Latent inhibition and contextual associations

Attenuated responding to a conditioned stimulus (CS) after preexposure to that CS (latent inhibition) has traditionally been attributed to reductions in CS associability. Alternatively, CS-context associations formed during CS preexposure later interfere with the acquisition or expression of CS-outcome associations. Three lick suppression experiments with rats contrasted these accounts. Presumably, exposure to the context attenuates the CS-context association without altering CS associability. With a fixed amount of CS preexposure, latent inhibition decreased with increasing context exposure during or after (but not before) CS preexposure. When the ratio of context preexposure duration to CS preexposure was fixed, latent inhibition increased with CS preexposure. These results suggest that latent inhibition is a direct function of the strength of CS-context associations formed during preexposure.     

Latent inhibition in human affective learning

This study presents the results of a new visual procedure designed to generate affective learning, namely the change in the affective rating of a previously neutral stimulus by simply pairing it with a liked or disliked stimulus. Specifically, an experiment was conducted to evaluate the effect of nonreinforced preexposures to the to-be-conditioned stimulus (a non-sense shape) on affective conditioning. This manipulation, intended to produce latent inhibition, typically results in retarded learning when the preexposed stimulus is paired with the unconditioned stimulus. The results revealed that it is possible to modify the affective value of a previously neutral non-sense shape by pairing it with a liked or disliked unconditioned stimulus, and that latent inhibition affects affective conditioning.     

Latent inhibition of US signal value.

Three experiments with rats examined the effects of preexposure to an unconditioned stimulus (US; a single food pellet) on the subsequent ability of that US to effectively signal the delivery of three food pellets during a US-US conditioning procedure. In Experiment 1, latent inhibition (LI) rats showed attenuated conditioning, compared to control (C) rats, when a single food pellet, delivered 10 minutes into a session, was followed by three additional pellets. In preexposure, one pellet had been delivered 10 minutes into each session (in group LI), or placed into the magazine at the beginning of each session (in group C). Experiment 2 showed that this effect was evident when the conditions of preexposure matched those of conditioning for group C, and Experiment 3 showed that the difference between groups LI and C was not a product of context conditioning, or latent inhibition to the noise of the feeder in group LI. Implications of these results for theories of latent inhibition are considered.     

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 of a CS during CS-US pairings

In each of three experiments rats were trained by the conditioned-emotional-response technique with a conditioned stimulus (CS) predicting a relatively weak shock, the unconditioned stimulus (US). In the second stage of training the intensity of the shock was increased, and it was found that subjects for whom the same CS was used in both stages acquired further suppression less readily than subjects that experiences a new CS in the second stage. The implication of these results for theories of attention and for theories of habituation is discussed. It is suggested that associations formed by the test CS during the first stage of training reduce the readiness of the stimulus to enter into new associations, either because an association between the stimulus and the context reduces further processing of the stimulus or because the association between the test stimulus and the weak shock attenuates the formation of an association with the stronger shock.     

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.     

Latent inhibition experiments with goldfish (Carassius auratus)

Evidence of latent inhibition was sought in a series of experiments with goldfish. In Experiment 1, goldfish were given nonreinforced preexposure to a color that subsequently predicted shock in an activity conditioning situation; their performance did not differ from that of control animals preexposed to a markedly different color. In Experiment 2, a group of goldfish given nonreinforced preexposure to a tone and an unstimulated control group were trained in an appetitive situation, with the tone serving either as a conditioned excitor or as a conditioned inhibitor. Preexposure had no significant effect in the conditioned excitation training, but it reduced the level of responding both to the positive stimulus and to the negative compound in the conditioned inhibition training. In Experiments 3 and 4, classical aversive conditioning was studied in the shuttle box. In Experiment 3, excitatory conditioning to a color was found to be impaired (relative to the performance of nonpreexposed control animals) as much by nonreinforced preexposure to the training color as by nonreinforced preexposure to a markedly different color; substantial variation in amount of preexposure was without significant effect. In the conditioned inhibition training of Experiment 4, animals with nonreinforced preexposure responded less than did unstimulated control animals both to the positive stimulus and to the negative compound. The results for goldfish can be understood on the assumption that the effect of preexposure in these animals is simply to reduce general responsiveness or level of arousal.     

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 and context change in psychometrically defined schizotypy

The disruption of latent inhibition within the schizophrenia spectrum has often been interpreted either as a result of increased attentional distractibility (attentional account) or as a result of deficient interference of past associations (associative account). The aim of the present investigation was to test competing predictions, as derived from the above theoretical accounts. In a visual search paradigm of latent inhibition, accuracy was examined as a function of prior experience with the target, and psychometrically defined schizotypy. In Experiment 1 (N=60), no context change was introduced. In accord with past evidence, latent inhibition was found to be intact in low-, but disrupted in high-schizotypy scorers, a result predicted both by attentional and associative accounts. In Experiment 2 (N=60), a context change was introduced. As predicted by past evidence, latent inhibition was disrupted in low-schizotypy scorers. However, latent inhibition was found to be intact in high-schizotypy scorers, a finding accommodated by attentional, but not associative accounts. Theoretical implications and alternative interpretations are also considered.     

Latent inhibition and conditioning after preexposure to the training context

Experiment 1, using the conditioned suppression technique with rats, showed that the retardation of learning produced by prior exposure to a stimulus (latent inhibition) was more marked in subjects given an initial phase of preexposure to the training context. This effect was confirmed and extended in Experiment 2 in which an appetitive conditioning procedure was used. Experiments 3 and 4, again using conditioned suppression, found no effect of preexposure to the context on the acquisition of suppression when training was given with a novel stimulus, either immediately after preexposure or after a delay; but context preexposure was again found to be effective when exposure to the to-be-conditioned stimulus was given in the delay interval between context preexposure and conditioning. The implications of these findings for accounts of the role of contextual factors in latent inhibition are discussed.     

Latent inhibition and learned helplessness in children: Similarities and differences

Four experiments used a common set of procedures to investigate the occurrence and the generalization of learned helplessness (LH) and latent inhibition (LI) in 10- to 11-year-old children. In Experiment 1, preexposure to response-outcome independence impaired performance (i.e., LH) on two subsequent tests: The first was similar to the preexposure situation, the second was not. Moreover, LH occurred whether preexposure involved positive or negative feedback. On the other hand, noncontingent stimulus preexposure did not impair subsequent performance, i.e., LI was not obtained in the first experiment. Experiment 2 replicated the LH findings of Experiment 1: LH occurred following preexposure to response-independent feedback, regardless of whether that feedback was positive or negative, and LH generalized to a situation that was different from the preexposure situation. In addition, the stimulus preexposure procedures of Experiment 2 were embedded in a “masking” task and, under these conditions, LI was obtained. Nevertheless, LI did not generalize to a testing situation that was different from the preexposure situation. Experiment 3 demonstrated that noncontingent stimulus preexposure impairs performance relative to a nonpreexposed control group, that the effect is dependent upon masking, that masking alone produces no performance decrement, and that LI is, indeed, stimulus specific. In Experiment 4, preexposure to response-outcome independence impaired subsequent performance on similar and dissimilar tests whether feedback was consistently positive, consistently negative, or randomly positive and negative over trials. In addition, stimulus preexposure produced LI only under conditions of masking and even then, LI was not evident in novel test situations. The results are discussed in terms of common and different mechanisms underlying the LI and LH phenomena.     

Latent inhibition disruption by MK-801 in a conditioned taste-aversion paradigm

N-Methyl-D-aspartate (NMDA) receptors appear to be involved in CS processing and memory consolidation. The present paper analyzed the effect of the non-competitive NMDA receptor antagonist Dizocilpine maleate (MK-801) on Latent Inhibition (LI)-retarded learning of a CS-US association after to-be-CS preexposures at time of testing, using Wistar rats as experimental subjects. If NMDA receptors are involved in CS processing, MK-801 administration should affect LI. In fact, previous experiments revealed that a 2.0mg/kg MK-801 dose, administered 20 h before preexposure and conditioning, abolished LI in a conditioned taste-aversion paradigm. In the present paper, MK-801 (0.2 mg/kg) was either injected after preexposure, after conditioning, or after both preexposure and conditioning stages. LI was abolished when MK-801 was injected after preexposure, but not when it was injected after conditioning. These results support the role of NMDA receptors in CS processing and memory consolidation.     

Latent inhibition and asymmetrical visual-spatial attention in children with ADHD.

The research was designed to determine whether the purported hemispheric asymmetries that are associated with attention deficit/hyperactivity disorder (ADHD) affect performance on a selective attention visual search task, and whether any obtained asymmetry will be modulated by methylphenidate. Two groups of children (8-15 years) with ADHD, one with methylphenidate treatment (ADHD+) and one without (ADHD+), were compared to matched controls on a two-stage visual search task. The task assessed right-left visual field asymmetries and the effects of changing a previous distractor into a target. Such a procedure, related to latent inhibition (LI; poorer performance to a previously irrelevant stimulus than to a novel one), can provide evidence for dysfunctional processing of irrelevant stimuli. All three groups exhibited the LI effect. The ADHD group, however, exhibited less LI for left- than right-side targets, an effect absent in the control and ADHD+ groups, suggesting a lateralized attentional deficit for ADHD+ that was normalized by methylphenidate.     

Latent inhibition: The effects of ITI and CS intensity during preexposure

Two experiments are reported which test the effects of intertrial interval (ITI) and stimulus intensity during nonreinforced preexposure in the latent inhibition paradigm. In Experiment 1, using mice in an escape-avoidance task, latent inhibition was a direct function of the duration of stimulus intertrial interval during preexposure. In Experiment 2, using rats in a CER task, latent inhibition was a direct function of stimulus intensity during preexposure. These findings are discussed in terms of equivalent effects which have been reported in the habituation paradigm.