Learning about cues that prevent an outcome: Conditioned inhibition and differential inhibition in human predictive learning

Inhibitory causal structures in serial and simultaneous feature negative learning

We have previously reported that human participants trained with a simultaneous feature negative discrimination (intermixed A+/AB− trials) show only modest transfer of inhibitory properties of feature B to a separately trained excitor in a summation test. Their self-reported causal structure suggested that many participants learned that the effect of feature B was somewhat specific to the excitor it had been trained with (modulation), rather than learning that the feature prevented the outcome (prevention). This pattern is reminiscent of the distinction between negative occasion-setting and conditioned inhibition in the animal conditioning literature. However, in animals, occasion-setting is more commonly seen with a serial procedure, in which the feature (B) precedes the training excitor (A). Accordingly, we ran three experiments to compare serial with simultaneous training in an allergist causal judgement task. Transfer in a summation test was stronger to a previously modulated test excitor compared to a simple excitor after both simultaneous and serial training. There was a numerical trend towards a larger effect in the serial group, but it failed to reach significance and the Bayes Factor indicated support for the null. Serial training had no differential effect on the self-reported causal structure and did not significantly reduce overall transfer. After both simultaneous and serial training, transfer was strongest in participants who reported a prevention structure, replicating and extending our previous results to a previously modulated excitor. These results suggest that serial feature negative training does not promote a qualitatively different inhibitory causal structure compared to simultaneous training in humans.

Can We Set Aside Previous Experience in a Familiar Causal Scenario?

Causal and predictive learning research often employs intuitive and familiar hypothetical scenarios to facilitate learning novel relationships. The allergist task, in which participants are asked to diagnose the allergies of a fictitious patient, is one example of this. In such studies, it is common practice to ask participants to ignore their existing knowledge of the scenario and make judgments based only on the relationships presented within the experiment. Causal judgments appear to be sensitive to instructions that modify assumptions about the scenario. However, the extent to which prior knowledge continues to affect competition for associative learning, even after participants are instructed to disregard it, is unknown. To answer this, we created a cue competition design that capitalized on prevailing beliefs about the allergenic properties of various foods. High and low allergenic foods were paired with foods moderately associated with allergy to create two compounds; high + moderate and low + moderate. We expected high allergenic foods to produce greater competition for associative memory than low allergenic foods. High allergenic foods may affect learning either because they generate a strong memory of allergy or because they are more salient in the context of the task. We therefore also manipulated the consistency of the high allergenic cue-outcome relationship with prior beliefs about the nature of the allergies. A high allergenic food that is paired with an inconsistent allergenic outcome should generate more prediction error and thus more competition for learning, than one that is consistent with prior beliefs. Participants were instructed to either use or ignore their knowledge of food allergies to complete the task. We found that while participants were able to set aside their prior knowledge when making causal judgments about the foods in question, associative memory was weaker for the cues paired with highly allergenic foods than cues paired with low allergenic foods regardless of instructions. The consistency manipulation had little effect on this result, suggesting that the effects in associative memory are most likely driven by selective attention to highly allergenic cues. This has implications for theories of causal learning as well as the way causal learning tasks are designed.

Individual differences in causal structures inferred during feature negative learning

Traditional associative learning theories predict that training with feature negative (A+/AB-) contingencies leads to the feature B acquiring negative associative strength and becoming a conditioned inhibitor (i.e., prevention learning). However, feature negative training can sometimes result in negative occasion setting, where B modulates the effect of A. Other studies suggest that participants learn about configurations of cues rather than their individual elements. In this study, we administered simultaneous feature negative training to participants in an allergist causal learning task and tested whether evidence for these three types of learning (prevention, modulation, configural) could be captured via self-report in the absence of any procedural manipulation. Across two experiments, we show that only a small subset of participants endorse the prevention option, suggesting that traditional associative models that predict conditioned inhibition do not completely capture how humans learn about negative contingencies. We also show that the degree of transfer in a summation test corresponds to the implied causal structure underlying conditioned inhibition, occasion-setting, and configural learning, and that participants are only partially sensitive to explicit hints about causal structure. We conclude that feature negative training is an ambiguous causal scenario that reveals individual differences in the representation of inhibitory associations, potentially explaining the modest group-level inhibitory effects often found in humans.

The effect of conditioned inhibitors and preexposed cues on the outcome-specific Pavlovian-to-instrumental transfer effect in humans

Using a human Pavlovian-to-instrumental transfer (PIT) task, Alarcón and Bonardi showed that the selective elevation of instrumental responding produced by excitatory transfer cues was reduced when these cues were presented with a conditioned inhibitor (CI), relative to a control cue that was simply preexposed. However, previous research has shown that preexposed cues might also acquire inhibitor-like properties. This study aimed to contrast the inhibitory properties of CIs and preexposed cues, using novel stimuli as controls, in summation and PIT tests. Participants were trained to perform two actions, each reinforced with a distinct outcome (O₁ or O₂). Two images were trained as CIs, each signalling the absence of one of the outcomes, by presenting them with a cue that was otherwise followed by that outcome (e.g., A→O₁, AI→no O₁). In contrast, the preexposed cues were simply presented in the absence of the outcomes. In the summation test, participants rated the likelihood of the outcomes in the presence of two independently trained excitatory cues, each presented with a CI, a preexposed cue, or a novel stimulus. Similarly, in the PIT test, participants performed both actions in the presence and absence of these compounds. In the summation test, the CIs and the preexposed cues reduced participants' expectations of the outcomes more than the novel stimuli. However, in the PIT test, only the CIs reduced the selective elevation of responding produced by the transfer cues. These results might reflect distinct properties of stimuli trained as CIs and those simply preexposed.

Second-order conditioning in human predictive judgements when there is little time to think

Associative accounts uniquely predict that second-order conditioning might be observed in human predictive judgements. Such an effect was found for cue X in two experiments in which participants were required to predict the outcomes of a series of training trials that included P + and PX−, but only when training was paced by requiring participants to make a prediction within 3 s on each trial. In Experiment 1 training on P + ended before training was given on PX − . In Experiment 2 trials with P+, PX−, T + and other cues were intermixed. In the unpaced group inhibitory learning was revealed by a summation test, TX versus TM, where M was a control stimulus. These results suggest either that pacing interferes with learning successive associations more than with learning simultaneous associations or that lack of time to think interferes with inferential processes required for this type of inhibitory learning.

Forward blocking in human learning sometimes reflects the failure to encode a cue–outcome relationship

In two “allergist” causal judgement experiments, participants were trained with a blocking design (A + |AB+). The procedure allowed different food cues to be paired with different fictitious allergic reactions. On test, participants were asked to rate the causal efficacy of the target cues and to recall the particular allergic reaction (outcome) that had followed each cue during training. Forward blocking was observed on the causal judgement measure and on the outcome recall measure in both Experiment 1 and Experiment 2. A backward blocking contingency was also trained in Experiment 2 (AB + |A+). Backward blocking was not observed either on the causal judgement or on the outcome recall measure. The evidence from the recall measure suggests that forward blocking in this task results from a failure to encode the B–outcome relationship during training. Associative and nonassociative mechanisms of forward blocking are discussed.

A dissociation between causal judgement and the ease with which a cause is categorized with its effect

The associative view of human causal learning argues that causation is attributed to the extent that the putative cause activates, via an association, a mental representation of the effect. That is, causal learning is a human analogue of animal conditioning. We tested this associative theory using a task in which a fictitious character suffered from two allergic reactions, rash (O1) and headache (O2). In a conditioned inhibition design with each of these two outcomes (A–O1/AX– and B–O2/BY–), participants were trained that one herbal remedy (X) prevented O1 and that the other (Y) prevented O2. These inhibitory properties were revealed in a causal judgement summation test. In a subsequent categorization task, X was most easily categorized with O1, and Y with O2. Thus, the categorization data indicated an excitatory X–O1 and Y–O2 association, the reverse of the inhibitory relationship observed on the causal judgement measure. A second experiment showed that this pattern of excitation and inhibition is dependent on intermixed A–O1 and AX– trials. These results are problematic for the standard application of associative activation theories to causal judgement. We argue instead that the inhibition revealed in the causal judgement task reflects inferential reasoning, which relies, in part, on the ability of the cue in question to excite a representation of the outcome, as revealed in the categorization test.

Effects of outcome and trial frequency on the inverse base-rate effect

The inverse base-rate effect is a bias in contingency learning in which participants tend to predict a rare outcome for a conflicting set of perfectly predictive cues. Although the effect is often explained by attention biases during learning, inferential strategies at test may also contribute substantially to the effect. In three experiments, we manipulated the frequencies of outcomes and trial types to determine the critical conditions for the effect, thereby providing novel tests of the reasoning processes that could contribute to it. The rare bias was substantially reduced when the outcomes were experienced at equal rates in the presence of predictive-cue frequency differences (Exp. 2), and when the predictive cues were experienced at equal rates in the presence of outcome frequency differences (Exp. 3). We also found a consistent common-outcome bias for novel cue compounds. The results indicate the importance of both cue and outcome frequencies to the inverse base-rate effect, and reveal a combination of necessary conditions that are not well captured by appealing to inferential strategies at test. Although both attention-based and inferential theories explain some aspects of these data, no existing theory fully accounts for these effects of relative novelty.

Tourette-like behaviors in the normal population are associated with hyperactive/impulsive ADHD-like behaviors but do not relate to deficits in conditioned inhibition or response inhibition

Attention-Deficit Hyperactivity Disorder (ADHD) and Tourette Syndrome (TS) present as distinct conditions clinically; however, comorbidity and inhibitory control deficits have been proposed for both. Whilst such deficits have been studied widely within clinical populations, findings are mixed—partly due to comorbidity and/or medication effects—and studies have rarely distinguished between subtypes of the disorders. Studies in the general population are sparse. Using a continuity approach, the present study examined (i) the relationships between inattentive and hyperactive/impulsive aspects of ADHD and TS-like behaviors in the general population, and (ii) their unique associations with automatic and executive inhibitory control, as well as (iii) yawning (a proposed behavioral model of TS). One hundred and thirty-eight participants completed self-report measures for ADHD and TS-like behaviors as well as yawning, and a conditioned inhibition task to assess automatic inhibition. A sub-sample of fifty-four participants completed three executive inhibition tasks. An exploratory factor analysis of the TS behavior checklist supported a distinction between phonic and motor like pure TS behaviors. Whilst hyperactive/impulsive aspects of ADHD were associated with increased pure and compulsive TS-like behaviors, inattention in isolation was related to reduced obsessive-compulsive TS-like behaviors. TS-like behaviors were associated with yawning during situations of inactivity, and specifically motor TS was related to yawning during stress. Phonic TS and inattention aspects of ADHD were associated with yawning during concentration/activity. Whilst executive interference control deficits were linked to hyperactive/impulsive ADHD-like behaviors, this was not the case for inattentive ADHD or TS-like behaviors, which instead related to increased performance on some measures. No associations were observed for automatic conditioned inhibition.

Second-order conditioning and conditioned inhibition: influences of speed versus accuracy on human causal learning

In human causal learning, excitatory and inhibitory learning effects can sometimes be found in the same paradigm by altering the learning conditions. This study aims to explore whether learning in the feature negative paradigm can be dissociated by emphasising speed over accuracy. In two causal learning experiments, participants were given a feature negative discrimination in which the outcome caused by one cue was prevented by the addition of another. Participants completed training trials either in a self-paced fashion with instructions emphasising accuracy, or under strict time constraints with instructions emphasising speed. Using summation tests in which the preventative cue was paired with another causal cue, participants in the accuracy groups correctly rated the preventative cue as if it reduced the probability of the outcome. However, participants in the speed groups rated the preventative cue as if it increased the probability of the outcome. In Experiment 1, both speed and accuracy groups later judged the same cue to be preventative in a reasoned inference task. Experiment 2 failed to find evidence of similar dissociations in retrospective revaluation (release from overshadowing vs. mediated extinction) or learning about a redundant cue (blocking vs. augmentation). However in the same experiment, the tendency for the accuracy group to show conditioned inhibition and the speed group to show second-order conditioning was consistent even across sub-sets of the speed and accuracy groups with equivalent accuracy in training, suggesting that second-order conditioning is not merely a consequence of poorer acquisition. This dissociation mirrors the trade-off between second-order conditioning and conditioned inhibition observed in animal conditioning when training is extended.

Deactivation and reactivation of the inhibitory power of a conditioned inhibitor: testing the predictions of an attentional-associative model

An attentional-associative model (Schmajuk, Lam, & Gray Journal of Experimental Psychology: Animal Behavior Processes, 22, 321-349, 1996) assumes that nonreinforced presentations of an inhibitory conditioned stimulus (CS) do not decrease its inhibitory associations. However, the model predicts that extended presentations will decrease attention to the inhibitor, thereby decreasing both (1) the expression of its inhibitory power in a summation test and (2) the rate of acquisition in a retardation test. The model also predicts that subsequent presentations of the inhibitory CS with a novel CS will increase both (1) and (2). Using a predictive learning design in humans, Experiment 1 examined the predictions involving the summation tests, whereas Experiments 2 and 3 examined the predictions involving the retardation tests. Experimental results were in agreement with the predictions of the model.

Positive and negative mediation as a function of whether the absent cue was previously associated with the outcome

After presenting two cues, A and B, together, later pairings of one of the cues alone with an outcome can generate changes in the associative value of the absent cue. These changes can be in the same direction as the present cue (i.e., positive mediation) or in the opposite direction to the present cue (i.e., negative mediation). We found both mediational effects in a human contingency task. In addition, we found that the direction of the change was determined by the existence of a prior association between the absent cue and the outcome. When a prior association exists, the absent cue tends to change its value in the opposite direction to the present cue, whereas when there is no prior association, the absent cue tends to change its value in the same direction as the present cue. Recent associative models (Stout & Miller, 2007) can explain our results.

Web-based experiment control software for research and teaching on human learning

In this article we describe some of the experimental software we have developed for the study of associative human learning and memory. All these programs have the appearance of very simple video games. Some of them use the participants' behavioral responses to certain stimuli during the game as a dependent variable for measuring their learning of the target cue-outcome associations. Some others explicitly ask participants to rate the degree of relationship they perceive between the cues and the outcomes. These programs are implemented in Web pages using JavaScript, which allows their use both in traditional laboratory experiments as well as in Internet-based experiments.

Pavlovian backward conditioned inhibition in humans: summation and retardation tests

Two experiments using human participants investigated whether a Pavlovian backward inhibitory treatment (nonreinforced trials in phase 1 followed by reinforced trials in phase 2; i.e., AX- followed by A+) produces a stimulus which can pass summation and retardation tests for inhibition. The rationale for conducting these experiments was that previous demonstrations of Pavlovian backward inhibition informed participants about the nature of the outcome before starting the experiment. According to some theoretical views, this is a potential confound. In the present experiments we used a predictive task in which participants had no knowledge about the outcome until phase 2, when reinforcement occurred. The results of Experiment 1 (summation test) and Experiment 2 (retardation test) provide a clear demonstration of backward conditioned inhibition.

A novel test of conditioned inhibition correlates with personality measures of schizotypy and reward sensitivity

Conditioned inhibition is demonstrated when the meaning of one signal (conditioned stimulus, CS) is qualified by another (conditioned inhibitor, CI). Whilst the CS presented alone reliably predicts the outcome (unconditioned stimulus, US), when presented in conjunction with the CI the otherwise expected US will not occur. Conditioned inhibition has long been established in animal research but there have been difficulties in establishing reliable procedures suitable for use in human research. Such procedures are necessary to investigate disorders in which cognitive inhibitory mechanisms are known to be deficient, e.g., schizophrenia. In healthy participants, individual differences in the tendency to show conditioned inhibition should be related to personality measures of cognitive inhibition. In the present study, this was measured using an automated test procedure, in which visual stimuli predict the occurrence or non-occurrence of a visual outcome US, and BIS/BAS and schizotypy scales. Conditioned inhibition was reliable across two alternative test variants, in which the non-occurrence of the US was specified differently, and was confirmed by summation tests. The level of CI shown was positively associated with BAS Reward Responsiveness but did not correlate significantly with any of the other BIS/BAS scales. Conversely, the level of CI shown was negatively associated with schizotypy. We suggest that this novel conditioned inhibition task should now be applied to investigate a range of disorders that have some basis in dysfunctional inhibitory processes, such as schizophrenia.

The effectiveness of inhibitors in human predictive judgments depends on the strength of the positive predictor

We tested whether the development of inhibitory strength, as measured by a summation test, is proportional to the strength of the positive cue (P) against which the inhibitory cue (I) is trained. P predicted the outcome, whereas the co-occurrence of P with I (PI) predicted no outcome. In Experiments 1, 2, and 3, we compared the latter design against a version in which P was overshadowed by another cue (X). In this design, the compound P degrees X predicted the outcome, but P degrees I degrees predicted no outcome. In all three experiments, overshadowed cue I degrees was less inhibitory than I. In Experiment 4, a P produced by fewer training trials also supported weaker inhibitory learning. Overall, the results were consistent with associative learning theories, especially Pearce's (1994) configural model. Contingency models need to make additional assumptions to accommodate this property of inhibitory learning.