Modulation of a discrete Pavlovian conditioned reflex by a putative emotive Pavlovian conditioned stimulus

Three experiments showed the modulation of a rabbit eyeblink conditioned response (CR) to a Pavlovian conditioned stimulus (CS) by 30-s stimuli (A & B) that had been differentially paired with paraorbital shock. The CS (Y) was a 1,050-ms cue that had been paired with paraorbital shock outside A or B. In testing, the amplitude of CRs was greater when Y was presented within A than within B. Differential modulation occurred whether shock in A had been preceded by another 1,050-ms cue, X(AX+,BX-;Experiment 1) or not (A+B-;Experiment 2). Experiment 3 compared the technique of Experiment 1 (AX+) with that of Experiment 2 (A+) and found the latter to be advantageous for facilitation of CRs to Y by A. These data are consistent with the predictions of a model of Pavlovian conditioning (AESOP, Wagner & Brandon, 1989) that distinguishes between emotive and sensory conditioning as did Konorski (1967).     

Demonstrator skill modulates observational aversive learning

Learning to avoid danger by observing others can be relatively safe, because it does not incur the potential costs of individual trial and error. However, information gained through social observation might be less reliable than information gained through individual experiences, underscoring the need to apply observational learning critically. In order for observational learning to be adaptive it should be modulated by the skill of the observed person, the demonstrator. To address this issue, we used a probabilistic two-choice task where participants learned to minimize the number of electric shocks through individual learning and by observing a demonstrator performing the same task. By manipulating the demonstrator’s skill we varied how useful the observable information was; the demonstrator either learned the task quickly or did not learn it at all (random choices). To investigate the modulatory effect in detail, the task was performed under three conditions of available observable information; no observable information, observation of choices only, and observation of both the choices and their consequences. As predicted, our results showed that observable information can improve performance compared to individual learning, both when the demonstrator is skilled and unskilled; observation of consequences improved performance for both groups while observation of choices only improved performance for the group observing the skilled demonstrator. Reinforcement learning modeling showed that demonstrator skill modulated observational learning from the demonstrator’s choices, but not their consequences, by increasing the degree of imitation over time for the group that observed a fast learner. Our results show that humans can adaptively modulate observational learning in response to the usefulness of observable information.     

Facilitation of instrumental behavior by a Pavlovian appetitive conditioned stimulus

Three experiments examined appetitive Pavlovian-instrumental interactions by presenting separately trained conditioned stimuli (CSs) during reinforced instrumental responding in rabbits. Intra-oral reinforcement was used to minimize interference from peripheral responses such as magazine approach. In experiment 1, the rabbits were first trained to perform an instrumental head-raising response for sucrose reward. A conditioned jaw movement response was then established to a 2-sec CS by pairing it with sucrose; a control stimulus was unpaired with sucrose. Instrumental responding maintained by a variable-interval 40-sec schedule was enhanced during 10-sec presentations of the paired, but not the unpaired, CS. Responding on a variable-ratio 15 schedule was unaffected except on trials on which the pre-CS baseline response rate was low; in such cases the paired CS caused a long-lasting acceleration of responding. Noncontingent presentation of the sucrose reinforcer itself briefly suppressed responding but had no long-term effect. In Experiment 2, a CS that had been conditioned at a 10-sec duration produced the same pattern of effects as in the first study, indicating that facilitation resulted from CS presentation rather than from the frustrative effects of non-reinforcement of the CS. In Experiment 3 an inhibitory CS blocked facilitation by the excitatory CS but did not itself affect instrumental responding. These results support the view that Pavlovian processes play a positive role in instrumental performance and suggest that previous findings of suppression by a short-duration CS reflect peripheral interference. The dependence of facilitation on the baseline level of responding is discussed in terms of associative and motivational theories of Pavlovian mediation.     

Wind as an aversive stimulus

Two monkeys were trained on an escape-avoidance procedure in which a lever press delayed exposure to wind by 20 sec. For 5 hr, subjects alternately worked 15 min and rested 15 min, and performed this schedule when the wind was 5, 10, and 20 mph and the temperatures were 50, 60, and 70° F. Analysis of variance showed that the percent of wind avoided was related to both the velocity of the wind and the temperature during the exposure. When the wind was 10 and 20 mph it was avoided almost continuously regardless of the temperature.     

Constraints on Pavlovian aversive conditioning: Implications for avoidance learning in the rat

Four experiments investigated the relative degree of control exerted by several conditional stimuli when each stimulus: (a) preceded shock, (b) followed shock, and preceded a shock-free interval, (c) was independent of shock, or (d) was novel. When the onset of an auditory stimulus had preceded shock (Experiments 1, 2A, and 3), it always exerted conditioned excitatory control. When the same stimulus preceded a shock-free interval, it never exerted conditioned inhibitory control. When the onset of light (Experiments 2B, 4), silence (2C), or darkness (1, 2D) preceded a shock-free interval, it always exerted conditioned inhibitory control. However, when one of the latter stimuli preceded shock, it failed to exert excitatory control. Several models of this phenomenon were tested. The implications of these results for the species-specific defence reaction and two-factor theory accounts of avoidance learning were outlined.     

Pavlovian conditioned stimulus effects upon instrumental choice behavior are reinforcer specific

In a transfer-of-control experiment with rats, Pavlovian CSs were tested for the specificity of their effects. The instrumental behavior consisted of a discriminative, conditional two-lever choice task in which qualitatively different appetitive reinforcers were contingent upon the two correct choices. In a Pavlovian phase, subjects experienced conditioning to establish either a CS⁺ or CS^? for one reinforcer or a CS⁺ or CS^? for the other reinforcer. Finally, in a test, these CSs were presented when there was the opportunity to make choice responses. The CS⁺s evoked choices of the lever which had eventuated in the reinforcer that had served as the Pavlovian US, while the CS^?s showed only a slight tendency to evoke the other choice responses. When the CSs were compounded with the original S^Ds, the CS⁺s had little effect upon the vigor of responding while the CS^?s reduced the vigor of responding to the S^D for the reinforcer that was the same as the US used in establishing the CS^?. The results are discussed in terms of associative mediational theory and the reinforcer specificity of Pavlovian conditioned excitation and inhibition.     

Stimulus aspects of aversive controls: stimulus generalization of conditioned suppression following discrimination training

A tone ending with unavoidable electrical shock was periodically presented to pigeons while they pecked a key for food. A second group of birds was exposed to these tone-shock contingencies and also to a second tone which never ended with shock. The gradient of stimulus generalization following training to a single stimulus was symmetrical, whereas the gradient following discrimination training was asymmetrical, but there was no evidence of peak shift. During testing, suppression to all tones gradually extinguished and in both groups the slope of the gradient increased markedly. A second experiment with the discrimination birds revealed that free shock caused a recovery of the gradient, but the asymmetry persisted.     

Transfer across drives of the discriminative effect of a Pavlovian conditioned stimulus

Previous results suggest that a stimulus paired in Pavlovian fashion with reward should exert some discriminative control over an unrelated operant response acquired under a different drive-reward system. In the following experiment, a stimulus was first paired with food reinforcement for a hungry rat. Subsequently, the animal learned to lever-press for water reinforcements when thirsty but not hungry. Finally, the control over lever-pressing of the food-paired stimulus was tested by presenting it at various times during extinction of the lever-pressing response. All animals in the experiment showed the expected effect; each emitted more lever-presses during periods of the food-paired stimulus than during alternate control periods.     

Modulation of unconditioned defense reflexes by a putative emotive Pavlovian conditioned stimulus

Four experiments showed differential modulation of defensive unconditioned responses (URs) in rabbits by contextual stimuli that Brandon and Wagner (1991) have shown similarly to modulate conditioned eyeblink responses. Two 30-s auditory cues, A and B, were differentially paired with shock. Tests were presentations of a response-eliciting probe stimulus within A, B, or a comparable blank interval, Experiments 1 and 2 demonstrated that A and B differentially facilitated eyeblink URs, and Experiments 3 and 4 showed that A and B similarly differentially facilitated startle responses elicited by airpuffs to the ear. These data are consistent with a characterization of Pavlovian conditioning that distinguishes between emotive and sensory conditioning and assumes that conditioned emotional responses similarly modulate specific conditioned and unconditioned defensive reflexes (Konorski, 1967; Wagner & Brandon, 1989).     

Effects of recent exposure to a conditioned stimulus on extinction of Pavlovian fear conditioning

In six experiments we studied the effects of a single re-exposure to a conditioned stimulus (CS; "retrieval trial") prior to extinction training (extinction-reconsolidation boundary) on the development of and recovery from fear extinction. A single retrieval trial prior to extinction training significantly augmented the renewal and reinstatement of extinguished responding. Augmentation of recovery was not observed if the retrieval and extinction training occurred in different contexts. These results contrast with those reported in earlier papers by Monfils and coworkers in rats and by Schiller and coworkers in humans. We suggest that these contrasting results could depend on the contrasting influences of either: (1) occasion-setting contextual associations vs. direct context-CS associations formed as a consequence of the retrieval trial or (2) discrimination vs. generalization between the circumstances of conditioning and extinction.     

The use of an unpleasant sound as the unconditional stimulus in aversive Pavlovian conditioning experiments that involve children and adolescent participants

Ethical considerations can prohibit the use of traditional unconditional stimuli (USs), such as electric shocks or loud tones, when children or adolescents participate in aversive Pavlovian conditioning experiments. The present study evaluated whether an unpleasant sound provides a viable alternative. Fifteen boys and girls aged 13 to 17 years completed a differential Pavlovian conditioning procedure in which a conditional stimulus (CS) was followed by the sound of metal scraping on slate. Acquisition of conditioned responses was found in startle blink magnitude, expectancy judgments of the sound, and skin conductance responses. Extinction of conditioned responses was found in all measures when the CS was no longer followed by the unpleasant sound. Subjective ratings and skin conductance responses indicated that the sound was unpleasant because of its qualitative features, rather than its intensity. The results support the use of an unpleasant sound as a low-risk alternative to traditional USs in aversive Pavlovian conditioning experiments with children and adolescents.     

Temporal contiguity and contingency judgments: A Pavlovian analogue

The two experiments reported examine the role of temporal contiguity on judgments of contingency in a human analogue of the Pavlovian task. The data show that the effect of the actual delay on contingency judgment depends on the observer’s expectation regarding the delay. for a fixed contingency between the cue and the outcome, ratings of the contingency are higher when the actual delay is congruent with the observer’s expectation than when it is incongruent. We argue that our data can be understood within the context of the temporal coding hypothesis.     

Control of appetitive and aversive taste-reactivity responses by an auditory conditioned stimulus in a devaluation task: a FOS and behavioral analysis

Through associative learning, cues for biologically significant reinforcers such as food may gain access to mental representations of those reinforcers. Here, we used devaluation procedures, behavioral assessment of hedonic taste-reactivity responses, and measurement of immediate-early gene (IEG) expression to show that a cue for food engages behavior and brain activity related to sensory and hedonic processing of that food. Rats first received a tone paired with intraoral infusion of sucrose. Then, in the absence of the tone, the value of sucrose was reduced (Devalue group) by pairing sucrose with lithium chloride (LiCl), or maintained (Maintain group) by presenting sucrose and LiCl unpaired. Finally, taste-reactivity responses to the tone were assessed in the absence of sucrose. Devalue rats showed high levels of aversive responses and minimal appetitive responses, whereas Maintain rats exhibited substantial appetitive responding but little aversive responding. Control rats that had not received tone-sucrose pairings did not display either class of behaviors. Devalue rats showed greater FOS expression than Maintain rats in several brain regions implicated in devaluation task performance and the display of aversive responses, including the basolateral amygdala, orbitofrontal cortex, gustatory cortex (GC), and the posterior accumbens shell (ACBs), whereas the opposite pattern was found in the anterior ACBs. Both Devalue and Maintain rats showed greater FOS expression than control rats in amygdala central nucleus, GC, and both subregions of ACBs. Thus, through associative learning, auditory cues for food gained access to neural processing in several brain regions importantly involved in the processing of taste memory information.     

Second-order conditioning of Pavlovian conditioned inhibition

Two experiments are reported which investigated the conditioning of inhibition to a neutral stimulus as a result of its repeated pairing with a previouslyconditioned inhibitor. Both experiments employed a conditioned suppression technique with rat subjects. Experiment 1 detected the second-order inhibition through the retarded acquisition of concurrently administered excitatory conditioning. Experiment 2 found similar retardation in the acquisition of excitatory fear conditioning following previous second-order conditioning of inhibition to the stimulus. Implications are discussed for theories of the nature of inhibition and for second-order conditioning as an assessment technique.