Are associative changes in acquisition and extinction negatively accelerated?

Performance to a conditioned stimulus typically shows a negatively accelerated change with Pavlovian conditioning or extinction. This is commonly attributed to negatively accelerated changes in the underlying associative learning. However, the absence of well-specified rules for mapping learning into performance makes it difficult to infer changes in the size of associative changes for stimuli occupying different points on the performance scale. This problem can be addressed by comparing responding to stimulus compounds each consisting of 2 stimuli, 1 of which is poorly conditioned and 1 of which is well conditioned, when either the former or the latter receives a specified amount of additional training. This permits comparison at a common performance level. Two magazine-approach experiments in rats and 2 autoshaping experiments in pigeons used this technique to assess the form of the associative changes in acquisition and extinction.

Retraining of extinguished Pavlovian stimuli.

Five Pavlovian magazine approach experiments with rat subjects examined the mechanisms by which reconditioning restores extinguished responding. Experiments 1, 2, and 3 found that retraining did not destroy the spontaneous recovery with the passage of time that is characteristic of extinguished stimuli. Experiments 4 and 5 found evidence that retaining after extinction enhanced the strength of the originally trained associations. Together these results suggest that, just as extinction does not destroy original acquisition but superimposes some decremental process, so retraining does not destroy that decremental process but instead superimposes further associative learning.

Unequal associative changes when excitors and neutral stimuli are conditioned in compound.

In four experiments a compound of a previously conditioned excitor and a neutral stimulus was either reinforced with food or nonreinforced. Two experiments used a magazine approach procedure in rats, and two used an autoshaping procedure in pigeons. All experiments employed a novel compound test procedure, which permitted evaluation of the size of the associative change that took place for the excitatory and neutral stimuli. Reinforcement of the compound resulted in greater increments in the associative strength of the neutral stimulus than of the excitor. Nonreinforcement of the compound resulted in greater decrements in the associative strength of the excitor than of the neutral stimulus. These results agree with earlier experiments with compounds of excitors and inhibitors and provide an additional challenge to contemporary error-correction models of conditioning.

Associative changes with a random CS-US relationship.

Three experiments examined conditioned magazine approach in rats when a positive unconditioned stimulus (US) bore a random relation to a conditioned stimulus (CS). Experiment 1 found that over the course of conditioning the CS initially elevated responding relative to the baseline but then lost the power to do so. Transfer tests revealed that a CS-US association developed early and persisted despite the decline in magazine responding. Experiment 2 confirmed the persistence of CS-US associations and found them to be more substantial when a different US occurred during the CS than in its absence. In Experiment 3, when the situation was exposed to US-alone presentations prior to introducing the CS, there was little evidence that a subsequent random relation between the CS and US produced an association between them. These results agree with those of blocking and overshadowing experiments using discrete CSs and support an interpretation of the random procedure in terms of competition between the background and CS for conditioning.

Associative changes in excitors and inhibitors differ when they are conditioned in compound.

When an AB stimulus compound is reinforced or nonreinforced, there are associative changes in both A and B elements. In many contemporary theories those changes are viewed as governed by a common error term, computed as the discrepancy between the total associative strength of the AB compound and that supported by the trial consequence. This implies that if A and B are equally salient, then the magnitude of their associative change should be the same, whatever their strengths prior to the AB trial. This implication was explored for a compound consisting of an excitatory A and an inhibitory B. A novel assessment procedure avoided the difficulty of making comparisons at different locations on the performance scale. Three experiments using a magazine approach preparation in rats and 3 using autoshaping in pigeons found evidence contradicting this implication. The excitatory A changed less than the inhibitory B when the compound was reinforced but more than B when the compound was nonreinforced.

Extinction can be enhanced by a concurrent excitor.

Five experiments used rat subjects to investigate the impact on extinction of the presence of other conditioned stimuli. In Experiments 1 (Pavlovian magazine approach) and 2 (instrumental discriminative training), an excitatory stimulus (X) was extinguished alone, in conjunction with a previously reinforced other stimulus (A), in conjunction with previously nonreinforced other stimulus (B), or it was spared extinction. Responding during extinction was greatest to AX, and subsequent testing of X alone showed AX extinction to have produced the most decrement to X. Experiment 3 found similar results using a within-subject design. Experiment 5 continued separate reinforced presentations of A during extinction. This procedure not only promoted extinction of X but also converted it into a conditioned inhibitor. These experiments bear on the mechanisms of overshadowing and stimulus processing, as well as provide information on the determinants of extinction.

Associative changes in elements and compounds when the other is reinforced.

Four experiments investigated the symmetry of associative changes in stimulus compounds and elements in a Pavlovian conditioned magazine-approach situation with rats. Experiment 1 used multiple groups to examine the associative changes in a conditioned element (A) as a result of its subsequent reinforcement in compound with a neutral X. These were compared with the changes in an AX compound when one of its elements (A) was subsequently reinforced alone. Although reinforcing A enhanced responding to the AX compound, compared with a control compound, reinforcing AX failed to enhance responding to A, compared with a control element. Experiments 2 and 3 made similar comparisons in a fully within-subject design, finding greater changes in a previously trained AX compound when A was subsequently conditioned than in a B element when BY was subsequently conditioned. Experiment 4 found associative decrements in A when it was reinforced in the presence of a moderately conditioned X. The results observed in each of these experiments are more consistent with an elemental model of conditioning than with a recently proposed configural model.

A note on depression of instrumental responding after one trial of outcome devaluation.

After a response has been rewarded with an outcome, subsequent devaluation of that outcome by the toxin LiCl reduces responding. Balleine and Dickinson (1991) argued that this effect depends on incentive learning, which requires reexposure to the outcome after its pairing with the toxin. However, Rescorla (1992) reported that a single pairing of the outcome with LiCl was sufficient to depress responding even without reexposure. This result has been attributed by Balleine and Dickinson (1992) to the use of a hypertonic solution. Two experiments are reported here which replicate the prior single trial effect using an equivalent level of toxin in an isotonic solution.

Control of instrumental performance by Pavlovian and instrumental stimuli.

Two experiments used rats to examine the transfer of control of a stimulus to a new instrumental response. That transfer was successful to the degree that the stimulus and the response shared a common outcome. The transfer was more substantial, however, when the stimulus signaled the availability of that outcome for another instrumental response compared with signaling its occurrence in a Pavlovian manner. That result suggests that the stimulus-outcome associations formed during instrumental training are not reducible to a Pavlovian association.

Depression of an instrumental response by a single devaluation of its outcome.

In three experiments rats were trained to make two different instrumental responses for different outcomes. Then the outcomes were given a single differential conditioning experience with lithium chloride. That differential treatment was sufficient to produce differential instrumental responding in a subsequent test. Re-exposure to the devalued outcome was not necessary for an impact on instrumental performance.

Evidence for an association between the discriminative stimulus and the response-outcome association in instrumental learning.

In 4 experiments, rats received 1 of several outcomes for engaging in various instrumental responses in the presence of discriminative stimuli. Discriminative stimuli shared some response-outcome relations but not others. When a response was subsequently extinguished in the presence of 1 discriminative stimulus, that produced relatively more decrement in responding in other stimuli that shared the same response-outcome relation. Other discriminative stimuli, in the presence of which that response had been reinforced by other outcomes and in which the original outcome had reinforced another response, were less affected. Moreover, postextinction devaluation of that outcome suggested that the particular response-outcome relation extinguished had undergone decrement. These results suggest that discriminative stimuli have relatively specific associations with the response-outcome relations that obtain in their presence.

The role of information about the response-outcome relation in instrumental discrimination learning.

In 4 instrumental learning experiments, the hierarchical organization among responses (R), outcomes (O), and stimuli (S) was examined. Each experiment explored the possibility that S becomes associated with the R-O relation by providing information about that relation. In each case, an analogy was developed to a paradigm that has been important for concluding that informational relations affect Pavlovian conditioning. Experiments 1 and 2 found an effect of the information that S provides about the R-O relation, using paradigms analogous to blocking and contingency experiments. Experiments 3 and 4 demonstrated a similar result, using a paradigm like that of relative validity. In each case, the experiments pointed to the importance of the information that S gives about the R-O relation, rather than about the individual R and O elements.

Effect of reinforcer devaluation on discriminative control of instrumental behavior.

Two experiments examined the effect of reinforcer devaluation on the ability of a discriminative stimulus (Sd) to control instrumental behavior in Sprague-Dawley rats. In Experiment 1 reinforcer devaluation reduced, but did not eliminate, the ability of the Sd to control performance of the original response and to transfer its control to a new response trained with the same reinforcer. The effect of devaluation was more complete in Experiment 2, in which the reinforcer was delivered directly into the oral cavity. However, retraining the response with a different reinforcer partially restored the ability of the Sd to control performance of that response. These results suggest that an Sd may not augment its trained responses when the reinforcer has been completely devalued but may promote responses with which it shares a reinforcer, as long as those responses are associated with some reinforcer that retains its value. The implications of these results for the way that discriminative stimuli control instrumental behavior are discussed.

Analysis of the unique cue in configural discriminations.

Four experiments used an autoshaping procedure with pigeons to investigate the basis of configural discriminations. The elements of both a negative patterning (A+, B+, AB-) and a conditional discrimination (AC+, BD+, AD-, BC-) were paired, in a second-order procedure with two new key lights, X and Y. Responding was then tested to X and Y presented in compound with each other and with A and B. The pattern of responding to compounds containing X and Y was like the pattern of responding to compounds containing their associates, A and B. This suggests that A and B can be replaced by their associates without disrupting responding to their compounds. Because X and Y are physically different from A and B, this in turn suggests that any unique cue controlling responding to their compounds does not depend on the physical presence of the component stimuli. Instead the unique stimulus appears to arise from the joint activation of memory representations.

Effect of a stimulus intervening between CS and US in autoshaping.

Five experiments explored the effect of placing a stimulus between the termination of a key light CS and the onset of a food US in an autoshaping preparation with pigeon subjects. Whether that stimulus was itself a key light evoking pecking or an auditory event failing to evoke pecking, it facilitated performance to the key light CS. The use of a within-subjects design made differential conditioning of background cues and stimulus generalization unlikely accounts. Experiment 3 found that extinction of the intervening stimulus did not remove the facilitative effect. Experiment 4 found that pairing the CS with food and the intervening stimulus did not produce the effect unless both occurred on the same trial. Together, these experiments rule out an account in terms of second-order conditioning of the CS by the intervening stimulus. Experiment 5 used an intervening stimulus in a second-order conditioning design to demonstrate that the stimulus acted to improve the association between the CS and the reinforcer. That experiment found the intervening stimulus to make responding to the CS more vulnerable to subsequent extinction of its reinforcer. Together, these experiments document a kind of catalytic effect of the intervening stimulus on the CS-reinforcer association.

Simultaneous second-order conditioning produces S-S learning in conditioned suppression.

Four experiments explored the consequences of simultaneous second-order conditioning of one stimulus (S2) by another (S1) in a conditioned suppression preparation. In two experiments, that mode of presentation produced second-order conditioning of S2 which was attenuated by subsequent extinction of S1. Sequential presentation of the same stimuli produced similar levels of conditioning of S2 which were not affected by extinction of S1, results that replicate previous findings. Two additional experiments found tht the sensitivity of a simultaneous S2 to changes in S1 also depended on that S1 receiving few separate reinforced or nonreinforced presentations prior to second-order conditioning . The results suggest circumstances under which the typical stimulus-response learning observed in second-order conditioned suppression can be converted into stimulus-response learning. An interpretation is suggested in terms of simultaneous presentation generating a unitary representation involving both S2 and S1 rather than an association between them.

An analysis of the facilitative effect of similarity on second-order conditioning.

Five experiments used autoshaping in pigeons to investigate the effect of stimulus similarity on second-order conditioning of one stimulus (S2) when it signals another, previously conditioned stimulus (S1). Experiment 1 found that the artificial induction of similarity between S2 and S1, by the addition of experimentally separable common elements, improved performance during second-order conditioning of S2. An analysis of these results is given in terms of stimulus similarity encouraging the selection of particular components of S1 for association with S2. That selection is described as a natural consequence of the temporal relations among components of S2 and S1 which their similarity ensures. The analysis is used to generate circumstances under which the normal facilitative effect of similarity could be reversed once observed (Experiment 2A and 2B) or prevented from developing initially (Experiments 3 and 4). These experiments support a particular account of how a qualitative relation can affect the course of conditioning. However, that account requires the introduction of no special principles of conditioning unique to the case of similarity.