Retardation in Human Discrimination Learning as a Consequence of Pre-exposure: Latent Inhibition or Negative Priming?

A series of experiments with human subjects, using black-and-white chequerboard patterns, demonstrated that non-reinforced pre-exposure could impair performance in a subsequent learning task. Subjects were invited to take part in a scenario similar to that of a computer simulated card game. Their task was to turn over a series of cards by mouse-clicking on a pack of cards lying face-down, and then to classify these cards intoone of twocategories. In a subsequent task, subjects were asked todiscriminate betweenpairs ofchequerboards, some of which had previously appeared in the initialcategorizationphase: either directly ('fronts') or incidentally ('backs') involved in categorization. In Experiment 1, for those stimuli used as the backs ofthe cards (thatis,those visible ontopof the packof cards), there was asignificant impairment in performance relative to non-pre-exposed control stimuli. Although the impairment appeared to be specific to the stimuli pre-exposed, when the pre-exposed 'backs' were minimally distorted in the discrimination task of Experiment 2, performance was still significantly impaired relative to non-pre-exposed control stimuli. The results of Experiment 2 donot support the interpretation that retardation in learning following masked pre-exposure in human experiments is comparable to latent inhibition following simple preexposure in other animals. Whilst the impairment in performance appears to be similar to that of latent inhibition, the results may, instead, be better understood in terms of the inhibitory processes involved in negative priming. If this is so, then serious doubt is cast on whether latent inhibition has ever been reliably demonstrated in adult humans.     

Enhanced Latent Inhibition Following Compound Pre-exposure

The influence of non-reinforced exposure to compound stimuli on subsequent appetitive classical conditioning was examined in five experiments with rats as the subjects. Non-reinforced exposure to a visual stimulus retarded subsequent acquisition of conditioned responding relative to a non-pre-exposed condition (latent inhibition). If the target stimulus was pre-exposed in compound with a second (non-target) stimulus, then latent inhibition was abolished. Exposure to the non-target stimulus prior to compound exposure had varying effects on subsequent conditioning to the target: 40 exposures to the non-target stimulus resulted in latent inhibition to the target stimulus that was comparable in magnitude to that observed when the target stimulus was exposed in isolation; 120 exposures to the non-target stimulus enhanced latent inhibition to the target stimulus.     

Attenuation of latent inhibition by post-acquisition reminder

Using lick suppression by water-deprived rats as an associative index, white noise-footshock pairings resulted in less manifest conditioning when repeated non-reinforced presentations of the white noise preceded conditioning than when no stimulus pre-exposure was given, i.e., latent inhibition was observed. However, the latent inhibition deficit was reduced in animals who received as a reminder treatment shock-alone presentations in another context during the retention interval. Animals conditioned without prior stimulus pre-exposure and those exposed to the white noise and shock unpaired during the conditioning phase of the study showed no change in lick suppression as a result of the reminder treatment. These results suggest that the behavioural deficit produced by non-reinforced pre-exposure to the to-be-conditioned stimulus arises at least in part from a reversible retrieval failure rather than a lack of acquisition.     

Signal transduction mechanisms within the entorhinal cortex that support latent inhibition of cued fear conditioning

Latent inhibition is a phenomenon by which pre-exposure to a conditioned-stimulus (CS), prior to subsequent pairings of that same CS with an unconditioned-stimulus (US), results in decreased conditioned responding to the CS. Previous work in our laboratory has suggested that the entorhinal cortex is critically involved in the establishment of latent inhibition of cued fear conditioning. Furthermore, utilizing systemic pharmacology, we have demonstrated a role for of NMDA receptors, protein kinase A (PKA), and mitogen activated protein kinase (MAPK, also known as ERK) in latent inhibition of cued fear conditioning, but until now, where these cell signaling cascades are critically activated during latent inhibition of cued fear was unknown. Here, we use direct drug infusion to demonstrate that cell signaling via NMDA receptors, the cAMP/PKA pathway, and the MAPK pathway within the entorhinal cortex are critically involved in latent inhibition of cued fear conditioning. In the present study, CS pre-exposed mice received 20 CS pre-exposures 24h prior to two pairings of the same CS with a 0.53 mA foot shock US, while control animals receive no pre-exposure to the CS. The NMDA antagonist APV (0.25 or 2.5 microg/side), the cAMP inhibitor Rp-cAMP (1.8 or 18.0 microg/side), or the MAPK inhibitor U0126 (0.1 or 1.0 microg/side) were directly infused into the entorhinal cortex prior to pre-exposure. All three drugs produced dose-dependent disruptions in latent inhibition of cued fear conditioning. Importantly, none of the drugs had any effect on cued fear conditioning when administered on training day, suggesting that the effects of each of the drugs were specific to CS pre-exposure. These results are discussed in relation to the potential mechanisms of plasticity that support latent inhibition of cued fear conditioning.     

Attenuation of latent inhibition after compound pre-exposure: Associative and perceptual explanations

Three experiments used rats as subjects and the conditioned emotional response (CER) paradigm to examine the effect of pre-exposure to a compound stimulus on the extent of latent inhibition to an element of that compound. In Experiment 1a a group of rats exposed to a compound that comprised a tone and a click exhibited less latent inhibition to the tone than did a group that had received pre-exposure to the tone in isolation. Experiment 1b showed that pre-exposure to the tone/click compound also resulted in an attenuation of latent inhibition to the click relative to a group that was pre-exposed to the click in isolation. Experiment 2 demonstrated that latent inhibition to the tone was left intact following pre-exposure to the tone in compound with a light. This pattern of results seems to be most plausibly explained in terms of the presence and absence of generalization decrement following compound pre-exposure.     

Duration of failure,causal attributions for failure,and subsequent reactions

Subjects were given a preliminary problem solving task of either short or long duration, and were told that they could shorten the duration of aversive noise bursts by correctly solving the problems. They were then given false feedback that they had done either well or poorly on the problems. Two groups of failing subjects were given information designed to lead them to attribute failure to either lack of ability or a difficult task. Two additional groups received “success” or “failure” feedback without any attributional cues. Failure-induced stress was reported to be greater under short duration conditions than under long duration conditions, and increased to the extent that subjects were led to believe they were personally responsible for failure. Following the preliminary failure period, task performance in the same situation and task performance and persistence in a different situation were assessed. In each case, performance and persistence decreased (a) following short-duration failure when subjects were led to attribute failure to a difficult task, and (b) following long-duration failure when subjects were led to attribute failure to lack of ability. These results are discussed within a framework that emphasizes the role of casual attributions in mediating the effects of failure.     

Attributions of causality and reactions to uncontrollable outcomes

The experiment tested the hypothesis that the stress experienced by a person who is unable to control aversive stimulation is not a function of lack of control per se, but of the attribution of causality that (s)he makes for failure to exert control. Subjects were given a problem-solving task, and were told that they could prevent aversive noise bursts by correctly solving the problems. Subjects then received false feedback that they had done either well or poorly on the problems. In addition, failing subjects received information that led them to attribute their performance either to their own lack of ability or to situational factors (task difficulty). Subjects who attributed their failure to their own incompetence felt considerably more stress than subjects who made situational attributions. In fact, the latter subjects experienced no more stress than subjects who were successful in controlling the stimulation. Surprisingly, subjects whose attributions for performance led them to feel personally incompetent performed better than the remaining subjects both on problems administered in the same situation, and on problems administered in a new and different situation. The implications of the results for future helplessness studies and for the learned helplessness model were discussed.     

Latent inhibition, context specificity, and context familiarity

In two appetitive licking experiments, thirsty rats were pre-exposed to two stimuli prior to conditioning sessions in which one or both of these stimuli were paired with water. Consistent with other results, latent inhibition was disrupted when conditioning took place in a context different from that in which stimulus pre-exposure had occurred. But in animals given prior exposure to the context of stimulus pre-exposure before the start of stimulus pre-exposure, substantial and equivalent latent inhibition was evident whether or not there was a change of context between stimulus pre-exposure and conditioning. These results are discussed in terms of current theories of latent inhibition.     

Latent inhibition in human adults without masking

Latent inhibition refers to attenuated responding to Cue X observed when the X-outcome pairings are preceded by X-alone presentations. It has proven difficult to obtain in human adults unless the preexposure (X-alone) presentations are embedded within a masking (i.e., distracting) task. The authors hypothesized that the difficulty in obtaining latent inhibition with unmasked tasks is related to the usual training procedures, in which the preexposure and conditioning experiences are separated by a set of instructions. Experiment 1 reports latent inhibition without masking in a task in which preexposure and conditioning occur without interruption. Experiments 2 and 3 demonstrate that this attenuation in responding to target Cue X does not pass a summation test for conditioned inhibition and is context specific, thereby confirming that it is latent inhibition. Experiments 3 and 4 confirm that introducing instructions between preexposure and conditioning disrupts latent inhibition.     

Latent inhibition is affected by phase of estrous cycle in female rats

Estrogen has been shown to have a strong modulatory influence on several types of cognition in both women and female rodents. Latent inhibition is a task in which pre-exposure to a neutral stimulus, such as a tone, later impedes the association of that stimulus with a particular consequence, such as a shock. Previous work from our lab demonstrates that high levels of estradiol (E2) administered to ovariectomized (OVX) female rats abolishes latent inhibition when compared to female rats with low levels of E2 or male rats. To determine if this E2-induced impairment also occurs with the natural variations of ovarian hormones during the estrous cycle, this behavior was investigated in cycling female rats. In addition, pre-pubertal male and female rats were also tested in this paradigm to determine if the previously described sex differences are activational or organizational in nature. In a latent inhibition paradigm using a tone and a shock, adult rats were conditioned during different points of the estrous cycle. Rats conditioned during proestrus, a period of high E2 levels, exhibited attenuated latent inhibition when compared to rats conditioned during estrus or metestrus, periods associated with low levels of E2. Moreover, this effect is not seen until puberty indicating it is dependent on the surge of hormones at puberty. This study confirms recent findings that high E2 interferes with latent inhibition and is the first to show this is based in the activational actions of hormones.     

Dream of absent-minded transgression: an empirical study of a cognitive withdrawal symptom.

Among 293 smokers abstinent for between 1 and 4 weeks, 33% reported having at least 1 dream about smoking. In most dreams, subjects caught themselves smoking and felt strong negative emotions, such as panic and guilt. Dreams about smoking were the result of tobacco withdrawal, as 97% of subjects did not have them while smoking, and their occurrence was significantly related to the duration of abstinence. They were rated as more vivid than the usual dreams and were as common as most major tobacco withdrawal symptoms. In subjects abstinent for 1 year, 63% recalled having dreams about smoking. They had on average 5 of them, and about a quarter occurred after the 6th month of abstinence. Having dreams about smoking was prospectively positively related to maintenance of abstinence. An explanation of this finding based on the association of smoking in dreams with aversive emotions is offered.     

Simultaneous Decision on the Number of Latent Clusters and Classes for Multilevel Latent Class Models

The Multilevel Latent Class Model (MLCM) proposed by Vermunt (2003) has been shown to be an excellent framework for analyzing nested data with assumed discrete latent constructs. The nonparametric version of MLCM assumes 2 levels of discrete latent components to describe the dependency observed in data. Model selection is an important step in any statistical modeling. The task of model selection for MLCM amounts to the decision on the number of discrete latent components at both higher and lower levels and is more challenging than standard Latent Class Models. In this article, simulation studies were conducted to systematically examine the effects of sample sizes, clusters/classes distinctness, and the number of latent clusters and classes on the performance of various information criteria in recovering the true latent structure. Results of the simulation studies are summarized and presented. The final section presents the remarks and recommendations about the simultaneous decision regarding the number of latent classes and clusters when applying MLCMs to analyze empirical data.     

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.     

Friend or foe? The role of latent inhibition in predator and non-predator labelling by coral reef fishes

In communities of high biodiversity, the ability to distinguish predators from non-predators is crucial for prey success. Learning often plays a vital role in the ability to distinguish species that are threatening from those that are not. Many prey animals learn to recognise predators based on a single conditioning event whereby they are exposed to the unknown predator at the same time as alarm cues released from injured conspecifics. The remarkable efficiency of such learning means that recognition mistakes may occur if prey inadvertently learn that a species is a predator when it is not. Latent inhibition is a means by which prey that are pre-exposed to an unknown species in the absence of negative reinforcement can learn that the unknown animal is likely not a threat. Learning through latent inhibition should be conservative because mistakenly identifying predators as non-predators can have fatal consequences. In this study, we demonstrated that a common coral reef fish, lemon damselfish, Pomacentrus moluccensis can learn to recognise a predator as non-threatening through latent inhibition. Furthermore, we showed that we could override the latent inhibition effect by conditioning the prey to recognise the predator numerous times. Our results highlight the ability of prey fish to continually update the information regarding the threat posed by other fishes in their vicinity.     

Facilitation of retention by white noise.

Second and fifth grade subjects were given three verbal tasks: serial, free recall, or paired-associate learning. Retention tests were administered immediately after the acquisition phase or following a long delay. Half the subjects were exposed to a 2-min period of bursts of white noise (arousal) immediately prior to the retention test. The finding of primary interest was that white noise produced substantial improvement in performance relative to a control condition. This effect may be more pronounced for long-term memory than for short-term memory. Although older children exhibited better long-term memory than younger subjects, no interaction of age with arousal condition was observed.     

Locus of control and the effects of success and failure in young and community-residing aged women1

A study was conducted to examine reactions to success and failure in young and elderly subjects. Young and aged women, previously classified as internals or externals according to scores on a version of Rotter's (1966) Locus of Control Scale, were asked to work on cognitive problems while listening to bursts of noise. Two experimental conditions were created. One group (perceived success) was led to believe they were successfully avoiding bursts of noise by correctly solving the problems. A second group (perceived failure) believed they were unsuccessful at the problems and not avoiding noises. To test the generality of the effects of the treatments, subsequent performance was assessed on first, a similar task administered by the original experimenter, and secondly, on a dissimilar task given by a different experimenter in another setting. Results on a similar task indicated that subjects showed poor performance following failure regardless of age or locus of control classification. However, internals performed better than externals after both success and failure treatments. Testing the generality of these effects with a dissimilar task, results indicated that externals tended to perform somewhat more poorly after failure and internals somewhat better after failure. However, these I-E differences in reactions to success and failure were largely due to the elderly group, and old-externals showed the poorest performance after failure. The results were interpreted in terms of the particular importance of locus of control as a determinant of adaptability to stress in the elderly.     

Some effects of noise on visual performance

A group of ten subjects showed impaired performance, when watch-keeping on a display made up of steam-pressure gauges, in 100 db. noise as compared with 70 db. On the easier task of watch-keeping on a display made up of small lights, another group of twenty subjects showed no overall effect of noise. Individual subjects who showed a practice effect on the latter task comparable to that shown by all subjects on the former one, however, also showed a similar effect of noise.

In addition, performance on the light-watching became relatively less efficient in noise with continued exposure: and although parts of the task were still adequately carried out, others were not. The fact that noise effects are thus functions of individual differences, of visibility of signal, and of length of performance in noise, allows us to explain the negative findings of many previous workers.     

Latent learning and latent inhibition in maze discriminations

Rats were trained on an elevated maze where the rewarded alternative was defined either in terms of intra-maze or in terms of extra-maze cues. Pre-exposure to these cues produced a small latent or perceptual learning effect, i.e. facilitated subsequent learning of both problems, by comparison with animals pre-exposed to the maze with no cues present. Experiment 2 examined whether the effect of pre-exposure on intra-maze discrimination learning varied with the nature of the intra-maze cues. When positive and negative arms were further differentiated by painting the walls white and black, a marginal perceptual learning effect was turned into significant latent inhibition, i.e. a retardation of subsequent learning. Pre-exposure thus reliably facilitated extra-maze discrimnation learning, and its beneficial effects on intra-maze discrimination could be reversed by reducing the overlap between the intra-maze cues. Perceptual learning may therefore depend on requiring animals to discriminate between stimuli containing many common elements.     

Age-related changes in auditory temporal processing

Two tone bursts separated by a silent interval and imbedded in a background white noise were presented to elderly subjects (M age = 71.3 years) and young subjects (M age = 22.2 years). Subjects were required to judge when the two tone bursts fused perceptually by adjusting the duration of tone-one. The bursts were separated by six discrete interstimulus intervals of 4, 8, 16, 24, 32, or 40 ms. The tone-two burst was held constant at 100 ms. Fusion point was defined as that critical tone-one duration at which the two tones fused (were perceived as one). Elderly subjects reached fusion point at longer critical tone-one durations than young subjects at each interval tested. The function relating tone-one duration and interval conformed to an exponential curve and is discussed with respect to an exponential decay model of the inhibitory interactions of neural systems responding to onsets and offsets of sensory events.     

Evaluation apprehension and the social facilitation/inhibition of learning

Sixty female subjects performed a paired-associates learning task either alone or under surveillance by the experimenter, who openly evaluated the subject's performance. To half of the subjects the experimenter described her evaluation as instrumental to the rendering of future help on a similar task; to the remaining half she gave no such promise. Subjects who were evaluated without the expectation of future help performed better than subjects who worked alone when the paired-associates list was easy, but less well when the list was difficult. For both types of list, evaluation with the added promise of future help produced performance no different from that of isolated subjects. Evaluation without the promise of help also produced a higher level of state anxiety than that observed in isolated subjects. The findings were discussed in terms of the effects of evaluation apprehension on the social facilitation and inhibition of learning.