Fears born and bred: toward a more inclusive theory of fear acquisition

Alleged differences between associative and non-associative perspectives are sometimes more apparent than real. The non-associative model describes a pathway to fear that is complementary to associative pathways. It does not seek to usurp conditioning models as applied to evolutionary-neutral fear. We discuss vexing definitional issues surrounding what qualifies as a conditioning event and what characterises the non-associative pathway. Genetic findings are shown to be consistent with the non-associative model of fear. Following discussion of the relation between stress-diathesis models and the non-associative position we conclude by urging a developmental, life-course approach to the understanding of fear acquisition.     

The comparator hypothesis of conditioned response generation: manifest conditioned excitation and inhibition as a function of relative excitatory strengths of CS and conditioning context at the time of testing

In the present research water-deprived rats were used in a conditioned lick suppression paradigm to test and further develop Rescorla's (1968) contingency theory, which posits that excitatory associations are formed when a conditioned stimulus (CS) signals an increase in unconditioned stimulus (US) likelihood and that inhibitory associations develop when the CS signals a decrease in US likelihood. In Experiment 1 we found that responding to a CS varied inversely with the associative status of the context in which the CS was trained and that this response was unaltered when testing occurred in a distinctively dissimilar context with a different conditioning history, provided associative summation with the test context was minimized. These results suggest that manifest excitatory and inhibitory conditioned responding is modulated by the associative value of the training context rather than that of the test context. In Experiment 2 it was demonstrated that postconditioning decreases in the associative value of the CS training context reduced the effective inhibitory value of the CS even when testing occurred outside of the training context. Moreover, this contextual deflation effect was specific to the CS training context as opposed to any other excitatory context. Collectively, these studies support the comparator hypothesis, which states that conditioned responding is determined by a comparison of the associative strengths of the CS and its training context that occurs at the time of testing rather than at the time of conditioning. This implies that all associations are excitatory and that responding indicative of conditioned inhibition reflects a CS-US association that is below (or near) the associative strength of its comparator stimulus. It is suggested that response rules which go beyond a monotonic relation between associative value and response strength can partially relieve learning theories of their explanatory burdens, thereby allowing for simpler models of acquisition.     

Is It What You Do,or When You Do It? The Roles of Contingency and Similarity in Pro‐Social Effects of Imitation

Being imitated has a wide range of pro‐social effects, but it is not clear how these effects are mediated. Naturalistic studies of the effects of being imitated have not established whether pro‐social outcomes are due to the similarity and/or the contingency between the movements performed by the actor and those of the imitator. Similarity is often assumed to be the active ingredient, but we hypothesized that contingency might also be important, as it produces positive affect in infants and can be detected by phylogenetically ancient mechanisms of associative learning. We manipulated similarity and contingency between performed and observed actions in a computerized task. Similarity had no positive effects; however, contingency resulted in greater enjoyment of the task, reported closeness to others, and helping behavior. These results suggest that the pro‐social effects of being imitated may rely on associative mechanisms.     

Olfactory learning in the one-day old rat: reinforcing effects of isoproterenol

Within 24 h of their birth-induced norepinephrine surge, rat pups were tested for effects of a beta-receptor agonist, isoproterenol, on olfactory learning. Experiment 1 found no effect of isoproterenol on conditioning by pairing an odor (CS) with intraoral saccharin infusions. There was, however, unexpectedly strong responding in the unpaired control condition, which had the same contingency between the CS and isoproterenol as the paired condition. Experiment 2 found that pairings of odor and isoproterenol alone were sufficient for enhancing responding to the odor. Experiment 3 determined that isoproterenol had acted independently as a US for associative conditioning rather than facilitating nonassociative learning by mere exposure to the odor. These effects of isoproterenol as a US are consistent with the results of previous studies with older rats.     

Aversive conditioning under conditions of restricted awareness: Effects on spatial cueing

In the literature on aversive conditioning there is still debate on the role of awareness. According to some authors, affective learning can occur with or without contingency learning (dual-process model), whereas others argue that a single process produces both affective responses and contingency knowledge. Although many studies have investigated these models, the results to date are inconclusive. Based on a review of the literature, a new series of experiments was designed to examine aversive conditioning in the absence of contingency awareness. In the present study we examined the effects of subliminal aversive conditioning on a spatial cueing task. Awareness was stringently tested after conditioning. Three kinds of awareness were distinguished: contingency awareness (awareness of the CS?US contingencies, where CS is the conditioned stimulus, and US is the unconditioned stimulus), perceptual awareness (awareness of the perceptual differences between the CSs), and US expectancy (awareness of a threat feeling when confronted with the CS+, but not when confronted with the CS?). The results of three experiments demonstrated that responses on the spatial cueing task were modulated by subliminal aversive conditioning. Importantly, none of the participants was contingency aware or able to perceptually discriminate between the conditioned stimuli. However, in Experiment 3, only those participants showing some level of postconditioning expectancy awareness exhibited conditioning effects. These experiments suggest that subliminal aversive conditioning produces small but significant effects, which may be modulated by expectancy awareness.     

A role for CS-US contingency in Pavlovian conditioning

Two experiments evaluated the role of conditioned stimulus-unconditioned stimulus (CS-US) contingency in appetitive Pavlovian conditioning in rats. In both experiments, some groups received a positively contingent CS signaling an increased likelihood of the US relative to the absence of the CS. These groups were compared with control treatments in which the likelihood of the US was the same in the presence and absence of the CS. A trial marker served as a trial context. Experiment 1 found contingency sensitivity. There was a reciprocal relationship between responding to the CS and the trial marker. Experiment 2 showed that this result was not stimulus or response specific. These results are consistent with associative explanations and the idea that rats are sensitive to CS-US contingency.     

Recency and primacy in causal judgments: Effects of probe question and context switch on latent inhibition and extinction

Traditional associative models assume that associative weights are updated on a trial-by-trial basis. As a result, it is usually expected that responses based on these weights will tend to reflect the most recently presented contingencies. However, a number of studies of human causal judgments have shown primacy effects, wherein judgments obtained at the end of a series of trials are more strongly influenced by a contingency that was in force early in the sequence than by a contingency that was in force later in the sequence. The experiments described in this article replicated other work showing that requesting causal judgments during a sequence can reverse primacy and produce strong recency effects. Evidence was also obtained to suggest that primacy effects are produced by an interaction between latent inhibition and extinction processes and that requesting a judgment affects both of these processes.     

评价性条件反射效应：无条件刺激的呈现时长、效价强度与关联意识的作用

以真实商标图案为条件刺激, 情绪图片为无条件刺激, 探索无条件刺激呈现时长、效价强度与关联意识对评价性条件反射效应的影响。实验通过结合四图再认测验与基于项目分析, 对关联意识的作用进行了详细探讨。结果表明, 评价性条件反射效应只发生在无条件刺激长呈现水平与无条件刺激强效价水平; 评价性条件反射效应的产生需要基于被试的关联意识。关联意识在呈现时长(效价强度)与评价性条件反射效应间的中介作用不显著。结果不支持评价性条件反射的内隐错误归因机制及联想-命题评价模型的相关论断, 部分支持命题性解释模型。     

The role of CS-US contingency in human evaluative conditioning

Recent studies suggest that in Pavlovian conditioning, two different processes may be operative: signal learning and evaluative learning, resulting in two qualitatively different associative structures. Signal-learning is hypothesized to be responsible for providing us with genuine predictors (CS) for significant events (US). This proposition logically entails that the statistical-correlational relation, i.e. the contingency between CS and US should be a crucial determinant of signal learning. Evaluative conditioning, on the other hand, refers to the observation that the mere pairing of neutral with (dis)liked stimuli changes the valence of the originally neutral stimuli in a (negative) positive direction. As argued elsewhere, evaluative conditioning is probably based on the CS acquiring a mere referential value to the US, without any genuine CS-US expectancy being involved. From this, it was hypothesized that evaluative conditioning might not be dependent on CS-US contingency. Using the standard evaluative conditioning paradigm, four different levels of CS-US contingency were created on a between-subject base. The overall effect of evaluative conditioning was strongly significant, and was not mediated by awareness of the CS-US relation. Of crucial importance, this conditioning effect did not interact with the level of contingency, supporting the hypothesis that CS-US contingency is not a crucial determinant of evaluative conditioning. Moreover, this effect was obtained in a situation in which Ss simultaneously evidenced to have consciously registered quite accurately the different levels of CS-US contingency.     

Learned irrelevance and retrospective correlation learning

In 1973 Mackintosh reported an interference effect that he called learned irrelevance in which exposure to uncorrelated (CS/US) presentation of the unconditional stimulus (US) and the conditioned stimulus (CS) interfered with future Pavlovian conditioning. It has been argued that there is no specific interference effect in learned irrelevance; rather the interference is the sum of independent CS and US exposure effects (CS + US). We review previous research on this question and report two new experiments. We conclude that learned irrelevance is a consequence of a contingency learning and a specific learned irrelevance mechanism. Moreover even the “independent exposure controls”, used in previous experiments to support the CS and US exposure account, provide support for the correlation learning process.     

What do memory data tell us about the role of contingency awareness in evaluative conditioning?

Evaluative conditioning (EC) refers to the effect that pairings of a conditioned stimulus (CS) with a valenced unconditioned stimulus (US) lead to changes in the evaluation of the CS. There have been recurring debates about whether EC requires awareness of the contingency between CSs and USs during learning. We argue that the memory performance data obtained in the standard paradigm remain ambiguous about the role of contingency awareness during the encoding of CS–US pairings. First, memory performance data are unable to distinguish between encoding-related versus retrieval-related effects. Second, the relation between memory performance and evaluation is correlational, which limits conclusions about causal relations between memory performance and EC effects. These ambiguities imply that any possible data pattern can be interpreted in at least two different ways. It is concluded that a resolution of the current debate requires alternative approaches in which contingency awareness is experimentally manipulated during the encoding of CS–US pairings.     

Both trace and delay conditioning of evaluative responses depend on contingency awareness

Whereas previous evaluative conditioning (EC) studies produced inconsistent results concerning the role of contingency knowledge, there are classical eye-blink conditioning studies suggesting that declarative processes are involved in trace conditioning but not in delay conditioning. In two EC experiments pairing neutral sounds (conditioned stimuli; CSs) with affective pictures (unconditioned stimuli; USs), we tested whether the type of conditioning procedure affects the relationship between awareness and EC. Auditory CSs and visual USs were either overlapping and co-terminating (Delay Conditioning Group), or they were separated by a short temporal gap (Trace Conditioning Group). In both groups, contingency awareness was manipulated by varying the duration at which the US was presented during conditioning. Furthermore, in addition to a post-conditioning measure of awareness, US detectability was measured concurrently during the learning phase in Experiment 2. US exposure duration affected both measures of awareness. The data of both experiments demonstrate that EC does not occur if the USs are presented at very brief durations, but reliable EC effects can be observed at longer US exposure durations. As there were no differences between trace and delay conditioning, the data suggest that contingency awareness plays a crucial role in trace and in delay conditioning of evaluative responses. These results challenge automatic association-formation accounts of EC, but they are in line with ‘single-process’ accounts assuming EC to be dependent on conscious declarative knowledge about CS–US contingencies.     

Conditioned suppression under positive, negative, and no contingency between conditioned and unconditioned stimuli

Using a conditioned suppression procedure, the effects of three contingent relationships between conditioned (CS) and unconditioned (US) stimuli were investigated. A traditional positive (if CS—then US) contingency suppressed response rate during the CS relative to responding during stimulus-free minutes of the session. A negative (if CS—then no US) contingency resulted in suppressed responding during CS-off minutes, and rate increases during the CS. A no-contingency control procedure, during which CS and US were randomly related, almost totally suppressed responding throughout the session and showed no differential effects of the CS on response rate. An analysis of changes in response rate during the minute after US-offset revealed acceleration under the no-contingency condition and, to a somewhat lesser degree, under the negative contingency. Both conditioned suppression and non-suppression are analyzed in terms of the temporal relationship between CS and US.     

Mechanisms underlying retarded emergence of conditioned responding following inhibitory training: evidence for the comparator hypothesis

The comparator hypothesis posits that conditioned responding is determined by a comparison at the time of testing between the associative strengths of the conditioned stimulus (CS) and stimuli proximal to the CS at the time of conditioning. The hypothesis treats all associations as being excitatory and treats conditioned inhibition as the behavioral consequence of a CS that is less excitatory than its comparator stimuli. Conditioned lick suppression by rats was used to differentiate four possible sources of retarded responding to an inhibitory CS. These include habituation to the unconditioned stimulus (US), latent inhibition to the CS, blocking of the CS-US association by the conditioning context, and enhanced excitatory associations to the comparator stimuli. Prior research has demonstrated the first three phenomena. Therefore, we employed parameters expected to highlight the fourth one--the comparator process. In Experiment 1, our negative contingency training was shown to produce a conditioned inhibitor that passed inhibitory summation and retardation tests. In Experiment 2 we found transfer of retardation from an inhibitory CS to a novel stimulus when the location where retardation-test training occurred was excitatory, which is indicative of contextual blocking and/or comparator effects. In Experiment 3, extinction of the conditioning context was found to attenuate retardation regardless of whether extinction occurred before or after the CS-US pairings of the retardation test. This indicates that much of the present retardation was due to the comparator process rather than to contextual blocking. Experiment 4 demonstrated that habituation to the US did not contribute to retardation in the present case. Collectively, these studies suggest that retardation following inhibitory training can be explained without recourse to any of the traditional mechanisms of conditioned inhibition.     

Responding to a conditioned stimulus depends on the current associative status of other cues present during training of that specific stimulus.

The comparator hypothesis is a response rule stating that responding to a Pavlovian conditioned stimulus (CS) reflects the associative strength of the CS relative to that of other cues (comparator stimuli) that were present during CS training. Thus, modulation of the associative strength of a CS's comparator stimulus should alter responding to that CS. These studies examined the stimulus specificity of this effect using within-subjects designs. Rats were trained on 2 CSs, each with a unique comparator stimulus, to determine the degree to which posttraining extinction of the comparator stimulus for one CS influences responding to the other CS. Using negative contingency (Experiments 1 and 2), overshadowing (Experiment 3), and local context (Experiment 4) preparations, stimulus specificity was observed. In each case, posttraining extinction of the comparator stimulus for one CS had greater impact on responding to that CS than on responding to the alternate CS.     

Memory for associative history of a conditioned stimulus

The common assumption that the current, but not the past, associative status of a conditioned stimulus (CS) is represented in memory is examined with respect to various behavioral phenomena within the existing literature and is found to be inadequate. This assumption is frequently expressed as associative path independence, which posits that the memorial effects of stimulus events occurring during a conditioning trial depend only on the associative strength of the CS at the initiation of that trial. Twelve laboratory phenomena are reviewed in which behavior is readily interpretated in terms of subjects remembering past as well as present associations. The possibility that behavior is influenced by past associative states as well as current associative strength is contrasted with several alternative explanations, including the suggestion that the current associative state of a CS is defined by variables in addition to associative strength. However, these alternatives are only partially successful without additional assumptions that increase their complexity. Contrary to many prevailing models, we conclude that subjects appear to retain the associative history of a CS.     

Sensitization,conditioning, and learning: Can they help us understand somatization and disability?

This paper reviews those features of non-associative and associative forms of learning, as elaborated in the experimental literature, that might contribute to experienced and reported discomfort in the workplace. Emphasis is given to sensitization, while noting that some models of habituation (e.g. the opponent process model) also produce sensitization-like effects as a by-product that could contribute to persistent complaints. Also noted are ways in which these non-associative processes may enhance associative learning of workplace-avoidance behaviors that are exceptionally persistent - even in the absence of further somatic discomfort.     

Classical heart-rate conditioning in the rat: The influence of curare and various setting operations

Conflicting reports concerning the success of classical conditioning of heart rate (HR) in curarized animals led to an experiment using a transfer design in which rats were classically conditioned either under curarized or restrained conditions. These conditions were then reversed for each group, giving a Curarized-Restrained (C-R) and a Restrained-Curarized (R-C) group. Results indicated that curare inhibits the conditional and unconditional HR response both during initial acquisition and after asymptotic levels of a HR CR have been attained. In addition, the C-R group did not acquire a CR during their later non-curarized restrained conditioning sessions, implying an inhibitory transfer from their earlier conditioning under curare. The UCRs during this period were normal for restrained rats. Analogous experimental“setting operations” prior to restrained conditioning were then explored by a second experiment which attempted to replicate the inhibitory transfer effect. The experimental operations investigated included: (1) restrained conditioning to investigate conditioned inhibition possibilities; (2) pseudo-conditioning types of randomized CS and UCS non-paired presentations to investigate associative vs. non-associative explanations; (3) CS-Only presentations to investigate possibilities that curare creates a blockage to the UCS, thus creating an inhibiting habituation to the CS; and (4) a group receiving curarization sessions, but no conditioning, to test the drug-only transfer effects. Results from the first and second experiments together indicated no inhibitory transfer effects under any prior experimental conditions except for those animals receiving classical conditioning while curarized. Only the CS-O group demonstrated any other kind of significant transfer effect; in this case a positive transfer accelerating later conditioning due to prior CS habituation sessions. These findings were discussed within the context of existing reports of curarized conditioning and setting operation effects on later conditioning, and various potential explanations and interpretations were explored.     

Determinants of Response Recovery in Extinction Following Response Elimination

Elimination of autoshaped responding by random or negatively-contingent response-reductive procedures may leave a previously acquired association intact; however, two previous studies suggest that response elimination by backward conditioning may have more permanent effects. In Experiments 1 and 3, the autoshaped responding of pigeons was eliminated by a backward or negative contingency. Although speed of recovery during a subsequent extinction phase was greater following the backward contingency in Experiment 3, level of recovery did not differ as a function of response elimination procedure in either experiment. A possible basis for the discrepancy between the present and previous findings is the contingency arranged between the conditioned and unconditioned stimuli (CS and US, respectively) during forward conditioning. In Experiments 1 and 2, probability of US presentation following the CS (p(US|CS) = 0.4 or 1.0) was varied within (Experiment 1) or between (Experiment 2) groups of birds. In both cases, level of recovery was higher following training under (p(US|CS) = 0.4). The results are consistent with a memory retrieval theory in which unreinforced trials function as a retrieval cue for not responding.     

Judgements of a 2 × 2 contingency table: Sequential processing and the learning curve

Shanks (1985) has used a video game to investigate how subjects estimate the effect of their behaviour in a task defined by a 2×2 contingency table. The subjects were able to distinguish positive and negative contingencies from zero contingencies. In addition, they showed a learning curve and a bias to rate zero contingencies with a high outcome density higher than low-density zero contingencies. He interpreted these data as being consistent with associative models derived from animal learning. In Experiment 1 we replicated these results using a task and instructions similar to his. In a second experiment we showed that the subjects' tendency to overestimate high-density zero contingencies did not arise because the “game” was so difficult that it interfered with processing the events. In this experiment subjects were given tables of the outcome frequencies that had been determined by the earlier subjects. These subjects were, if anything, less accurate in rating the zero contingencies. We point out several logical problems with Shanks's initial task. The task did not represent a true 2×2 contingency, and aspects of it were physically impossible. In Experiment 3 we modified the task to represent a true 2×2 contingency. Using this task, we found a similar pattern of results, except that there was no evidence of the learning curve predicted by the associative models. We conclude that there is little in our data to rule out a “rule-based” analysis of contingency judgements.