Trial spacing and trial distribution effects in Pavlovian conditioning: Contributions of a comparator mechanism.

Two experiments, involving a total of 144 rats, investigated a potential basis for trial spacing and trial distribution effects. In Exp 1, a CS (e.g., CS A) was trained with either massed (e.g., A?→?A?→?A) or spaced (e.g., A A A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Exp 2, different CSs were trained in either a massed (e.g., A?→?A?→?A?→?B?→?B?→?B?→?C?→?C?→?C) or a distributed (e.g., A?→?B?→?C?→?A?→?B?→?C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects were, at least in part, reversible deficits in performance rather than failures of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A direct laboratory comparison of Pavlovian conditioning and traditional associative learning.

24 adult human Ss were presented with a learning task which combined salivary conditioning with traditional associative learning: paired-associate learning of a 50 word Russian-English vocabulary and serial motor learning of a sequence of 100 adjacent bolts. Conditioning proceeded best when Ss did not know they were being conditioned, while associative learning was reasonably effective when Ss knew what they were associating. The view is expressed that the present data support strongly the hypothesis that Pavlov's laws of conditioning are primarily laws of unconscious biological learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amygdalar unit activity during three learning tasks: Eyeblink classical conditioning, Pavlovian fear conditioning, and signaled avoidance conditioning.

Neural activity in central and basolateral amygdala nuclei (CeA and BLA, respectively) was recorded during delay eyeblink conditioning, Pavlovian fear conditioning, and signaled barpress avoidance. During paired training, the CeA exhibited robust learning-related excitatory activity during all 3 tasks. By contrast, the BLA exhibited minimal activity during eyeblink conditioning, while demonstrating pronounced increases in learning-related excitatory responsiveness during fear conditioning and barpress avoidance. In addition, the relative amount of amygdalar activation observed appeared to be related to the relative intensity of the unconditioned stimulus and somatic requirements of the task. Results suggest the CeA mediates the Pavlovian association between sensory stimuli and the BLA mediates the modulation of instrumental responding through the assignment of motivational value to the unconditioned stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unblocking in Pavlovian appetitive conditioning.

Two experiments, with 280 Sprague-Dawley rats, demonstrated unblocking in an appetitive conditioning preparation. One stimulus, A, was first paired with either a low-value reinforcer (1 food pellet) or a high-value reinforcer (1 food pellet followed by 2 more food pellets). A 2nd stimulus, X, was then added to A, and the compound was reinforced with either the high- or low-value reinforcer. Conditioning to X was blocked if the same reinforcer was used in both phases of the experiment, but there was substantial conditioning to X when the reinforcer value was shifted either up or down when X was introduced. Exp I demonstrated this unblocking phenomenon using a design that minimized the potential contribution of generalization decrement. Exp II examined the effects of a variety of posttraining manipulations on conditioned responding to the added X cue after unblocking procedures. Among Ss that received downshifts in reinforcer value when X was introduced, responding was affected by several posttraining manipulations, including changes in context value. Those manipulations had smaller effects on the responding of Ss that received upshifts in reinforcer value and no effects on responding in control conditions. Findings are considered in relation to the model of conditioning outlined by R. A. Rescorla and A. R. Wagner (1972). (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unblocking in Pavlovian fear conditioning.

Six experiments used rats to study blocking and unblocking of fear learning. An excitatory stimulus (A) blocked fear learning to a neutral stimulus (B). Unblocking of B occurred if the AB compound signaled an increase in unconditioned stimulus (US) intensity or number. Assessments of associative change during blocking showed that more was learned about B than A. Such assessments during unblocking revealed that more was learned about B than A following an increase in US intensity but not US number. These US manipulations had no differential effects on single-cue learning. The results show that variations in US intensity or number produce unblocking of fear learning, but for each there is a different profile of associative change and a potentially different mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two kinds of attention in Pavlovian conditioning: Evidence for a hybrid model of learning.

Four appetitive Pavlovian conditioning experiments with rats examined the rate at which the discrimination between compounds AY and AX was solved relative to the discrimination between compounds AY and BY. In Experiments 1 and 2, these discriminations were preceded by training in which A and B were continuously reinforced and X and Y were partially reinforced. Consistent with the Pearce and Hall (1980) model, the results showed that the AY/AX discrimination was solved more readily than the AY/BY discrimination. In Experiments 3 and 4, the discriminations were preceded by feature-positive training in which trials with AX and BY signaled food but trials with X and Y did not. Consistent with the Mackintosh (1975) model, the results showed that the AY/BY discrimination was solved more readily than the AY/AX discrimination. These results are discussed with respect to a hybrid model of conditioning and attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential and simultaneous feature positive discriminations: Occasion setting and configural learning in human Pavlovian conditioning.

Using a conditioned suppression preparation, the authors investigated sequential (X→A+/A–) versus simultaneous (XA+/A–) feature positive (FP) discrimination learning in humans. The sequential discrimination was expected to be resolved by means of a Feature X Modulated Target A–US association and the simultaneous discrimination by a feature X–US association. After sequential FP training, extinction of Feature X did not affect discriminative X→A/A responding (Experiment 1), and X transferred its modulatory ability only to new targets, B, that had also been modulated (Experiment 2). This suggests that the sequential FP discrimination indeed resulted in occasion setting. Unlike expected, Feature X Extinction did not affect discriminative XA/A responding after simultaneous FP training (Experiment 3), while at the same time Feature X did show the predicted nonselective transfer to new targets, B (Experiment 4). J. M. Pearce's (1987) configural learning theory can account for most but not all findings of Experiments 3 and 4. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial prefrontal cortex and Pavlovian conditioning: Trace versus delay conditioning.

Pavlovian eyeblink (EB) conditioning was studied in both trace and delay paradigms in rabbits (Oryctolagus cuniculus) with either medial prefrontal cortex (mPFC) lesions or sham lesions. mPFC lesions of prelimbic cortex (Brodmann's Area 32) retarded EB conditioning in the trace but not the delay paradigm. However, this effect was significant only when the conditioned stimulus (CS) was 500 rather than 100 ms in duration. Lesions of the anterior cingulate cortex (Area 24) did not affect EB conditioning in a trace paradigm. Accompanying CS-evoked heart rate slowing was attenuated under all conditions by the mPFC lesions, although this result was not always statistically significant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ethanol enhancement of Pavlovian conditioning.

60 New Zealand albino rabbits were tested for Pavlovian conditioning and extinction of eye-blink (EB) and heart-rate (HR) responses following water or various doses of oral ethanol (375–2,500 mg/kg). The highest dose suppressed both EB and HR conditioning during training, whereas the lowest dose enhanced HR responses during training and increased EB responses during later extinction in a symmetrically state-dependent manner. An intermediate dose (750 mg/kg) administered during training enhanced HR responses and suppressed EB responses but increased EB responses during later extinction following either ethanol or water. Ethanol treatments also suppressed unconditioned responses (UCRs) to shock and increased locomotor activity; however, these effects differed qualitatively from those that ocurred during Pavlovian training and extinction. Results suggest that very low doses of ethanol can enhance the ability of stimuli to elicit Pavlovian conditioned reflexes and impair the ability to adaptively modify these reflexes when stimulus contingencies later change. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cingulate cortex: Its role in Pavlovian conditioning.

Three experiments with New Zealand albino rats examined the role of anterior and posterior cingulate cortex in Pavlovian conditioning. Tones served as CSs, and paraorbital electric shock served as the UCS. Anterior cingulate lesions attenuated conditioned heart rate (HR) decelerations, relative to posterior cingulate or sham lesions, but enhanced the magnitude of the bradycardiac component of the orienting reflex. Posterior cingulate lesions enhanced the bradycardiac component of the CR, particularly late in training, relative to anterior or sham lesions. Somatomotor eye-blink conditioning, shock thresholds, and HR UCRs were unaffected by cingulate lesions. Electrical stimulation of cingulate cortex revealed effective sites for eliciting HR and blood pressure (BP) changes only in anterior cingulate cortex. Relatively large (70–200 beats/min) HR decelerations accompanied by small (1–5-mm Hg) BP depressor responses were elicited by stimulation of this area; the HR decreases were abolished by methylatropine nitrate but were unaffected by either propranolol hydrochloride or phentolamine hydrochloride. Results are discussed in terms of cingulate involvement in the mediation of the cardiovascular component of a response pattern related to stimulus processing. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation and overshadowing in Pavlovian fear conditioning.

The present experiments addressed a fundamental discrepancy in the Pavlovian conditioning literature concerning responding to a target cue following compound reinforced training with another cue of higher salience. Experiment 1 identified one determinant of whether the target cue will be overshadowed or potentiated by the more salient cue, namely contiguity between compound CS termination and US presentation. Overshadowing and potentiation were observed with delay and trace procedures, respectively. Experiments 2 and 3 contrasted elemental and configural explanations of potentiation. Both experiments supported a configural account. Experiments 3 and 4, by manipulating prior learning experiences to bias subjects to encode the same compound elementally or configurally, demonstrated decreased potentiation and overshadowing, respectively. Overall, these experiments demonstrate potentiation with nontaste stimuli and identify one variable that determines whether overshadowing or potentiation will occur. Moreover, they show that prior experiences can determine how a compound is encoded and are compatible with the idea of flexible encoding as a principle of information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Marking effects in Pavlovian trace conditioning.

[Correction Notice: An erratum for this article was reported in Vol 13(3) of Journal of Experimental Psychology: Animal Behavior Processes (see record 2008-10750-001). The last sentence in the second paragraph of the Discussion on page 128 should read as follows: "A second possibility is that in the marked ITI group, the marking of irrelevant events in the middle of the intertrial interval promoted associations between those events and food, which then interfered with the learning of an association between SI and food."] In four experiments we investigated pigeons' acquisition of a successive discrimination with a trace autoshaping procedure. The conditioned stimuli were 5-s presentations of colored key lights, one of which was followed by food after a 5-s delay. In Experiment 1, which used spatially defined cues, we found that acquisition of differential responding to the reinforced cue was facilitated when a brief flash of light immediately followed both reinforced and nonreinforced cues. Experiment 2 found a similar enhancement by the added light flash in a purely visual discrimination. Experiment 3 found that the flash facilitated learning only when presented immediately after the discriminative cues, and not when it occurred immediately before the cues or at the time of reinforcement. A fourth experiment found this facilitation effect only when the flash and reinforcement occurred on the same trial. These results are interpreted in terms of marking: The flash enhanced learning because it triggered a backward scan through recent memory to search for possible predictors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modafinil and memory: Effects of modafinil on Morris water maze learning and Pavlovian fear conditioning.

Modafinil has been shown to promote wakefulness and some studies suggest the drug can improve cognitive function. Because of many similarities, the mechanism of action may be comparable to classical psychostimulants, although the exact mechanisms of modafinil's actions in wakefulness and cognitive enhancement are unknown. The current study aims to further examine the effects of modafinil as a cognitive enhancer on hippocampus-dependent memory in mice. A high dose of modafinil (75 mg/kg ip) given before training improved acquisition on a Morris water maze. When given only before testing, modafinil did not affect water maze performance. We also examined modafinil (0.075 to 75 mg/kg) on Pavlovian fear conditioning. A low dose of pretraining modafinil (0.75 mg/kg) enhanced memory of contextual fear conditioning (tested off-drug 1 week later) whereas a high dose (75 mg/kg) disrupted memory. Pretraining modafinil did not affect cued conditioning at any dose tested, and immediate posttraining modafinil had no effect on either cued or contextual fear. These results suggest that modafinil's effects of memory are more selective than amphetamine or cocaine and specific to hippocampus-dependent memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of Pavlovian conditioning: Role of protection from habituation in spinal conditioning.

Conditioned antinociception can be established in spinal rats by pairing stimulation to one hind leg (the conditioned stimulus [CS]) with an intense tailshock (the unconditioned stimulus [US]). After this training, the paired CS (CS+) elicits greater antinociception on the tail-flick test than a CS that was explicitly unpaired (CS–). Five experiments are reported that suggest that this effect reflects protection from habituation. Experiment 1 showed that the CS (legshock) induces antinociception before training. Presenting the CS alone weakened (habituated) its antinociceptive impact (Experiment 2). Less habituation was observed when the CS was paired with the US (Experiment 3). Decreasing habituation to the CS– (by increasing the interval between trials) and facilitating habituation to the CS+ (by increasing the number of trials) effectively eliminated the CS+/CS– difference (Experiments 4 and 5). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response rate and reinforcement rate in Pavlovian conditioning.

Four experiments used delay conditioning of magazine approach in rats to investigate the relationship between the rate of responding, R, to a conditioned stimulus (CS) and the rate, r, at which the CS is reinforced with the unconditioned stimulus (US). Rats were concurrently trained with four variable-duration CSs with different rs, either as a result of differences in the mean CS-US interval or in the proportion of CS presentations that ended with the US. In each case, R was systematically related to r, and the relationship was very accurately characterized by a hyperbolic function, R = Ar/(r +c). Accordingly, the reciprocal of these two variables—response interval, I (= 1/R), and CS-US interval, i (= 1/r) – were related by a simple affine (straight line) transformation, I = mi+b. This latter relationship shows that each increment in the time that the rats had to wait for food produced a linear increment in the time they waited between magazine entries. We discuss the close agreement between our findings and the Matching Law (Herrnstein, 1970) and consider their implications for both associative theories (e.g., Rescorla & Wagner, 1972) and nonassociative theories (Gallistel & Gibbon, 2000) of conditioning. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Pavlovian conditioning of sexual arousal: Parametric and background manipulations.

Recent studies have shown that a Pavlovian conditioned stimulus (CS) for unconsummated sexual arousal can increase the rate of copulation in the rat. The present report includes 5 experiments examining the effects of parametric manipulations on the conditioned arousal response in 216 male and more than 136 ovariectomized female Long-Evans hooded rats. Results show that 6–9 trials are necessary for reliable conditioning, but extinction is somewhat slower than acquisition. The function for the CS/unconditioned stimulus (UCS) interval is quadratic, with a minimum of several minutes required for effective conditioning. In the 1st 3 experiments, it appeared that background cues were conditioned as well as the designated CSs, and this was tested explicitly in the last 2 studies. In one, the effect of background cues was shown by training and testing in different situations; in the 2nd, background cues were shown to be subject to latent inhibition. Results demonstrate the influence of Pavlovian learning in sexual behavior and help to provide the basis for an animal model of the acquisition of deviant sexual arousal in humans. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian conditioning of sexual arousal: First- and second-order effects.

Four experiments examined the conditioning of sexual arousal in 81 male Long-Evans hooded rats. In each case, the unconditioned response (UCR) was unconsummated arousal after exposure to a female. There was evidence of a substantial conditioned effect, as shown by decreases in the time to complete copulation during postconditioning conditioned stimulus/stimuli (CS) tests. It was also possible to establish a 2nd-order conditioned response (CR), which retained its strength even after extinction of the 1st-order response. Results confirm the power of Pavlovian contingencies in sexual responding. The locus and mode of action of this CR and its function are discussed. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Opioid regulation of Pavlovian overshadowing in fear conditioning.

In Pavlovian overshadowing, a stimulus that predicts a biologically important event reduces conditioning to another, equally predictive stimulus. We tested the effects of an opioid antagonist and dopamine agonist on the ability of a salient white noise to overshadow a less salient light. Rats were conditioned to fear a light or a noise–light compound using a mild footshock. Compound-conditioned rats trained under the saline vehicle revealed significant overshadowing of the light by the noise. This overshadowing effect was significantly attenuated in rats trained under the opioid antagonist naltrexone, consistent with an opioid-mediated negative feedback model of conditioning. In line with predictions made by negative feedback-type models, we failed to obtain overshadowing with few trials, suggesting that the processes underlying conditioning during initial trials do not contribute to the opioid-dependent Pavlovian overshadowing obtained in our preparation. Lastly, we compared the involvement of dopamine-mediated and opioid-mediated processes in overshadowing by conditioning rats under the partial dopamine D1 receptor agonist SKF 38393 or the opioid antagonist naltrexone. Both naltrexone and SKF 38393 were found to attenuate overshadowing; however, the behavioral profiles produced by each pharmacological manipulation were distinct. Collectively, these studies demonstrate an important role for both opioid- and dopamine-mediated processes in multiple-trial overshadowing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Second-order conditioning and Pavlovian conditioned inhibition: Operational similarities and differences.

Procedures for establishing 2nd-order excitation (CS1-unconditioned stimulus [UCS] trials followed by CS2-CS1 trials) are highly similar to those for Pavlovian conditioned inhibition (CS1-UCS trials interspersed with CS2-CS1 trials). Conditioned suppression in rats was used to identify the critical operational differences that result in 2nd-order excitation as opposed to Pavlovian inhibition. No, few, or many CS2-CS1 trials were either interspersed with or given after CS1-UCS trials. CS2 proved excitatory only after few CS2-CS1 trials, either interspersed or sequential (Exp 1). In contrast, CS2 proved inhibitory on both summation (Exp 2) and retardation (Exp 3) tests only after many CS2-CS1 trials, and then only when the excitatory status of CS1 was preserved. Apparently, the critical difference for establishing 2nd-order excitation or Pavlovian inhibition is the number of CS2-CS1 pairings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)