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.     

Pavlovian aversive to instrumental appetitive transfer: Evidence for across-reinforcement blocking effects

Rats received Pavlovian aversive (shock) conditioning in which white noise was established for different groups as a CS+, CSO, or CS?. Then, in an appetitive T-maze discrimination, the CSs were presented contingent upon a designated correct response for which food reinforcement was factorially varied at 0, 1, 2, or 4 pellets. Although the CS+ suppressed and the CS? facilitated speed of running in the correct arm at the start of discrimination training, these effects extinguished rapidly and did not interact with reward magnitude. Furthermore, choice learning was faciltated by the CS+ and retarded by the CS?, with these effects being comparable for the 1- to 4-pellet reinforcement conditions, but absent for the 0-pellet condition. These findings are difficult to reconcile with a transfer interpretation positing a general signaling property of the CS and are better interpreted as across-reinforcement blocking effects: By predicting a preferred outcome (safety) comparable to the preferred outcome of food reinforcement, the CS? blocks (retards) the association of reinforcement and the S^D; conversely, by predicting a nonpreferred (shock) outcome discrepant from the preferred food outcome, the CS+ “counterblocks” (enhances) the association of reinforcement and the S^D.     

Perceptual learning transfer in an appetitive Pavlovian task

In two experiments, rats were given intermixed or blocked preexposure to two similar compound stimuli, AX and BX. Following preexposure, conditioning trials took place in which AX (Experiment 1) or a novel compound stimulus NX (Experiment 2) was paired with a food-unconditioned stimulus in an appetitive Pavlovian preparation. Animals that were given alternated preexposure showed lower generalization from AX to BX (Experiment 1) and from NX to a new compound, ZX (Experiment 2), than animals that were given blocked preexposure, a perceptual learning and a perceptual learning transfer effect, respectively.     

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.     

Negative priming and occasion setting in an appetitive Pavlovian procedure

Rats received training in which two auditory target stimuli, X and Y, were signaled by two visual stimuli, A and B, and followed by food (i.e., A-->X+, B-->Y+). The test consisted of presentations of X and Y preceded either by the same signal as during training (same trials: A-->X, B-->Y) or by the alternative signal (different trials: A-->Y, B-->X). After 8 training sessions, the animals responded less on same trials than on different trials; this effect was significantly reduced after 24 training sessions. In two additional experiments, animals that had also experienced presentations of A and B alone, either before or during training, showed the opposite pattern of results, responding more on same trials than on different trials. These results are interpreted as being due to the interaction between the effects of occasion setting and negative priming (see Wagner, 1981).     

Signaling and affective functions in Pavlovian conditioning

The present study employed a Pavlovian-instrumental-transfer paradigm to investigate the role of conditioned fear in appetitive discrimination learning. Each of three Pavlovian training procedures was used to establish a conditioned fear excitor (CS+), a “neutral” CS (CSo), and a conditioned fear inhibitor (CS?). Then, the CSs were administered to rats in the three groups contingent upon the rewarded response in a difficult visual discrimination. In addition, half of each group received shock punishment for each incorrect response. Relative to CSo, CS+ facilitated performance in contrast to the usual interfering effect of conditioned suppressors; conversely, CS? retarded performance even when its reinforcing action (fear inhibition) was potentiated by punishment for the incorrect response. These results, together with other findings showing a reversed outcome when the CSs are administered for the incorrect response, indicate that Pavlovian conditioning comprises both general signaling and affective functions, the former reflecting a basic “expectancy” or nominal type of cognitive processing in the rat.     

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.     

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.     

Frustrative nonrelief in instrumental escape conditioning

The generality of the frustration effect in an aversive stimulus conditioning procedure was examined by training and testing 40 rats in a double cold-waterway escape conditioning apparatus. Experimental and control procedures analogous to appetitive conditioning experiments (e.g., Amsel & Roussel, 1952; Wagner. 1959) indicated that frustrative nonrelief (i.e., reinforcement omission) in the first goal tank yielded significant increments in swimming speed in the second waterway, and that these increments in performance were dependent upon initial training with continuous relief (i.e., reinforcement) in the first goal tank. Extensions of the generality of the frustration effect are discussed.     

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.     

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.     

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.     

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.     

Spontaneous recovery after Pavlovian conditioning with multiple outcomes

In four experiments using rats, a Pavlovian conditioned stimulus (CS) was paired with a positive outcome, either pellets or liquid sucrose. That outcome was then either omitted altogether or replaced by another outcome. Although performance to the CS deteriorated only when the outcome was omitted, both procedures resulted in the CS’s ability to evoke greater responding after the passage of time. These results suggest that a similar outcome-independent depressive process develops when a Pavlovian CS is paired either with nonreinforcement or with a different outcome; that process then appears to dissipate with time.     

Concurrent extinction does not render appetitive conditioning context specific

In an experiment with rats, an appetitive conditioning method was used to investigate the generality of the hypothesis that extinction should arouse attention to contextual cues, resulting in all learning in that context becoming context specific. Rats received appetitive conditioning with a tone either while extinction of a flasher occurred (Group With Extinction) or while it did not (Group No Extinction). Half of each group was subsequently tested in extinction in the context in which training had taken place or in a different context. The results revealed a three-way interaction of extinction and context with trials, in a direction opposite to the one the hypothesis would suggest. When rats were tested in a different context, there was generally better responding in Group With Extinction than in Group No Extinction. In the same context, there was generally lower responding in Group With Extinction than in Group No Extinction. Subsequent testing showed an ABA recovery effect. Results are discussed in terms of the challenges they pose for the revised retrieval theory presented by Callejas-Aguilera and Rosas (2011).     

A Pavlovian analysis of food-attraction conditioning in the snailHelix aspersa

Following brief pairing of an odor with a feeding experience (food-attraction conditioning), snails will lower their tentacles when subsequently presented with that odor alone. Three experiments investigated the possible behavioral mechanism mediating food-attraction conditioning in the snailHelix aspersa. It is suggested that food-attraction conditioning is an example of Pavlovian conditioning. In this case, the odor (conditioned stimulus) is paired with oral stimulation (unconditioned stimulus), which elicits lowering of the tentacles (unconditioned response). Following conditioning, the odor comes to elicit lowering of the tentacles (conditioned response). Experiment 1 ruled out nonassociative effects, such as habituation and sensitization, using an unpaired control group. Experiment 2 provided further evidence against a role for habituation of neophobia, through the demonstration of extinction following conditioning. In Experiment 3, an omission procedure was used to rule out the possible role of instrumental contingencies.     

Pavlovian conditioning with ingested saline solution as the US

Experience with 2% saline as the sole available fluid for drinking produced a decrement in preference for .9% saline in a two-bottle test with water as the alternative. This outcome was interpreted as a consequence of Pavlovian conditioning, with the taste of salt acting as the conditioned stimulus and postingestive consequences of saline ingestion acting as the unconditioned stimulus. An overshadowing group experienced salt mixed with vanilla as its sole fluid during the conditioning phase. This group showed an attenuated saline aversion relative to a group that drank 2% saline solution during the conditioning phase. In addition, a vanilla aversion developed in the former group. In the second experiment, conditioning of the aversion to the taste of vanilla mixed with 2% saline was attenuated by preexposing the vanilla. The results support a Pavlovian analysis of the modification of salt preference through experience with the postingestive consequences of saline ingestion.     

Pavlovian conditioning in multiple contexts: Competition between contexts for comparator status

Water-deprived rats were used to investigate the effects of training a CS in more than one context on conditioned lick suppression. In each experiment, partial reinforcement of the CS was intermingled with unsignaled presentations of the US. In Experiment 1, subjects were either trained in one context alone, trained consecutively in two contexts (such that all training in one context occurred prior to any training in the second context), or trained alternately in two contexts. Following training, the first context, the second context, or neither context was extinguished. Testing of the CS occurred in a third (neutral) context. To the extent that either training context became established as a comparator stimulus for the CS, the comparator hypothesis (Miller & Matzel, 1988) predicts an increase in excitatory responding to the CS following extinction of that context. Subjects trained in a single context exhibited appreciable fear of the CS only when the CS’s training context had been extinguished. Additionally, subjects trained consecutively in the two contexts showed increased fear of the CS following extinction of the second, but not the first training context (i.e., a recency effect). Subjects trained alternately in the two contexts showed no increased fear of the CS as a result of either context alone being extinguished. In Experiment 2, subjects trained alternately in two contexts showed increased fear of the CS only when both training contexts were extinguished, suggesting that both training contexts had become comparator stimuli. These data indicate that multiple training contexts can either compete or act synergistic-ally in modulating responding to a Pavlovian trained CS as a function of the order of training in the different contexts.     

Integration of cardiac responses to serial stimuli after Pavlovian conditioning in rats

The expression of cardiac responses to sequences of two sounds was studied in restrained rats following discriminative trace or delay conditioning. Stimuli paired with a tail shock 10 sec later (CS1) elicited conditioned bradycardia. Unpaired or neutral stimuli (CS0) elicited mostly tachycardia. Rats did not learn to suppress responding to nonreinforced sequences with an interval of 6 sec between sounds. Responses to the second stimulus were significantly augmented following a CS1 stimulus, but not following a CS0 stimulus. Real-time summation of simple responses provided a more complete and quantitative prediction of dual responses than did resetting or facilitation. These results extend the time range over which summation may be observed from less than 2 sec to at least 16 sec. They appear to be inconsistent with models involving competition between unitary representations of stimuli in short-term memory and suggest the existence of multiple stimulus traces with independent time courses.     

Facilitation of appetitive conditioning with naturalistic conditioned stimuli: CS and US factors

Adding limited female cues to a conditioned stimulus (CS) facilitates conditioned male sexual responding. In two experiments, we examined the mechanisms of this facilitation effect. The color of the female cues on the CS was varied in Experiment 1. Similarity between the CS plumage color and the color of the live female (the unconditioned stimulus [US]) could only partially account for the results. The extent to which the facilitation effect represents a specialization of sexual behavior was examined in Experiment 2 by comparing conditioning with either food or copulation as the US. The CSs with female cues elicited more approach and grab responses regardless of which US was used. However, uniquely sexual conditioned responses (mounts and cloacal contacts) were enhanced only when sexual reinforcement served as the US. These findings suggest that the facilitation effect of female cues represents a general feature of appetitive behavior systems.