Contextual control of appetitive conditioning: influence of a contextual stimulus generated by a partial reinforcement procedure.

Three experiments with rat subjects examined the effects of a context switch after conditioning treatments in which the conditioned stimulus (CS) was either paired with food on every presentation (continuous reinforcement) or on some of its presentations (partial reinforcement). In each experiment, a target CS was given one of these treatments in Context A, and another CS was given a treatment during sessions that were intermixed in Context B. Final tests of the target CS in Context A and Context B often revealed no loss of responding with the switch to B. However, a loss was observed when partial reinforcement had been associated with Context A and continuous reinforcement had been associated with Context B. Those conditions caused equal decrements in responding to partially reinforced and continuously reinforced targets. The results suggest that under the present conditions partial reinforcement can generate a contextual stimulus that becomes associated with the physical context and controls responding to the CS.

A modern learning theory perspective on the etiology of panic disorder.

Several theories of the development of panic disorder (PD) with or without agoraphobia have emerged in the last 2 decades. Early theories that proposed a role for classical conditioning were criticized on several grounds. However, each criticism can be met and rejected when one considers current perspectives on conditioning and associative learning. The authors propose that PD develops because exposure to panic attacks causes the conditioning of anxiety (and sometimes panic) to exteroceptive and interoceptive cues. This process is reflected in a variety of cognitive and behavioral phenomena but fundamentally involves emotional learning that is best accounted for by conditioning principles. Anxiety, an anticipatory emotional state that functions to prepare the individual for the next panic, is different from panic, an emotional state designed to deal with a traumatic event that is already in progress. However, the presence of conditioned anxiety potentiates the next panic, which begins the individual's spiral into PD. Several biological and psychological factors create vulnerabilities by influencing the individual's susceptibility to conditioning. The relationship between the present view and other views, particularly those that emphasize the role of catastrophic misinterpretation of somatic sensations, is discussed.

Theories of associative learning in animals.

Theories of associative learning are concerned with the factors that govern association formation when two stimuli are presented together. In this article we review the relative merits of the currently influential theories of associative learning. Some theories focus on the role of attention in association formation, but differ in the rules they propose for determining whether or not attention is paid to a stimulus. Other theories focus on the nature of the association that is formed, but differ as to whether this association is regarded as elemental, configural, or hierarchical. Recent developments involve modifications to existing theories in order to account for associative learning between two stimuli, A and B, when A is accompanied, not by B, but by a stimulus that has been paired with B. The implications of the theories for understanding how humans derive causal judgments and solve categorization problems is considered.

The effects of neurotoxic hippocampal lesions on two effects of context after fear extinction.

Three conditioned suppression experiments with rats examined the role of the hippocampus in 2 effects of context after extinction. Reinstatement is the context-specific recovery of fear to an extinguished conditioned stimulus (CS) that occurs following independent presentations of the unconditioned stimulus (US), after extinction. Renewal is the recovery of fear when the CS is presented in the context in which it was conditioned, after extinction in a different context. Results indicated that neurotoxic lesions of the hippocampus, performed before conditioning, abolished reinstatement, which depends on context-US associations, but not renewal, which does not. This dissociation is not the result of differences in the recentness of context learning that ordinarily governs the 2 effects. The results suggest that the hippocampus is necessary for some, but not all, types of contextual learning.

A learning theory perspective on lapse, relapse, and the maintenance of behavior change.

Behavior change processes studied in the learning laboratory, such as extinction and counterconditioning, do not involve destruction of the original learning. Instead, they often result in new behavior that is strongly dependent on the current context, whether provided by external cues, internal state, recent events, or time. Lapse and relapse effects may therefore occur after various manipulations of the context. Theory and preliminary evidence suggests that long-term maintenance of changed behavior may be promoted by a number of factors, including situating the new learning in the most relevant contexts, providing retrieval cues after the new learning is complete, and varying the contexts in which the new learning takes place. Furthermore, because original learning is often more context free than the learning that replaces it, the most efficient way to reduce risk behavior in the general population may be to find ways to ensure that healthy behaviors and attitudes are learned first.

Hippocampus and context in classical conditioning.

Recent evidence suggests that contextual learning encompasses a variety of changes in learning and performance processes. Only some of these changes depend on the hippocampus. Specialized functions proposed for the hippocampus in contextual learning include the construction and consolidation of contextual memory representations, incidental contextual learning, and inhibitory contextual learning.

Stimulus generalization, context change, and forgetting.

Forgetting is often attributed to retrieval failure caused by background contextual cues changing over time. However, generalization between stimuli may increase over time and make them increasingly interchangeable. If this effect occurs with contextual cues, it might cancel any effect of a changing context. The authors review the evidence and suggest a resolution of this paradox. Although generalization gradients can change over time, the effect is not always strong. Increased responding to nontarget stimuli is not often shown, and few studies have demonstrated such changes with contextual cues in a way that rules out other interpretations. Even this example of forgetting may be caused by retrieval failure. The physical contexts manipulated in learning and memory experiments themselves occur within a superordinate temporal context and can thus be forgotten with no inherent challenge to a context-change account of forgetting.

Additivity of the effects of retention interval and context change on latent inhibition: toward resolution of the context forgetting paradox.

Three experiments with rats examined retention interval and context switch effects factorially in the latent inhibition paradigm. In Experiment 1, a 28-day retention interval abolished a context switch effect on latent inhibition. In Experiment 2, re-exposure to the contexts before conditioning re-established the context switch effect at the 28-day interval. In this case, the retention interval and context switch effects were additive: Latent inhibition was weakest when the retention interval and context switch were combined. Experiment 3 replicated the context switch effect at the 28-day interval. The results suggest that context switch and retention interval effects may be based on the same process. Context switch effects may weaken over time because physical contexts are embedded in superordinate temporal contexts; animals fail to retrieve physical context when the temporal context changes. This view helps resolve a paradox that has been noted for contextual change theories of forgetting.

The role of the rat hippocampal system in several effects of context in extinction.

The effect of fornix lesions on some effects of manipulating the context on performance in extinction were studied. In renewal, subjects' responding to an extinguished conditioned stimulus (CS) recovered when the CS was presented in the context in which it had been conditioned after extinction in a different context. In reinstatement, it recovered when the CS was tested after independent presentation of the unconditioned stimulus (US; an effect mediated by contextual conditioning.) In spontaneous recovery, it recovered after the passage of time, that is, when the CS was tested in a new temporal context. In the conditioned suppression method, fornix lesions had no effect on conditioning, extinction, renewal, or spontaneous recovery; however, they abolished the reinstatement effect. The results suggest that the hippocampal system may be important in the formation of context-US associations, but not in other types of learning about the context.

Context-specificity of target versus feature inhibition in a feature-negative discrimination.

Four experiments with rats examined the effects of a context switch on inhibition that was acquired during a feature-negative discrimination. A target conditioned stimulus was paired with food when it was presented alone but occurred without food when it was combined with a feature stimulus. A context switch following training did not disrupt inhibition conditioned to the feature. However, responding to the target was more difficult to inhibit when it was tested in a different context. It is suggested that both the target and the feature acquired inhibition and that the target's inhibition was especially sensitive to the context. The feature may inhibit responding to the target (a) by directly suppressing the representation of the food and (b) by activating the target's own inhibitory association with food, which is at least partly context-specific. Implications for theories of inhibition and negative occasion-setting are discussed.

Context, time, and memory retrieval in the interference paradigms of Pavlovian learning.

In this article I review research and theory on the "interference paradigms" in Pavlovian learning. In these situations (e.g., extinction, counterconditioning, and latent inhibition), a conditioned stimulus (CS) is associated with different unconditioned stimuli (USs) or outcomes in different phases of the experiment; retroactive interference, proactive interference, or both are often observed. In all of the paradigms, contextual stimuli influence performance, and when information is available, so does the passage of time. Memories of both phases are retained, and performance may depend on which is retrieved. Despite the similarity of the paradigms, conditioning theories tend to explain them with separate mechanisms. They also do not provide an adequate account of the context's role, fail to predict the effects of time, and overemphasize the role of learning or storage deficits. By accepting 4 propositions about animal memory (i.e., contextual stimuli guide retrieval, time is a context, different memories are differentially dependent on context, and interference occurs at performance output), a memory retrieval framework can provide an integrated account of context, time, and performance in the various paradigms.

Effects of contextual conditioning and unconditional stimulus presentation on performance in appetitive conditioning.

Four experiments with rat subjects examined the effects of contextual conditioning on conditioned appetitive performance. Experiment 1 compared the effects of contextual conditioning on performance to conditioned stimuli (CSs) with different conditioning histories. Contextual conditioning enhanced performance to the CS if the CS had first been conditioned and then extinguished, but had no effect on performance when the CS had been merely paired or unpaired with food. Experiments 2 and 3 then asked whether the effect on the extinguished CS was due to contextual conditioning acting as a cue for conditioning. In Experiment 2, extinction procedures in which extra unconditioned stimuli (USs) were presented during the intertrial intervals were found to reduce the CS's sensitivity to enhancement by contextual conditioning, but had no effect on spontaneous recovery. In Experiment 3, USs added to conditioning or extinction acquired the ability to cue the corresponding performance. Under some conditions, USs added to conditioning could suppress performance (Experiment 4). The results suggest that contextual conditioning has complex effects that can be better understood by recognizing that contextual conditioning, as well as the USs that create it, may acquire discriminative control over conditioned responding.

A retrieval cue for extinction attenuates spontaneous recovery.

Four experiments with rats in an appetitive conditioned magazine entry preparation examined spontaneous recovery after extinction. Spontaneous recovery was obtained 6 days but not 5 hr following extinction; recovery depended on the passage of time but not on the removal of a cue that was featured in extinction or on the reintroduction of early-session cues. A cue featured in extinction attenuated recovery when presented on the test. The attenuation effect depended on the cue's correlation with extinction; a cue featured in conditioning did not attenuate recovery. The extinction cue did not evoke responding on its own, suggesting that it was not a conditioned excitor. Retardation tests and a summation test did not reveal that it was a conditioned inhibitor. The cue might work by retrieving a memory of extinction. Spontaneous recovery thus occurs because the subject fails to retrieve an extinction memory. Other accounts of spontaneous recovery are discussed.

State-dependent fear extinction with two benzodiazepine tranquilizers.

Four experiments with rats were run to investigate whether fear extinction conducted under the influence of a benzodiazepine transfers to the undrugged state. Fear was conditioned by pairing an experimental chamber with footshock and was assessed by observing freezing, a characteristic response of the rat to stimuli associated with shock. In Experiment 1, extinction of the chamber cues under chlordiazepoxide (librium) or diazepam (valium) was compared with extinction under a placebo; both drugs interfered with extinction in a dose-dependent manner as indicated by freezing during an undrugged test. Further results with chlordiazepoxide suggested that the effect depended on the drug's specific combination with extinction and that it occurred even though the extinction procedure otherwise eliminated fear completely (Experiment 2). Repeated preexposure to the drug, and the development of partial tolerance to its sedative effects, did not weaken the interference effect (Experiment 3). Other evidence suggested that the drug signaled or retrieved extinction instead of disrupting learning or consolidation (Experiment 4). The results are consistent with research suggesting that extinguished fear can be "renewed" if the exteroceptive contextual stimuli are changed after extinction. Extinction combined with either unique exteroceptive or interoceptive cues may be specific to its context.

Associative control of tolerance to the sedative effects of a short-acting benzodiazepine.

The role of Pavlovian conditioning in tolerance to the depressant effect of a benzodiazepine (midazolam) on the ambulatory activity of rats was examined. The depression of activity by low doses (1.0 and 4.0 mg/kg, ip) of midazolam diminished quickly over repeated doses given at 48-hr intervals (Experiment 1). Equivalent tolerance was observed in groups measured at 2 min and 30 min after drug injection. When challenged with saline, however, drug-tolerant animals tested immediately after injection were hyperactive in comparison with nontolerant controls, whereas equivalent groups tested 30 min after injection were not. A second context was designed, and its discriminability from the original was established by assessing context-specific suppression of activity following exposure to mild electric shock (Experiment 2). In Experiment 3A, although tolerant animals tested in the drug-associated context remained fully tolerant, a second group demonstrated a complete loss of tolerance when given the drug in a saline-associated context. Both groups were fully tolerant when tested again in the drug-associated context after 14 drug-free days. In Experiment 3B, tolerance was significantly reduced by 14 extinction exposures to the drug-associated environment without the drug. These results are uniquely predicted by associative models of drug tolerance and may have implications for the clinical use of this class of drugs.

Contextual control of the extinction of conditioned fear: tests for the associative value of the context.

Four conditioned suppression experiments examined the influence of contextual stimuli on the rat's fear of an extinguished conditioned stimulus (CS). When rats received pairings of a CS with shock in one context and then extinction of the CS in another context, fear of the CS was renewed when the CS was returned to and tested in the original context (Experiments 1 and 3). No such renewal was obtained when the CS was tested in a second context after extinction had occurred in the conditioning context (Experiment 4). In Experiment 2, shocks presented following extinction reinstated fear of the CS, but only if they were presented in the context in which the CS was tested. In each experiment, the associative properties of the contexts were independently assessed. Contextual excitation was assessed primarily with context-preference tests in which the rats chose to sit in either the target context or an adjoining side compartment. Contextual inhibition was assessed with summation tests. Although reinstatement was correlated with demonstrable contextual excitation present during testing, the renewal effect was not. Moreover, there was no evidence that contextual inhibition developed during extinction. The results suggest that fear of an extinguished CS can be affected by the excitatory strength of the context but that independently demonstrable contextual excitation or inhibition is not necessary for contexts to control that fear.

Relative potency of foods and drinks as targets in aversion conditioning.

The potency of food stimuli as targets in aversion learning was examined using an interference paradigm. In the first study, foods interfered with liquid aversions but liquids did not interfere with food aversions. In the second study, food aversions were found to be resistant to interference by other foods. These findings suggest that foods are relatively potent targets in aversion conditioning in that they are resistant to interference by both foods and drinks. The final study examined the contribution of flavor intensity and nutrient density to the potency of aversion conditioning. The relative potency of foods over drinks may reflect differences in their intensity as well as their different roles in toxin avoidance and nutrient selection.

Role of conditioned contextual stimuli in reinstatement of extinguished fear.

If the unconditioned stimulus (US) is presented independently of the conditioned stimulus (CS) following extinction, the conditioned response may be reinstated to the CS. Three experiments are reported that suggest that reinstatement is mediated by conditioning to contextual stimuli that are present during both US presentation and testing. Shocks presented to rats following the extinction of conditioned suppression reliably reinstated suppression to the CS, but only when they were presented in the context in which testing was later to occur. Reinstatement was also reversed by extinguishing fear to the context through nonreinforced exposure to the context between shock presentation and testing. Reinstatement was obtained in these experiments in spite of procedures that have been used in the past to minimize the influence of context conditioning. Moreover, fear of the context was never detected directly by depressed bar-press rates in the absence of the CS. The results do not support the hypothesis that reinstatement results from an increment in the strength of a memory of the US that has been weakened during extinction. Problems inherent in controlling and detecting levels of context conditioning that may influence behavior toward nominal CSs are discussed.