Number and time in acquisition,extinction and recovery

We measured rate of acquisition, trials to extinction, cumulative responses in extinction, and the spontaneous recovery of anticipatory hopper poking in a Pavlovian protocol with mouse subjects. We varied by factors of 4 number of sessions, trials per session, intersession interval, and span of training (number of days over which training extended). We find that different variables affect each measure: Rate of acquisition [1/(trials to acquisition)] is faster when there are fewer trials per session. Terminal rate of responding is faster when there are more total training trials. Trials to extinction and amount of responding during extinction are unaffected by these variables. The number of training trials has no effect on recovery in a 4-trial probe session 21 days after extinction. However, recovery is greater when the span of training is greater, regardless of how many sessions there are within that span. Our results and those of others suggest that the numbers and durations and spacings of longer-duration “episodes” in a conditioning protocol (sessions and the spans in days of training and extinction) are important variables and that different variables affect different aspects of subjects' behavior. We discuss the theoretical and clinical implications of these and related findings and conclusions—for theories of conditioning and for neuroscience.     

Partial reward training level and reward magnitude: Effects on acquisition and extinction

Two groups of 10 rats each received either a large magnitude (0.90 g) or a small magnitude (0.18 g) of partial reward (PR) and seven successive acquisition-extinction sessions in the runway. The large magnitude PR group ran much faster than the small magnitude PR group in the early acquisition sessions with differences between the groups declining over sessions. In the early extinction sessions, the large magnitude PR group showed greater resistance to extinction than the small magnitude PR group, but in the late extinction sessions this relation reversed itself. Finally, resistance to extinction decreased over sessions, this decrease being greater under a large than under a small magnitude of PR.     

疼痛恐惧的形成、泛化与消退

疼痛恐惧源于把疼痛等同于伤害的灾难化信念及对疼痛的负性解释, 它在慢性疼痛和能力丧失的发生和发展过程中起着重要作用。疼痛恐惧可以通过联合学习和观察学习等方式获得, 并且在具有相似特征的刺激中存在泛化现象。通过教育干预和等级暴露疗法等可以成功消退疼痛恐惧, 在消退过程中要控制安全信息等因素的不良影响。在疼痛恐惧的获得与消退中, 主要有杏仁核, 脑岛和前扣带皮层等脑区参与。未来的研究可以集中在深入探讨疼痛恐惧形成中的泛化及消退后的恢复、再巩固等现象, 加强其临床上的应用, 并综合心理、生物和认知神经科学, 研究疼痛恐惧的获得、泛化与消退的深层机制。     

Generalization gradients for acquisition and extinction in human contingency learning

Two experiments investigated the perceptual generalization of acquisition and extinction in human contingency learning. In Experiment 1, the degree of perceptual similarity between the acquisition stimulus and the generalization stimulus was manipulated over five groups. This successfully generated a generalization gradient of acquisition. In the subsequent phase, the response to the generalization stimulus was extinguished in each group. Finally, the acquisition stimulus was presented again. The response recovered differently over groups, thereby establishing the generalization gradient of extinction. In Experiment 2, the acquisition stimulus itself was extinguished before the set of generalization stimuli was tested between groups. One group evidenced a response recovery at test, which suggests that the gradient of acquisition is somewhat broader than the gradient of extinction.     

Context switch effects on acquisition and extinction in human predictive learning

Four experiments tested context switch effects on acquisition and extinction in human predictive learning. A context switch impaired probability judgments about a cue-outcome relationship when the cue was trained in a context in which a different cue underwent extinction. The context switch also impaired judgments about a cue trained in a context different from the extinction context, whenever this training was concurrent with extinction of another cue. After extinction, new cue-outcome relationships learned, even in a different task, became context specific. Moreover, renewal was consistently observed. It is suggested that context switch effects result from a process by which ambiguity leads participants to attend to the contexts.     

Comparison of the rates of associative change during acquisition and extinction

Five experiments used a compound test procedure to compare the rate parameters for the associative changes resulting from reinforcement and nonreinforcement. Experiments 1 and 4, using a magazine-approach procedure in rats, found initial acquisition to proceed more rapidly but to generalize less broadly than extinction. Experiments 2 and 5 repeated these observations in an autoshaping preparation with pigeons. Experiment 3 found no evidence for differential disruption of acquisition and extinction in testing. These results were obtained in a test procedure that compares responding with stimulus compounds in order to remove the differences in overall performance, which have complicated inferences about associative changes in earlier experiments.     

Babies by bar-press: Maternal behavior in the rat

Pregnant rats were trained to press a bar for food rewards: Postpartum these Ss were tested when each bar-press delivered a rat pup (S’s own or foster) into the food cup. Ss repetitively bar-pressed, snatched up the pup as it tumbled down the chute and retrieved the pup into the adjacent nest box. Ss lived with 6 nursing pups but bar-pressed for hundreds: E removed all but 6 pups from the nest box after S had accumulated about 20. Maximal performance was 684 responses in a 3-h period. This technique is currently being used to study weaning and hormonal factors involved in the rat’s maternal motivation.     

Amygdala and hippocampal activity during acquisition and extinction of human fear conditioning

Previous functional magnetic resonance imaging (fMRI) studies have characterized brain systems involved in conditional response acquisition during Pavlovian fear conditioning. However, the functional neuroanatomy underlying the extinction of human conditional fear remains largely undetermined. The present study used fMRI to examine brain activity during acquisition and extinction of fear conditioning. During the acquisition phase, participants were either exposed to light (CS) presentations that signaled a brief electrical stimulation (paired group) or received light presentations that did not serve as a warning signal (control group). During the extinction phase, half of the paired group subjects continued to receive the same treatment, whereas the remainder received light alone. Control subjects also received light alone during the extinction phase. Changes in metabolic activity within the amygdala and hippocampus support the involvement of these regions in each of the procedural phases of fear conditioning. Hippocampal activity developed during acquisition of the fear response. Amygdala activity increased whenever experimental contingencies were altered, suggesting that this region is involved in processing changes in environmental relationships. The present data show learning-related amygdala and hippocampal activity during human Pavlovian fear conditioning and suggest that the amygdala is particularly important for forming new associations as relationships between stimuli change.     

Runway acquisition and extinction as a joint function of magnitude of reward and percentage of rewarded acquisition trials

To determine the joint effects of partial reward and reward magnitude on acquisition and extinction rates, and on acquisition and extinction asymptotes, 215 Wistar albino rats were trained in a Hunter straight runway. The experimental design was a 4 × 4 × 2 factorial combining four reward magnitudes, four reward percentages, and two experimenters. The data revealed that the acquisition rate was an increasing function of both percentage and magnitude of reward and that neither reward magnitude nor percentage of reward significantly affected acquisition asymptote. For extinction, it was found that, for continuous schedules, the larger the reward magnitude the less the resistance to extinction and, for partial schedules, the larger the reward magnitude the greater the resistance to extinction. These results were interpreted within the framework of the sequential effects hypothesis (Capaldi, 1966).