Pavlovian inhibitory conditioning and tolerance to pentobarbital-induced hypothermia in rats

In this experiment we investigated inhibitory Pavlovian conditioning in the development of tolerance to pentobarbital-induced hypothermia. During an initial phase, one group of rats (discrimination group) received training in which, on alternate days, one conditional stimulus (CS+) was associated with administration of 30 mg/kg pentobarbital, and a different conditional stimulus (CS-) was associated with administration of physiological saline. During the phase, control groups received either exposure to both CSs but not the drug or to the drug but no CSs or to neither the CSs nor the drug. Subsequently, half the rats in each group received injections of pentobarbital in the presence of one of the CSs and the remaining half in the presence of the other CS. Rats from the discrimination group injected with pentobarbital in the presence of CS+ displayed the most tolerance (i.e., smallest drug effect), whereas rats from the discrimination group injected with pentobarbital in the presence of CS- displayed the least tolerance (i.e., greatest drug effect). The attenuation of tolerance seen in rats of the discrimination group injected in the presence of CS- provides evidence of inhibitory Pavlovian conditioning. Additional evidence of inhibitory conditioning was provided by the fact that CS2 enhanced the hypothermic effects of pentobarbital in the discrimination group, whereas CS1 attenuated these effects. Implications of the results for the nature of inhibitory conditioning are discussed.     

On the role of covarying functions in stimulus class formation and transfer of function

This experiment investigated whether directly trained covarying functions are necessary for stimulus class formation and transfer of function in humans. Initial class training was designed to establish two respondent-based stimulus classes by pairing two visual stimuli with shock and two other visual stimuli with no shock. Next, two operant discrimination functions were trained to one stimulus of each putative class. The no-shock group received the same training and testing in all phases, except no stimuli were ever paired with shock. The data indicated that skin conductance response conditioning did not occur for the shock groups or for the no-shock group. Tests showed transfer of the established discriminative functions, however, only for the shock groups, indicating the formation of two stimulus classes only for those participants who received respondent class training. The results suggest that transfer of function does not depend on first covarying the stimulus class functions.     

Context Specificity of Excitation and Inhibition in Ambiguous Stimuli

Two experiments examined the susceptibility of excitation and inhibition to contextual change when the conditioned stimulus (CS) was ambiguous using an appetitive conditioning paradigm. In Experiment 1, excitation to a CS was lost with a context switch when inhibition had been learned to the CS in a prior feature-negative (FN) discrimination. Control groups that had received either more or less excitatory conditioning in the absence of inhibitory pretraining showed no loss. In Experiment 2 inhibition was lost with a context switch in a group that had received excitatory and then inhibitory conditioning with the CS. No loss was observed in a group that had not received excitatory pretraining. The results suggest that contexts are especially likely to control performance to ambiguous CSs when they can modulate the second of two learned associations. Results are discussed in terms of their implications for occasion setting and modern conditioning theory.     

Contralateral transfer of inhibitory and excitatory eyelid conditioning in the rabbit

In Experiment I, rabbits received training to establish a clicker as a conditioned inhibitor. In a subsequent test phase this stimulus was used as a signal for shock either to the eye reinforced during initial training or to the opposite eye. Learning to the clicker was slower in both conditions than in the appropriate control groups. The second experiment replicated the results of those subjects trained and tested with opposite eyes and ruled out the possibility that the slower learning was due to the effects of latent inhibition. Experiment III demonstrated that excitatory conditioning to a clicker to one eye facilitated future excitatory conditioning to that stimulus to the opposite eye. These results are consistent with the view that inhibitory and excitatory conditioning both involve the acquisition of a general, motivational conditioned response which is capable of mediating the transfer of conditioning across different response systems.     

Analysis of the learned irrelevance effect in appetitive Pavlovian conditioning

In Experiments 1 and 2 rats received uncorrelated presentations of a light conditioned stimulus (CS) and a food unconditioned stimulus (US) on each day of a preexposure phase. Control subjects received the same number of USs during the first half of preexposure and the same number of CSs during the second. Uncorrelated preexposure retarded inhibitory conditioning. Experiment 3 showed, however, that the different patterns of US preexposure experienced by the two groups could in itself influence the course of subsequent inhibitory conditioning. When this factor was equated by restricting the uncorrelated treatment to the first half of the pre-exposure phase (Experiment 2) or by extending the control treatment throughout the phase (Experiment 4) it was found that uncorrelated preexposure retarded excitatory conditioning, but facilitated inhibitory conditioning. This outcome challenges an interpretation in terms of the concept of learned irrelevance, which predicts that uncorrelated preexposure should retard both forms of conditioning.     

Classical Delay Eyeblink Conditioning in in 4- and 5-Month-Old Human Infants

Abstract-Simple delay classical eyeblink conditioning, using a tone conditioned stimulus (CS) and airpuff unconditioned stimulus (US), was studied in cross-sectional samples of 4- and 5-month-old healthy, full-term infants. Infants received two identical training sessions, 1 week apart. At both ages, infants experiencing paired tones and air-puffs demonstrated successful conditioning over two sessions, relative to control subjects who had unpaired training. Conditioning was not evident, however, during the first session. Two additional groups of 5-month-olds received varied experiences during Session 1, either unpaired presentations of the CS and US or no stimulus exposure, fol-lowed by paired conditioning during Session 2. Results from these groups suggest that the higher level of conditioning observed following two sessions of paired conditioning was not the result of familiarity with the testing environment or the stimuli involved but, rather, the result of retention of associative learning not expressed during the first conditioning session.     

Augmentation, not blocking, in an A+/AX+ flavor-conditioning procedure

An A+/AX+ Pavlovian conditioning design typically produces weakened or blocked conditioning to stimulus X. Two experiments were conducted in which rats first received an odor (A+) paired with an emetic US, and then received odor and taste (AX+) paired with the US. In both experiments, the preconditioned odorfacilitated conditioning to the taste. In Experiment 1, a group that received two odor-illness pairings in A+ conditioning had a stronger taste aversion than a group that only had a single odor-illness pairing. Experiment 2 demonstrated that the strengthened taste aversion in the A+/AX+ condition was not due to stimulus generalization. The results represent a unique outcome in the flavor-aversion literature that is similar to potentiation. We propose that this facilitated conditioning to X in the A+/AX+ design be termedaugmentation.     

Hippocampal lesions attenuate latent inhibition and the decline of the orienting response in rats

Two experiments using rats assessed the effect of dorsal hippocampal lesions on the orienting response (OR) elicited by a discrete light and on the subsequent associability of that light. In both experiments subjects received extensive nonreinforced exposure to the light, and it was found that the decline in the OR evident in sham-operated animals was severely attenuated by hippocampal lesions. Subsequently the light was paired with condensed milk in Experiment 1, and it was found that conditioning was faster in the lesioned than in the sham-operated group. Experiment 2 used a conditioned inhibition procedure whereby the light was presented in a nonreinforced compound with a tone which, when presented alone, acted as a signal for condensed milk. Again this discrimination was mastered more rapidly by lesioned animals. Relevant control groups indicated no differences between lesioned and sham-operated animals in learning about a novel light. Thus, hippocampal lesions influence both the loss of associability of a stimulus and the decline in the OR it elicits, which, in turn, suggests that the OR acts as an index of stimulus associability.     

The biological function of Pavlovian conditioning: Learned inhibition of aggressive behavior in territorial fish

Following Pavlovian discrimination training, stimuli predicting the appearance of a territory intruder (an excitatory conditional stimulus, CS+) or the absence of that event (an inhibitory conditional stimulus, CS−) were presented to pairs of territorial male fish immediately before their first aggressive interaction. Pairmates that both received excitatory stimuli prior to the confrontation were significantly more aggressive than a control group which received the same training but which received neither a CS+ nor a CS− in the test. Pairmates in which both received a CS− were significantly less aggressive than the control group. In these three groups, no differences in aggression were observed between the individual members of a single pair. Two additional groups were composed of pairs whose members received different stimuli prior to the test. Although no differences were found between pairmates in the group in which one member received a pretest CS− while the other member received no stimulus presentation, large differences in aggressive behavior were obtained when one fish received a CS+ and its pairmate received a CS−. We discuss the behavioral ecology of terriorial behavior in fish and attempt to show the potential importance of these results in this naturalistic context. In addition, we discuss the implications of an ecological approach for causal analyses of inhibitory learning.     

One-trial conditioned suppression: effects of instructions on extinction

Two experimental groups of undergraduate volunteers received a single Pavlovian conditioning trial consisting of a paired presentation of a tone conditioned stimulus (CS) and a shock unconditioned stimulus (UCS). Control groups received either the CS alone or the UCS alone. Subjects from one experimental group were subsequently instructed that they would not receive further shocks, while the other experimental group received no such instructions. The CS alone was then presented once to all four groups while subjects were engaged in a button-pressing task maintained by slide reinforcement. During the latter phase, rate of button-pressing was measured. Classically conditioned suppression of button-pressing was obtained in the noninstructed experimental group but not in the instructed group. The results demonstrate that suppression can be a sensitive index of Pavlovian conditioning in humans but question the use of conditioned suppression as an adequate experimental analog of clinically observed anxiety-motivated behavior.     

Blocking and unconditioned response diminution in human classical autonomic conditioning

Four experiments examined blocking and UR diminution in human SCR conditioning. In Experiment 1, CS_X was conditioned in compound with previously conditioned CS_A, in one group, or in a compound with another novel stimulus, CS_N, in an additional group. UR diminution occurred, but there was no post-compound difference in CRs in the two groups and no difference in responding to CS_X and CS_A following equal training on each, i.e., no blocking. The correlation between blocking and UR diminution was not significant. In Experiment 2, two groups received a blocking procedure, but one was tested on CS_X and one on CS_A. UR diminution occurred, but there were no post-compound CR or UR differences. There was again no within-subjects blocking effect. The correlation between blocking and UR diminution was not significant, but this correlation was significant when data from Experiments 1 and 2 were combined. In Experiment 3, a differential conditioning procedure was used, followed by reinforcement of two compounds, one with CS_A+ and one with CS_A-. One subgroup was tested on CS_A+ and CS_A- with reinforcement; another was tested without reinforcement. UR diminution occurred, and there was significant blocking, but only after two nonreinforced tests. Blocking and UR diminution were significantly correlated. In Experiment 4, four groups received compound conditioning after initial training with CS_A. The compound contained CS_X and CS_A for three groups and two novel CSs for the fourth. Ten nonreinforced test trials were run. The three blocking groups received two CS_As plus eight CS_Xs, four CS_As plus six CS_Xs, or all CS_Xs. The fourth group received ten nonblocked CS_Xs. CR magnitude to blocked CS_X was significantly smaller than to nonblocked CS_X during the last six test trials, but not initially. Blocking and UR diminution were not correlated, in disagreement with the first three studies. The results indicated that repeated nonreinforced test trials are needed for blocking to be observed in this preparation. The proposition that blocking and UR diminution are both due to reduced processing of the US received only partial support.     

Transfer of conditioned appetitive stimuli to conditioned aversive excitatory and inhibitory stimuli

The transfer of Pavlovian appetitive stimuli to Pavlovian aversive stimuli was examined in three experiments. In Experiment 1, rats received appetitive (Ap) conditioning designed to establish a flashing-light stimulus as either a CS+, CSo, or CS? for food, or to maintain it as a novel stimulus for US-alone subjects. Then, the stimulus was employed as a signal for weak shock in conditioned-emotional-response (CER) training. Both acquisition and extinction results showed that the ApCS+ facilitated and the ApCS? retarded aversive excitatory conditioning relative to the ApCSo and US-alone controls. Experiment 2 replicated the findings of Experiment 1 with both a moderate and a severe shock in CER training. In Experiment 3, different groups received the same appetitive conditioning as before, but to a flashing-light stimulus which was then employed as a signal for no shock in CER training. The ApCS? facilitated and the ApCS+ retarded aversive inhibitory conditioning relative to ApCSo and US-alone controls. Collectively, these findings establish that, in Pavlovian conditioning, transfer of an appetitive CS to an aversive excitor or inhibitor is facilitated by maintaining the initial conditioning contingency.     

Latent inhibition and stimulus generalization of the classically conditioned nictitating membrane response in rabbits (Oryctolagus cuniculus) following dorsal hippocampal ablation.

Rabbits received 0 to 450 exposures of a tone conditioned stimulus (CS) prior to classical defensive conditioning of the nicitating membrane response based on an infraorbital eye shock unconditioned stimulus. Tone preexposure resulted in retarded conditioning in normal rabbits. This latent inhibition effect was not present in animals with bilateral dorsal hippocampectomy produced by aspiration. Control animals with bilateral neocortical and callosal aspiration lesions demonstrated a latent inhibition effect similar to that shown by normal nonoperated animals. The failure of CS preexposure to retard conditioning in hippocampal rabbits was not due to differences in threshold of the conditioned response to the CS or to differences in response mechanisms as determined by tests of habituation and dishabituation of the unconditioned response. A subsequent experiment employed combined-cue summation tests to confirm the fact that preexposure did not endow the tone with conditioned as well as latent inhibitiory properties. Finally, tests of stimulus generalization along the auditory frequency dimension indicated flatter relative gradients for hippocampals than for nonoperated controls, with cortical controls in between. These findings were discussed in terms of Douglas' model of hippocampal function.     

Context specificity of conditioning and latent inhibition: Evidence for a dissociation of latent inhibition and associative interference

Conditioning may generalize from one context to another when latent inhibition (the effect on subsequent conditioning of prior unreinforced exposure to the stimulus) does not. Experiment 1 studied conditioned approach and licking by rats to a stimulus paired with the delivery of water and confirmed that latent inhibition could be abolished by a change of context, while prior aversive conditioning to the stimulus, produced by pairing it with mild shock, interfered with the acquisition of conditioned approach and licking regardless of this change of context. Thus even when conditioning and latent inhibition were measured in the same way, the former generalized across contexts, and the latter did not. Experiment 2 showed that the effects not only of unreinforced exposure to a stimulus but also of presentation of the stimulus uncorrelated with the delivery of water were confined to the context in which they occurred. Thus the generalization of conditioning from one context to another and the failure of latent inhibition to generalize cannot be attributed to the occurrence of rein-forcers during conditioning and their absence in latent inhibition. This conclusion was confirmed in Experiment 3, where animals received both aversive conditioning trials and unreinforced presentations of other stimuli in the treatment phase of the experiment, but were then conditioned to one of these stimuli paired with water. Once again, the effects of aversive conditioning transferred perfectly from one context to another, while those of unreinforced presentations did not. Latent inhibition, these results suggest, is not easily explained by supposing that animals associate an unreinforced stimulus with zero consequences and have to unlearn this association when the stimulus is then paired with a reinforcer.     

Blocking as a retrieval failure: Reactivation of associations to a blocked stimulus

Conditioned lick suppression in rats was used to examine the effectiveness of three different “reminder” treatments in reactivating associations to a blocked stimulus in a Kamin blocking paradigm. Experiment I indicated that with our parameters prior tone-footshock pairings could block manifestation of a light-footshock association that would otherwise be evident following pairings of a light-tone compound stimulus with footshock. In Experiment II, exposure to either the US, the blocked stimulus (light), or the apparatus cues between the compound conditioning trials and testing decreased blocking. Experiments III(a) and III(b) replicated the unblocking effects seen in Experiment II and included control groups that received the identical training and reminder treatments except for the omission of the light from the compound stimulus. These latter animals failed to display behaviour comparable to the blocked and reminded subjects, thereby establishing the associative basis of suppression to the light in the animals reminded following treatment known to produce blocking. Experiment IV also replicated the results of Experiment II and included control groups that received identical light-tone compound trials and reminder treatments without prior conditioning to the tone alone. In these control groups, reminder treatments tended to disrupt rather than increase evidence of conditioning to the light. The results suggest that associations are formed to the added element of a compound despite prior conditioning to the initial element, and that failure on the test trial to retrieve these associations to the blocked CS, rather than a failure to attend to or learn about the added element, is at least in part responsible the Kamin blocking effect.     

Unpaired shocks during extinction weaken the contextual renewal of a conditioned discrimination

Extinction is generally more fragile than conditioning, as illustrated by the contextual renewal effect. The traditional extinction procedure entails isolated presentations of the conditioned stimulus. Extinction may be boosted by adding isolated presentations of the unconditioned stimulus, as this should augment breaking the contingency between the two stimuli. In a human conditioning experiment with on-line expectancy ratings and electrodermal responding as dependent variables, 32 participants were differentially conditioned to two neutral figures using electric shock. After a change of context, one group received normal extinction treatment whereas another group received explicitly unpaired presentations of the figures and shock. At test, the two figures were presented in the original context again. For both measures, only the group that received normal extinction showed renewal of the conditioned discrimination. These results suggest that unpaired shocks during extinction strengthen the extinction learning.     

Reminder-induced recovery of associations to an overshadowed stimulus

The possibility of reversing the deficit produced by overshadowing through the use of memory reactivation was investigated. Using lick suppression as a measure of associative strength, water-deprived rats were conditioned in a Pavlovian paradigm which produced reliable overshadowing of a flashing light by a tone. It was found, however, that exposure to the overshadowed stimulus outside of the conditioning context during the retention interval (reminder treatment) caused an increase in lick suppression during testing in animals that had undergone overshadowing, relative to nonreminded overshadowed animals. Subjects that received the reminder treatment but were conditioned without overshadowing showed no increase in lick suppression. Additional control groups ensured that the increase in suppression observed in the overshadowed subjects following reminder treatment was not due to nonspecific fear. The results suggest that the performance deficit produced by overshadowing is due at least in part to a reversible failure to efficiently retrieve associations to the overshadowed stimulus at the time of testing, rather than a failure to form those associations during conditioning.     

Conditioning of electrodermal responses through vicarious instigation and through perceived threat to a performer

Abstract.— In order to demonstrate vicarious classical conditioning, and to investigate the necessity of vicarious instigation for vicarious conditioning of skin conductance responses, two groups of 32 students each observed a performer ( P ) allegedly trying to solve easy and difficult number series displayed for both the P and the observers ( Os ). Difficult problems served as CS+ and easy ones as CS-for os in both groups; indicated shock to the P as unconditioned stimulus (UCS) for one group, and perceived threat of shock to P as UCS for the other. Within the two groups half of the os were instructed to empathize with the P , whereas the other half was instructed just to watch her movements. The results demonstrated vicarious instigation and conditioning for the group having indicated shock as UCS, and conditioning without instigation for the group having perceived threat of shock as UCS. Since results for the conditioned response and the vicariously instigated response go beyond earlier interpretations, a theoretical elaboration in the cognitive direction is argued for.     

Mechanisms of blocking by contextual stimuli

The influence of contextual stimuli on the conditioning and performance of responding to a discrete stimulus was examined in the US preexposure paradigm using both context shift manipulations and a measure of context conditioning. Four groups of rats received both repeated exposure to an electric shock US in one context (Context 1), and repeated nonshocked exposure to a second context (Context 2). Two additional groups of rats received exposure to these contexts, but never received shock presentations. Rats exposed to shock learned to escape from the stimuli of Context 1, but did not escape from the stimuli provided by Context 2. Rats not exposed to shock failed to escape from either context. All rats then received a single CER conditioning session in which four pairings of a 3-min noise CS and shock US were presented. Half the rats received those CS-US pairings in the excitatory Context 1, while the remaining rats received those pairings in the neutral Context 2. Finally, half the rats in each of the CER conditioning treatments received extinction test trials of the noise CS in Context 1, while the remaining rats received those test trials in Context 2. Thus, this design factorially manipulated the presence of excitatory or neutral contextual stimuli during both conditioning and testing of a discrete CS. In comparison with the two groups of rats never preexposed to shock alone, attenuation in acquisition of conditioned suppression observed during test trials occurred only when CER conditioning had been administered in the excitatory Context 1, and this effect was manifested when testing occurred in either the excitatory Context 1 or the neutral Context 2. These results support the model of R. A. Rescorla and A. R. Wagner (1972) (in A. H. Black & W. F. Prokasy (Eds.) Classical Conditioning II, pp. 64–99, New York: Appleton-Century-Crofts) which asserts that contextual stimuli and sicrete CSs compete for limited associative strength supportable by a given US.     

A comparison of repeated exposure to fearful and disgusting stimuli among spider phobics

This study examined the role of fear and disgust in repeated exposure among spider phobics. Thirty spider phobics were randomly assigned to one of two experimental groups. Both groups completed measures of fear and disgust and performed two initial standardized Behavioral Avoidance Tests (BATs; one with a fear stimulus – live tarantula, and one with a disgust stimulus – dead rat). One group was then repeatedly exposed to the tarantula and the other to the dead rat. Results of the study indicated that exposure to either the disgust stimulus or the live tarantula was associated with significant decreases in fear, avoidance, and disgust. However, it was found that repeated exposure to the fear stimulus produced a greater decrease in avoidance behavior. Results suggest that both types of exposure can be effective in alleviating associated symptoms and provide additional evidence that disgust sensitivity plays a role in the treatment of spider phobia. Copyright © 2010 John Wiley & Sons, Ltd.