Stimulus hierarchy generalization in systematic desensitization

A group of snake phobic Ss were desensitized to the first 5 items of a standard 7 item snake fear hierarchy in which the items were ordered on the basis of distance from a snake. This group and a no-treatment control group (which did not receive the desensitization) were treated for fear of all the hierarchy stimuli in terms of ratings both before and after the desensitization. The Ss rated their fear responses to all the stimuli as presented to them in (1) real form (2) by slide, and (3) in imaginal form. The results verified all four experimental hypotheses: (1) The experimental Ss showed greater fear reduction than the control Ss to both the training stimuli (the stimuli on which desensitization done) and the generalization stimuli (the other two stimuli), (2) The systematic desensitization (SD) group showed (a) more fear reduction to the last training stimuli than to the lower generalization stimulus and (b) more to the latter than to the higher generalization stimulus, (3) The SD group showed less fear reduction to the generalization stimuli in their real form than in both the slide and imaginai modalities (in the desensitization each stimulus presentation was done first in slide form and then in imaginal form), and (4) There were significant overall individual differences in generalization of fear reduction to the generalization stimuli.     

Within-compound associations between the context and the conditioned stimulus

Three experiments were conducted to test for the presence of associations between contextual cues and the nominal conditioned stimulus (CS) in fear conditioning. Rats were given tone-footshock pairings and were tested for their fear of the nominal CS, the tone, in a different context. Experiments 1 and 2 demonstrated that rats given nonreinforced exposure to the training context following conditioning were less fearful of the CS. Experiment 3 indicated that additional footshock presentations in the training context following conditioning produced greater fear of the CS. In both procedures postconditioning treatments designed to directly alter only the associative strength of the training context yielded parallel changes in the conditioned response to the CS. These data suggest that within-compound associations are formed between the context and the CS during classical conditioning.     

Potentiation of the acoustic startle response by a conditioned stimulus paired with acoustic startle stimulus in rats

The hypothesis that the standard acoustic startle habituation paradigm contains the elements of Pavlovian fear conditioning was tested. In a potentiated startle response paradigm, a startle stimulus and a light conditioned stimulus (CS) were paired. A startle stimulus then was tested alone or following the CS. Freezing behavior was measured to index conditioned fear. The startle response was potentiated on CS trials, and rats froze more in CS than in non-CS periods. In Experiment 1, response to a previously habituated, weak startle stimulus was potentiated. In Experiment 2, response to the same stimulus used as the unconditioned stimulus (US) in training was potentiated. This CS-potentiated response retarded the course of response decrements over training sessions as compared with an explictly unpaired control group. Conditioned fear is a standard feature of this habituation paradigm, serves to potentiate the startle response, and provides an associative dimension lacking in the habituation process per se.     

Investigating the effectiveness of brief cognitive reappraisal training to reduce fear in adolescents

As adolescent anxiety is common and costly, identifying effective strategies to reduce symptoms is a priority. This study tested whether adolescents could learn to use cognitive reappraisal strategies to attenuate fear during extinction learning. Fifty-seven participants (12–15 years) viewed images of two neutral faces, one which was paired with a fearful expression and shrieking scream (conditioned threat stimulus) and the other that was never paired with the aversive outcome (conditioned safety stimulus) during fear acquisition. Before extinction, participants either received cognitive appraisal training, which explored alternative, benign meanings associated with the scream or a control activity. Self-reported fear ratings in the cognitive reappraisal group were significantly lower to both the conditioned threat and safety stimuli after extinction than the control group. These findings did not characterise fear-potentiated startle data. Potential reasons for the lack of consistency between measures are considered.     

Measurement of fear of the conditioned stimulus and of situational cues at several stages of two-way avoidance learning

In Experiment 1, subjects were trained in a signaled two-way avoidance task to a criterion of either 2, 10, or 20 consecutive avoidance responses. Subsequently, they were allowed to escape, in the absence of shock, from one compartment of the avoidance apparatus to an adjacent safe box. For one group at each criterion level, the conditioned stimulus (CS) was presented during these trials; for another group, it was not (NCS). The rate and level of learning of the escape response were taken to reflect the amount of fear of the CS and situational cues present at the end of avoidance training for the CS groups and the amount of fear of the situational cues alone for the NCS groups. Under the CS condition, all groups learned equally well; under the NCS condition, learning occurred only in the two-criterion group. This pattern of results suggests that, as avoidance training continued, differential reinforcement led to the formation of a discrimination so that a substantial amount of fear was elicited by the CS plus situational cues but only a minimal amount by the situational cues alone. Such a loss of fear of situational cues would, according to effective reinforcement theory, serve to maintain or even increase reinforcement as avoidance training progressed. The results of Experiment 2, by ruling out some alternative explanations, supported the interpretation that the learning of the instrumental escape response in the first experiment was based on prior fear conditioning.     

Nicotine Produces a Within-Subject Enhancement of Contextual Fear Conditioning in C57BL/6 Mice Independent of Sex

Nicotine enhances learning including contextual fear conditioning. The present study extends previous work on nicotine and conditioned fear to examine the nature of nicotine's enhancement of contextual fear conditioning and sex differences in contextual fear conditioning in C57BL/6 mice using a within-subjects design. Mice were trained by pairing of an auditory stimulus of 80 dB, 6 cps train of broad-band clicks conditioned stimulus (CS) with a 2 sec., 0.35 mA shock unconditioned stimulus (US). Twenty-four hours later mice were tested for freezing in the original context, and one hour later mice were retested in the same context. A 0.5 mg/kg dose of nicotine was given either for three conditions: (1) before training, testing, and retesting; (2) before training and retesting; and (3) before retesting only. The use of a within-subjects design allowed for testing if nicotine would produce state-dependent deficits in contextual fear conditioning. Nicotine did enhance contextual fear conditioning in the groups that received nicotine for both training and testing. Nicotine, however, did not alter freezing when given on training but not testing or testing but not training. No sex differences, however, existed for conditioning or for nicotine's effects on conditioning. These results suggest that nicotine enhanced acquisition and retrieval processes but did not produce state-dependent deficits when administered just for training or just for testing.     

Nicotine produces a within-subject enhancement of contextual fear conditioning in C57BL/6 mice independent of sex

Nicotine enhances learning including contextual fear conditioning. The present study extends previous work on nicotine and conditioned fear to examine the nature of nicotine’s enhancement of contextual fear conditioning and sex differences in contextual fear conditioning in C57BL/6 mice using a within-subjects design. Mice were trained by pairing of an auditory stimulus of 80 dB, 6 cps train of broad-band clicks conditioned stimulus (CS) with a 2 sec., 0.35 mA shock unconditioned stimulus (US). Twenty-four hours later mice were tested for freezing in the original context, and one hour later mice were retested in the same context. A 0.5 mg/kg dose of nicotine was given either for three conditions: (1) before training, testing, and retesting; (2) before training and retesting; and (3) before retesting only. The use of a within-subjects design allowed for testing if nicotine would produce state-dependent deficits in contextual fear conditioning. Nicotine did enhance contextual fear conditioning in the groups that received nicotine for both training and testing. Nicotine, however, did not alter freezing when given on training but not testing or testing but not training. No sex differences, however, existed for conditioning or for nicotine’s effects on conditioning. These results suggest that nicotine enhanced acquisition and retrieval processes but did not produc state-dependent deficits when administered just for training or just for testing.     

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。     

条件性恐惧记忆消退返回的性别差异

采用预期判断任务考察男女性对已消退的条件性恐惧记忆是否会出现消退返回的现象。结果表明: (1)在对已习得的条件性恐惧记忆消退后4个小时进行测试, 被试整体会出现明显的消退返回现象; (2)对消退返回现象的性别差异进行比较, 女性比男性的消退返回现象更突出, 并且差异显著; (3)与男性相比, 女性对条件性恐惧记忆具有易习得难消退的趋势, 但是性别差异不显著。研究结果验证了消退返回现象存在的普遍性, 并且有着显著的性别差异, 为以后对创伤后应激障碍患者的治疗应考虑性别因素提供了心理学依据。     

Eye movements of children, adults, and elderly persons during inspection of dot patterns

The effectiveness of three fading and two nonfading procedures were compared in training kindergarten children on an oddity problem in which shape was the relevant dimension. The fading procedures employed supplementary cues which were gradually eliminated during training. The cues included either saturating the odd stimulus with a red color, saturating the nonodd stimuli with a red color, or varying the degree of illumination of the nonodd stimuli. One nonfading group received training on a structurally simpler oddity problem prior to transfer to a more complex oddity problem, and a second nonfading group received the standard oddity training procedure. While significant differences in acquisition were not obtained between training groups, the oddity task performance and the results from a test of dimensional observation revealed that the fading procedures were differentially effective in transferring Ss′ observation from the dimension of the fading cue to that relevant for solution of the oddity problem.     

Transfer of inhibition after serial and simultaneous feature negative discrimination training

Three experiments examined the nature of inhibitory learning in Pavlovian simultaneous (A+, XA-) and serial (A+, X → A-) feature negative discrimination prodecures in a conditioned suppression situation with rat subjects. The feature (X) trained with simultaneous procedures readily inhibited suppression conditioned to another excitor (B) that was not involved in the feature negative discrimination with X. But the feature trained with serial procedures showed little or no ability to inhibit suppression conditioned to other excitors. These results were obtained with both between- and within-subjects designs, with a variety of test procedures, and after extinction of the A excitor used to establish the inhibition to X. They suggest that nature of the inhibition learned in feature negative discriminations depends on the temporal arrangement of stimuli. We favored the possibility that inhibitors established using simultaneous stimulus arrangements modulate behavior by acting on a representation of the unconditioned stimulus, but inhibitors established with serial procedures act on particular conditioned stimulus-unconditioned stimulus associations.     

AX+, BX- discrimination learning in the fear-potentiated startle paradigm: possible relevance to inhibitory fear learning in extinction

The neural mechanisms of fear suppression most commonly are studied through the use of extinction, a behavioral procedure in which a feared stimulus (i.e., one previously paired with shock) is nonreinforced repeatedly, leading to a reduction or elimination of the fear response. Although extinction is perhaps the most convenient index of fear inhibition, a great deal of behavioral work suggests that postextinction training conditioned stimuli are both excitatory and inhibitory, making it difficult to determine whether a neural manipulation affects inhibition, excitation, or some combination thereof. For this reason we sought to develop a behavioral procedure that would render a stimulus primarily inhibitory while at the same time avoiding some of the issues raised by the traditional conditioned inhibition paradigm, namely second-order conditioning, external inhibition, and configural learning. Using the fear-potentiated startle paradigm, we adapted an AX+, BX- training procedure in which stimuli A and X were presented simultaneously and paired with shock, and stimuli B and X were presented simultaneously in the absence of shock. In testing, high levels of fear-potentiated startle were seen in the presence of A and AX and much lower levels were seen in the presence of B and AB, as would be predicted if stimulus B were a conditioned inhibitor. We believe this method is a viable alternative to the traditional conditioned inhibition training procedure and will be useful for studying the neural mechanisms of fear inhibition.     

Non-differential return of fear in humans after a reinstatement procedure

The present experiment investigated reinstatement of fear in humans using a differential fear conditioning preparation. In this experiment, one neutral stimulus (conditioned stimulus; CS+) was paired with an aversive stimulus (unconditioned stimulus; US) during the acquisition phase, while another neutral stimulus was not (CS−). This procedure led to a difference in responding between the CS+ and the CS− (i.e., differential conditioning). After this acquisition phase, an extinction phase followed, during which both CSs were presented without the US, resulting in a decrease in differential conditioned responding. Reinstatement refers to the return of extinguished conditioned responses due to the experience of US-only trials after the extinction phase. This phenomenon was investigated by presenting half of the participants (reinstatement group) with unpredictable USs after the extinction phase. The control group did not receive these USs after the extinction procedure. The results show that return of fear was clearly apparent after the reinstating USs. This return of fear was, however, not limited to the CS+. An increase in ‘conditioned’ responding was also observed for the control stimulus. This interesting observation will be discussed against the background of a number of recent theoretical conceptualizations of reinstatement.     

Fear inhibition and species specific defense reaction termination may contribute independently to avoidance learning

A series of three experiments was conducted to test the proposal of Cicala and Owen (Learning and Motivation, 1976, 7, 356–367) that warning signal termination reinforces avoidance learning by permitting fear to dissipate and that a feedback signal reinforces avoidance learning through conditioned inhibition of fear. A CER procedure with a second-by-second analysis was used to measure fear elicitation and fear reduction following classical conditioning or avoidance training. The results show that a feedback signal produces rapid and marked fear reduction, suggesting an inhibitory process. Although warning signal termination produced fear reduction, the slowness of this process suggests fear dissipation and not an inhibitory process. The combination of both events reduced fear no more effectively than a feedback signal alone. It is suggested that warning signal termination is effective in some avoidance learning situations not because it reduces fear, but possibly because it helps terminate an avoidance response that closely resembles a species specific defense reaction.     

Auditory specific fear conditioning results in increased levels of synaptophysin in the basolateral amygdala

Auditory fear conditioning is one of the most well characterized models used in studies of learning and memory. In order to ensure the animals have been conditioned to fear the auditory stimulus, animals are generally tested for their response to this stimulus in a different context to that used for training. For this reason it is often unclear how much contextual fear conditioning the animals also acquire when they are trained. In this study, we have established a protocol for fear conditioning in mice which is explicit for auditory cues; mice trained using this protocol, show a very low fear response to contextual cues encountered during training. We have undertaken analysis to look for potential brain changes associated with this model by measuring levels of the synaptic vesicle protein, synaptophysin, in the basolateral nuclei of the amygdala following auditory fear conditioning. Our results show levels of synaptophysin were significantly higher in mice which learnt to associate the auditory stimulus with fear, in comparison to all non-learning control animals. These findings support the idea that synaptic plasticity associated with formation of fear conditioning to a single specific conditioned stimulus occurs within the basolateral nuclei of the amygdala. Furthermore, our results demonstrate the usefulness of this model in looking for changes in the brain specific for a defined learning event.     

Variations in explicitly unpaired training are differentially effective in producing conditioned inhibition

To evaluate a contingency interpretation of conditioned inhibition (CI), rats were given “explicity unpaired” training in which the locus and duration of a CS within the inter-US (shock) interval were systematically manipulated for different groups. Summation and retardation tests in Experiment 1 indicated that stronger CI resulted from both a backward and a trace CS than from a midlocus CS of equal or greater duration. Complementing these findings, the same tests in Experiment 2 showed that, by comparison with novel-stimulus controls, CI developed to a trace CS but not to a mid-locus CS, nor to a trace CS that was accompanied by an immediate signal for the US. These findings argue against a contingency interpretation of CI and favor a contiguity interpretation stressing the short-term rehearsal of stimulus events. Such rehearsal of the US allows a backward CS, but not a mid-locus CS with an extended US-CS interval, to be discriminated as a signal for nonreinforcement, and thus to develop as a conditioned inhibitor. Similarly, excitatory conditioning to the memory trace of a CS allows the nominal trace CS to develop as a signal for nonreinforcement, and thus as a conditioned inhibitor, but not when its memory trace is overshadowed by another CS that immediately precedes the US. In short, the development of CI is facilitated when excitation is mediated by the memorial processing of either the US or a discrete CS for the US rather than by contextual cues.     

Stimulus specificity in avoidance learning

The present experiments address the issue of stimulus specificity in fear and avoidance learning. First, it was established that light stimuli are effective warning signals (WS) in shuttle avoidance. Then light stimuli were shown to produce conditioned suppression in the conditioned emotional response situation comparable to that produced by noise conditioned stimuli. Finally, the effectiveness of noise onset and noise offset as feedback signals was tested. This was assessed under conditions of immediate and delayed termination of a light WS. Delayed termination of a light WS interfered with avoidance learning and the introduction of noise offset as a feedback signal enhanced it. The only demonstration of stimulus specificity was the failure of noise onset to function as a feedback signal.     

The effects of single-component extinction of a three-component serial CS on resistance to extinction of the conditioned avoidance response

Central to a fear interpretation of how avoidance responses are maintained in the absence of further CS-UCS pairings is the underlying assumption of an existing gradient of fear across the CS-UCS interval. Extrapolations based on this gradient lead to a number of differential predictions concerning the topography of avoidance responding during extinction. The present research was concerned with the differential effects of extinguishing separate components of the CS complex upon responding to the complete CS complex during extinction. In Phase 1 of the study, rats were classically conditioned to a three-component serial CS (S₁/S₂/S₃) followed by shock. Each subject was then given avoidance training in a one-way apparatus to a criterion of one successful avoidance. In Phase 2, subjects were divided into four groups, with three of the groups receiving nonreinforced exposure for 25 trials to one of the components of the serial CS (S₁, S₂, or S₃). The fourth group (S₀) was exposed for the same period of time to the apparatus cues. In Phase 3, the total stimulus complex was reintroduced in its original order, and animals were tested until extinction of the instrumental response was reached. The results are consistent with the hypothesis that a fear gradient exists in extinction and decreases in magnitude as the distance from the point of UCS onset increases.     

Fear generalization in humans: Impact of verbal instructions

Fear generalization lies at the heart of many anxiety problems, but little is known about the factors that can influence this phenomenon. The present study investigated whether verbal instructions about specific stimulus features can influence conditioned fear generalization. All participants were fear conditioned to a yellow triangle, using an electric shock. Participants had received pre-experimental instructions saying that the shapes (or colours) of the stimuli were informative for the occurrence of shock (group Shape and group Colour, respectively). Next, generalization was tested to presentations of a blue triangle (same shape) as well as a yellow square (same colour). Fear reactions were measured through skin conductance and online ratings of shock-expectancy. The results showed strongest generalization to the same shape stimulus in group Shape, versus the same colour stimulus in group Colour. Hence, the same learning experience can have opposite effects in terms of fear generalization, depending on verbally transmitted information about the relative importance of individual stimulus features.     

Differential effects of forward or simultaneous conditioned stimulus-unconditioned stimulus intervals on the defensive behavior system of the Norway rat (Rattus norvegicus)

To test several predictions derived from a behavior-systems approach, the authors assessed Pavlovian fear conditioning in rats after 30 trials of forward, simultaneous, or unpaired training. Direct evidence of conditioned fear was collected through observation of flight and freezing reactions during presentations of the conditioned stimulus (CS) alone. The authors also tested the CS's potential to reinforce an instrumental escape response in an escape-from-fear paradigm. On the one hand, rats that received forward training showed conditioned freezing, but no conditioned flight was observed. On the other hand, rats that received simultaneous training showed conditioned flight, but no conditioned freezing was observed. Rats that received either forward or simultaneous pairings showed instrumental learning of the escape-from-fear response. Implications for several theories of Pavlovian conditioning are discussed.