Recent learned helplessness/irrelevance research in Japan: Conceptual framework and some experiments on learned irrelevance

In Section 1, a conceptual framework within which to study learned helplessness (LH), learned irrelevance (LI) and the related phenomena is introduced. In Section 2, three rat experiments on LI conducted in our laboratory using a conditioned suppression of licking preparation are introduced. In Experiment 1, the phenomena of LI and general LI were confirmed. In Experiment 2, random presentations of CSt/US were found to interfere with subsequent initial excitatory conditioning to CSl under random CSl/US presentations. In Experiment 3, pre-paired presentations of CSn or CSt with US before random CSt/US presentations was found to have an attenuating effect on the development of general LI.     

A Comparison of Latent Inhibition and Learned Irrelevance Pre-Exposure Effects in Rabbit and Human Eyeblink Conditioning

The learning of an association between a CS and a US can be retarded by unreinforced presentations of the CS alone (termed latent inhibition or LI) or by un-correlated presentations of the CS and US (termed learned irrelevance or LIRR). In rabbit eyeblink conditioning, there have been some recent failures to replicate LI. LIRR has been hypothesized as producing a stronger retardation effect than LI based on both empirical studies and computational models. In the work presented here, we examined the relative strength of LI and LIRR in eyeblink conditioning in rabbits and humans. In both species, a number of preexposure trials sufficient to produce LIRR failed to produce LI (Experiments 1 & 3). Doubling the number of CS pre-exposures did produce LI in rabbits (Experiment 2), but not in humans (Experiment 4). LI was demonstrated in humans only after manipulations including an increased inter-trial interval or ITI (Experiment 5). Overall, it appears that LIRR is a more easily producible pre-exposure retardation effect than LI for eyeblink conditioning in both rabbits and humans. Several theoretical mechanisms for LI including the conditioned attention theory, stimulus compression, novelty, and the switching theory are discussed as possible explanations for the differences between LIRR and LI. Overall, future work involving testing the neural substrates of pre-exposure effects may benefit from the use of LIRR rather than LI.     

Learned Irrelevance Is Not the Sum of Exposure to CS and US

In three experiments hungry rats received appetitive conditioning trials with a light that signalled the delivery of sucrose solution. In Experiment 1, prior exposure to uncorrelated presentations of the conditioned stimulus (CS) and unconditioned stimulus (US) retarded conditioning significantly more than did prior exposure to the CS alone. In Experiments 2 and 3, groups exposed to uncorrelated presentations of the CS and US within the same session conditioned significantly more slowly than groups given separate sessions of exposure to the CS followed by sessions of exposure to the US (or vice versa). Some part of the learned irrelevance effect depends on exposure to a zero correlation between the CS and US, perhaps because this promotes learning that the CS predicts no change in the probability of the US.     

A comparison of latent inhibition and learned irrelevance pre-exposure effects in rabbit and human eyeblink conditioning

The learning of an association between a CS and a US can be retarded by unreinforced presentations of the CS alone (termed latent inhibition or LI) or by un-correlated presentations of the CS and US (termed learned irrelevance or LIRR). In rabbit eyeblink conditioning, there have been some recent failures to replicate LI. LIRR has been hypothesized as producing a stronger retardation effect than LI based on both empirical studies and computational models. In the work presented here, we examined the relative strength of LI and LIRR in eyeblink conditioning in rabbits and humans. In both species, a number of pre-exposure trials sufficient to produce LIRR failed to produce LI (Experiments 1 & 3). Doubling the number of CS pre-exposures did produce LI in rabbits (Experiment 2), but not in humans (Experiment 4). LI was demonstrated in humans only after manipulations including an increased inter-trial interval or ITI (Experiment 5). Overall, it appears that LIRR is a more easily producible pre-exposure retardation effect than LI for eyeblink conditioning in both rabbits and humans. Several theoretical mechanisms for LI including the conditioned attention theory, stimulus compression, novelty, and the switching theory are discussed as possible explanations for the differences between LIRR and LI. Overall, future work involving testing the neural substrates of pre-exposure effects may benefit from the use of LIRR rather than LI.     

General Learned Irrelevance and Its Prevention

Random presentation of a tone and an electric shock to rats interfered with subsequent acquisition of a light–shock association. This interference, or “general learned irrelevance” phenomenon, however, could be prevented by prior learning of a positive relationship between the tone and the shock or that between a noise and the shock. These results strongly support the ideas that animals learn irrelevant stimulus relationships and that prior experience of stimulus relevance prevents learning irrelevance. The similarity of this observed prevention effect to an immunization effect on learned helplessness phenomena is discussed.     

Is the context specificity of latent inhibition a sufficient explanation of learned irrelevance?

In three experiments, rats were pre-exposed either to uncorrelated presentations of a light and sucrose pellets (group CS/US) or to equivalent presentations of the light and pellets in separate sessions (control). In Experiment 1, subsequent conditioning to the light proceeded more slowly in group CS/US than in the control group, whether this conditioning was excitatory, with the light signalling the delivery of pellets, or inhibitory, with the light signalling their absence. Bonardi and Hall (1996) have argued that this learned irrelevance effect may be reducible to latent inhibition, which would be stronger in group CS/US because they are both pre-exposed and conditioned to the CS in the presence of traces of previous USs occurring in the same session. This analysis implies that group CS/US should have conditioned more rapidly to the CS than controls on the first trial of each session in Experiment 1, but this did not happen. It also implies that the learned irrelevance effect should be reversed if conditioning trials are given at a rate of one per day . Experiments 2 and 3 found no support for this prediction. We conclude that learned irrelevance effects cannot always be reduced to latent inhibition.     

Retardation of autoshaping following pretraining with unpredictable food: Effects of changing the context between pretraining and testing

In Experiment 1, pigeons exposed to US ONLY pretraining were observed to be retarded in the acquisition of autoshaping relative to naive controls; however, gross changes in contextual stimuli between pretraining and testing alleviated the retardation effect. In Experiment 2, groups of pigeons exposed to CS ONLY, US ONLY, or random CS-US presentations (TRC) were tested for the acquisition of autoshaping. The US ONLY and TRC groups were retarded relative to naive controls. The context change manipulation eliminated the US ONLY retardation effect and attenuated, but did not eliminate, the TRC retardation effect. Context blocking accounts for the US ONLY effect and contributes to the TRC effect; however, context-independent retardation following TRC pretraining suggests the operation of the learned irrelevance cognition.     

Analysis of the learned irrelevance effect in appetitive Pavlovian conditioning

In Experiments 1 and 2 rats received uncorrelated presentations of a light conditioned stimulus (CS) and a food unconditioned stimulus (US) on each day of a preexposure phase. Control subjects received the same number of USs during the first half of preexposure and the same number of CSs during the second. Uncorrelated preexposure retarded inhibitory conditioning. Experiment 3 showed, however, that the different patterns of US preexposure experienced by the two groups could in itself influence the course of subsequent inhibitory conditioning. When this factor was equated by restricting the uncorrelated treatment to the first half of the pre-exposure phase (Experiment 2) or by extending the control treatment throughout the phase (Experiment 4) it was found that uncorrelated preexposure retarded excitatory conditioning, but facilitated inhibitory conditioning. This outcome challenges an interpretation in terms of the concept of learned irrelevance, which predicts that uncorrelated preexposure should retard both forms of conditioning.     

Associative changes with a random CS-US relationship

Three experiments examined conditioned magazine approach in rats when a positive unconditioned stimulus (US) bore a random relation to a conditioned stimulus (CS). Experiment 1 found that over the course of conditioning the CS initially elevated responding relative to the baseline but then lost the power to do so. Transfer tests revealed that a CS-US association developed early and persisted despite the decline in magazine responding. Experiment 2 confirmed the persistence of CS-US associations and found them to be more substantial when a different US occurred during the CS than in its absence. In Experiment 3, when the situation was exposed to US-alone presentations prior to introducing the CS, there was little evidence that a subsequent random relation between the CS and US produced an association between them. These results agree with those of blocking and overshadowing experiments using discrete CSs and support an interpretation of the random procedure in terms of competition between the background and CS for conditioning.     

Associability of a previously conditioned stimulus as a function of qualitative changes in the US

Hall and Pearce (1979) reported retarded manifestation of conditioned responding to repeated CS-strong shock pairings as a result of prior CS-weak shock pairings. These authors suggested that a latent inhibition (LI)-like process reduced the associability of the CS during weak shock conditioning despite excitatory associations between CS and weak shock being formed. The present experiments examined the possibility that the negative transfer from CS-weak shock conditioning in Stage 1 to CS-strong shock conditioning in Stage 2 observed by Hall and Pearce was due at least in part to the similarity between weak and strong shock rather than, or in addition to, a general loss of CS associability. Specifically, the transfer of decreased associability to conditioning with a dissimilar US was investigated. Consistent with Hall and Pearce, who gave multiple training trials in Stage 2, Experiment 1 found the development of conditioned responding owing to a single CS-strong shock pairing in Stage 2 to be retarded by prior CS-weak shock pairings and compared this effect to conventional LI. In Experiment 2, partial attenuation of the negative transfer following CS-weak shock was obtained by substituting ice water immersion for strong shock, that is, by making the strong US qualitatively dissimilar from the weak US. In contrast, conventional LI resulting from preconditioning CS-only exposures was equivalent for strong shock in Experiment 1 and ice water immersion in Experiment 2. A possible mechanism for the sensitivity to qualitative US changes of the observed negative transfer is 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.     

Superlatent inhibition and spontaneous recovery: differential effects of pre- and postconditioning CS-alone presentations after long delays in different contexts

In two pairs of three-stage conditioned taste aversion experiments, we examined the effects of delay interval (1 or 21 days) between the second and third stages, and of context in which the animals spent the delay (same as or different from the context of the other stages) on latent inhibition (LI) and spontaneous recovery following extinction. In the LI experiments (Experiments 1A and 1B), the first stage comprised nonreinforced presentations to saccharin or to water. In the second stage, rats were conditioned by saccharin paired with LiCl. In the extinction experiments (Experiments 2A and 2B), the order of the stages was reversed. For all experiments, Stage 3, the test stage, consisted of three presentations of saccharin alone. There was a super-LI effect in the saccharin-preexposed group that spent the 21-day delay in the different context (Experiment 1A). When the delay was spent in the same context, there was no difference in the amount of LI between the short- and long-delay groups (Experiment 1B). Conversely, there was a spontaneous recovery effect in the long-delay/same-context group (Experiment 2B), but not in the long-delay/different-context group (Experiment 2A). The pattern of results, incompatible with current explanations of delay-induced changes in memory performance, was interpreted in terms of an interaction between the delay conditions (same or different delay context), which modulate the extinction of previously acquired context-CS-nothing associations (during CS-alone presentations), and primacy effects.     

Learned helplessness in groups

Group learned helplessness is demonstrated in Experiment I. Groups of 2 tried to turn off noise by their joint action. In the solvable group (S), noise offset was contingent on their sequence of button pushing. In the yoked, unsolvable group (U), noise offset was independent of all sequences of button pushes they produced. In a practice group (O). subjects practiced coordinated sequences of button pushes with their partners, but heard no noise. Later, all 3 groups were tested in pairs in a shuttlebox which required coordinated joint responding to turn off noise. The unsolvable group escaped more poorly than the other 2 groups, paralleling helplessness effects with individuals. Experiment 2 and 3 found no transfer from individual helplessness training to group testing and no transfer from group helplessness training to individual testing. We suggest that the same mechanism, the expectation of response ineffectiveness, may mediate both individual and group learned helplessness.     

Delay-induced attenuation of latent inhibition with a conditioned emotional response depends on CS–US strength

Latent Inhibition (LI) attenuation when a long delay is introduced between acquisition and test phases has been repeatedly observed using aversive conditioning procedures (e.g., Aguado, Symonds, & Hall, 1994). This effect has been used as evidence to support those theories that consider LI to be the result of a retrieval failure. We designed three experiments intended to control for a possible effect of incubation of fear as a possible source of delay-induced attenuated LI. Specifically, we examined the effects of a retention interval between conditioning and testing stages on LI using a 3-stage conditioned emotional response procedure (preexposure, conditioning, and testing). Experiment 1 showed that the LI effect was completely abolished in the delayed testing condition. Experiment 2 evaluated whether a process of fear incubation, developed during the retention interval but obscured by a ceiling effect, produced the attenuation of LI. To this end, we reduced magnitude of conditioning by decreasing US intensity and number of acquisition trials. Experiment 3 directly assessed the relationship between CS–US strength and fear incubation. Experiments 2 and 3 revealed that the apparent reduction of LI after the delay was, at least partially, the result of an incubation effect that is a function of the strength of the CS–US association. The results are discussed with respect to their implications for the different theories of LI.     

A Behavioural Preparation for the Study of Human Pavlovian Conditioning

Conditioned suppression is a useful technique for assessing whether subjects have learned a CS-US association, but it is difficult to use in humans because of the need for an aversive US. The purpose of this research was to develop a non-aversive procedure that would produce suppression. Subjects learned to press the space bar of a computer as part of a video game, but they had to stop pressing whenever a visual US appeared, or they would lose points. In Experiment 1, we used an A+/B- discrimination design: The US always followed Stimulus A and never followed Stimulus B. Although no information about the existence of CSs was given to the subjects, suppression ratio results showed a discrimination learning curve-that is, subjects learned to suppress responding in anticipation of the US when Stimulus A was present but not during the presentations of Stimulus B. Experiment 2 explored the potential of this preparation by using two different instruction sets and assessing post-experimental judgements of CS A and CS B in addition to suppression ratios. The results of these experiments suggest that conditioned suppression can be reliably and conveniently used in the human laboratory, providing a bridge between experiments on animal conditioning and experiments on human judgements of causality.     

Learned irrelevance and retrospective correlation learning

In 1973 Mackintosh reported an interference effect that he called learned irrelevance in which exposure to uncorrelated (CS/US) presentation of the unconditional stimulus (US) and the conditioned stimulus (CS) interfered with future Pavlovian conditioning. It has been argued that there is no specific interference effect in learned irrelevance; rather the interference is the sum of independent CS and US exposure effects (CS + US). We review previous research on this question and report two new experiments. We conclude that learned irrelevance is a consequence of a contingency learning and a specific learned irrelevance mechanism. Moreover even the “independent exposure controls”, used in previous experiments to support the CS and US exposure account, provide support for the correlation learning process.     

Latent inhibition: A trace conditioning phenomenon?

An informal model of latent inhibition (LI), the trace hypothesis, is described. This hypothesis holds that preexposure (PE) to the to-be-conditioned stimulus alters the salience (associability) of the CS such that only the onset and initial segments, but not the later segments, are capable of supporting conditioning when paired with a US. Thus, LI is effectively a trace conditioning phenomenon. Four experiments used rats and a one-trial fear-conditioning task to test predictions which stem from this hypothesis. Experiment 1 showed conditioning performance decreased as trace intervals increased between 0 and 12 s, thus demonstrating the sensitivity of this task to trace intervals proposed by the trace hypothesis to produce LI. Consistent with the trace hypothesis, LI was found to be an increasing function of the CS duration (Experiment 2), the number of PE trials (Experiment 3), and the US onset during a 15-s CS (Experiment 4). These data are somewhat problematic for several explanations of LI, but, in general, the trace hypothesis extends extant explanations by focusing on changes in salience within a given presentation of the CS.     

US habituation,like CS extinction,produces a decrement in conditioned fear responding that is NMDA dependent and subject to renewal and reinstatement

Just as fear can be learned, it can also be inhibited. The most common way of reducing learned fear is through extinction, where the conditioned stimulus (CS) previously paired with an aversive unconditioned stimulus (US) is repeatedly presented on its own. Another, much less commonly studied, way to inhibit learned fear is by habituating, or devaluing, the US. In this procedure, fear responding to a CS is reduced by repeatedly presenting the US in the absence of the CS following the conditioning phase. The purpose of the present study was to directly compare the effects of US habituation and CS extinction on a learned fear response (freezing). Experiment 1 demonstrated that US habituation given either after (Experiment 1A) or before (Experiment 1B) fear conditioning reduced freezing to the CS at test. We then showed that the reduction in freezing resulting from either US habituation or CS extinction was context-specific (i.e., a change in context led to a renewal of the learned fear response; Experiment 2) and, furthermore, was attenuated when a pre-test shock was given (i.e., reinstatement of fear was observed in both cases; Experiment 3). Finally, Experiment 4 demonstrated that an injection of the NMDA antagonist MK-801 prior to US habituation impaired long-term retention of the learning that takes place during this procedure. Together, these results suggest that the decrement in conditioned fear responses produced by US habituation and CS extinction could rely on overlapping processes.     

Preexposure to the CS alone,US alone,or CS and US uncorrelated: Latent inhibition,blocking by context or learned irrelevance?

Three experiments on conditioned suppression in rats examined the extent to which preexposure to the CS, the US, or uncorrelated presentations of both interfere with future conditioning. Experiment 1 suggested that the interference caused by preexposure to the US alone may result from blocking by contextual cues: signaling the US during preexposure attenuated the interference. Experiment 2 demonstrated that signaling the US by another stimulus did not attenuate the interference caused by exposure to uncorrelated presentations of CS and US. Experiment 3 replicated the results of Experiments 1 and 2 and directly compared the magnitude of these deficits. The results of these experiments imply that the effects of exposure to uncorrelated presentations of CS and US are not reducible to the sum of the effects of exposure to CS or US alone.