Unconditioned Stimulus Representation Research Articles

Turning negative memories around: Contingency versus devaluation techniques

Background and objectivesIt is assumed that fear responses can be altered by changing the contingency between a conditioned stimulus (CS) and an unconditioned stimulus (US), or by devaluing the present mental representation of the US. The aim of the present study was to compare the efficacy of contingency- and devaluation-based intervention techniques on the diminishment in – and return of fear. We hypothesized that extinction (EXT, contingency-based) would outperform devaluation-based techniques regarding contingency measures, but that devaluation-based techniques would be most effective in reducing the mental representation of the US. Additionally, we expected that incorporations of the US during devaluation would result in less reinstatement of the US averseness. MethodsHealthy participants received a fear conditioning paradigm followed by one of three interventions: extinction (EXT, contingency-based), imagery rescripting (ImRs, devaluation-based) or eye movement desensitization and reprocessing (EMDR, devaluation-based). A reinstatement procedure and test followed the next day. ResultsEXT was indeed most successful in diminishing contingency-based US expectancies and skin conductance responses (SCRs), but all interventions were equally successful in reducing the averseness of the mental US representation. After reinstatement EXT showed lowest expectancies and SCRs; no differences were observed between the conditions concerning the mental US representation. LimitationsA partial reinforcement schedule was used, resulting in a vast amount of contingency unaware participants. Additionally, a non-clinical sample was used, which may limit the generalizability to clinical populations. ConclusionEXT is most effective in reducing conditioned fear responses.

Incentive contrast effects regulate responding to a flavor presented in compound with a saccharin unconditioned stimulus in rats.

A flavor conditioned stimulus (conditional stimulus; CS) presented in simultaneous compound with a sweet-tasting unconditioned stimulus (US) acquires a certain sweetness and/or hedonic value. The present study examined whether responding to the flavor CS is influenced by postconditioning changes in the strength of the sweet US representation. In each experiment, rats were exposed to presentations of each of 2 flavors, A and B, in simultaneous compound with a 0.4% saccharin solution, and then tested with presentations of CS A in water. Experiments 1 and 2 showed that responding to CS A depended on its pairing with saccharin and increased with the training-to-test interval. Experiment 3 showed that a progressive reduction in the saccharin concentration of the trained compounds led to an increase in responding to CS A when tested in the absence of saccharin. Experiments 4 and 5 showed that, after a 7-day training-to-test delay, responding to CS A decreased following pretest exposure to a strong saccharin solution, and increased following pretest exposure to a very weak saccharin solution. These findings are taken to imply that incentive contrast effects regulate responding to a flavor CS. Hence, responding to the flavor CS increases with the training-to-test interval as the representation of the sweet US decays; decreases following pretest exposure to very sweet solutions as these reinstate the decayed sweet US representation (negative contrast); and increases following pretest exposure to weakly sweet solutions as these are perceived as less attractive than the CS itself (positive contrast). (PsycINFO Database Record

Experimental extinction in Pavlovian conditioning: behavioural and neuroscience perspectives.

This paper reviews the behavioural and neuroscience literatures on extinction in Pavlovian conditioning with a view towards finding possible points of contact between these two often independent lines of investigation. Recent discoveries at the behavioural level indicate (1) that conditioned stimulus (CS)-unconditioned stimulus (US) associations specific in their sensory content are fully preserved during extinction, (2) that inhibitory stimulus-response associations appear to be learned during extinction, (3) that extinction is influenced by the level of activation of the US representation during nonreinforced trials, (4) that decreases in attention can influence conditioned performance during extinction, and (5) that contexts acquire an ability to modulate learning during both conditioning and extinction. Recent discoveries at the neural systems level suggest (1) that the hippocampus is important in context-specific learning during extinction, (2) that the prefrontal cortex is possibly important in long-term memory for extinction, (3) that the basolateral amygdala may be important in sustaining attention to a CS during extinction, (4) that NMDA receptors are important either in neural plasticity during extinction or by affecting the value of the US representation during extinction, and (5) that the GABAergic system may partially mediate inhibitory learning during extinction. It is concluded that both of these levels of analysis can benefit the other in the pursuit of a more comprehensive understanding of extinction.

Effects of US devaluation on win-stay and win-shift radial maze performance in rats.

Previous studies have shown double dissociations between win-stay and win-shift radial maze learning in terms of their underlying neural substrates. To examine the content of the associations formed in the two tasks, the authors devalued the food unconditioned stimulus (US) by taste aversion to differentiate stimulus-stimulus(CS-US) and stimulus-response (CS-CR) learning. US devaluation was performed in rats that were over- or undertrained on the win-stay task. Devaluation substantially reduced food consumption on the maze but failed to disrupt choice accuracy, regardless of the amount of training. Devaluation did not affect latency in overtrained rats but did increase latency in undertrained rats. In the win-shift task, devaluation caused rats to reject the reinforcer, yet they continued to accurately win-shift, but with significantly longer latencies (Experiment 3). The results suggest that an S-R association may mediate performance after extended win-stay training. In contrast, a US representation appears to be recalled during early win-stay and win-shift performance.

Reinstatement of fear to an extinguished conditioned context

Rats were shocked in the black but not the white compartment of a shuttlebox and then exposed to the black compartment in the absence of the shock unconditioned stimulus (US) to extinguish fear responses (passive avoidance). In five experiments, rats were then shocked in a reinstatement context (distinctively different from the shuttlebox) to determine the conditions that reinstate extinguished fear responding to the black compartment. Rats shocked immediately upon exposure to the reinstatement chamber failed to show either reinstatement of avoidance of the black compartment or fear responses (freezing) when tested in the reinstatement chamber. In contrast, rats shocked 30 sec after exposure to the reinstatement chamber exhibited both reinstatement of avoidance of the black compartment and freezing responses in the reinstatement chamber (Experiment 1). Rats shocked after 30 sec of exposure to the reinstatement chamber but then exposed to that chamber in the absence of shock failed to exhibit reinstatement of the avoidance response and did not freeze when tested in the reinstatement chamber (Experiment 2). Rats exposed to a signaled shock in the reinstatement chamber and then exposed to that chamber in the absence of shock also failed to exhibit reinstatement of the avoidance response (Experiment 5). These rats showed fear responses to the signal but not to the reinstatement chamber. Finally, rats exposed for some time (20 min) to the reinstatement chamber before shock exhibited reinstatement of the avoidance response but failed to freeze when tested in the reinstatement chamber (Experiments 3 and 4). These results are discussed in terms of the contextual conditioning (Bouton, 1994) and the US representation (Rescorla, 1979) accounts of postextinction reinstatement.

The effect of temporal relationship of stimulus compound on ambiguous discrimination in the pigeon's autoshaping

Pigeons learned a serial amibiguous discrimination task (FA+, A-, FB-, B+), in which the serial presentation of a feature and one target (FA) and the presentation of the other target alone (B) were followed by an unconditioned stimulus (US), but the serial FB presentation and the presentation of A alone were unreinforced. The successful performance of this task supported Holland's (1983, 1985) model of the feature modulation asserting that the feature occasion-sets each target-US association, rather than Rescorla's (1985) model asserting that the feature modulates the threshold of the US representation. The result that the simultaneous presentation of the feature and the target did not produce better discrimination than the serial presentation suggested a ‘bidirectional occasion-setting’ function of the feature. However, the insertion of the temporal gap between the feature and the target deteriorated the discrimination, a result that disagreed with previous studies of occasion-setting in the rats. Some possible reasons of the detrimental effect of the gap were discussed, and a unique-cue strategy was suggested as a possible alternative account of the discrimination.

Effects of priming unconditioned stimulus representation in short-term memory on Pavlovian conditioning.

A series of four experiments evaluated eyelid conditioning in the rabbit under circumstances in which the unconditioned stimulus (US) could variously be assumed to be prerepresented (primed) in short-term memory at the time of its presentation in pairing with a conditioned stimulus (CS). In both between- and within-subjects comparisons, less conditioning resulted when CS-US pairings were shortly preceded by US presentations than when not. The decremental effect of the pretrial priming US depended upon the similarity of such US to the subsequent conditioning US included in the CS-US pairing and could be removed by the interpolation of a distractor stimulus between the priming US and the CS-US pair. Finally, a similar decrement in conditioning was observed if a weak priming US was administered prior to the conditioning US but after the CS, that is, within the CS-US interval. The overall pattern of data supports Wagner's thesis that stimuli are rendered generally less effective when they are primed in short-term memory.

Effects of priming unconditioned stimulus representation in short-term memory on Pavlovian conditioning.

Effects of priming unconditioned stimulus representation in short-term memory on Pavlovian conditioning.

The effect of two ways of devaluing the unconditioned stimulus after first- and second-order appetitive conditioning.

Rats received first- and second-order conditioning based upon a food unconditioned stimulus (UCS). They then received one of two manipulations designed to reduce the value of that food, satiation, or pairing of food with high-speed rotation. The effects of these manipulations were assessed during extinction tests of the conditioned stimuli (CSs). Compared with controls, both manipulations reduced the activity produced by the first-order CS but did not affect that produced by a second-order CS. The results are interpreted as consistent with those from aversive UCSs in implying the involvement of a UCS representation in first- but not in second-order conditioning. They also suggest that a major effect of satiation is to reduce the value of the UCS.