Reacquisition following extinction in appetitive conditioning

In four experiments utilizing an appetitive conditioning preparation, reacquisition of conditioned responding was found to occur both rapidly and slowly following extinction. In Experiment 1, acquisition of responding to a tone that had been conditioned and extinguished occurred more rapidly than acquisition in either a group that received equivalent exposure to the food unconditioned stimulus or a “rest” control group that received only exposure to the apparatus in the first two phases. However, reacquisition was impaired relative to acquisition in a “learning-experienced” group that had previously received conditioning and extinction with a different stimulus. Experiments 2 and 3 produced similar results, but also found that high responding during reacquisition was confined to trials that followed reinforced, rather than nonreinforced, trials. Experiment 4, in which very few initial conditioning trials were used, produced reacquisition that was slow compared with both learning-experienced and rest controls. The results are consistent with a role for sequential learning: Reacquisition is rapid when animals have learned that reinforced trials signal other reinforced trials.     

Context effects on conditioning,extinction, and reinstatement in an appetitive conditioning preparation

Three experiments with rat subjects examined the effects of contextual stimuli on performance in appetitive conditioning. A 10-sec tone conditioned stimulus (CS) was paired with a food-pellet unconditioned stimulus (US); conditioning was indexed by the observation of headjerking, a response of the rat to auditory stimuli associated with food. In Experiment 1, a context switch following initial conditioning did not affect conditioned responding to the tone; however, when the response was extinguished in the different context, a return to the original conditioning context “renewed” extinguished responding. These results were replicated in Experiments 2 and 3 after equating exposure to the two contexts (Experiment 2) and massing the conditioning and extinction trials (Experiment 3). The results of Experiment 1 also demonstrated that separate exposure to the US following extinction reinstates extinguished responding to the tone; this effect was further shown to depend at least partly on presenting the US in the context in which testing is to occur (Experiments 2 and 3). Overall, the results are consistent with previous data from aversive conditioning procedures. In either appetitive or aversive conditioning, the context may be especially important in affecting performance after extinction.     

Role of exteroceptive background context in taste-aversion conditioning and extinction

In two experiments, saccharin (CS) and lithium chloride (US) were paired in a context consisting of specific visual, auditory, tactual, and olfactory cues. The saccharin aversion was then extinguished in a context free from conditioning-context cues. Later, saccharin preference tests were given in the presence and absence of these cues. The results indicated that the background cues of the conditioning trial controlled the amount of saccharin drunk on extinction trials, and, furthermore, that extinction of the taste aversion was context specific; i.e., groups given extinction trials in a different (from conditioning) context retained their saccharin aversion in the conditioning context only. The results indicate an important role played by the exteroceptive context in taste-aversion conditioning.     

Pavlovian appetitive discriminative conditioning inAplysia californica

Three experiments demonstrated Pavlovian appetitive discrimination learning in the marine mollusc,Aplysia californica. In each experiment, subjects were exposed to two conditioned stimuli; one stimulus (CS+) was paired with food presentations and the other stimulus (CS?) was never followed by food. In Experiments 1 and 3 different chemosensory stimuli were used, and in Experiment 2 different tactile stimuli were used. For both types of conditioned stimuli, bite responses occurred significantly more often to the CS+ than to the CS?. Experiment 2 also showed thatAplysia could learn a reversal of this discrimination. Experiment 3 showed that nonreinforced presentations of CS+ resulted in a decline in the frequency of conditioned biting. The implications of these results for neurobiological analyses of learning are discussed.     

Overexpectation in appetitive Pavlovian and instrumental conditioning

In three experiments that used appetitive preparations with rats, we examined the effects of reinforcing a compound consisting of two previously reinforced stimuli on subsequent responding to those stimuli. Experiment 1 showed that a Pavlovian conditioned stimulus given this treatment evoked fewer magazine entries when presented alone than did a reinforced stimulus that did not receive the compound treatment. Experiment 2 examined inhibition of delay and generalization decrement accounts for the results of Experiment 1. Experiment 3 extended this finding to an instrumental learning paradigm.     

Pavlovian appetitive conditioning under curare in rats

A CS was paired with rewarding intracranial stimulation while Ss were immobilized by curare. Tests of the activity response to the CS were carried out before and after conditioning. With either simple or discriminative conditioning, activity to the rewarded CS increased after training. These results are comparable to those in studies using food reward and support the hypothesis that a central motivational state is conditioned to stimuli preceding reward.     

Temporal integration in Pavlovian appetitive conditioning in rats

We used an appetitive sensory preconditioning procedure to investigate temporal integration in rats in two experiments. In Phase 1, rats were presented with simultaneous compound trials on which a 10-sec conditioned stimulus (CS) X was embedded within a 60-sec CS A. In Group Early, CS X occurred during the early portion of CS A, whereas in Group Late, CS X occurred during the latter portion of CS A. In Phase 2, CS X was paired simultaneously with sucrose. On a subsequent test with CS A, the rate of magazine entries peaked during the early portions of the stimulus in Group Early and during the latter portions of the stimulus in Group Late (Experiments 1 and 2). Similar response peaks were not observed on tests with a control stimulus that had been presented in compound with a stimulus that did not signal reward (Experiment 2).     

Classical-classical transfer: Effects of prior appetitive conditioning upon aversive conditioning in rabbits

An appetitive-ayersive transfer experiment with rabbits determined that prior paired and unpaired tone CS and water US presentations, given in jaw-movement (JM) conditioning, respectively facilitated and retarded the acquisition of the nictitating membrane (NM) CR when the tone was subsequently paired with a shock US. In addition, the unpaired tone and water deliveries reduced the level of JM conditioning that was undertaken following the completion of NM CR acquisition. Finally, the reacquisition of the NM CR was accompanied by a large savings effect in contrast to the failure of the JM CR to display reacquisition savings. When the present findings are compared to the results of previous work addressing the influence of prior NM conditioning procedures upon subsequent JM CR acquisition, an asymmetry in appetitive-aversive interactions is indicated. This asymmetry encourages a reinterpretation of the opponent-process explanation of appetitive-aversive interactions. Moreover, the observed effects of the unpaired CS suggest the operation of a salience factor.     

Enhanced Pavlovian conditioning with a change in appetitive reinforcer

In three experiments, rats received appetitive conditioning with two unconditioned stimuli (US₊ and US*) that supported a similar conditioned response. Stimulus A was first paired with US₊, and then, for a second stage of training, the compound AB was paired with US*. Subsequent test trials with A revealed an abnormally strong conditioned response. The findings from additional groups indicated that such enhanced conditioning with A depended on the presence of B in the second stage and on the use of US₊ and US* for the two training stages. A modification to a configural theory of conditioning is proposed in order to explain the results.     

Trial and intertrial durations in appetitive conditioning in rats

The effects of trial (T) and intertrial (I) durations were examined in two Pavlovian conditioning experiments with rats, in which a noise conditioned stimulus (CS) was paired with food delivery. In Experiment 1,T was either 10 or 20 sec, andI ranged from 15 to 960 sec, in separate groups of rats. The acquisition rate and final level of conditioned responding showed ratio invariance: They were better predicted by theI/T ratio than byI orT alone. In Experiment 2, theI/T ratio was 6.0 in all the groups, andT was 20, 40, 80, or 160 sec. Ratio invariance was not observed: Despite the commonI/T ratio, the rate of acquisition, final level of conditioned responding, and the ability of the CS to block conditioning of another stimulus differed among the groups. At the same time, the temporal distribution of conditioned responding withinT was similar in all the groups throughout conditioning and extinction and showed superpositioning when normalized acrossT. Many but not all aspects of the data were consistent with scalar timing theory.     

Blocking and enhancement of fear conditioning by appetitive CSs

Prior research on Pavlovian-to-instrumental transfer has shown that when a CS previously associated with shock (AvCS+) is presented contingent upon a choice response to a discriminative stimulus for food reinforcement, it facilitates discrimination learning. Conversely, a response-contingent CS previously associated with the absence of shock (AvCS?) retards discrimination learning. To evaluate whether these findings reflect across-reinforcement blocking and enhancement effects, two experiments investigated the effects of appetitively conditioned stimuli on fear conditioning to a novel stimulus that was serially compounded with the appetitive CS during conditioned-emotional-response (CER) training. Although there were no differential effects of the appetitive CSs in CER acquisition, Experiment 1, using a relatively weak shock US, showed that a CS previously associated with food (ApCS+) retarded CER extinction to the novel stimulus, in evidence of enhanced fear conditioning to that stimulus. In addition, Experiment 2, using a stronger shock US, showed that a CS previously associated with the absence of food (ApCS?) facilitated CER extinction to the novel stimulus, in evidence of weaker fear conditioning to that stimulus. These results parallel traditional blocking effects and indicate not only that an ApCS+ and an ApCS? are functionally similar to AvCSs of opposite sign, but that their functional similarity is mediated by common central emotional states.     

Secondary extinction in Pavlovian fear conditioning

Pavlov (1927/1960) reported that following the conditioning of several stimuli, extinction of one conditioned stimulus (CS) attenuated responding to others that had not undergone direct extinction. However, this secondary extinction effect has not been widely replicated in the contemporary literature. In three conditioned suppression experiments with rats, we further explored the phenomenon. In Experiment 1, we asked whether secondary extinction is more likely to occur with target CSs that have themselves undergone some prior extinction. A robust secondary extinction effect was obtained with a nonextinguished target CS. Experiment 2 showed that extinction of one CS was sufficient to reduce renewal of a second CS when it was tested in a neutral (nonextinction) context. In Experiment 3, secondary extinction was observed in groups that initially received intermixed conditioning trials with the target and nontarget CSs, but not in groups that received conditioning of the two CSs in separate sessions. The results are consistent with the hypothesis that CSs must be associated with a common temporal context during conditioning for secondary extinction to occur.     

Contextual effects in latent inhibition with an appetitive conditioning procedure

In three experiments, rats received presentations of a diffuse 30-sec stimulus (a light) and of food, and their tendency to enter the food tray was monitored. Experiment 1 showed that when the light was made to signal the delivery of food, the response of entering the food tray increased in frequency during the stimulus. The acquisition of this conditioned response to the light was retarded in subjects that had received preexposure to the stimulus. In Experiments 2 and 3, subjects received preexposure to the stimulus, some in the same context as that subsequently used for stimulus-food pairings and some in a different context. Those experiencing the change of context acquired the response more readily. It is argued that these results demonstrate a latent inhibition effect that is attenuated by contextual change.     

The effects of varying the interreinforcement interval on appetitive contextual conditioning

Appetitive contextual conditioning in rats and ringdoves was investigated in six experiments. In Experiment 1, differential contextual training produced greater anticipatory activity in rats in the presence of a context paired with food than it did in rats in the presence of a different context in which food was never presented. Furthermore, the rats showed a preference for the context associated with food when they were given a simultaneous choice test between contexts. In Experiment 2, rats were more active in and preferred a context associated with a variable-time 30-sec (VT30) schedule as opposed to a VT180 schedule. Experiment 3 was a between-subjects replication of the previous experiment. As expected, rats exhibited significantly more anticipatory activity in a context in which food had been presented on a VT30 schedule than they did in a context in which food had been presented on a VT180 schedule. Experiment 4 showed that anticipatory activity was a reflection of context-US associations in ringdoves, and in Experiments 5 and 6, ringdoves also exhibited an inverse relationship between the. amount of anticipatory activity and the length of the interreinforcement interval (IRI). These results reveal a relation between ERI and contextual conditioning opposite from that obtained in studies of aversive conditioning.     

Dissociation of conditioned appetitive and consummatory sexual behavior: Satiation and extinction tests

Sexual responses were conditioned in male Japanese quail using the opportunity to copulate with a female as the unconditioned stimulus (US). The conditioned stimulus (CS) was a 3-D object made of a taxidermically prepared female quail head mounted on a terry-cloth body. Both appetitive conditioned responses (approach and proximity to the CS) and consummatory conditioned responses (mount and cloacal contact directed toward the CS) developed when 2-min presentations of the CS were followed immediately by the US, but not when the CS and US were separated by trace intervals of 10 or 20 min (Experiment 1). Postconditioning sexual satiation suppressed conditioned cloacal contact responses more than conditioned approach to the CS (Experiment 2), and “acute” extinction suppressed both conditioned mounting and conditioned cloacal contact responses more than conditioned approach to the CS (Experiment 3). These results demonstrate a functional dissociation between conditioned appetitive and consummatory responses and imply that the motivational and/or associative mechanisms underlying the two types of behavior are distinct.     

Retention of a running response following appetitive acquisition,extinction, and discrimination

In Experiment 1, hungry rats received 30 rewarded runway trials and then either extinction trials followed by retention tests or just retention tests. Different groups were tested after retention intervals of 1 min, 1, 3, or 24 h, or 30 days. Retention of extinction training was a nonmonotonic, cubic function of time for the early portion of the response chain, with good retention at 1 min and 3 h and little retention at 1 h, 24 h, or 30 days. In the latter portions of the response chain, retention of extinction decreased monotonically with time. Retention following reward-only training varied little in time, though slight losses occurred after 30 days. Experiments 2–3 differed from Experiment 1 in imposing nonchoice discrimination training (reward vs. nonreward) instead of extinction following 30 rewarded trials. After different time intervals (.017, .75, 1.25, 3, and 24 h in Experiment 1; and .017, 1, and 3 h in Experiment 2), retention tests revealed poorest discrimination at intermediate intervals in the initial portion of the response chain, i.e., a Kamin effect appeared. The deficit seemed the result of a loss of response suppression to the cue that signaled nonreward. In latter segments of the response chain, a Kamin effect tended not to appear. Implications for a number of observations and theoretical views are noted.     

Conditioned inhibition training of the competing cue after compound conditioning does not reduce cue competition

In each of two experiments, we studied Pavlovian fear conditioning (as assessed by barpress conditioned suppression) in 32 albino rats. Following a two-stage cue-competition procedure (A+ then AX+), we subjected the competing cue (A) to conditioned inhibition training (B+, BA?) before testing the target cue (X). Conditioned inhibition training was designed to weaken the putative A-unconditioned stimulus (US) association, perhaps changing it to an A-no-US association. Performance-deficit theories of cue competition, such as comparator theory and retrieval-interference theory, predict that such procedures should weaken cue competition, causing Conditioned Stimulus X (CS X) to evoke strong responding. The same prediction can be deduced from recent acquisition-focused models (Dickinson &; Burke, 1996; Van Hamme &; Wasserman, 1994). In opposition to this prediction, however, we found in both experiments that conditioned inhibition training had no detectable effect on cue competition even though it successfully abolished conditioned responding to CS A. In Experiment 2, moreover, we found evidence against the hypothesis that the weak response to CS X was due to generalization decrement rather than to cue competition. Results favor early learning-deficit theories of cue competition over performance-deficit theories and over the recent acquisition-focused models.     

The impact of context relevance during extinction learning

In two predictive-learning experiments, we investigated the role of the informational value of contexts for the formation of context-specific extinction learning. The contexts were each composed of two elements from two dimensions, A and B. In Phase 1 of each experiment, participants received acquisition training with a target cue Z in context A1B1 (the numbers assign particular values on the context dimensions). In Phase 2, participants were trained with conditional discriminations between two other cues, X and Y, for which only one of the two context dimensions was relevant. In a third phase, participants received extinction trials with cue Z in context A2B2. During a final test phase, we observed that a partial change of the extinction context disrupted extinction performance when the extinction context was changed on the dimension that had been trained as being relevant for the conditional discrimination. However, when the extinction context was changed on the irrelevant context dimension, extinction performance was not affected. Our results are consistent with the idea that relevant contexts receive more attention than do irrelevant contexts, leading to stronger context-specific processing of information learned in the former than in the latter type of contexts.     

Outcome-selective effects of intertrial reinforcement in a Pavlovian appetitive conditioning paradigm with rats

The outcome-selective effects of presenting intertrial unconditioned stimuli (USs) in a rat appetitive conditioning paradigm were examined in two experiments. In both experiments, two stimuli were paired with different outcomes, while one of these outcomes was also presented in the intertrial interval (A+, B*, +). Two measures of learning, stimulus-elicited magazine approach and Pavlovian-to-instrumental transfer, were used to examine these effects. The presence of freely occurring outcomes in the intertrial interval (ITI) was observed to interfere more with the learning of a new association (Experiment 1) and to degrade more an already established association (Experiment 2) when the conditioned stimulus had been paired with the same outcome as that occurring in the ITI. An outcome-selective effect of ITI USs distinguishes among accounts of contingency based on general performance, attentional, and motivational mechanisms from those based on more specific associative mechanisms. Overall, the data highlight the importance of specific encoding processes in the analysis of associative learning.     

The effect of US omission in classical aversive and appetitive conditioning of rabbits

Rabbits (Oryctolagus cuniculus) were given either a 100% or a 50% reinforcement schedule in classical conditioning. Two groups received an aversive US (shock) and two groups received an appetitive US (water to the oral cavity). With parameter estimates for the two-phase model serving as the dependent variables, it was possible to define more precisely the effect of US omission with the intermittent reinforcement schedule. For the aversive preparation, the major effect of intermittent reinforcement was to increase the duration of Phase 1, a phase during which response likelihood remains constant at its initial value. Only a small proportion of subjects reflected the effect of US omission during Phase 2, the “learning” phase, this being a low operator limit following trials on which neither the CR nor the US occurred. The major effect of US omission for the appetitive preparation was in Phase 2, primarily a result of a minority of subjects having a low operator limit following trials on which neither the CR nor the US occurred. Many subjects required separate operators for trials on which the CR did or did not occur. The results were interpreted to pose difficulties for strength theories of conditioning, and the limitation implied for successful application of the Rescorla-Wagner theory are discussed. The implications of the data for response-contingent interpretations and for individual differences are also discussed.