Effects of naloxone on acquisition and extinction of jump-up avoidance behavior in rats

Two experiments were carried out to assess the effects of the opioid antagonist, naloxone, on the acquisition and extinction of shock avoidance by rats in the jump-up apparatus. In Experiment 1 naloxone pretreatment facilitated acquisition but had no effect on extinction of avoidance behavior. In the second experiment the effect of naloxone on acquisition was replicated and in addition, it was shown that naloxone enhanced freezing when a response prevention or flooding procedure was introduced. Again naloxone failed to alter the course of extinction, nor did it interact with the effects of flooding which, by itself, facilitated extinction. The results suggest that naloxone's effects are limited to increasing the functional intensity of the US, and provide further support for the dissociation between extinction of avoidance behavior and other indices of fear.     

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.     

Acquisition and extinction of signaled avoidance as a function of intermittent reinforcement

Signaled, shuttle-box avoidance responding in female rats of the Fischer₃₄₄ strain was examined as a function of four separate contingencies of intermittent reinforcement. In Experiment 1, when avoidance responses during acquisition were reinforced 25% of the time with prompt CS termination, animals responded equally often during acquisition and significantly more often during extinction than animals who received such reinforcement on a 100% schedule. Similar results were found under a trace procedure in Experiment 2 when avoidance responses were reinforced 25% of the time with informational feedback stimuli. In contrast, during Experiment 3, when animals were shocked on only 25% of the trials on which they failed to respond, the level of avoidance responding during both acquisition and extinction was significantly less than it was when animals were shocked on a 100% schedule. Comparable results were found in Experiment 4 when avoidance responses during acquisition averted shock on only 25% of the trials. Thus, intermittent reinforcement contingencies involving response-contingent feedback stimuli and shock have differential effects on avoidance responding during both acquisition and extinction trials under the signaled avoidance procedure.     

Some factors involved in the comparison of response systems: acquisition, extinction, and transfer of head-poke and lever-press Sidman avoidance

Head poking, a suggested natural escape reaction to shock for the rat, was compared to lever pressing in a Sidman avoidance study. Both responses could be emitted at any time, but only one was effective in a given session. Acquisition and extinction of the two responses were compared under both signalled and unsignalled avoidance. Then, a test for transfer was conducted in which acquisition conditions were re-instated, but the effectiveness of the responses was reversed. Three differences between responses were noted: (a) head poking was superior in reducing shock rates under signalled conditions; (b) head poking was more resistant to extinction, especially under signalled conditions; (c) under unsignalled conditions, animals were unable to learn to head poke if they had previously learned to lever press. Findings a and c were pursued in later experiments. Finding a depended on the location of the warning signal with respect to the response system. When the lever press required approach to the warning signal, the head poke was superior. But when the head poke required approach to the warning signal, the two responses were equally effective. Finding c depended on the absence of feedback for head poke during transfer. Two conclusions are offered: first, the two responses appear to obey the same laws when their topographical differences are taken into account. Second, response feedback appears to be more critical in transfer than in original acquisition.     

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).