A role for CS-US contingency in Pavlovian conditioning

EXPRESS: Determinants of Extinction in a Streamed Trial Procedure

The strength of an association between a cue and its outcome is influenced by both the probability of the outcome given the cue and the probability of the outcome in the absence of the cue. Once an association has been formed, extinction is the procedure for reducing responding indicative of the association by repeated presentation of the cue without the outcome. The present experiments tested whether cumulative frequency and/or cumulative duration of these events affects associative extinction in a streamed trial extinction procedure with human participants. Experiment 1 assessed the effects of parametric manipulations of the frequency and duration of either the cue by itself or cue-outcome coabsence. In Experiment 1, participants proved relatively insensitive to manipulation of the event's duration. In contrast, judgments of the association by participants decreased when the frequency of cue-alone events was increased, even when the durations of those events were decreased so that cumulative exposure to the cue was equated. No effect of either the duration or the frequency of cue-outcome coabsence was observed. Experiment 2 demonstrated that the effect of cue-alone (i.e., extinction trial) frequency generalizes across a wide range of parameters for initial acquisition achieved by cue-outcome pairings. Experiment 3 tested for an interaction between event duration during initial learning and event duration during extinction. Collectively, these results indicate that the cumulative frequency, and not the cumulative duration, of extinction trials as well as the duration of the cue-outcome coabsences between extinction trials controls the effectiveness of an extinction procedure.

Delay of reinforcement versus rate of reinforcement in Pavlovian conditioning

Conditioned stimulus (CS) duration is a determinant of conditioned responding, with increases in duration leading to reductions in response rates. The CS duration effect has been proposed to reflect sensitivity to the reinforcement rate across cumulative exposure to the CS, suggesting that the delay of reinforcement from the onset of the cue is not crucial. Here, we compared the effects of delay and rate of reinforcement on Pavlovian appetitive conditioning in mice. In Experiment 1, the influence of reinforcement delay on the timing of responding was removed by making the duration of cues variable across trials. Mice trained with variable duration cues were sensitive to differences in the rate of reinforcement to a similar extent as mice trained with fixed duration cues. Experiments 2 and 3 tested the independent effects of delay and reinforcement rate. In Experiment 2, food was presented at either the termination of the CS or during the CS. In Experiment 3, food occurred during the CS for all cues. The latter experiment demonstrated an effect of delay, but not reinforcement rate. Experiment 4 ruled out the possibility that the lack of effect of reinforcement rate in Experiment 3 was due to mice failing to learn about the nonreinforced CS exposure after the presentation of food within a trial. These results demonstrate that although the CS duration effect is not simply a consequence of timing of conditioned responses, it is dependent on the delay of reinforcement. The results provide a challenge to current associative and nonassociative, time-accumulation models of learning. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Western-style diet impairs stimulus control by food deprivation state cues: Implications for obesogenic environments

In western and westernized societies, large portions of the population live in what are considered to be "obesogenic" environments. Among other things, obesogenic environments are characterized by a high prevalence of external cues that are associated with highly palatable, energy-dense foods. One prominent hypothesis suggests that these external cues become such powerful conditioned elicitors of appetitive and eating behavior that they overwhelm the internal, physiological mechanisms that serve to maintain energy balance. The present research investigated a learning mechanism that may underlie this loss of internal relative to external control. In Experiment 1, rats were provided with both auditory cues (external stimuli) and varying levels of food deprivation (internal stimuli) that they could use to solve a simple discrimination task. Despite having access to clearly discriminable external cues, we found that the deprivation cues gained substantial discriminative control over conditioned responding. Experiment 2 found that, compared to standard chow, maintenance on a "western-style" diet high in saturated fat and sugar weakened discriminative control by food deprivation cues, but did not impair learning when external cues were also trained as relevant discriminative signals for sucrose. Thus, eating a western-style diet contributed to a loss of internal control over appetitive behavior relative to external cues. We discuss how this relative loss of control by food deprivation signals may result from interference with hippocampal-dependent learning and memory processes, forming the basis of a vicious-cycle of excessive intake, body weight gain, and progressive cognitive decline that may begin very early in life.

Outcome probability modulates anticipatory behavior to signals that are equally reliable

A stimulus is a reliable signal of an outcome when the probability that the outcome occurs in its presence is different from in its absence. Reliable signals of important outcomes are responsible for triggering critical anticipatory or preparatory behavior, which is any form of behavior that prepares the organism to receive a biologically significant event. Previous research has shown that humans and other animals prepare more for outcomes that occur in the presence of highly reliable (i.e., highly contingent) signals, that is, those for which that difference is larger. However, it seems reasonable to expect that, all other things being equal, the probability with which the outcome follows the signal should also affect preparatory behavior. In the present experiment with humans, we used two signals. They were differentially followed by the outcome, but they were equally (and relatively weakly) reliable. The dependent variable was preparatory behavior in a Martians video game. Participants prepared more for the outcome (a Martians' invasion) when the outcome was most probable. These results indicate that the probability of the outcome can bias preparatory behavior to occur with different intensities despite identical outcome signaling.

Pseudocontingencies derived from categorically organized memory representations

Pseudocontingencies (PCs) allow for inferences about the contingency between two variables X and Y when the conditions for genuine contingency assessment are not met. Even when joint observations X i and Y i about the same reference objects i are not available or are detached in time or space, the correlation r(X i ,Y i ) is readily inferred from base rates. Inferred correlations are positive (negative) if X and Y base rates are skewed in the same (different) directions. Such PC inferences afford useful proxies for actually existing contingencies. While previous studies have focused on PCs due to environmental base rates, the present research highlights memory organization as a natural source of PC effects. When information about two attributes X and Y is represented in a hierarchically organized categorical memory code, as category-wise base rates p(X) and p(Y), the reconstruction of item-level information from category base rates will naturally produce PC effects. Three experiments support this contention. When the yes base rates of two respondents in four questionnaire subscales (categories) were correlated, recalled and predicted item-level responses were correlated in the same direction, even when the original responses to specific items within categories were correlated in the opposite direction.

A test of Rescorla and Wagner's (1972) prediction of nonlinear effects in contingency learning

According to most theories, in a simple contingency learning situation, excitatory learning occurs when the probability of the unconditioned stimulus in the presence of the conditioned stimulus (p(1)) is higher than the probability of the unconditioned stimulus in the absence of the conditioned stimulus (p(2)). In Rescorla and Wagner's (1972) model, this prediction varies, depending on the parameters used. In the following experiments, we evaluated whether the difference between p(1) and p(2) that is required to produce excitatory conditioning is the same, independent of the specific value of p(1), or whether this difference varies proportionally to p(1)'s value. To do so, an appetitive procedure of Pavlovian conditioning with rats was used. In four experiments, we compared different levels of contingency (low, medium and high) and found that the difference between p(1) and p(2) that is required to produce excitatory conditioning increases when the value of p(1) is higher. The possibility of analyzing contingency learning as a discrimination between p(1) and p(2) is also discussed.

Making the illusory correlation effect appear and then disappear: The effects of increased learning

The acquisition of a negative evaluation of a fictitious minority social group in spite of the absence of any objective correlation between group membership and negative behaviours was described by Hamilton and Gifford (1976) as an instance of an illusory correlation. We studied the acquisition and attenuation through time of this correlation learning effect. In two experiments we asked for participants’ judgements of two fictitious groups using an online version of a group membership belief paradigm. We tested how judgements of the two groups changed as a function of the amount of training they received. Results suggest that the perception of the illusory correlation effect is initially absent, emerges with intermediate amounts of absolute experience, but diminishes and is eliminated with increased experience. This illusory correlation effect can be considered to reflect incomplete learning rather than a bias due to information loss in judgements or distinctiveness.

Instrumental outcome devaluation with representation-mediated conditioning

In three experiments, rats were trained to perform two instrumental behaviours (R1 and R2) in the presence of discriminative stimuli (Sd1 and Sd2, respectively) to obtain a common food outcome (O1). Acquisition of the two discriminations was followed by switching the outcome accompanying R2 performance from O1 to a new one (O2). Experiment 1 showed paired presentations of O2 with a lithium chloride (LiCl) injection resulted in a reduction in the R2 performance. In the subsequent two experiments, each Sd was paired with LiCl injection and its effects on outcome consumption and instrumental performance were investigated. A reduction in the O2 consumption subsequent to the Sd devaluation was found in Experiments 2 and 3. Experiment 3 revealed a reduced R2 performance in an extinction test, following the animals' consummatory access to the outcomes in training context. These results demonstrate representation-mediated outcome devaluation in the course of the Sd devaluation.

Acquired appetitive responding to intravenous nicotine reflects a Pavlovian conditioned association

Recent research examining Pavlovian appetitive conditioning has extended the associative properties of nicotine from the unconditioned stimulus or reward to include the role of a conditional stimulus (CS), capable of acquiring the ability to evoke a conditioned response. To date, published research has used presession extravascular injections to examine nicotine as a contextual CS in that appetitive Pavlovian drug discrimination task. Two studies in the current research examined whether a nicotine CS can function discretely, multiple times within a session using passive iv infusions. In Experiment 1, rats readily acquired a discrimination in conditioned responding between nicotine and saline infusions when nicotine was selectively paired with sucrose presentations. In Experiment 2, rats were either trained with nicotine paired with sucrose or explicitly unpaired with sucrose. The results showed that rats trained with explicitly unpaired nicotine and sucrose did not increase dipper entries after the infusions. Nicotine was required to be reliably paired with sucrose for control of conditioned responding to develop. Implications of these findings are discussed in relation to tobacco addiction, learning theory, and pharmacology.

Neurogenesis, learning and associative strength

Though the role of the hippocampus in processes of learning and memory is well established, the role of new neurons generated there is less understood. Training on some associative learning tasks increases the likelihood that new cells in the subgranular zone of the dentate gyrus will survive. In the rat, an effective training procedure is trace eyeblink conditioning, in which a conditioned stimulus (CS) is paired with an aversive stimulation to the eyelid (unconditioned stimulus; US), but the stimuli are separated by a temporal gap. Here, we manipulated the asymptote or rate of acquisition during trace conditioning, and examined survival of cells generated 1 week before training. Acquisition was disrupted by decreasing associative strength by insertion of unpredicted USs or slowed with latent inhibition. The number of cells was increased in animals that were trained with trace conditioning, irrespective of the decrease in associative strength or slowed acquisition. Disrupting acquisition with unsignaled USs still increased cell numbers, suggesting that the learning effect on cell survival is not dependent on reliable expression of the conditioned response. Further, animals in the latent inhibition conditions that learned but required more trials also retained more of the new cells than animals requiring fewer trials. The number of cells that survived after the effective training procedures was similar to the number of cells that were available for rescue at the beginning of training. Thus, learning can rescue the majority of cells expressed at the beginning of training, and does so most effectively when acquisition requires many trials.

Depressive realism and the effect of intertrial interval on judgements of zero, positive, and negative contingencies

In three experiments we tested how the spacing of trials during acquisition of zero, positive, and negative response-outcome contingencies differentially affected depressed and nondepressed students' judgements. Experiment 1 found that nondepressed participants' judgements of zero contingencies increased with longer intertrial intervals (ITIs) but not simply longer procedure durations. Depressed groups' judgements were not sensitive to either manipulation, producing an effect known as depressive realism only with long ITIs. Experiments 2 and 3 tested predictions of Cheng's (1997) Power PC theory and the Rescorla-Wagner (1972) model, that the increase in context exposure experienced during the ITI might influence judgements most with negative contingencies and least with positive contingencies. Results suggested that depressed people were less sensitive to differences in contingency and contextual exposure. We propose that a context-processing difference between depressed and nondepressed people removes any objective notion of "realism" that was originally employed to explain the depressive realism effect (Alloy & Abramson, 1979).

Interoceptive Pavlovian conditioning with nicotine as the conditional stimulus varies as a function of the number of conditioning trials and unpaired sucrose deliveries

In rats, the pharmacological (interoceptive) effects of nicotine can serve as a signal (conditional stimulus) in a Pavlovian (classical) conditioning task. In this task, nicotine administration (0.4 mg base/kg, subcutaneous) is typically paired with intermittent access to a liquid sucrose unconditional stimulus; sucrose is withheld on saline sessions. An increase in sucrose receptacle entries (goal tracking) on nicotine sessions indicates conditioning. Given our limited understanding of the functional relationships controlling conditioned responding to a nicotine conditional stimulus, the present research examined nicotine's sensitivity to several manipulations shown to affect the conditioned responding in more widely studied Pavlovian conditioning tasks that use exteroceptive conditional stimuli: number of nicotine conditional stimulus-sucrose unconditional stimulus pairings per session (0, 3, 9, 18, or 36) and the impact of sucrose deliveries in saline sessions. Differential goal tracking developed in fewer sessions and asymptotic conditioned responding magnitude was greater with more nicotine-sucrose pairings. Further, goal tracking was more resistant to extinction (unconditional stimulus withheld) with more conditional-unconditional stimulus pairings during the acquisition phase. The discrimination was not acquired when sucrose presentations (9 or 18) also occurred during saline sessions. Furthermore, expression of the discrimination was disrupted when sucrose was presented in saline sessions; this disruption resulted from goal tracking in saline sessions. These results are consistent with the notion that nicotine-evoked goal tracking results from interoceptive conditioning processes.

Depressive realism and outcome density bias in contingency judgments: the effect of the context and intertrial interval

The perception of the effectiveness of instrumental actions is influenced by depressed mood. Depressive realism (DR) is the claim that depressed people are particularly accurate in evaluating instrumentality. In two experiments, the authors tested the DR hypothesis using an action-outcome contingency judgment task. DR effects were a function of intertrial interval length and outcome density, suggesting that depressed mood is accompanied by reduced contextual processing rather than increased judgment accuracy. The DR effect was observed only when participants were exposed to extended periods in which no actions or outcomes occurred. This implies that DR may result from an impairment in contextual processing rather than accurate but negative expectations. Therefore, DR is consistent with a cognitive distortion view of depression.

A comparative approach to cue competition with one and two strong predictors

The relative validity effect (Wagner, Logan, Haberlandt, & Price, 1968) demonstrated that a strong cue or cause reduces responding to, or judgments of, a weaker cue or cause. We report two experiments with human subjects using relative validity preparations in which we investigate one- and two-cue competition effects. Previously, we investigated the effect using instrumental and Pavlovian conditioning preparations with rats. In the first experiment, we used a procedure analogous to the animal preparations. In the second experiment, we used a different probabilistic procedure. The results with humans and rats are very similar. In each species we find similar interference with processing the moderate predictor with one or with two strong competitors. These results are not well predicted by most associative models.