Protection from latent inhibition provided by a conditioned inhibitor.

Two conditioned suppression experiments with rats investigated the influence on latent inhibition of compounding a Pavlovian conditioned inhibitor with the target cue during preexposure treatment. Results were compared with those of subjects that received conventional latent inhibition training, no preexposure, or preexposure to the target cue in compound with a neutral stimulus. In Experiment 1, greater attenuation of the latent inhibition effect was observed in subjects that received target preexposure in compound with a Pavlovian conditioned inhibitor relative to subjects that received preexposure with a neutral stimulus or to the target alone. In Experiment 2, this protection from latent inhibition was attenuated if the excitor that was used to train the conditioned inhibitor was extinguished between preexposure and target training. The results are consistent with an account offered by the extended comparator hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus preexposure, comparison, and changes in the associability of common stimulus features

In four experiments, rats received preexposure either to both of two compound flavours (AX and BX), or to just one (BX). Experiment 1 demonstrated a perceptual learning effect, showing that, for animals given preexposure to both flavours, an aversion conditioned to AX generalized only poorly to BX. Subsequent experiments assessed the properties of the common feature, X. Experiment 3 showed that the two preexposure treatments did not differ in the extent to which they produced habituation of the neophobia evoked by X. Experiment 2 showed that conditioning to X proceeded more rapidly in subjects given preexposure to both AX and BX than in subjects preexposed to BX alone. In Experiment 4, a similar effect was found when the elements of the compounds were presented serially. It is concluded that the perceptual learning effect of Experiment 1 occurs in spite of the fact that preexposure to two stimuli tends to maintain the associability of their common elements.     

CS-US preexposure effects on trace eyeblink conditioning in young rats: Potential implications for functional brain development.

Recent studies of delay eyeblink conditioning (EBC) in young rats have demonstrated different effects of various conditioned and unconditioned stimulus (CS-US) preexposure conditions on learning at different ages. The present study extends this research to trace EBC. Subjects experienced 1 of 3 preexposure conditions (paired CS-US, unpaired CS-US, or no stimuli) at either 20 or 24 days of age. Four days later, they were conditioned using either trace (Experiment 1) or delay (Experiment 2) EBC parameters. Results were similar at both ages tested. Paired preexposure facilitated acquisition of delay but not trace relative to context preexposure. Unpaired preexposure impaired acquisition of both delay and trace. These behavioral findings provide a foundation for hypotheses about the functional maturation of cerebellar, hippocampal, and entorhinal learning circuits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preexposure effects in the spatial domain: Dissociation between latent inhibition and perceptual learning.

In 4 experiments, rats were given intermixed or blocked preexposure to an array of landmarks that subsequently defined the location of a hidden goal in a Morris pool task. Previous research has shown that intermixed preexposure to pairs of adjacent landmarks retards learning whereas preexposure to individual landmarks facilitates subsequent learning (J. Prados, V. D. Chamizo, & N. J. Mackintosh, 1999). Accordingly, in Experiment 1, intermixed and blocked preexposure to pairs of adjacent landmarks was found to retard learning. In Experiment 2, however, a scheduling effect was found: Rats given intermixed preexposure to the individual landmarks learned faster than rats given blocked or no preexposure. Experiment 3 showed that intermixed (but not blocked) preexposure to pairs of landmarks resulted in a facilitatory effect when preexposure and test were carried out in different contexts. Experiment 4 replicated within a single experiment the main results observed in Experiments 1 and 3. This pattern of results suggests that intermixed preexposure engages learning processes other than latent inhibition that facilitate subsequent learning of the navigation task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hyperstriatal lesions and attention in the pigeon.

In two experiments, pigeons with bilateral lesions of the hyperstriatum were compared with unoperated control birds on tasks designed to test an attentional account of hyperstriatal function. In both experiments, hyperstriatal lesions disrupted reversal learning but did not influence the retardation of learning associated with either nonreinforced preexposure to the to-be-conditioned stimulus (Experiment 1) or prior nondifferential reinforcement to the to-be-discriminated stimuli (Experiment 2). There was, however, evidence of an impairment in both the acquisition and maintenance of autoshaped responding in lesioned birds, an impairment that may reflect a disruption of classical associations in hyperstriatal pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factors governing single-trial contextual fear conditioning in the weanling rat.

Although contextual fear conditioning emerges later in development than explicit-cue fear conditioning, little is known about the stimulus parameters and biological substrates required at early ages. The authors adapted methods for investigating hippocampus function in adult rodents to identify determinants of contextual fear conditioning in developing rats. Experiment 1 examined the duration of exposure required by weanling rats at postnatal day (PND) 23 to demonstrate contextual fear conditioning. This experiment demonstrated that 30 s of context exposure is sufficient to support conditioning. Furthermore, preexposure enhanced conditioning to an immediate footshock, the context preexposure facilitation effect (CPFE), but had no effect on contextual conditioning to a delayed shock. Experiment 2 demonstrated that N-methyl-D-aspartate (NMDA) receptor inactivation during preexposure impairs contextual learning at PND 23. Thus, the conjuctive representations underlying the CPFE are NMDA-dependent as early as PND23 in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual effects in conditioning, latent inhibition, and habituation: Associative and retrieval functions of contextual cues.

Rats were used as subjects in four experiments to investigate the transfer of learning from one context to another. Subjects received two sessions of training each day, one in each of two different contexts. Experiment 1 showed that the habituation of the unconditioned response to a stimulus presented in one context was left intact when the stimulus was presented in another context, but that latent inhibition was attenuated when preexposure and conditioning phases occurred in different contexts. Experiments 2 and 3 demonstrated that a conditioned response made on the basis of an appetitive reinforcer was diminished when conditioning and testing occurred in different contexts, but that aversive conditioning was not influenced by the context in which testing occurred. In Experiment 4, the presence of an aversive reinforcer during training did not preclude the occurrence of context-specific conditioning on the basis of an appetitive reinforcer. Associative and retrieval-based interpretations of the results are explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ibotenic acid lesions of the basolateral, but not the central, amygdala interfere with conditioned taste aversion: Evidence from a combined behavioral and anatomical tract-tracing investigation.

Rats (Rattus norvegicus) with almost complete ibotenic acid lesions (at least 90%) of the basolateral amygdaloid complex (BLA) failed to learn a conditioned taste aversion (CTA; Experiment 1A). In these same BLA rats, the bidirectional parabrachial–insular pathway that courses through the central nucleus of the amygdala (Ce) was shown to be spared (Experiment 1B), indicating that the BLA per se is critical for CTA learning. In contrast to the deleterious effect of BLA lesions on CTA, ibotenic acid lesions of the Ce did not block CTA learning (Experiment 2). Nonreinforced preexposure to the gustatory stimulus attenuated CTA acquisition in normal rats, and, under these conditions, rats with BLA lesions were no longer impaired (Experiment 3). Thus, ibotenic acid lesions centered over the Ce, sparing a considerable extent of the BLA, together with the testing procedure used in previous experiments (e.g., L. T. Dunn & B. J. Everitt, 1988), led to the belief that the CTA deficits reported after electrolytic lesions of the amygdala were the result of incidental damage to fibers of passage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention and relative novelty in human perceptual learning.

Four experiments examined the role of attention in human perceptual learning. In Experiment 1, participants were preexposed to a pair of visual (checkerboard) stimuli AX and BX, with common elements X and unique features A and B. A same-different task was then used to assess discrimination of AX and BX and a pair of control stimuli, CY and DY. In addition, participants' eye movements were recorded to assess the role of attentional processes. The results showed that preexposure enhanced discrimination between AX and BX. Furthermore, participants showed greater attention to the preexposed unique features A and B than to the novel unique features C and D, as measured by the eye gaze monitor. Experiments 2 and 3 examined the prediction that perceptual learning is due to the relative familiarity of the common and unique stimulus features. Experiment 4 replicated the intermixed-blocked effect and showed that the way in which AX and BX are presented is also important for perceptual learning. The results generally support the idea that intermixed preexposure to AX and BX increases attention to the unique stimulus features A and B. Some aspects of the results are consistent with a relative novelty account, whereas others implicate a high-level attentional process that is not driven by stimulus novelty. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The influence of passive preexposure on escape from a Morris pool.

In 3 experiments rats were preexposed to the landmarks that surround a Morris pool by being placed on a submerged platform within the pool. They were then required to escape from the pool by swimming to the platform, which was in a location that had not been used during preexposure. Preexposure facilitated subsequent escape from the pool, provided that the platform was not moved during preexposure and the relative position of the landmarks to each other remained constant throughout preexposure. In contrast, if during preexposure the platform was moved from session to session (Experiment 1), or the array of landmarks was altered unsystematically from trial to trial (Experiments 2 and 3), then subsequent learning to escape from the pool was disrupted. These findings suggest that the effects of preexposure to the landmarks in a Morris pool is determined by whether or not they are of relevance for identifying the location of the platform. When they are relevant, then subsequent learning is facilitated, but when they are irrelevant, then subsequent learning is disrupted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An immediate-shock freezing deficit with discrete cues: A possible role for unconditioned stimulus processing mechanisms.

Five experiments with C57BL/6 mice (Mus musculus) investigated whether failures in shock processing might contribute to deficits in freezing that occur after an animal receives a shock immediately on exposure to a conditioning context. Experiment 1 found that more contextual freezing resulted from delayed shocks than from immediate shocks across 4 shock intensities. Experiment 2 extended the immediate-shock freezing deficit to discrete stimuli. Experiment 3 found that preexposure to the to-be-conditioned cue did not facilitate immediate cued conditioning. Experiment 4 found that context preexposure enhanced context-evoked fear after an immediate shock. Experiment 5 found that context preexposure also enhanced immediate cued conditioning. These findings are problematic for current theories of the immediate-shock freezing deficit that focus exclusively on processing of the conditioned stimulus, and they suggest that failures in shock processing may contribute to the deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of primary motivation in stimulus preexposure effects.

It is currently a matter of debate whether the deficit in conditioning observed after stimulus preexposure is one of acquisition or one of performance. The major criticism of performance-based theories is their inability to specify what is learned during nonreinforced preexposure that may influence subsequent acquisition of conditioned responding. Experiments 1 and 2 used an excitatory appetitive conditioning procedure and Experiment 3 used an inhibitory appetitive conditioning procedure, with rats as subjects, and consistently found that the effects of preexposure to a stimulus transferred to conditioning only when the reinforcer was relevant to the motivational state in which that preexposure was conducted. This finding suggests that during preexposure, rats learn that a stimulus is unrelated to events of relevance to their current motivational state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning of event sequences is based on response-effect learning: Further evidence from a serial reaction task.

Four experiments provide converging evidence that serial learning in a serial reaction task is based on response–effect learning, mediated by the learning of the relations between a response and the stimulus that follows it. In Experiment 1, the authors varied the stimulus sequence and the response–stimulus relations while holding the response sequence constant. Learning effects depended on the complexity of the response–stimulus relations but not on the stimulus–stimulus relations. In Experiment 2, transfer of serial learning from 1 stimulus sequence to another was only found when both sequences had identical response–stimulus relations. In Experiment 3, a variation of the stimulus sequence alone had no effect on serial learning, whereas in Experiment 4 learning effects increased when the response–stimulus relations but not the stimulus–stimulus relations were simplified. These findings suggest that serial learning is based on mechanisms of voluntary action control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

I like it because I said that I like it: Evaluative conditioning effects can be based on stimulus-response learning.

Evaluative conditioning (EC) effects are often assumed to be based on a learned mental link between the CS (conditioned stimulus) and the US (unconditioned stimulus). We demonstrate that this link is not the only one that can underlie EC effects, but that if evaluative responses are actually given during the learning phase also a direct link between the CS and an evaluative response—a CS-ER link—can be learned and lead to EC effects. In Experiment 1, CSs were paired with USs and participants were asked to evaluate the pairs during the conditioning phase. Resulting EC effects were unaffected by a later revaluation of the USs, suggesting that these EC effects can be attributed to CS-ER learning rather than to CS-US learning. Experiment 2 replicated Experiment 1 with the difference that no evaluative responses were given during the learning phase. EC effects in this study were influenced by US revaluation, suggesting that these EC effects are mainly based on CS-US learning. In Experiment 3, it was shown that EC effects can be found even if the USs are entirely removed from the procedure and the CSs are only paired with enforced evaluative responses. Together the experiments show that the valence of a stimulus can change because of a contingency with an evaluative response. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Sex differences, context preexposure, and the immediate shock deficit in Pavlovian context conditioning with mice.

The acquisition of context fear in rats is affected by variables such as the sex of the animal, the placement to shock interval (PSI), and preexposure to the context. The current experiments assessed the effects of these variables on context conditioning in mice (C57BL/6). In Experiment 1, mice were placed in a chamber and received a single shock 5 s, 20 s, 40 s, 60 s, 180 s, or 720 s later. Increasing the PSI produced corresponding increases in conditional freezing during the context test. In addition, male mice acquired more context conditioning than female mice did but only at intermediate PSIs. In Experiment 2, preexposure to the context before training alleviated the sex difference found with an intermediate PSI. The results are discussed in terms of configural learning theory and are argued to be contrary to the predictions of scalar expectancy theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The molecular biology of neuronal nicotinic acetylcholine receptors

Two experiments were performed to evaluate the effects of three different elaborative activities on concept learning. Experiment 1 consisted of 60 undergraduates, while Experiment 2 consisted of 54 undergraduates. In both experiments, subjects studied a passage which asked them to create personal examples of the target concepts, contrast the target concepts, or expand on the effects of the target concepts. Subjects took a criterion test which consisted of recall of concept definitions and teaching examples, classification of novel examples, and problem solving scenarios. In both experiments, the condition which asked subjects to contrast the target concepts produced significantly better performance than the other two conditions. Possible explanations focus on: (1) the degree to which the different elaborative activities influence the richness and/or distinctiveness of the encoded information, and (2) the relation among the focus of the elaborative activity, the experimental text, and the measured criterion outcomes.     

Memory for, and salience of, the unique features of similar stimuli in perceptual learning.

In two experiments, participants received exposure to complex checkerboards (e.g., AX and BX) that consisted of small distinctive features (A and B) superimposed on a larger common background (X). Subsequent discrimination between AX and BX, assessed by a same-different task, was facilitated when the stimuli were presented on alternate trials in preexposure—a perceptual learning effect (Experiment 1). The hypothesis that this form of exposure results in more accurate representations of the unique features was supported in Experiment 1, which showed that participants were well able to match the color of the feature with its shape. Experiment 2 showed that exposure to A and B in isolation, intermixed with presentations of AX and BX, enhanced the perceptual learning effect, which confirmed that the better encoding of the unique features during intermixed preexposure is a direct cause of the enhanced discrimination observed following preexposure on this schedule. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Cigarette smoking predicts development of depressive symptoms among U.S. adolescents

Latent inhibition (LI) refers to retarded conditioning to a stimulus as a consequence of its nonreinforced preexposure. LI is impaired in acute schizophrenic patients and in rats treated with amphetamine. Neuroleptic drugs enhance LI, and this effect is selective and specific for this class of drugs. The present experiments tested the proposition that neuroleptic-induced enhancement of LI stems from decreased capacity of stimulus-preexposed animals to switch responding according to the new stimulus-reinforcement contingency in the conditioning stage. LI was assessed using an off-baseline conditioned emotional response (CER) procedure in rats licking for water, consisting of three stages: preexposure to the-to-be conditioned stimulus, tone; conditioning, in which the preexposed stimulus was paired with a foot-shock; and test, in which LI was indexed by animals' degree of suppression of licking during tone presentation. Whereas in previous studies that demonstrated LI enhancement by neuroleptics, preexposure consisted of 10 to 40 tones, and conditioning included two tone-shock pairings, the present experiments used 40 tone preexposures, followed by an extended conditioning stage with five tone-shock pairings. It was expected that under these conditions no LI effect would be evident in untreated animals, but that animals treated with a neuroleptic drug, either during the entire LI procedure or only in conditioning, would show LI. Experiments 1 and 2 showed that LI was obtained in rats treated with haloperidol (0.1 mg/kg in experiment 1, 0.03 and 0.2 mg/kg in experiment 2) but not in the untreated controls. Experiment 3 showed that the same outcome was obtained when haloperidol (0.1 mg/kg) administration was confined to the conditioning stage. Experiment 4 showed that clozapine (5 mg/kg)-treated animals showed LI when the drug was confined to conditioning, but not to the preexposure stage. The implications of these results for the mechanism of action of neuroleptic drugs are discussed.     

The Origin of Exemplar Effects in Rule-Driven Categorization.

S. W. Allen and L. R. Brooks (1991) have shown that exemplar memory can affect categorization even when participants are provided with a classification rule. G. Regehr and L. R. Brooks (1993) argued that stimuli must be individuated for such effects to occur. In this study, the authors further analyze the conditions that yield exemplar effects in this rule application paradigm. The results of Experiments 1-3 show that interchangeable attributes, which are not part of the rule, influence categorization only when attention is explicitly drawn on them. Experiment 4 shows that exemplar effects can occur in an incidental learning condition, whether stimulus individuation is preserved or not. The authors conclude that the influence of exemplar learning in rule-driven categorization stems from the attributes specified in the rule or in the instructions, not from the stimulus gestalts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The generation effect and the modeling of associations in memory

The search of associative memory (SAM) model of Gillund and Shiffrin (1984) was applied to data of two experiments that examined the generation effect (Slamecka & Graf, 1978). Subjects studied a list of related word pairs, in which they either read both words in the pair or generated the right- hand response term using the left-hand stimulus term plus the response word fragment as generation cues. Experiment 1 manipulated encoding condition within subjects and used an incidental learning procedure. Experiment 2 manipulated encoding condition between subjects and used an intentional learning procedure. Memory was tested with recognition, cued recall, and free recall. A higher order association model gave a better and more parsimonious fit to the results than did an item-level association model. The relationship between various versions of SAM and current accounts of the generation effect are discussed, particulary the two-factor theory of Hirshman and Bjork (1988).