y were presented alone, and in extinction, revealed that A acquired greater control of instrumental responding than Y. Experiment 3 revealed that following AB+, X+, Y+ training, A and B served as more effective discriminative stimuli for instrumental responding than X and Y. Overall, these results imply that the associability of stimuli conditioned in compound is higher than stimuli conditioned in isolation. These results are discussed in terms of attentional theories of associative learning.     

Summation effects in human learning: evidence from patterning discriminations in goal-tracking

Participants in two human goal-tracking experiments were simultaneously trained with negative patterning (NP) and positive patterning (PP) discriminations (A+, B+, AB–, C–, D–, CD+). Both elemental and configural models of associative learning predict a PP advantage, such that NP is solved less readily than PP. However, elemental models like the unique cue approach additionally predict responding in AB– trials to be initially stronger than that in A+ and B+ trials due to summation of associative strength. Both experiments revealed a PP advantage and a strong summation effect in AB– trials in the first half of the experiments, irrespective of whether the same US was used for both discriminations (Experiment 1) or two different USs (Experiment 2). We discuss that the correct predictions of the unique cue approach are based on its assumptions of non-normalized and context-independent stimulus processing rather than elemental processing per se.     

Similarity and Discrimination Learning

The role played by similarity in discrimination learning was examined in four experiments using compound stimuli. In Experiment 1, pigeons received training in which food was presented after stimulus A, compound AB, but not compound ABC—A+ BC+ ABCo. The A+ ABCo discrimination was acquired more readily than was the BC+ ABCo discrimination. In the remaining experiments, training was of the form, A+ B+ C+ AB+ AC+ BC+ ABCo. The discrimination between the single stimuli A+ B+ C+ and ABCo consistently developed more readily than between the pairs of stimuli AB+ AC+ BC+, and ABCo. The results are shown to be more consistent with a configural than with an elemental theory of conditioning.     

Changes in cue associability across training in human causal learning

A series of experiments studied the amount learned about two food cues (A and B) whose presentation in a meal was followed by an allergy (+) in a fictitious patient. Participants were trained with A+ and C+ in Phase 1 and then with AB+ or AB++ in Phase 2. Subsequent testing revealed that BC was more allergenic than AD, showing that more had been learned about B than A in Phase 2. Participants were also trained with A+, then with AB+, and finally with AB++. The results of interpolating AB+ between A+ and AB++ training were consistent with the hypothesis that pretraining with Cue A selectively suppressed attention to its associate across the AB+ trials and, thereby, reduced the amount subsequently learned about B on AB++ trials.     

Retrospective revaluation effects following serial compound training and target extinction

Using a conditioned suppression task, two experiments examined retrospective revaluation effects after serial compound training in a release from overshadowing design. In Experiment 1, serial X → A+ training produced suppression to target A, which was enhanced when preceded by feature X, whereas X by itself elicited no suppression. Subsequent A− presentations extinguished responding to A, but had no effect on either responding to X → A or X alone. However, the addition of A− trials did enhance the ability of feature X to elicit suppression to a novel target, B, suggesting retrospective revaluation of X’s properties. Experiment 2 showed that the enhanced transfer effect, observed in Experiment 1, was independent of the training history of the target (B− or Y → B+/B−). Together, these results suggest that feature X did not retrospectively acquire excitatory strength or occasion setting power, but rather a generalized ability to increase responding to any other cue.     

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.     

Superconditioning from a reduced reinforcer

In four autoshaping experiments pigeons received conditioned inhibition training of the form A++, AB-, where ++ is a strong reinforcer and - is nonreinforcement. Subsequent AB+ training, in which + is a moderate reinforcer, resulted in enhanced conditioning of A, relative to an A stimulus receiving no treatment, one receiving A+ treatment, and one receiving A++ treatment. This enhancement of conditioning to Aconstitutes a demonstration of “superconditioning”. The presence of the inhibitory B sufficiently enhanced the reinforcing power of the moderate reinforcer (+) that it was able to further increase the excitation controlled by A. This occurred even though A had previously been paired with a stronger reinforcer (++). Superconditioning was also observed when A and B were extinguished prior to treatment with + or were originally neutral stimuli followed by + in the presence of an inhibitor trained elsewhere.     

Conditions favoring superconditioning of irrelevant conditioned stimuli

Three appetitive conditioning experiments with rats found partial learning of complex XA+, XB+, XAB- (+ stands for reinforced; - stands for unreinforced) negative patterning discriminations with intermixed A+ and B+ trials (Experiment 1). AB+ trials (Experiment 2), and A+, B+, and AB+ trials (Experiment 3). In all experiments, differential responding emerged more slowly during the learning of the negative patterning discriminations than during learning of the XA+, XB+, XC- control discriminations. Additionally, the negative patterning groups responded more to X than to a separately reinforced Y on unreinforced test trials: thus, X derived superexcitatory properties. This pattern was reversed in the control groups. Results are consistent with theories that allow for different activation patterns when elements are combined.     

The Effect of Stimulus Preexposure on Responding during a Compound Stimulus

In two experiments with rats, three stimuli, A, B, and X, were used for an AX+ BX+ Xo discrimination in which food was presented after the simultaneous presentation of A and X, or B and X, but never after X by itself. For one group in each experiment, X was repeatedly presented by itself before the start of discrimination training. This manipulation weakened responding on test trials in which the three stimuli were presented together. The results are interpreted in terms of a configural theory of conditioning that assumes that preexposure to a stimulus will reduce its capacity to promote generalization among different configurations to which it belongs.     

Stimulus control of Pavlovian facilitation

Two experiments were conducted using an autoshaping procedure with pigeons to examine whether dimensional stimulus control by a Pavlovian facilitator parallels the control established following operant discrimination training. Facilitation training consisted of the presentation of a black vertical line on a white background as the B stimulus in a feature-positive discrimination in which the A stimulus (white keylight) was followed by grain presentation only if preceded by B. In this way, B facilitates or sets the occasion for pecking at A. Subsequent testing for generalization along the line-orientation dimension produced decremental gradients when the facilitation paradigm incorporated an explicit feature-negative stimulus (B−). These results parallel the decremental control obtained following operant discrimination training and suggest that Pavlovian facilitators and instrumental discriminative stimuli are functionally equivalent.     

Representational blending in human conditional learning: Implications for associative theory.

In two experiments, participants were presented with pictures of different foods (A, B, C, D, X,) and learned which combinations resulted in an allergic reaction in a fictitious patient, Mr X. In Problem 1, when A or B (but not C or D) was combined with food X an allergic reaction occurred, and when C or D (but not A or B) was combined with Y an allergic reaction occurred. In Experiment 1, participants also received Problem 2 in which A, B, C, and D interacted with foods V and W either in the same way as X and Y, respectively, or in a different way. Participants performed more proficiently in the former than in the latter condition. In Experiment 2, after training on Problem 1, participants judged whether or not novel combinations of foods (e.g., AB, CD, AD, CB) would cause an allergic reaction in Mr X. They were no more likely to indicate that AB or CD would cause an allergic reaction than AD or CB, but made their judgements more rapidly and with greater confidence on AB and CD trials than on AD and CB trials. These results (1) indicate that shared representations come to be addressed by the components of similar compounds (e.g., AX and BX) that have predicted the same outcome (an allergic reaction), and (2) are inconsistent with standard, associative theories of learning, but (3) are consistent with findings from nonhuman animals and with a connectionist interpretation of these findings.     

A dissociation between causal judgment and outcome recall

It has been suggested that causal learning in humans is similar to Pavlovian conditioning in animals. According to this view, judgments of cause reflect the degree to which an association exists between the cause and the effect. Inferential accounts, by contrast, suggest that causal judgments are reasoning based rather than associative in nature. We used a direct measure of associative strength, identification of the outcome with which a cause was paired (cued recall), to see whether associative strength translated directly into causal ratings. Causal compounds AB+ and CD+ were intermixed with A+ and C- training. Cued-recall performance was better for cue B than for cue D; thus, associative strength was inherited by cue B from the strongly associated cue A (augmentation). However, the reverse was observed on the causal judgment measure: Cue B was judged to be less causal than D (cue competition). These results support an inferential over an associative account of causal judgments.     

No time-stretching illusion when a tone is followed by a noise

A sine tone is perceived as longer when it is preceded by a more intense noise than when presented in isolation. This is the time-stretching illusion. We conducted an experiment where the method of constant stimuli was used to examine whether a tone would also be stretched when it was followed by a noise. The duration of a tone was overestimated when it was preceded by a noise, but not when followed by a noise or when located between two consecutive noises. Moreover, the increasing of the noise intensity (from ?6 to +6 dB) relative to the tone intensity resulted in larger overestimations, but only in the condition where a tone was preceded by a noise. In brief, the duration of a tone is stretched when this tone is preceded by a noise and if this tone is not followed by a noise.