Revaluation manipulations produce emergence of underselected stimuli following simultaneous discrimination in humans

Stimulus overselectivity occurs when only one of potentially many aspects of the environment controls behaviour. In four experiments, human participants were trained and tested on a trial-and-error simultaneous discrimination task involving two two-element compound stimuli. Overselectivity emerged in all experiments (i.e., one element from the reinforced compound controlled behaviour at the expense of the other). Following revaluation (extinction) of the previously overselected stimulus, behavioural control by the underselected stimulus element emerged without any direct training of that stimulus element. However, while a series of extinction manipulations targeting the revaluation of the overselected stimulus produced differential extinction of that stimulus, they did not result in differential emergence of the previously underselected stimuli. The results are discussed with respect to the theoretical implications for attention-based accounts of overselectivity.     

Factors impacting emergence of behavioral control by underselected stimuli in humans after reduction of control by overselected stimuli

Stimulus overselectivity occurs when only one of potentially many aspects of the environment controls behavior. Adult participants were trained and tested on a trial-and-error discrimination learning task while engaging in a concurrent load task, and overselectivity emerged. When responding to the overselected stimulus was reduced by reinforcing a novel stimulus in the presence of the previously overselected stimulus in a second trial-and-error discrimination task, behavioral control by the underselected stimulus became stronger. However, this result was only found under certain circumstances: when there was substantial overselectivity in the first training phase; when control by the underselected stimulus in the first phase was particularly low; and when there was effective reduction in the behavioral control exerted by the previously overselected stimuli. The emergence of behavioral control by the underselected stimulus suggests that overselectivity is not simply due to an attention deficit, because for the emergence to occur, the stimuli must have been attended to and learned about in the training phase; but that a range of additional learning factors may play a role.     

Age trends in stimulus overselectivity

Stimulus overselectivity refers to the phenomenon whereby stimulus control over behavior is exerted only by a limited subset of the total number of stimuli present during discrimination learning. It often is displayed by individuals with autistic spectrum disorders or learning disabilities, but is not exclusive to those groups. The present studies investigated the impact of aging on stimulus control and overselectivity. Three age groups--18-22, 47-55, and 70-80 year olds-were studied in two experiments. All participants were trained on a simple discrimination task, randomly assigned to one of two conditions (either with or without a distractor task), and then tested for the emergence of overselectivity (Experiment 1). In Experiment 2 responding controlled by the overselected stimulus elements was reduced by introducing a verbal punisher. In subsequent tests, control of behavior by the previously underselected elements from Experiment 1 was enhanced across the two younger age groups but not the oldest group of participants. The results are discussed in relation to the attention-deficit and overshadowing accounts of overselectivity.     

Stimulus salience and retrospective revaluation

The effect of conditioning or extinguishing the more salient element of a previously reinforced compound on responding to the less salient element of that compound was assessed in rats. Experiment 1 established that the 2 elements making up an audiovisual compound differed significantly in salience. In Experiment 2A, compound conditioning was followed by either reinforcement or extinction of either the less or more salient element. On test, evidence of retrospective revaluation of the less salient element was found but not of the more salient element. In Experiment 2B, extinction of the more salient element was found to be more effective than its reinforcement in producing retrospective revaluation of the less salient element. The implications of these results are discussed.     

Reduction of stimulus overselectivity with nonverbal differential observing responses

Three individuals with mental retardation exhibited stimulus overselectivity in a delayed matching-to-sample task in which two sample stimuli were displayed on each trial. Intermediate accuracy scores indicated that participants could match one of the samples but not both of them. Accuracy in a baseline condition was compared to accuracy with a differential observing response procedure. This procedure prompted participants to make simultaneous identity-matching responses that required observation and discrimination of both sample stimuli. These observing responses were never followed by differential consequences. When observing responses were prompted, participants' accuracy scores improved. In a return to the baseline condition, when differential observing responses were no longer prompted, accuracy returned to intermediate levels. The results show that stimulus overselectivity can be greatly reduced by a behavioral intervention that controls observing behavior and verifies discrimination, but that exposure to such procedures alone may be insufficient for lasting benefits.     

Conditioned Inhibition Produced by Extinction of a Conditioned Stimulus

Four experiments used a conditioned taste aversion procedure to examine the potential for CS-alone extinction treatment to produce a conditioned stimulus that possesses inhibitory properties. In Experiment 1, saccharin was paired with LiCl, and then saccharin was presented alone for several trials to produce extensive behavioral extinction. Animals receiving this treatment were retarded in reacquiring conditioned responding to saccharin relative to control subjects receiving conditioning to the flavor for the first time. In Experiment 2, the extinguished saccharin stimulus was shown to decrease conditioned responding to a known excitor when the two stimuli were presented in compound as a summation test. Experiments 3A and 3B replicated the findings of Experiments 1 and 2 while providing evidence that the effects were not due to the differential effects of neophobia during testing. These three experiments revealed that an extinguished conditioned excitor passes retardation and summation tests for conditioned inhibition. Experiment 4 found that extinction of a known excitor was slowed when the excitor was extinguished in compound with a previously extinguished conditioned stimulus. That is, an extinguished CS provided protection from extinction to another CS, a finding also consistent with the view that extinction produces conditioned inhibition.     

Analysis of the pavlovian properties of signals for punishment

Rats learned to suppress lever pressing in the presence of a compound stimulus that signalled either response-independent shock (conditioned suppression) or response-dependent shock (punishment). Suppression to one element of this compound was blocked if the other element had previously signalled the same contingency as that holding in the presence of the compound. Two experiments, however, failed to find significant evidence of blocking if the pretrained element had signalled conditioned suppression and the compound signalled a punishment contingency. On the other hand, if one stimulus signalled punishment of one response it was able to block the acquisition of control by the second stimulus when the compound signalled punishment of a different response. Finally, although animals showed no suppression to one element of a compound signalling conditioned suppression if the other had previously signalled punishment, this apparent blocking effect concealed that what they learned was that the added element signalled the cancellation of the instrumental contingency. These results provide little support for the view that stimuli signalling punishment contingencies suppress responding in whole or in part by virtue of their Pavlovian relation to shock.     

Conditioned inhibition produced by extinction-mediated recovery from the relative stimulus validity effect: a test of acquisition and performance models of empirical retrospective revaluation

Empirical retrospective revaluation is a phenomenon of Pavlovian conditioning and human causal judgment in which posttraining changes in the conditioned response (Pavlovian task) or causal rating (causal judgment task) of a cue occurs in the absence of further training with that cue. Two experiments tested the contrasting predictions made by 2 families of models concerning retrospective revaluation effects. In a conditioned lick-suppression task, rats were given relative stimulus validity training, consisting of reinforcing a compound of conditioned stimuli (CSs) A and X and nonreinforcement of a compound of CSs B and X, which resulted in low conditioned responding to CS X. Massive posttraining extinction of CS A not only enhanced excitatory responding to CS X, but caused CS B to pass both summation (Experiment 1) and retardation (Experiment 2) tests for conditioned inhibition. The inhibitory status of CS B is predicted by the performance-focused extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001), but not by acquisition-focused models of empirical retrospective revaluation (e.g., A. Dickinson & J. Burke, 1996; L. J. Van Hamme & E. A. Wasserman, 1994).     

Reducing stimulus overselectivity through an increased observing-response requirement

An adult with autism and a mild intellectual disability participated in a 0-s delayed matching-to-sample task. In each trial, two sample stimuli were presented together until the participant completed an observing-response requirement consisting of 1 or 10 mouse clicks in the baseline and experimental phases, respectively. One of the two sample stimuli then appeared randomly as a comparison stimulus (S+), along with two other comparison stimuli (S-). Higher levels of correct responding occurred under the larger observing-response requirement, and the proportion of errors related to one of the two sample stimuli decreased. Thus, stimulus overselectivity was reduced without requiring differential observing responses.     

Interaction between preexposure and overshadowing: Further analysis of the extended comparator hypothesis

Three experiments with rats used conditioned suppression of barpress to test predictions of the extended comparator hypothesis, which assumes that the effectiveness of (first-order) comparator stimuli in modulating responding to a target conditioned stimulus (CS) is itself modulated by other (second-order) comparator stimuli. Experiment 1 demonstrated that both pretraining exposure to the target CS alone (i.e., CS-preexposure effect, also known as latent inhibition) and pretraining exposure to a compound of the target CS and nontarget CS (i.e., compound-CS-preexposure effect) counteract overshadowing, and that posttraining deflation (i.e., extinction) of the overshadowing stimulus attenuates responding to the target CS when overshadowing is preceded by a CS-preexposure treatment (i.e., yields a CS-preexposure effect), but not when overshadowing is preceded by a compound-CS-preexposure treatment. Experiment 2 examined the consequences of posttraining associative inflation of the overshadowing stimulus or the preexposure companion stimulus following conjoint compound-CS-preexposure and overshadowing treatment. Experiment 3 examined the consequences of posttraining inflation of the overshadowing stimulus or the context following conjoint CS-alone preexposure and overshadowing treatment. The results support the expression-focused comparator view in contrast to recent acquisition-focused models of retrospective revaluation.     

Stimulus overselectiv1ty of autistic children in a two stimulus situation

Autistic and normal children were trained to respond to a complex stimulus involving an auditory component (white noise) and a visual component (red floodlight). After the Ss had acquired this discrimination, the individual components were presented singly to assess their control over the Ss' behavior. The autistic Ss' unlike the normals, demonstrated stimulus overselectivity in that seven out of nine Ss responded to only one of the components. These results were consistent with those of a previous study where autistics showed stimulus overselectivity in an experiment involving three modalities. In both experiments, the previously non-functional stimulus was made functional when trained separately.     

Aspects of the reinforcer learned in second-order Pavlovian conditioning

Four experiments used an autoshaping procedure in pigeons to explore learning about the reinforcer in a second-order conditioning paradigm. Experiment 1 conditioned two visual second-order stimuli (S2), using as reinforcers two visual first-order stimuli (S1), each of which had previously been paired with food. Animals for which the S2 stimuli were each consistently paired with one particular S1 developed second-order responding more rapidly than did animals for which the identity of S1 varied from trial to trial. Moreover, following consistent pairings, extinction of an S1 had a depressive effect upon second-order responding which was peculiar to the S2 with which it had been paired. Both results suggest that in this preparation the organism identifies a particular S1 as the reinforcer for each S2. The remaining experiments examined the details of that identification. A compound S1, itself composed of two separable elements, was used to reinforce an S2. Subsequent extinction of either element of S1 led to a depression in the responding to S2, which indicates that both elements were involved in the second-order conditioning. Moreover, the use of several complex discriminations, which produced different behavior to S1 and to its elements, suggested that the organism had associated the S2 with the compound S1 rather than with its separate elements. However, even complete extinction of the response to S1 left some residual behavior to S2, which indicates that a portion of the second-order conditioning is independent of the current state of the reinforcer. These results demonstrate that in some situations the organism associates a conditioned stimulus with a rich representation of the reinforcer.     

Resistance to extinction following habituation to behaviourally disruptive novel stimuli

Three experiments tested the prediction, derived from generalized frustration theory (Amsel, 1972), that habituation to behaviourally disruptive stimuli increases resistance to extinction in the runway. In each experiment, rats received initial consistent reinforcement (CRF) training and then either continued CRF (Groups C), partial reinforcement (PRF) training (Groups P), or CRF accompanied by presentations of a novel tactile, tone, or obstacle stimulus (Groups D) in Experiments 1-3, respectively. PRF increased resistance to extinction whether non-reinforcement disrupted behaviour (Experiment 1) or not (Experiments 2 and 3). The tactile and obstacle stimuli very substantially disrupted behaviour, and the tone produced a modest disruption of behaviour. All subjects habituated to the disruptive effects of these stimuli, but Group D was not more resistant to extinction than Group C in any experiment. The results suggest that non-reinforcement has unique stimulus properties, a consequence of which is that habituation to other sources of disruptive stimulation does not promote responding to non-reinforcement in extinction.     

Reevaluation of things past

The ability of rats to reevaluate previously presented information in light of subsequently provided information was evaluated using a CER (conditioned emotional response) procedure. In Experiment 1, rats suppressed responding to a compound light + tone stimulus that was repeatedly paired with shock. Groups of rats were then presented with only one element of the compound (the tone), either presented alone or paired with shock, for 15 days. During this 15-day period, two control groups received trials with the shock alone or neither stimulus nor shock. All of the rats were then tested with the other element of the compound (the light). Rats that had received the tone paired with shock during the intervening training continued to suppress to the light, whereas rats that had received the tone alone showed rapid extinction of the CER to light. The control groups showed that this effect was not due to the number of shock presentations received. A subsequent experiment also demonstrated that these results were not due to nonspecific stimulus effects. Apparently, a subsequent change in the associative strength of one element results in a similar change to the other element of a previously established compound stimulus.     

Blocking and unconditioned response diminution in human classical autonomic conditioning

This paper summarizes the results of three experiments on blocking and unconditioned response diminution in human SCR conditioning. Recent theories of conditioning propose that reduced processing of the unconditioned stimulus due to conditioning results in reduced unconditioned response magnitude and in blocking of conditioning of a second conditioned stimulus when it is in compound with the previously conditioned stimulus. In these experiments, clear evidence of diminution of the unconditioned response was obtained in all three studies, but blocking was found only in the third study, which employed a within-subject design and in which the blocking was observed only after at least one extinction trial on both the blocked and nonblocked stimuli. Order of testing was not a factor in this delayed blocking effect. These results do not support the view that blocking occurs because of reduced processing of the unconditioned stimulus in the unconditioned response diminution sense.     

Within compound Associations Mediate the Retrospective Revaluation of Causality Judgements

The role of within-compound associations in the retrospective revaluation of causality judgements was investigated in a two-stage procedure in which the subjects were asked to learn whether or not different food stimuli caused an allergic reaction in hypothetical patients. In the compound-cue stage a number of compound cues, each consisting of a competing stimulus and a target stimulus, were associated with the reaction across a series of trials, whereas in the single-cue stage the subjects had the opportunity to learn which of the competing cues, when presented alone, caused the reaction. Each target stimulus was presented with the same competing cue across all compound trials in the consistent condition, but with a different competing cue on each trial in the varied condition. In a forward procedure, in which the single-cue stage preceded compound cue training, judgements of the causal effectiveness of the target stimuli were reduced or blocked by training them in compound with a competing cue that had been previously paired with the reaction. Moreover, the magnitude of this reduction was comparable in the consistent and varied conditions. This was not true, however, when the single- and compound-cue stages were reversed in the backward procedure. Judgements for target cues compounded with competing cues that were subsequently paired with the reaction were reduced only in the consistent condition. If it is assumed that stronger associations were formed between the competing and target stimuli during the compound-cue stage in the consistent condition than in the varied condition, this pattern suggests that the retrospective revaluation of causality judgements can be mediated by the formation of within-compound associations.     

Extinction can be enhanced by a concurrent excitor

Five experiments used rat subjects to investigate the impact on extinction of the presence of other conditioned stimuli. In Experiments 1 (Pavlovian magazine approach) and 2 (instrumental discriminative training), an excitatory stimulus (X) was extinguished alone, in conjunction with a previously reinforced other stimulus (A), in conjunction with previously nonreinforced other stimulus (B), or it was spared extinction. Responding during extinction was greatest to AX, and subsequent testing of X alone showed AX extinction to have produced the most decrement to X. Experiment 3 found similar results using a within-subject design. Experiment 5 continued separate reinforced presentations of A during extinction. This procedure not only promoted extinction of X but also converted it into a conditioned inhibitor. These experiments bear on the mechanisms of overshadowing and stimulus processing, as well as provide information on the determinants of extinction.     

Deepened extinction following compound stimulus presentation: noradrenergic modulation

Behavioral extinction is an active form of new learning involving the prediction of nonreward where reward has previously been present. The expression of extinction learning can be disrupted by the presentation of reward itself or reward-predictive stimuli (reinstatement) as well as the passage of time (spontaneous recovery) or contextual changes (renewal). The following experiments replicated the demonstration that presenting multiple previously rewarded stimuli in compound during extinction enhances extinction learning. To explore the pharmacological basis for this we next examined the effects of pharmacological treatments that either facilitated or blocked noradrenergic activity to test the hypothesis that increased noradrenergic activity at the time of extinction training would improve, whereas blockade of noradrenergic activity would impair the extinction of appetitive stimulus-reward memories. Different groups of rats were trained in a discriminative stimulus paradigm to lever-press for food reward. Once stable responding was achieved, responding was extinguished for 2 d. Prior to a third extinction session, rats received systemic administration of either saline, yohimbine (α2 antagonist), atomoxetine (norepinephrine reuptake inhibitor), or propranolol (β-receptor antagonist). Spontaneous recovery of responding to the stimuli was tested 4 wk later. Our results indicate that increasing noradrenergic activity during extinction augments extinction learning resulting in less recovery of responding at test. These results have important implications for models of relapse to drug seeking and the development of extinction-based therapies.     

The role of contextual associations in producing the partial reinforcement acquisition deficit

Three conditioned suppression experiments with rats as subjects assessed the contributions of the conditioned stimulus (CS)-context and context-unconditioned stimulus (US) associations to the degraded stimulus control by the CS that is observed following partial reinforcement relative to continuous reinforcement training. In Experiment 1, posttraining associative deflation (i.e., extinction) of the training context after partial reinforcement restored responding to a level comparable to the one produced by continuous reinforcement. In Experiment 2, posttraining associative inflation of the context (achieved by administering unsignaled outcome presentations in the context) enhanced the detrimental effect of partial reinforcement. Experiment 3 found that the training context must be an effective competitor to produce the partial reinforcement acquisition deficit. When the context was down-modulated, the target regained behavioral control thereby demonstrating higher-order retrospective revaluation. The results are discussed in terms of retrospective revaluation, and are used to contrast the predictions of a performance-focused model with those of an acquisition-focused model.     

Deepened extinction from compound stimulus presentation

Three experiments with rats and 2 with pigeons explored the effect of presenting 2 extinguished excitatory stimuli in compound. Four learning situations were used: Pavlovian magazine approach, Pavlovian fear conditioning, and instrumental discriminative instrumental learning in rats, as well as Pavlovian sign tracking in pigeons. All 5 experiments confirmed D. Reberg's (1972) observation that even after extinction of the individual stimuli, presenting them in compound evoked substantial responding. Moreover, nonreinforcement of that compound deepened extinction of an element more substantially than did additional presentation of that element alone. Such compound exposure reduced spontaneous recovery, reduced reinstatement, and slowed subsequent reconditioning. The primary determinant seemed to be the enhanced associative strength rather than the enhanced conditioned responding that occurred during the nonreinforced compound.