Priming and trial spacing in extinction: Effects on extinction performance,spontaneous recovery,and reinstatement in appetitive conditioning

Previous research in this laboratory suggests that priming of the conditional stimulus (CS) in short-term memory may play a role in the trial-spacing effects in appetitive conditioning. For example, a nonreinforced presentation of a CS 60 s before a reinforced trial with the same CS produced slower acquisition than a CS presentation that occurred 240 s before the reinforced trial. The results were consistent with the self-generated priming mechanism proposed by Wagner (e.g., Wagner 1978, 1981). The present experiments extended the earlier work by examining the effects of trial spacing in extinction rather than acquisition. After conditioning with a mixture of intertrial intervals (ITIs), rats received extinction with ITIs of 60 or 240 s, longer or shorter values, or different ways of “chunking” extinction trials in time. Although trial spacing produced effects on extinction performance that were consistent with our previous research on acquisition, there were few long-term differences in spontaneous recovery or in reinstatement. Short ITIs in extinction appear to affect extinction performance more than they affect extinction learning. Mechanisms of trial spacing in conditioning and extinction are discussed.     

Effects of contextual conditioning and unconditional stimulus presentation on performance in appetitive conditioning

Four experiments with rat subjects examined the effects of contextual conditioning on conditioned appetitive performance. Experiment 1 compared the effects of contextual conditioning on performance to conditioned stimuli (CSs) with different conditioning histories. Contextual conditioning enhanced performance to the CS if the CS had first been conditioned and then extinguished, but had no effect on performance when the CS had been merely paired or unpaired with food. Experiments 2 and 3 then asked whether the effect on the extinguished CS was due to contextual conditioning acting as a cue for conditioning. In Experiment 2, extinction procedures in which extra unconditioned stimuli (USs) were presented during the intertrial intervals were found to reduce the CS's sensitivity to enhancement by contextual conditioning, but had no effect on spontaneous recovery. In Experiment 3, USs added to conditioning or extinction acquired the ability to cue the corresponding performance. Under some conditions, USs added to conditioning could suppress performance (Experiment 4). The results suggest that contextual conditioning has complex effects that can be better understood by recognizing that contextual conditioning, as well as the USs that create it,Mayacquire discriminative control over conditioned responding.     

Analysis of us-preexposure effects in appetitive conditioning

In two experiments, rats received preexposure to one type of food followed by autoshaping in which presentation of one lever was associated with the preexposed food, and presentation of another lever with a novel type of food pellet. In both it was found that acquisition of the leverpress response occurred more readily on the lever associated with the novel food. This example of the US (unconditioned stimulus) preexposure effect is not to be explained in terms of the development of competing responses during preexposure. Explanations in terms of blocking by contextual cues and of habituation to the US are considered.     

The role of extinction and reinstatement in attentional bias to threat: a conditioning approach

We investigated the effects of extinction and reinstatement on attentional bias to fear-conditioned signals in healthy individuals using an emotional modification of a spatial cueing paradigm. Spatial cues were emotionally modulated using differential conditioning. The CS+ was sometimes followed by an aversive electrocutaneous stimulus (UCS), whereas the CS- was never followed by the UCS. During a subsequent extinction phase no UCS was presented anymore. The reinstatement phase started with one or four unpredicted UCS-only trials for half of the participants (reinstatement group). For the other half there were no additional UCS presentations (control group). We found that attention was biased to threat signals during acquisition. This biased attention largely disappeared during extinction. During the reinstatement phase attentional bias to threat signals re-emerged in the reinstatement group, but not in the control group.     

Lesions of rat infralimbic cortex enhance recovery and reinstatement of an appetitive Pavlovian response

The prefrontal cortex (PFC) has a well-established role in the inhibition of inappropriate responding, and evidence suggests that the infralimbic (IL) region of the rat medial PFC (MPFC) may be involved in some aspects of extinction of conditioned fear. MPFC lesions including, but not those sparing the IL cortex increase spontaneous recovery of extinguished conditioned fear when tested 24 h after an initial extinction session. The current experiment extended these findings by use of appetitive rather than aversive conditioning. Ten IL-lesioned and 11 sham-operated rats were trained on a Pavlovian task in which a conditioned stimulus (CS) was followed by food pellets (the unconditioned stimulus or US). IL lesions had no effect on extinction of the conditioned response (CR, magazine entries) during the first extinction session. However, the level of spontaneous recovery between the first extinction session and a second, 24 h later, was increased in IL-lesioned rats relative to sham animals. In contrast, evidence of savings measured between the extinction sessions did not differ between groups. Furthermore, reinstatement of the CR following unsignaled delivery of the US was also increased in IL-lesioned rats.     

CS Intensity effects on rabbit nictitating membrane conditioning,extinction and generalization

One purpose of the present experiments was to determine if the Grice and Hunter (1964) observation of augmented within-versus between-Ss CS intensity effects in human eyelid conditioning would be obtained in conditioning of the rabbit’s nictitating membrane response under two (Experiment 1) and four (Experiment 2) CS intensity values. In addition, a determination was made of the effects of CS intensity upon extinction and stimulus intensity generalization gradients. The studies revealed that: (a) while acquisition performance was positively related to CS intensity, the effect was independent of the between and within-S manipulation of CS intensity; (b) rate of response decrement in extinction was an inverse function of CS intensity; and (c) a positively sloped intensity generalization gradient was obtained when the training stimulus was the low-intensity one. Overall, these results are most consistent with Hull’s (1949) stimulus intensity dynamism account of CS intensity effects in conditioning.     

Differential acquisition,extinction, and reinstatement of conditioned suppression in mice

In animals, the reappearance of conditioned fear responses after extinction has been primarily investigated using single-cue conditioning paradigms. However, a differential paradigm can overcome several of the disadvantages associated with a single-cue procedure. In the present study, the reinstatement phenomenon was assessed in mice using a differential conditioned suppression paradigm. In a first phase, one conditioned stimulus (CS + ) was consistently paired with an unconditioned stimulus (US; footshock) while another CS (CS–) was not, resulting in selective suppression of previously trained instrumental behaviour during the CS + . After the extinction phase, half of the animals (reinstatement group) were presented with unsignalled USs, while the other half were not (control group). A differential return of conditioned responding was observed in the reinstatement group, but not in the control group. The implications of these findings for future conditioning research are discussed.     

Differential acquisition, extinction, and reinstatement of conditioned suppression in mice

In animals, the reappearance of conditioned fear responses after extinction has been primarily investigated using single-cue conditioning paradigms. However, a differential paradigm can overcome several of the disadvantages associated with a single-cue procedure. In the present study, the reinstatement phenomenon was assessed in mice using a differential conditioned suppression paradigm. In a first phase, one conditioned stimulus (CS + ) was consistently paired with an unconditioned stimulus (US; footshock) while another CS (CS-) was not, resulting in selective suppression of previously trained instrumental behaviour during the CS + . After the extinction phase, half of the animals (reinstatement group) were presented with unsignalled USs, while the other half were not (control group). A differential return of conditioned responding was observed in the reinstatement group, but not in the control group. The implications of these findings for future conditioning research are discussed.     

The influence of extinction and counterconditioning instructions on evaluative conditioning effects

In three experiments, we tested the influence of instructions about an allegedly upcoming extinction or counterconditioning phase on evaluative conditioning (EC) effects. After an acquisition phase in which neutral stimuli were related to positive or negative stimuli via instructions (Experiments 1 and 2a) or actual pairings (Experiment 2b), three different groups of participants were either informed that in the next phase the neutral stimuli would be presented without positive or negative stimuli (extinction instruction), that the neutral stimuli in the next phase would be paired with stimuli of the opposite valence than before (counterconditioning instruction), or received no further instructions. Afterwards, liking of the originally neutral stimuli was measured either with an evaluative rating (Experiment 1) or with an Implicit Association Test (IAT; Experiments 2a and 2b). EC was reduced in the counterconditioning condition of Experiment 1 and in the joint analysis of Experiments 2a and 2b. The extinction instruction led to a reduction of EC only in Experiment 1. Finally, whether the acquisition phase consisted of instructions about CS–US pairings (Experiment 2a) or the actual experience of CS–US pairings (Experiment 2b) did not significantly impact the observed changes in liking. Overall, our results suggest that similar mechanisms might mediate instruction- and experienced-based EC. Our results are in line with propositional models of EC but can be explained also by association formation models and dual process models of EC, provided that certain auxiliary assumptions are made.     

Avoidance conditioning as a function of appetitive stimulus pretraining: Response and stimulus transfer effects

Pretrained appetitive discriminative stimuli were used as warning signals in subsequent avoidance learning. In Expt 1 identical responses were required in pretraining and in avoidance learning. An appetitive S+ facilitated avoidance learning in rats in comparison to S? or a stimulus previously uncorrelated with food. In Expt 2, the type of response in pretraining and in avoidance learning was varied. Groups with homogeneous responses in the two situations replicated Expt 1 results, whereas groups with different responses in pretraining and avoidance learning failed to show an advantage when S+ served as warning; in the heterogeneous response groups, S? was as effective as S+. Inhibitory factors in the heterogeneous groups were discussed as an explanation for these results.     

Sequential response effects in the white rat during conditioning and extinction on a DRL schedule,

Sequential IRT data were obtained for three rats on a DRL 60-sec reinforcement schedule. It was found that first-order sequential dependencies exist under this schedule, including the partial dependence of the length of any given IRT on the length of the preceding IRT. The sequential analysis also served to extend the finding in the literature, based on frequency distributions, that the likelihood of a reinforced IRT is greater after a reinforced IRT than a non-reinforced IRT. Rapid extinction and reconditioning were obtained.     

Transfer of the partial reinforcement extinction effect between escape (shock) and appetitive (food) conditioning

In the first experiment rats were given partial reinforcement or continuous reinforcement in either an escape or an appetitive paradigm. Subsequently, the rats received continuous reinforcement training under motivational conditions opposite those experienced earlier. Finally, responses were extinguished according to the motivational conditions experienced in the second phase. The results indicated that partial reinforcement in the initial phase operated to increase resistance to extinction in the last. In a second experiment this intermotivational partial reinforcement extinction effect was shown to survive interpolated experiences with extinction, a 1-week rest period, and continuous reinforcement reacquisition. A third experiment examined the influence of intramodal versus intermodal nonreinforcement-reinforcement sequences on the intermotivational partial reinforcement extinction effect. Interactive effects between similarity of aversive outcome (escape nonreinforcement, appetitive nonreinforcement) and reinforcement type (negative, positive) were found. The theoretical implications of the data from all three experiments are discussed.