Mediated conditioning versus retrospective revaluation in humans: The influence of physical and functional similarity of cues

Two experiments assessed whether similarity between the two elements of a compound would influence the degree of mediated extinction versus recovery from overshadowing in human causal judgements. In both Experiments 1 and 2, we assessed the influence of extinguishing one element of a two-element compound on judgements about the other element. In Experiment 1 we manipulated the physical similarity of the two elements of the compound; in Experiment 2, we used equivalence and distinctiveness pretraining in order to vary their functional similarity. We found that these procedures influenced mediated extinction and recovery from overshadowing as a function of both physical and acquired similarity and distinctiveness, respectively. The implications of these results for previously reported differences between humans and nonprimate animals are discussed.     

Failure of serial taste-taste compound presentations to produce overshadowing of extinction of conditioned taste aversion

Two experiments were conducted to study overshadowing of extinction in a conditioned taste aversion preparation. In both experiments, aversive conditioning with sucrose was followed by extinction treatment with either sucrose alone or in compound with another taste, citric acid. Experiment 1 employed a simultaneous compound extinction treatment and found results indicative of overshadowing of extinction. By contrast, Experiment 2, in which extinction treatment involved serial compound presentations, failed to obtain evidence of overshadowing of extinction. The results of Experiment 2 indicate that the serial presentation of two tastes was processed as equivalent to the separate presentation of the tastes. The results are discussed in relation to: (1) Convergent evidence from research on latent inhibition, (2) competing theories of learning and, (3) their possible adaptive value in food-selection learning.     

Recovery of an overshadowed association achieved by extinction of the overshadowing stimulus

Three experiments are reported in which conditioned lick suppression by water-deprived rats was used as an index of associative strength. In Experiment 1, overshadowing of a light by a tone was observed when the light-tone compound stimulus was paired with foot shock. After initial compound pairings, the tone-shock association was extinguished in one group of subjects. Subsequently, these animals demonstrated significantly higher levels of suppression to the light relative to a control group in which the tone had not been extinguished. Experiment 2 replicated this effect while failing to find evidence to support the possibilities that extinction presentations of the overshadowing tone act as retrieval cues for the light-shock association, or that, via second-order conditioning, the light-shock association is actually formed during extinction of the tone. Experiment 3 determined that the recovery from overshadowing observed in Experiments 1 and 2 was specific to the extinction of the overshadowing stimulus rather than the extinction of any excitatory cue. Collectively, these results suggest that the debilitated response to an overshadowed stimulus does not represent an acquisition failure, but rather the failure of an acquired association to be manifest in behavior.     

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.     

The extinction of within-compound flavor associations

Three experiments studied extinction of the associations which are formed between two flavors presented in a simultaneous compound. In Experiment 1 those associations were identified by a sensory preconditioning procedure in which the poisoning of one element of the compound led to the rejection of the other element. Separate presentation of either element between their joint occurence and the poisoning of one element sharply attenuated the rejection of the other element. That attenuation was interpreted in terms of the extinction of within-compound associations. Experiment 2 obtained similar results with an alternative extinction procedure in which the elements of the original compound were presented in other compounds. Experiment 3 obtained similar results when the existence of the within-compound associations was determined by an alternative assessment procedure in which one element of the compound was made more attractive by the induction of a specific hunger. These experiments suggest that within-compound associations can be extinguished when the elements are separately presented outside of the compound. Experiments 2 and 3 make less plausible an alternative interpretation of the effects of separate element presentation in terms of reduction of the novelty of the element. The findings may be taken as implying that the elements of a simultaneously presented compound are joined by a single symmetrical association which acts at various points during a sensory preconditioning experiment.     

Counteraction between overshadowing and degraded contingency treatments: support for the extended comparator hypothesis

Four experiments using rats in a Pavlovian lick-suppression preparation investigated the effects of combining 2 treatments known for their response-decrementing effects, namely, overshadowing and degraded contingency. Contrary to most contemporary learning theories, the extended comparator hypothesis predicts that these 2 treatments will counteract each other, and therefore, less of a decrement in conditioned responding should be observed than with either treatment alone. Experiments 1 and 2 confirmed this prediction in first-order conditioning and sensory preconditioning preparations, respectively. Experiment 3 demonstrated that posttraining extinction of the training context resulted in a recovery from degraded contingency and reversed the counteractive effect on overshadowing. Finally, Experiment 4 demonstrated that posttraining extinction of the overshadowing stimulus resulted in recovery from simple overshadowing and also reversed the counteractive effect on degraded contingency. These results are consistent with the extended comparator hypothesis but not traditional or recent acquisition-focused models.     

Contrasting reduced overshadowing and blocking

Preexposure of a cue without an outcome (X-) prior to compound pairings with the outcome (XZ-->O) can reduce overshadowing of a target cue (Z). Moreover, pairing a cue with an outcome (X-->O) before compound training can enhance its ability to compete with another cue (i.e., blocking). Four experiments were conducted in a conditioned bar-press suppression preparation with rats to determine whether spacing of the X- or X-->O trials would differentially affect reduced overshadowing and blocking. Experiment 1a showed that reduced overshadowing was larger with massed trials than with spaced trials. Experiment 1b found that blocking was larger with spaced trials than with massed trials. Experiments 2a and 2b indicated that these effects of trial spacing were both mediated by the associative status of the context at test. The results are interpreted in the framework of contemporary learning theories.     

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.     

Cue competition effects in the planarian

The learning abilities of planarian worms (Dugesia tigrina) were assessed by using a number of Pavlovian conditioning paradigms. Experiment 1 showed that planaria were susceptible to basic conditioning in that they readily developed a conditioned response to a change in ambient luminance when it was consistently paired with an electric shock over a number of trials. In Experiment 2, the change in luminance was presented in a compound with a vibration stimulus during conditioning. Subsequent tests revealed poor conditioning of the elements compared with control groups in which the animals were conditioned in the presence of the elements alone, an instance of overshadowing. In Experiment 3, pre-training of one of the elements before compound conditioning resulted in blocking of learning about the other element. These results add to other studies that have reported cue competition effects in animal species belonging to different phyla (chordate, mollusk, arthropod), suggesting that learning in these phyla could be ruled by similar principles. The results are discussed adopting an evolutionary-comparative approach.     

Extinction of conditioned taste aversions: Effects of concentration and overshadowing

Extinction of conditioned taste aversions was examined as a function of taste concentration and of the presence of an additional taste. The results of Experiment 1 were consistent with previous evidence in that a conditioned aversion to high concentration saline was more persistent in extinction than an aversion to a low concentration. However, when floor effects were avoided the rate of extinction was faster for the higher (1%) concentration than for 0.2% saline (Experiment 2), a result consistent with accounts of extinction in other preparations. Three further experiments examined extinction of a conditioned sucrose aversion. The addition of 1% saline, but not of 0.2% saline, to sucrose during extinction produced overshadowing ("protection from extinction"; Experiment 3). Such overshadowing by saline was detected after two, but not after a single extinction trial (Experiment 4). This last finding suggests that under the conditions of the present experiments sweet and salty tastes function as elemental stimuli competing for loss of associative strength. No overshadowing was found when almond (an aqueous odour) was used in place of saline as the added stimulus, even when high concentrations of almond were used that produced observable neophobia (Experiments 5A and 5B).     

Retrospective revaluation effects in the conditioned suppression procedure

In four experiments using the conditioned suppression procedure, rats received initial reinforced training with two compound stimuli, AX and BY, each compound consisting of one auditory and one visual element. After a second phase of training consisting of nonreinforced presentations of A, the suppression governed by X and Y was tested. In Experiment 1 X evoked slightly less suppression than Y (a mediated extinction effect). This outcome was obtained when the auditory cues served as Xand Y(Experiment 1a), when the visual cues served as Xand Y(Experiment 1b), and when the number of nonreinforced presentations of Awas increased (Experiment 1c) from 18 to 216. In Experiment 2, however, in which the initial training was given with serial compounds (i.e., A ⇒ X and B ⇒ Y) X evoked more suppression than Y (a recovery-from-overshadowing effect). It was argued that extinction of A engages two learning processes, one increasing the effective associative strength of its associate (X) and one reducing it, and that the balance between these two depends on the specific conditions of training.     

Extinction of Within-event Learning Is Contextually Controlled and Subject to Renewal

Five experiments examined within-event learning in rats by inducing an appetite for one of the elements (salt) of a compound stimulus and assessing preference for the other element (almond). Almond preference was conditional upon (1) the almond flavour having been presented in compound with the salt, and (2) the assessment being conducted when the rats were out of sodium balance (Experiment 1). Presentations of the compound in one environment (A) and of the salt and almond elements in a second environment (B) resulted in greater almond preference when rats were tested in A than in B (Experiment 2). Almond preference was reduced when separate presentations of the compound and almond (Experiment 3) or of the compound and salt (Experiment 4) occurred in the same environments but not when these presentations occurred in different environments. Rats exposed to the compound in A and then extinguished to the elements in either A or B showed a reduced almond preference when tested in the extinction environment, but not when tested in the other environment (Experiment 5). Thus, extinction of within-event learning is context-specific and subject to renewal. The results were interpreted in terms of an associative model whereby separate presentations of the elements result in a symmetrical inhibitory link which is contextually gated (Bouton, 1993).     

Perceptual and categorical judgements of colour similarity

Consideration is given to the tasks that make judgements of colour similarity based on perceptual similarity rather than categorical similarity. Irrespective of whether colour categories are taken to be universal (Berlin & Kay, 1969) or language induced (Davidoff, Davies, & Roberson, 1999), it is widely assumed that colour boundaries, and hence categorical similarity, would be used when categorising colours. However, we argue that categorical similarity is more reliably used in implicit than in explicit categorisation. Thus, in Experiment 1, we found that category boundaries may be overridden in the explicit task of matching-to-sample: There was a similar strong tendency to ignore colour boundaries and to divide the range of coloured stimuli into two equal groups in both Westerners and in a remote population (Himba). In Experiment 2, we showed that a distinctive stimulus (focal colour) in the range affected the equal division in a matching-to-sample task. Experiment 3 tested the stability of a category boundary in an implicit task (visual search) that assessed categorical perception; only for this task was categorisation largely immune to range effects and largely based on categorical similarity. It is concluded that, even after colour categories are acquired, perceptual rather than categorical similarity is commonly used in judgements of colour similarity.     

Being similar while judging right and wrong: The effects of personal and situational similarity on moral judgements

This study investigated the effects of similarity with the transgressor and the victim on the perceived immorality of the transgression. Participants read two stories describing a person that cheated on their partner and a police officer that mistreated somebody. In the first story we manipulated participants' personal similarity to the transgressor and in the second their personal similarity to the victim. In each story, participants' past situational similarity to the target character was assessed according to their previous experiences of being in the same position. Results show that both personal and past situational similarity to the transgressor determine less severe moral judgements, while personal and past situational similarity with the victim have the opposite effect. We also tested several potential mediators of these effects, derived from competing theoretical accounts of the influence of similarity on perceived responsibility. Empathy emerged as mediating most of the effects of similarity on moral judgements, except those induced by past situational similarity with the victim. The foreseen probability of being in a similar situation mediated only the effects of similarity to the transgressor, and not those of similarity to the victim. Overall, results highlight the complex mechanisms of the influences of similarity on moral judgements.     

Trial spacing is a determinant of cue interaction

Four conditioned lick suppression experiments with rats examined the effect of trial spacing on cue interaction. Experiments 1 and 2 found overshadowing to be eliminated with massed compound stimulus-outcome pairings and the usual trial spacing effect to be reversed with compound acquisition trials. Experiment 3 found that whether acquisition compound-outcome pairings were massed or spaced determined the effect of posttraining extinction treatment. Extinction of the overshadowing cue reduced responding following massed training and increased responding following spaced training. Extinction of the context decreased responding following massed training. Experiment 4 found the conditioning and devaluation results to be associative and stimulus specific. These results are in accord with the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001).     

Overshadowing of subsequent events and recovery thereafter

Four experiments using a conditioned lick suppression preparation with rats were conducted to examine whether overshadowing of subsequent events could be obtained in Pavlovian backward conditioning (i.e. unconditioned stimulus [US] before conditioned stimulus [CS]), and to determine whether such overshadowing could be reversed without further training with the overshadowed CS, as has been reported in overshadowing of antecedent events. In Experiment 1, a backward-conditioned CS overshadowed a second backward-conditioned CS. Two posttraining manipulations, extinction of the overshadowing CS (Experiment 2) and shifting of the temporal relationship of the overshadowing CS to the US (Experiment 3), increased responding to the overshadowed CS. These results constitute the first unambiguous demonstration of stimulus competition between subsequent events using first-order conditioning, and they show that, like overshadowing with forward conditioning, such overshadowing is due, at least in part if not completely, to a failure to express information that had been acquired.     

An inhibitory within-compound association attenuates overshadowing

According to the comparator hypothesis (Miller & Matzel, 1988), cue competition depends on the association between a target stimulus (X) and a competing cue (e.g., an overshadowing cue [A]). Thus, it was expected that overshadowing would be reduced by establishing an inhibitory-like relationship between X and A before compound conditioning. In three lever press suppression experiments with rats, this expectation was supported. Experiment 1 showed that establishing an inhibitory X-A relationship reduced overshadowing. In Experiment 2, degrading the inhibitory-like relationship before conditioning allowed reinforced AX compound trials to result in overshadowing. Experiment 3 replicated the results of Experiment 2 when the inhibitory relationship was degraded after compound conditioning. The results support the view that within-compound associations are necessary not only for retrospective revaluation, but also for conventional cue competition.     

Proactive interference between cues trained with a common outcome in first-order Pavlovian conditioning

The nature of interference between cues (X, A) trained apart with a common outcome (O; an unconditioned stimulus) was explored by assessing proactive interference in first-order Pavlovian conditioning (i.e., A-O, X-O, resulting in attenuated responding to X). Three lick-suppression studies were conducted with water-deprived rats. Posttraining extinction of the interfering cue (A) attenuated proactive interference (Experiment 1), which mirrors the observation that extinction of the competing cue can reduce competition between cues trained together (e.g., recovery from overshadowing). Proactive interference was also attenuated with manipulations known to attenuate interference between outcomes trained apart (e.g., counterconditioning), namely reminder cues (Experiment 2) and renewal (Experiment 3). The findings suggest that similar processes underlie interference between cues trained apart, between cues trained together, and between outcomes trained apart.     

The effects of distinctiveness on memory and metamemory for face-name associations

We examined the influence of face and name distinctiveness on memory and metamemory for face-name associations. Four types of monitoring judgements were solicited during encoding and retrieval of face-name pairs that contained distinct or typical faces (Experiment 1) or names (Experiment 2). The beneficial effects of distinctiveness on associative memory were symmetrical between faces and names, such that relative to their typical counterparts, distinct faces enhanced memory for names, and distinct names enhanced memory for faces. These effects were also apparent in metamemory. Estimates of prospective and retrospective memory performance were greater for face-name associations that contained a distinct face or name compared with a typical face or name, regardless of whether the distinct item was a cue or target. Moreover, the predictive validity of prospective monitoring improved with name distinctiveness, whereas the predictive validity of retrospective monitoring improved with facial distinctiveness. Our results indicate that distinctiveness affects not only the strength of the association between a face and a name, but also the ability to monitor that association.     

The Influence of Retention Interval on the US Preexposure Effect: Changes in Contextual Blocking over Time

A number of studies manipulating the length of the interval between conditioning and testing indicate spontaneous recovery from overshadowing, suggesting that certain instances of overshadowing represent a deficit in memory retrieval rather than a failure of animals to form an association between the overshadowed stimulus and the US. The present series of experiments examined the influence of lengthening the retention interval on blocking, another stimulus selection phenomenon that is typically interpreted as an acquisition deficit. The results indicated that when subjects were tested shortly (3 days) after training conditioning to a taste blocked subsequent conditioning to an odor conditioned in compound with that taste (Experiment 1), whereas prior conditioning to an odor did not block subsequent conditioning to a taste conditioned in compound with that odor (Experiment 2). This pattern of results was essentially unchanged when testing occurred at a longer (21-day) retention interval. However, there was evidence of a US preexposure effect in Experiment 2 when subjects in the US ONLY control condition were tested at the 3-day retention interval, but not when testing occurred 21 days after conditioning. Experiments 3 and 4 examined whether this loss of the US preexposure effect over time might actually represent a change in the degree of contextual blocking as the retention interval is lengthened. Exposure to the conditioning context either during the interval between Phase 1 and Phase 2 of conditioning (Experiment 3) or prior to Phase 1 of conditioning (Experiment 4) alleviated this US preexposure effect suggesting that the loss of the US preexposure effect as the retention interval is lengthened observed in Experiment 2 is due to changes in the degree of blocking by contextual stimuli over time. The results are discussed in terms of differential susceptibility of forgetting of two functional roles played by a contextual stimuli in the current situation-context as a CS and context as a retrieval cue for other CS-US associations.