Aversive and appetitive electrodermal classical conditioning using pictures as stimuli

The principal goal of this study was to verify whether it was possible to obtain both aversive and appetitive electrodermal classical conditioning, using pictures as conditioned stimuli (CS), and unconditioned stimuli (US). Additionally, we tried to verify whether, as a consequence of such conditioning, diminution of the unconditioned response (UR) was observed. With this aim, IAPS (?International Affective Picture System?) pictures were selected as stimuli. A picture showing a burnt face was used as the aversive US (USav), and a picture showing a scene with erotic content was used as the appetitive US (USap). As the aversive CS (CSav), and appetitive CS (CSap), two images with intermediate values of valence and arousal showing male faces were selected. In the experimental group, 10 CSav/USav and 10 CSap/USap trials were presented. In the control group 10 CSav, CSap, USav, and USap trials were presented in pseudorandom order. Skin conductance response (SCR) elicited by both the CSs and the USs was scored. Results showed aversive conditioning, but neither appetitive conditioning nor UR diminution. Problems to obtain conditioning using pictures as stimuli and possible options to overcome them in future research are discussed.     

Pavlovian conditioning of Hermissenda: current cellular, molecular, and circuit perspectives

The less-complex central nervous system of many invertebrates make them attractive for not only the molecular analysis of the associative learning and memory, but also in determining how neural circuits are modified by learning to generate changes in behavior. The nudibranch mollusk Hermissenda crassicornis is a preparation that has contributed to an understanding of cellular and molecular mechanisms of Pavlovian conditioning. Identified neurons in the conditioned stimulus (CS) pathway have been studied in detail using biophysical, biochemical, and molecular techniques. These studies have resulted in the identification and characterization of specific membrane conductances contributing to enhanced excitability and synaptic facilitation in the CS pathway of conditioned animals. Second-messenger systems activated by the CS and US have been examined, and proteins that are regulated by one-trial and multi-trial Pavlovian conditioning have been identified in the CS pathway. The recent progress that has been made in the identification of the neural circuitry supporting the unconditioned response (UR) and conditioned response (CR) now provides for the opportunity to understand how Pavlovian conditioning is expressed in behavior.     

External inhibition in a goldfish(carassius auratus) classical conditioning situation

Goldfish were classically conditioned with a light as the CS and shock as the US. The UR was a decrease in respiration. After 15 or 60 conditioning trials the fish were tested with novel stimuli (clicks) during the CS-US interval. High and moderate intensity novel stimuli produced a significant decrease in CRs (external inhibition) for fish with 60 conditioning trials (5.5 or 10.5 sec CS-US interval), but not fish with 15 conditioning trials. Low intensity novel stimuli produced no evidence for disinhibition (an increase in CRs). Control groups(e.g., groups with random presentations of the CS and US) showed that the external inhibition for fish with 60 conditioning trials was inhibition of a true CR.     

Evaluative conditioning depends on higher order encoding processes

Evaluative conditioning (EC) is commonly conceived as stimulus-driven associative learning. Here, we show that internally generated encoding activities mediate EC effects: Neutral conditioned stimuli (CS) faces were paired with positive and negative unconditioned stimuli (US) faces. Depending on the encoding task (Is CS a friend vs. enemy of US?), Experiment 1 yielded either normal EC effects (CS adopting US valence) or a reversal. This pattern was conditional on the degree to which encoding judgements affirmed friend or enemy encoding schemes. Experiments 2a and 2b replicated these findings with more clearly valenced US faces and controlling for demand effects. Experiment 3 demonstrated unconditional encoding effects when participants generated friend or enemy relations between CS and US faces. Explicitly stated friend or enemy relations in Experiment 4 left EC effects unaffected. Together, these findings testify to the importance of higher order cognitive processes in conditioning, much in line with recent evidence on the crucial role of conditioning awareness.     

Evaluative conditioning depends on higher order encoding processes

Evaluative conditioning (EC) is commonly conceived as stimulus-driven associative learning. Here, we show that internally generated encoding activities mediate EC effects: Neutral conditioned stimuli (CS) faces were paired with positive and negative unconditioned stimuli (US) faces. Depending on the encoding task (Is CS a friend vs. enemy of US?), Experiment 1 yielded either normal EC effects (CS adopting US valence) or a reversal. This pattern was conditional on the degree to which encoding judgements affirmed friend or enemy encoding schemes. Experiments 2a and 2b replicated these findings with more clearly valenced US faces and controlling for demand effects. Experiment 3 demonstrated unconditional encoding effects when participants generated friend or enemy relations between CS and US faces. Explicitly stated friend or enemy relations in Experiment 4 left EC effects unaffected. Together, these findings testify to the importance of higher order cognitive processes in conditioning, much in line with recent evidence on the crucial role of conditioning awareness.     

The role of contingency in classical conditioning

The assumption that classical conditioning depends on a contingent relation between the conditioned stimulus (CS) and the unconditioned stimulus (US), which was proposed some decades ago as an alternative to the traditional contiguity assumption, still is widely accepted as an empirical generalization, if no longer as a theoretical postulate. The first support for the contingency assumption was provided by experiments in which occasional CS-US pairings produced no response to the CS in random training--i.e., training in which the probability of the US was the same in the presence and absence of the CS. Those early experiments, the results of which too often are taken at face value, are reconsidered along with various later experiments that show conditioning, both of the CS and its context, in random training. The evidence suggests that CS-US contingency is neither necessary nor sufficient for conditioning and that the concept has long outlived any usefulness it may once have had in the analysis of conditioning.     

Acute stress impairs trace eye blink conditioning in females without altering the unconditioned response

Exposure to an acute stressor of inescapable swimming or intermittent tail shocks impairs classical eye blink conditioning 24h later in female rats. This effect is often attributed to a deficit in "learning," but since stress has been shown to induce analgesia, an alternative explanation is that stressor exposure reduces conditioning by lessening the perceived intensity of the unconditioned stimulus (US). To address this possibility we examined the amplitude of the unconditioned response (UR) during training and found that although exposure to the stressor impaired trace conditioning, there was no difference in the UR amplitude. We also found that eye blink responses to different US intensities (4-12 V) in the absence of training were unaffected by stressor exposure. Taken together, these experiments indicate that the stress-induced impairment of conditioning in females is not due to a decreased perception of US strength.     

Essential neuronal pathways for reflex and conditioned response initiation in an intracerebellar stimulation paradigm and the impact of unconditioned stimulus preexposure on learning rate

It has been demonstrated previously that pairing of tone CS and intracerebellar stimulation of lobule HVI white matter as the US produces conditioning that is robust and in many ways similar to that obtained with an airpuff US. The first study in this report addressed the effect of interpositus lesions on conditioned performance in rabbits trained with white matter stimulation as the US. It was found that interpositus lesions effectively eliminated the CR irrespective of the behavioral response measured. In addition, it was shown that the interpositus lesions also abolished the UR, providing strong evidence that the effects of the electrical stimulation were confined to the cerebellum and did not require the activation of brainstem structures. The second experiment examined performance on US-alone trials of varying durations. Response initiation within 100 ms of the US onset, regardless of US duration, indicated that reflex generation could not be due to rebound excitation of the interpositus following termination of Purkinje cell inhibition of that structure but instead likely reflects orthodromic activation of interpositus neurons via climbing fiber and/or mossy fiber collaterals. The impact of US preexposure on associative conditioning in this paradigm was also determined. Animals which received only 108 US-alone trials were massively impaired during subsequent training compared to rabbits that received fewer than 12 US-alone trials.     

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.     

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.     

Learning with arbitrary versus ecological conditioned stimuli: Evidence from sexual conditioning

Laboratory investigations of Pavlovian conditioning typically involve the association of an arbitrary conditioned stimulus (CS) with an unconditioned stimulus (US) that has no inherent relation to the CS. However, arbitrary CSs are unlikely to become conditioned outside the laboratory, because they do not occur often enough with the US to result in an association. Learning under natural circumstances is likely only if the CS has a preexisting relation to the US. Recent studies of sexual conditioning have shown that in contrast to an arbitrary CS, an ecologically relevant CS is resistant to blocking, extinction, and increases in the CS-US interval and results in sensitized responding and stronger second-order conditioning. Although the mechanisms of these effects are not fully understood, these findings have shown that signature learning phenomena are significantly altered when the kinds of stimuli that are likely to become conditioned under natural circumstances are used. The implications of these findings for an ecological approach to the study of learning are discussed.     

Associative changes with a random CS-US relationship

Three experiments examined conditioned magazine approach in rats when a positive unconditioned stimulus (US) bore a random relation to a conditioned stimulus (CS). Experiment 1 found that over the course of conditioning the CS initially elevated responding relative to the baseline but then lost the power to do so. Transfer tests revealed that a CS-US association developed early and persisted despite the decline in magazine responding. Experiment 2 confirmed the persistence of CS-US associations and found them to be more substantial when a different US occurred during the CS than in its absence. In Experiment 3, when the situation was exposed to US-alone presentations prior to introducing the CS, there was little evidence that a subsequent random relation between the CS and US produced an association between them. These results agree with those of blocking and overshadowing experiments using discrete CSs and support an interpretation of the random procedure in terms of competition between the background and CS for conditioning.     

Conditioning the unconditioned response: modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to an unconditioned stimulus (US) in the absence of a conditioned stimulus (CS). Three experiments monitored rabbit nictitating (Oryctolagus cuniculus) membrane unconditioned responses to 5 intensities and 4 durations of periorbital electrical stimulation before and after CS or US manipulation. CRM occurred after 12 days of CS-US pairings but not following unpaired CS/US presentations or restraint. CRM survived CS-alone and CS/US-unpaired extinction of the conditioned response (CR) but not presentations of the US alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without eliminating CRs. Data indicate CRM is a reliable, associative effect that is more than a generalized CR and may not be explained by habituation, stimulus generalization, contextual conditioning, or bidirectional conditioning.     

非条件刺激降低再评估对条件性恐惧消退的影响

诸多情绪障碍治疗的关键在于促进条件性恐惧反应的消退, 研究证明非条件刺激再评估能够引起恐惧反应的变化。本研究将非条件刺激降低再评估范式应用于消退训练, 以主观预期值、皮电反应作为恐惧反应指标, 考察恐惧习得后非条件刺激强度降低对条件性恐惧消退的影响, 并运用评价性条件作用探讨非条件刺激再评估的作用机制。结果表明：在消退阶段, 降低组对条件刺激的皮电反应显著低于控制组。同时评价性条件作用结果显示：经过非条件刺激再评估, 降低组较控制组对条件刺激的评价更为正性。说明非条件刺激降低再评估有效改变条件刺激的负性效价, 降低个体的恐惧反应、促进恐惧消退。     

US habituation,like CS extinction,produces a decrement in conditioned fear responding that is NMDA dependent and subject to renewal and reinstatement

Just as fear can be learned, it can also be inhibited. The most common way of reducing learned fear is through extinction, where the conditioned stimulus (CS) previously paired with an aversive unconditioned stimulus (US) is repeatedly presented on its own. Another, much less commonly studied, way to inhibit learned fear is by habituating, or devaluing, the US. In this procedure, fear responding to a CS is reduced by repeatedly presenting the US in the absence of the CS following the conditioning phase. The purpose of the present study was to directly compare the effects of US habituation and CS extinction on a learned fear response (freezing). Experiment 1 demonstrated that US habituation given either after (Experiment 1A) or before (Experiment 1B) fear conditioning reduced freezing to the CS at test. We then showed that the reduction in freezing resulting from either US habituation or CS extinction was context-specific (i.e., a change in context led to a renewal of the learned fear response; Experiment 2) and, furthermore, was attenuated when a pre-test shock was given (i.e., reinstatement of fear was observed in both cases; Experiment 3). Finally, Experiment 4 demonstrated that an injection of the NMDA antagonist MK-801 prior to US habituation impaired long-term retention of the learning that takes place during this procedure. Together, these results suggest that the decrement in conditioned fear responses produced by US habituation and CS extinction could rely on overlapping processes.     

Effect of posttrial episodes on conditioning in compound conditioned stimuli

The effect of signaled and nonsignaled posttrial episodes (PTEs) on conditioning to the target CS of a preceding compound CS-US trial was examined in two conditioned emotional response (CER) experiments with rats. Experiment 1 revealed that a nonsignaled PTE, a second shock US, interfered with conditioning to the preceding target CS and that the interference effect of the PTE was greater when it occurred 5 sec as opposed to 1,800 sec after the preceding compound CS-US trial. Experiment 2 revealed that if the shock PTE was signaled by a CS, its ability to interfere with conditioning was reduced. This second study also revealed that omission of an "expected" US interfered with conditioning to the target CS. The implications of these data for information processing models of Pavlovian conditioning are discussed.     

Is the devil in the detail? Evidence for S-S learning after unconditional stimulus revaluation in human evaluative conditioning under a broader set of experimental conditions

Whether valence change during evaluative conditioning is mediated by a link between the conditional stimulus (CS) and the unconditional stimulus (US; S-S learning) or between the CS and the unconditional response (S-R learning) is a matter of continued debate. Changing the valence of the US after conditioning, known as US revaluation, can be used to dissociate these accounts. Changes in CS valence after US revaluation provide evidence for S-S learning but if CS valence does not change, evidence for S-R learning is found. Support for S-S learning has been provided by most past revaluation studies, but typically the CS and US have been from the same stimulus category, the task instructions have suggested that judgements of the CS should be based on the US, and USs have been mildly valenced stimuli. These factors may bias the results in favour of S-S learning. We examined whether S-R learning would be evident when CSs and USs were taken from different categories, the task instructions were removed, and more salient USs were used. US revaluation was found to influence explicit US evaluations and explicit and implicit CS evaluations, supporting an S-S learning account and suggesting that past results are stable across procedural changes.     

Simultaneous classical conditioning of two effector systems

The experiment reported here was an attempt to develop an experimental procedure for independent classical conditioning of two different response systems, the skin conductance response (SCR) and the eyelid response. In a differential conditioning design with human subjects (N = 50) two different unconditioned stimuli were used, a white noise (US1) and airpuff (US2). Two conditioned stimuli (CS11 and CS12) were paired with US1, and two other CSs (CS21 and CS22) were paired with US2. A special trial architecture was used to accomplish measurement of both anticipatory SCR and eyelid responses during each trial. Significant eyelid differentiation as well as significant SCR (especially second interval responses) differentiation developed.     

状态焦虑对条件恐惧习得和消退的影响

采用44名正常女性大学生作为被试, 通过心理社会压力暴露的方法诱发焦虑组被试的状态焦虑, 采用主观预期值作为指标, 考察焦虑对条件恐惧习得和消退的直接影响, 并探讨这种影响是否也表现在评价性条件作用上。结果表明：心理社会压力暴露显著提高了焦虑组被试的状态焦虑。在习得阶段, 状态焦虑降低了被试对条件刺激的辨别条件恐惧反应, 具体而言, 状态焦虑降低了被试对CS+的主观预期值, 但是却提高了对CS?的主观预期值; 在消退阶段, 状态焦虑抑制了被试对条件刺激的消退。状态焦虑的影响也表现在评价性条件作用上, 和控制组相比, 焦虑组在习惯化和消退阶段对条件刺激表现出了更为负性的效价评定。