Fear expression and return of fear following threat instruction with or without direct contingency experience

Prior research showed that mere instructions about the contingency between a conditioned stimulus (CS) and an unconditioned stimulus (US) can generate fear reactions to the CS. Little is known, however, about the extent to which actual CS–US contingency experience adds anything beyond the effect of contingency instructions. Our results extend previous studies on this topic in that it included fear potentiated startle as an additional dependent variable and examined return of fear (ROF) following reinstatement. We observed that CS–US pairings can enhance fear reactions beyond the effect of contingency instructions. Moreover, for all measures of fear, instructions elicited immediate fear reactions that could not be completely overridden by subsequent situational safety information. Finally, ROF following reinstatement for instructed CS+s was unaffected by actual experience. In summary, our results demonstrate the power of contingency instructions and reveal the additional impact of actual experience of CS–US pairings.     

Fear generalization in humans: Impact of prior non-fearful experiences

Fear generalization lies at the heart of many anxiety problems, and is therefore an important target for prevention and/or treatment. Here, we investigated whether fear generalization towards a specific stimulus can be weakened by prior non-fearful experiences with that stimulus. Using the standard human fear conditioning procedure, all participants received paired presentations of a geometric figure and an electric shock. This was followed by a test phase in which a similar but different figure was presented. Electrodermal responding and ratings of shock-expectancy measured the level of fear generalization towards this test stimulus. Crucially, half of the participants had been preexposed to that stimulus (without shock). The results show significantly less generalization in this group, suggesting that prior non-fearful experiences can protect against fear generalization. These results may inspire novel ways to prevent the development of clinical anxiety.     

Verbal instruction abolishes fear conditioned to racial out-group faces

Previous research has shown resistance to extinction of fear conditioned to racial out-group faces, suggesting that these stimuli may be subject to prepared fear learning. The current study replicated and extended previous research by using a different racial out-group, and testing the prediction that prepared fear learning is unaffected by verbal instructions. Four groups of Caucasian participants were trained with male in-group (Caucasian) or out-group (Chinese) faces as conditional stimuli; one paired with an electro-tactile shock (CS+) and one presented alone (CS−). Before extinction, half the participants were instructed that no more shocks would be presented. Fear conditioning, indexed by larger electrodermal responses to, and blink startle modulation during the CS+, occurred during acquisition in all groups. Resistance to extinction of fear learning was found only in the racial out-group, no instruction condition. Fear conditioned to a racial out-group face was reduced following verbal instructions, contrary to predictions for the nature of prepared fear learning.     

Classical fear conditioning in the anxiety disorders: a meta-analysis

Fear conditioning represents the process by which a neutral stimulus comes to evoke fear following its repeated pairing with an aversive stimulus. Although fear conditioning has long been considered a central pathogenic mechanism in anxiety disorders, studies employing lab-based conditioning paradigms provide inconsistent support for this idea. A quantitative review of 20 such studies, representing fear-learning scores for 453 anxiety patients and 455 healthy controls, was conducted to verify the aggregated result of this literature and to assess the moderating influences of study characteristics. Results point to modest increases in both acquisition of fear learning and conditioned responding during extinction among anxiety patients. Importantly, these patient-control differences are not apparent when looking at discrimination studies alone and primarily emerge from studies employing simple, single-cue paradigms where only danger cues are presented and no inhibition of fear to safety cues is required.     

Instructed fear learning,extinction, and recall: additive effects of cognitive information on emotional learning of fear

The effects of instruction on learning of fear and safety are rarely studied. We aimed to examine the effects of cognitive information and experience on fear learning. Fourty healthy participants, randomly assigned to three groups, went through fear conditioning, extinction learning, and extinction recall with two conditioned stimuli (CS+). Information was presented about the presence or absence of conditioned stimulus–unconditioned stimulus (CS–US) contingency at different stages of the experiment. Information about the CS–US contingency prior to fear conditioning enhanced fear response and reduced extinction recall. Information about the absence of CS–US contingency promoted extinction learning and recall, while omission of this information prior to recall resulted in fear renewal. These findings indicate that contingency information can facilitate fear expression during fear learning, and can facilitate extinction learning and recall. Information seems to function as an element of the larger context in which conditioning occurs.     

对条件化恐惧反应的抑制效应:指导性与习惯性情绪调节的作用

为了考察实验室指导性与个体习惯性情绪调控策略对恐惧反应的影响,先使用问卷调查了81名大学生的习惯性重评与抑制水平,随后将被试分为两组,指导其在条件化恐惧习得过程中进行主动的情绪调节或自然观看,24h后进行恐惧的表达测试。结果发现,习惯性抑制水平与恐惧习得及表达水平呈显著负相关,且指导性情绪调节与习惯性抑制均显著降低了恐惧习得及表达水平。这提示指导性与习惯性情绪调节策略均能够削弱应激的伤害以保护个体。     

状态焦虑对条件性恐惧泛化的影响

恐惧的过度泛化是焦虑障碍患者重要的潜在病因,探索焦虑对恐惧泛化的影响具有重要意义。本研究在恐惧习得后,通过恐惧创伤电影范式诱发状态焦虑组被试的焦虑水平,采用主观预期值和皮电反应值作为指标,考察状态焦虑对条件性恐惧泛化的影响。结果表明,恐惧创伤电影范式显著提高了状态焦虑组被试的焦虑水平。在泛化阶段,状态焦虑组被试表现出更强的恐惧泛化,对与条件刺激相似的泛化刺激表现出更强烈的恐惧以及更高的预期。状态焦虑使得被试恐惧泛化的消退更慢,持续时间更长。研究同时发现,在状态焦虑下,被试对条件刺激的辨识出现增强趋势。研究结果提示在对经历负性事件个体进行临床干预时,可通过降低其焦虑水平来减少过度泛化。     

The renewal of extinguished conditioned fear with fear-relevant and fear-irrelevant stimuli by a context change after extinction

The acquisition, extinction, and subsequent recovery of conditioned fear can be influenced by the nature of the conditional stimulus (CS) and the context in which the CS is presented. The combined effects of these factors were examined in a differential fear-conditioning procedure with humans. Fear-relevant or fear-irrelevant CSs were followed by a shock unconditional stimulus (US) during acquisition and presented alone during extinction. The CSs were images presented upon different background contexts. Half the participants received the same context during acquisition and extinction and the remaining received different contexts. All participants received test trials in the same context as acquisition. In Experiment 1 (N=64), a renewal of shock expectancy and skin conductance responses was found during test for fear-relevant and fear-irrelevant CSs when extinction was given in a different context. In Experiment 2 (N=72), renewal for fear-relevant stimuli was enhanced when acquisition and test was given in an indoor office context and extinction in an outdoor bush context. The opposite context configuration produced the strongest renewal for fear-irrelevant stimuli. The return of extinguished conditioned fear can occur to fear-relevant stimuli that are commonly associated with clinical fears and its strength may be enhanced when the stimuli are encountered in certain contexts after extinction.     

Brain activity associated with omission of an aversive event reveals the effects of fear learning and generalization

During fear learning, anticipation of an impending aversive stimulus increases defensive behaviors. Interestingly, omission of the aversive stimulus often produces another response around the time the event was expected. This omission response suggests that the subject detected a mismatch between what was predicted and what actually occurred, thereby providing an indirect measure of cognitive expectancy. Here, we used functional magnetic resonance imaging to investigate whether omission-related brain activity reflects fear expectancy during learning and generalization of conditioned fear. During conditioning, a face expressing a moderate amount of fear (conditioned stimulus, CS+) signaled delivery of an aversive shock unconditioned stimulus (US), whereas the same face with a neutral expression was unreinforced. In a subsequent generalization test, subjects were presented with faces expressing more or less fear intensity than the CS+. Psychophysiological results revealed an increase in the skin conductance response (SCR) during learning when the US was omitted. Omission-related SCRs were also observed during the generalization test following the offset of high- but not low-intensity face expressions. Neuroimaging results revealed omission-related neural activity during learning in the anterior cingulate cortex, parietal cortex, insula, and striatum. These same regions also showed omission-related responses during the generalization test following highly expressive fearful faces. Finally, regression analysis on omission responses during the generalization test revealed correlations in offset-related SCRs and neural activity in the dorsomedial prefrontal cortex and posterior parietal cortex. Thus, converging psychophysiological and neural activity upon omission of aversive stimulation provides a novel metric of US expectancy, even to generalized cues that had no prior history of reinforcement.     

Generalization of conditioned fear along a dimension of increasing fear intensity

The present study investigated the extent to which fear generalization in humans is determined by the amount of fear intensity in nonconditioned stimuli relative to a perceptually similar conditioned stimulus. Stimuli consisted of graded emotionally expressive faces of the same identity morphed between neutral and fearful endpoints. Two experimental groups underwent discriminative fear conditioning between a face stimulus of 55% fear intensity (conditioned stimulus, CS+), reinforced with an electric shock, and a second stimulus that was unreinforced (CS−). In Experiment 1 the CS− was a relatively neutral face stimulus, while in Experiment 2 the CS− was the most fear-intense stimulus. Before and following fear conditioning, skin conductance responses (SCR) were recorded to different morph values along the neutral-to-fear dimension. Both experimental groups showed gradients of generalization following fear conditioning that increased with the fear intensity of the stimulus. In Experiment 1 a peak shift in SCRs extended to the most fear-intense stimulus. In contrast, generalization to the most fear-intense stimulus was reduced in Experiment 2, suggesting that discriminative fear learning procedures can attenuate fear generalization. Together, the findings indicate that fear generalization is broadly tuned and sensitive to the amount of fear intensity in nonconditioned stimuli, but that fear generalization can come under stimulus control. These results reveal a novel form of fear generalization in humans that is not merely based on physical similarity to a conditioned exemplar, and may have implications for understanding generalization processes in anxiety disorders characterized by heightened sensitivity to nonthreatening stimuli.Fear generalization occurs when a fear response acquired to a particular stimulus transfers to another stimulus. Generalization is often an adaptive function that allows an organism to rapidly respond to novel stimuli that are related in some way to a previously learned stimulus. Fear generalization, however, can be maladaptive when nonthreatening stimuli are inappropriately treated as harmful, based on similarity to a known threat. For example, an individual may acquire fear of all dogs after an aversive experience with a single vicious dog. In this case, recognizing that a novel animal is related to a feared (or fear-conditioned) animal is made possible in part by shared physical features to the fear exemplar, such as four legs and a tail. On the other hand, fear generalization may be selective for those features that are associated with natural categories of threat; a harmless dog may not pose a threat, but possesses naturally threatening features common to other threatening animals, such as sharp teeth and claws. Moreover, the degree to which an individual fearful of dogs responds with fear may be related to either the physical similarity to the originally feared animal (e.g., from a threatening black dog to another black dog), or the intensity of those threatening features relative to the originally feared animal (e.g., sharp teeth from one animal to sharp teeth of another animal). Therefore, fear generalization based on perceptual information may occur via two routes—similarity to a learned fear exemplar along nonthreatening physical dimensions or along dimensions of fear relevance. Given that fear generalization often emerges as a consequence of conditioning or observational learning, it is important to determine which characteristics of novel stimuli facilitate fear generalization and the extent to which generalization processes can be controlled.Early explanations of stimulus generalization emphasized that an organism''s ability to generalize to nonconditioned stimuli is related to both the similarity and discriminability to a previously conditioned stimulus (CS) (Hull 1943; Lashley and Wade 1946). While Lashley and Wade (1946) argued that generalization was simply a failure of discriminating between a nonconditioned stimulus (CS−) and the reinforced CS (CS+), contemporary views contend that generalization enables learning to extend to stimuli that are readily perceptually distinguished from the CS (Pearce 1987; Shepard 1987; McLaren and Mackintosh 2002). This latter view has been supported by empirical studies of stimulus generalization in laboratory animals (Guttman and Kalish 1956; Honig and Urcuioli 1981). In these studies, animals were reinforced for responding to a CS of a specific physical quality such as color, and then tested with several different values along the same stimulus dimension as the CS (e.g., at various wavelengths along the color spectrum). Orderly gradients of responses are often reported that peak at or near the reinforced value and decrease as a function of physical similarity to the CS along the stimulus dimension (Honig and Urcuioli 1981). Further generalization was shown to extend from the CS+ to discriminable nonconditioned stimuli, suggesting that generalization is not bound to the organism''s ability to discriminate stimuli (Guttman and Kalish 1956, 1958; Shepard 1987).Interestingly, when animals learn to distinguish between a CS+ and a CS−, the peak of behavioral responses often shift to a new value along the dimension that is further away from the CS− (Hanson 1959). For instance, when being trained to discriminate a green CS+ and an orange CS−, pigeons will key peck more to a greenish-blue color than the actual CS+ hue. Intradimensional generalization of this sort is reduced when animals are trained to discriminate between two or more stimulus values that are relatively close during conditioning (e.g., discriminating a green-yellow CS+ from a green-blue CS−), suggesting that the extent of generalization can come under stimulus control through reinforcement learning (Jenkins and Harrison 1962). Spence (1937) described the transposition of response magnitude as an effect of interacting gradients of excitation and inhibition formed around the CS+ and CS−, respectively, which summate to shift responses to values further from the inhibitory CS− gradient. In all, early theoretical and empirical treatments of stimulus generalization in nonhuman animals revealed that behavior transfers to stimuli that are physically similar, but can be discriminated from a CS, and that differential reinforcement training can both sharpen the stimulus gradient and shift the peak of responses to a nonreinforced value.Although this rich literature has revealed principles of generalization in nonhuman animals, few studies of fear generalization have been conducted in humans (for review, see Honig and Urcuioli 1981; Ghirlanda and Enquist 2003). Moreover, the existing human studies have yet to consider the second route through which fear responses may generalize—via gradients of fear relevance. While a wide range of neutral stimuli, such as tones or geometric figures, can acquire fear relevance through conditioning processes, other stimuli, such as threatening faces or spiders, are biologically prepared to be fear relevant (Lanzetta and Orr 1980; Dimberg and Öhman 1996; Whalen et al. 1998; Öhman and Mineka 2001). Compared with fear-irrelevant CSs, biologically prepared stimuli capture attention (Öhman et al. 2001), are conditioned without awareness (Öhman et al. 1995; Öhman and Soares 1998), increase brain activity in visual and emotional processing regions (Sabatinelli et al. 2005), and become more resistant to extinction when paired with an aversive unconditioned stimulus (US) (Öhman et al. 1975). Although the qualitative nature of the CS influences acquisition and expression of conditioned fear, it is unknown how generalization proceeds along a gradient of natural threat. For instance, human studies to date have all tested variations of a CS along physically neutral stimulus dimensions, such as tone frequency (Hovland 1937), geometric shape (Vervliet et al. 2006), and physical size (Lissek et al. 2008). These investigations implicitly assume that the generalization gradient is independent of the conditioned value (equipotentiality principle). In other words, since the stimuli are all equally neutral prior to fear learning, fear generalization operates solely as a function of similarity along the reinforced physical dimension. However, since fear learning is predisposed toward fear-relevant stimuli, generalization may be selective to those shared features between a CS+ and CS− that are associated with natural categories of threat. Examining generalization using fear-relevant stimuli is thus important to gain better ecological validity and to develop a model system for studying maladaptive fear generalization in individuals who may express exaggerated fear responses to nonthreatening stimuli following a highly charged aversive experience (i.e., post-traumatic stress disorder or specific phobias).To address this issue, the present study examined generalization to fearful faces along an intradimensional gradient of fear intensity. A fearful face is considered a biologically prepared stimulus that recruits sensory systems automatically for rapid motor responses (Öhman and Mineka 2001), and detecting fearful faces may be evolutionarily selected as an adaptive response to social signals of impending danger (Lanzetta and Orr 1980; Dimberg and Öhman 1996). During conditioning, an ambiguous face containing 55% fear intensity (CS+) was paired with an electric shock US, while a relatively neutral face (11% fear intensity) was explicitly unreinforced (CS−) (Experiment 1). Skin conductance responses (SCR) were recorded as a dependent measure of fear conditioning. Before and following fear conditioning, SCRs were recorded in response to face morphs of the same actor expressing several values of increasing fear intensity (from 11% to 100%; see Fig. 1). A total of five values along the continuum were used: 11% fear/88% neutral, 33% fear/66% neutral, 55% fear/44% neutral, 77% fear/22% neutral, and 100% fear. For clarity, these stimuli are herein after labeled as S1, S2, S3, S4, and S5, respectively.Open in a separate windowFigure 1.Experimental design. (A) Pre-conditioning included six presentations of all five stimulus values without the US. (B) Fear conditioning involved discriminative fear learning between the S3, paired with the US (CS+), and either the unreinforced S1 (Experiment 1) or the unreinforced S5 (Experiment 2) (CS−). (C) The generalization test included nine presentations of all five stimuli (45 total), with three out of nine S3 trials reinforced with the US. Stimuli are not drawn to scale.Testing generalization along an intradimensional gradient of emotional expression intensity allows for an examination of the relative contributions of fear intensity and physical similarity on the magnitude of generalized fear responses. If fear generalization is determined purely by the perceptual overlap between the CS+ and other morph values, without regard to fear intensity, then we would expect a bell-shaped generalization function with the maximum SCR centered on the reinforced (intermediate) CS+ value (S3), less responding to the directly adjacent, but most perceptually similar values (S2 and S4), and the least amount of responding to the most distal and least perceptually similar morph values (S1 and S5). This finding would be in line with stimulus generalization reported along fear-irrelevant dimensions (Lissek et al. 2008) and in stimulus generalization studies using appetitive instrumental learning procedures (Guttman and Kalish 1956). If, however, fear generalization is biased toward nonconditioned stimuli of high fear intensity, then an asymmetric generalization function should result with maximal responding to the most fear-intense nonconditioned stimuli. This finding would suggest that fear generalization is selective to the degree of fear intensity in stimuli, similar to studies of physical intensity generalization gradients in nonhuman animals (Ghirlanda and Enquist 2003). We predicted that the latter effect would be observed, such that the magnitude of SCRs will disproportionately generalize to stimuli possessing a greater degree of fear intensity than the CS+ (Experiment 1). A secondary goal was to determine whether fear generalization to nonconditioned stimuli can be reduced through discriminative fear learning processes. Therefore, a second group of participants was run for whom the CS− was the 100% fearful face (Experiment 2). In this case, we predicted that discriminative fear conditioning between the CS+ (55% intensity) and the most fear-intense nonconditioned stimulus would sharpen the generalization gradient around the reinforced CS+ value, and that responses to the most fear-intense stimulus would decrease relative to Experiment 1. Moreover, this discriminative fear-learning process may provide evidence that fear generalization is influenced by associative learning processes and is not exclusively driven by selective sensitization to stimuli of high fear relevance (Lovibond et al. 1993). Finally, we were interested to discover whether generalization processes would yield subsequent false memory for the intensity of the CS+ in a post-experimental retrospective report. In sum, the present study has implications for understanding how fear generalization is related to the degree of fear intensity of a nonconditioned stimulus, the extent to which discrimination training efforts can thwart the generalization process, and how fear generalization affects stimulus recognition.     

Fear generalisation in individuals with high neuroticism: increasing predictability is not necessarily better

Fear generalisation, a process by which conditioned fear spreads to similar but innocuous stimuli, is key in understanding why some individuals feel unsafe in objectively non-threatening situations. Both trait neuroticism and lack of predictability about the likelihood of feared consequences are associated with negative affect in the face of ambiguity and may increase the degree to which fear generalises. Undergraduates (N?=?129) with varying degrees of neuroticism were randomised to either high- or low-instructional predictability conditions prior to fear acquisition. A fear generalisation test measured risk ratings and attentional bias on a modified dot-probe paradigm. Among individuals with higher neuroticism, providing instructional predictability did not reduce fear; these individuals reported higher risk and increased attentional bias toward ambiguous stimuli. Overall, for individuals with higher neuroticism, predictability information hurt rather than helped interpretation of ambiguous stimuli, challenging a common conceptualisation of predictability as a factor that reduces fear.     

应激激素对恐惧消退作用的神经生理机制

恐惧消退是指反复呈现条件刺激（conditioned stimulus, CS）而不匹配无条件刺激（unconditioned stimulus, US）,从而消除个体已有的恐惧反应。应激激素,如去甲肾上腺素（Norepinephrine,NE）和糖皮质激素（Glucocorticoids,GCs）,可通过影响腹内侧前额叶、杏仁核和海马等与消退学习有关的神经回路的活动,调节恐惧消退学习效果。NE和GCs对恐惧消退学习的调节作用受激素水平与激素用药时间的影响,且其调节效果存在性别差异。未来研究需进一步探索应激激素如何影响恐惧消退学习效果,并思考如何利用其影响效果促进暴露疗法疗效。     

Pavlovian Disgust Conditioning and Generalization: Specificity and Associations With Individual Differences

Although studies have identified differences between fear and disgust conditioning, much less is known about the generalization of conditioned disgust. This is an important gap in the literature given that overgeneralization of conditioned disgust to neutral stimuli may have clinical implications. To address this knowledge gap, female participants (n = 80) completed a Pavlovian conditioning procedure in which one neutral food item (conditioned stimulus; CS+) was followed by disgusting videos of individuals vomiting (unconditioned stimulus; US) and another neutral food item (CS–) was not reinforced with the disgusting video. Following this acquisition phase, there was an extinction phase in which both CSs were presented unreinforced. Importantly, participants also evaluated generalization stimuli (GS+, GS?) that resembled, but were distinct from, the CS after each conditioning phase. As predicted, the CS+ was rated as significantly more disgusting and fear inducing than the CS? after acquisition and this pattern persisted after extinction. However, disgust ratings of the CS+ after acquisition were significantly larger than fear ratings. Participants also rated the GS+ as significantly more disgusting, but not fear inducing, than the GS? after acquisition. However, this effect was not observed after extinction. Disgust proneness did predict a greater increase in disgust and fear ratings of the CS+ relative to the CS? after acquisition and extinction. In contrast, trait anxiety predicted only higher fear ratings to the CS+ relative to the CS? after acquisition and extinction. Disgust proneness nor trait anxiety predicted the greater increase in disgust to the GS+ relative to the GS? after acquisition. These findings suggest that while conditioned disgust can generalize, individual difference variables that predict generalization remain unclear. The implications of these findings for disorders of disgust are discussed.     

The effects of verbal information on children's fear beliefs about social situations

Two experiments explored the role of verbal information in changing children's fear-related beliefs about social situations. In Experiment 1, 118 6- to 8- and 12- to 13-year-olds heard positive, negative, or no information about individuals' experiences of three social situations. Fear beliefs regarding each situation were assessed before and after this manipulation. Verbal information had no significant influence on children's fear beliefs. In Experiment 2, the same paradigm was used with 80 12- to 13-year-olds, but the information took the form of multiple attitude statements about the situations expressed by groups of peers, older children, or adults. An affective priming task of implicit attitudes was used to complement the explicit questions about fear beliefs. Negative information influenced both explicit and implicit fear beliefs. The source of information and the child's own social anxiety did not moderate these effects. Implications for our understanding of the socialisation of childhood fears are discussed.     

基于知觉的恐惧泛化的认知神经机制

恐惧泛化是条件性恐惧反应转移到另一个相似但安全的刺激的现象。适当的恐惧泛化对人类有积极意义, 而过度的恐惧泛化则不利于个体有效地适应环境。基于知觉的恐惧泛化研究揭示了恐惧泛化的规律, 因而被广泛应用。本文首先梳理了对知觉恐惧泛化的相关研究, 介绍恐惧泛化的经典理论基础—巴普洛夫条件反射以及恐惧泛化梯度; 其次简要回顾基于多个感觉通道(即视觉、听觉、情景)的知觉恐惧泛化研究现状; 再次, 分别对海马、杏仁核、脑岛和前额叶等脑区在恐惧泛化中的作用进行回顾, 进一步总结出恐惧泛化的神经环路结构模型。最后, 简要区分了基于知觉的恐惧泛化和正在兴起的基于概念的恐惧泛化, 进而指出未来研究需要结合基于概念的恐惧泛化、区分被试对刺激的辨别力、增加恐惧刺激材料的准确性及多样化、结合激素等个体差异和多模态脑成像数据来展开。     

分类和概念对恐惧泛化的影响机制

恐惧泛化与多种焦虑障碍的病理基础密切相关。例如创伤后应激障碍个体往往持续地逃避与创伤事件有关的刺激,遭受着创伤痛苦折磨。本文在厘清知觉辨别与恐惧泛化关系的基础上,着力于高级认知过程(分类与概念相似性、典型性和人工概念)对恐惧泛化的影响,回顾了恐惧泛化的相关神经机制,并揭示恐惧泛化对焦虑障碍患者的临床治疗启示。未来研究应将知觉和高级认知维度的恐惧泛化进行整合研究,同时扩充恐惧习得和泛化的神经回路,以促进人类恐惧泛化更深入的研究。     

Verbal instructions targeting valence alter negative conditional stimulus evaluations (but do not affect reinstatement rates)

Negative conditional stimulus (CS) valence acquired during fear conditioning may enhance fear relapse and is difficult to remove as it extinguishes slowly and does not respond to the instruction that unconditional stimulus (US) presentations will cease. We examined whether instructions targeting CS valence would be more effective. In Experiment 1, an image of one person (CS+) was paired with an aversive US, while another (CS?) was presented alone. After acquisition, participants were given positive information about the CS+ poser and negative information about the CS? poser. Instructions reversed the pattern of differential CS valence present during acquisition and eliminated differential electrodermal responding. In Experiment 2, we compared positive and negative CS revaluation by providing positive/negative information about the CS+ and neutral information about CS?. After positive revaluation, differential valence was removed and differential electrodermal responding remained intact. After negative revaluation, differential valence was strengthened and differential electrodermal responding was eliminated. Unexpectedly, the instructions did not affect the reinstatement of differential electrodermal responding.     

The spread of fear: Symbolic generalization mediates graded threat-avoidance in specific phobia

Overgeneralization of fear and threat-avoidance represents a formidable barrier to successful clinical treatment of anxiety disorders. While stimulus generalization along quantifiable physical dimensions has been studied extensively, less consideration has been given to symbolic generalization, in which stimuli are indirectly and arbitrarily related. The present study examined whether the magnitude and extent of symbolic generalization of threat-avoidance and threat-beliefs differed between spider-phobic and nonphobic individuals. Initially, participants learned two sets of stimulus equivalence relations (A1?=?B1?=?C1; A2?=?B2?=?C2). Next, one cue (B1) was established as a conditioned stimulus (CS?+?; threat) that signalled onset of spider images and prompted avoidance, and another cue (B2) was established as a CS– (safety cue) that signalled the absence of such images. Subsequent testing showed that phobics compared to nonphobics exhibited greater symbolic generalization of threat-avoidance to threat cues A1 and C1 (indirect CS+ threat cues related via symmetry and equivalence, respectively), while all individuals showed nonavoidance to indirect safety cues A2 and C2. The enhanced symbolic generalization of threat-beliefs and avoidance behaviour observed in spider phobics warrants further investigation.     

Reinstatement of fear responses in human aversive conditioning

The treatment of choice for a number of anxiety disorders is exposure therapy. However, successful reduction of fear through exposure is sometimes followed by a (partial) return of symptoms of fear (return of fear, ROF; Clin. Psychol. Rev. 9 (1989) 147). Several possible learning mechanisms have been suggested to explain ROF (e.g. mechanisms related to spontaneous recovery, renewal, reacquisition and reinstatement). The present study focuses on reinstatement, which refers to the observation that mere US-only presentations can 'reinstate' previously extinguished fear responses. Although animal research has repeatedly demonstrated this phenomenon, little is known about fear reinstatement in humans. The present study employed a differential aversive conditioning procedure: after acquisition and a subsequent extinction procedure, a series of four unpredicted US-only trials was scheduled in the reinstatement group. The control group did not receive additional US presentations. A significant reinstatement effect was observed for US-expectancy ratings and fear ratings in the reinstatement group, but not in the control group. No differences were observed in a reaction time measure of resource allocation to the conditioned stimuli. These findings constitute a first demonstration of reinstatement of conditioned fear responses in humans. Implications for exposure treatment and suggestions for future research are discussed.     

Switching from approach to withdrawal is easier than vice versa

The preparedness theory of classical conditioning proposed by Seligman (1970, 1971) has been applied extensively over the past 40 years to explain the nature and “source” of human fear and phobias. In this review we examine the formative studies that tested the four defining characteristics of prepared learning with animal fear-relevant stimuli (typically snakes and spiders) and consider claims that fear of social stimuli, such as angry faces, or faces of racial out-group members, may also be acquired utilising the same preferential learning mechanism. Exposition of critical differences between fear learning to animal and social stimuli suggests that a single account cannot adequately explain fear learning with animal and social stimuli. We demonstrate that fear conditioned to social stimuli is less robust than fear conditioned to animal stimuli as it is susceptible to cognitive influence and propose that it may instead reflect on negative stereotypes and social norms. Thus, a theoretical model that can accommodate the influence of both biological and cultural factors is likely to have broader utility in the explanation of fear and avoidance responses than accounts based on a single mechanism.