Transfer of negative occasion setting and conditioned inhibition across conditioned and unconditioned stimuli

The transfer of negative occasion setting and conditioned inhibition across conditioned stimuli (CSs) and unconditioned stimuli (USs) was examined in four experiments that used Pavlovian appetitive feature negative discrimination training procedures with rats. After training with simultaneous compounds (A+, XA-), X inhibited conditioned responding (CRs) elicited by other CSs and CRs supported by other appetitive USs that had not been involved in discrimination training. After training with serial compounds (A+, X----A-), X's power to set the occasion for nonresponding transferred across CSs and USs only if those events had also been involved in serial feature negative discrimination training. The results supported the suggestion that the acquisition of negative occasion setting involves the representation of individual events in a higher order memory system, separate from that involved in simple association, and that negative occasion setters act only on events that are represented in that system.     

Motivational properties of conditioned suppression

Two experiments were performed to investigate the interaction of baseline appetitive drive and incentive on the conditioned suppression of instrumental behavior exhibited in the presence of a preaversive stimulus. In one experiment, suppression of lever pressing of rats working on an intermittent food reinforcement schedule was considerably enhanced following partial satiation with food. In a second experiment, using a similar baseline, suppression was shown to be diminished by an increase in concentration of the baseline incentive. These results are consistent with the hypothesis that the instrumental suppression of the conditioned emotional response (CER) is a consequence of an algebraic interaction of hunger with fear.     

Blocking between occasion setters and contextual stimuli

Two appetitive conditioning experiments with rats used a blocking procedure to compare the mechanisms through which contexts and positive occasion setters control responding to conditioned stimuli (CSs) in discrimination learning. In Experiment 1, a light (L) initially set the occasion for food reinforcement of a tone CS (T). Then a compound of L and a novel context signaled reinforcement of T. Previous learning about L blocked contextual control of responding to T. Blocking was not due to simple excitation conditioned to L during discrimination training; comparable excitation to L in a control group did not result in blocking. Conversely, in Experiment 2, initial learning about the context blocked the acquisition of occasion setting to L. Excitation conditioned to the context could not account for the blocking. In general, the results suggest that contexts and occasion setters may control responding to CSs through similar mechanisms.     

Effects of contextual conditioning and unconditional stimulus presentation on performance in appetitive conditioning

Four experiments with rat subjects examined the effects of contextual conditioning on conditioned appetitive performance. Experiment 1 compared the effects of contextual conditioning on performance to conditioned stimuli (CSs) with different conditioning histories. Contextual conditioning enhanced performance to the CS if the CS had first been conditioned and then extinguished, but had no effect on performance when the CS had been merely paired or unpaired with food. Experiments 2 and 3 then asked whether the effect on the extinguished CS was due to contextual conditioning acting as a cue for conditioning. In Experiment 2, extinction procedures in which extra unconditioned stimuli (USs) were presented during the intertrial intervals were found to reduce the CS's sensitivity to enhancement by contextual conditioning, but had no effect on spontaneous recovery. In Experiment 3, USs added to conditioning or extinction acquired the ability to cue the corresponding performance. Under some conditions, USs added to conditioning could suppress performance (Experiment 4). The results suggest that contextual conditioning has complex effects that can be better understood by recognizing that contextual conditioning, as well as the USs that create it,Mayacquire discriminative control over conditioned responding.     

Occasion-setting training renders stimuli more similar: Acquired equivalence between the targets of feature-positive discriminations

In two experiments rats received training on two concurrent appetitive feature-positive discriminations. A preliminary test in Experiment 1 confirmed previous demonstrations of the transfer of occasion-setting properties—the feature from one of these discriminations was better able to facilitate responding to the occasion-set target CS from the second discrimination than to a control stimulus that had not been the subject of occasion-setting. The source of this transfer was investigated in a second phase of training, and in Experiment 2. In both experiments one of the occasion-set CSs was paired with food, and generalization of appetitive conditioned responding from this stimulus to the second occasion-set CS, and to a control cue, was examined. There was more generalization from the first occasion-set CS to the second CS that had also been occasion-set than to the control cue. This is taken as evidence that occasion-set CSs are rendered more similar as a result of their common training history. The implications of these findings for explaining transfer of occasion setting are discussed.     

Temporal landmarks: proximity prevails

Subjects in conditioning experiments time their conditioned responses relative to the onsets of the conditioned stimuli (CSs). These onsets are temporal landmarks, by reference to which subjects may estimate the location of the unconditioned stimulus (US) in time. In a serial compound conditioning paradigm, a long duration CS comes on first, followed later by a second shorter CS, creating both a long-range and a short-range predictor of the US. We ask whether displacing the short-range predictor relative to the long-range predictor causes subjects to strike a compromise between the different temporal locations predicted by the two CSs. In three experiments with pigeons, we varied the training conditions so as to favor or militate against this outcome. However, in all conditions, there was no compromise; after the onset of the displaced short-range CS, the timing of conditioned responding was governed by it alone. This result contrasts with the compromises that are seen when the feeding time predicted by a CS is put in conflict with the time predicted by the circadian clock, and with the similar compromises sometimes seen when a nearby spatial landmark is displaced relative to a larger spatial context. Electronic Publication     

Combining CSs Associated with the Same or Different USs

In three experiments, hungry rats received appetitive training with four stimuli, A, B, X, and Y. In each Experiment, A and B were paired with one unconditioned stimulus (US; e.g. food pellets) whereas X and Y were paired with a second US (e.g. sucrose). Subsequently, rats responded more vigorously to combinations of stimuli associated with different USs (A-Y & X-B) than to combinations of stimuli associated with the same US (A-B &X-Y; Experiments 1, 2, & 3). This effect was observed when the stimuli were presented simultaneously and during the second elements of serial compounds (Experiments 2 & 3). Moreover, combining CSs associated with different USs resulted in a more marked CR than combining CSs that had each been paired with both US1 and US2 (Experiment 3). These results suggest that the sensory properties of appetitive reinforcers have an important influence on performance.     

Recent and Remote Extinction Cues Reduce Spontaneous Recovery

Five appetitive conditioning experiments with rats examined the ability of extinction cues (ECs) to reduce spontaneous recovery after extinction procedures that varied the temporal relation between the ECs and the conditioned stimulus (CS) and included presentations of additional events (e.g. other stimuli correlated with extinction, CSs, and the US). In extinction, two different ECs were presented either closely in time before (i.e. recent to), or more distant (i.e. remote) from a nonreinforced CS. Both recent and remote ECs reduced spontaneous recovery to the CS when present during testing (Experiments 1-4). Each EC reduced recovery despite the addition during extinction of a second EC and CS (Experiments 1, 3, and 4), and the US (Experiment 3). Experiments 4 and 5 investigated the recent and remote ECs' tendency to control a serial occasion setting discrimination involving the target CS under explicit training conditions. Neither EC gained such discriminative control. Possible explanations of the results are discussed, including configural learning, occasion setting, and contextual cue control.     

Backward conditioning as an extinction procedure

In two conditioned suppression experiments, rats received Pavlovian forward defense conditioning in which tonal conditioned stimuli (CSs) terminated with the onset of scrambled grid shock unconditioned stimuli (USs). After this experience, the rats then received a Pavlovian backward conditioning procedure in which the same USs now terminated with the onset of the same CSs. Although the two experiments differed greatly in terms of CS and US parameters, number of forward and backward pairings, and in terms of the general techniques used to establish and measure the Pavlovian conditioned response (CR), the results of both experiments agreed in showing that backward conditioning can indeed weaken a CR based on forward pairings. The results also show that, under some conditions, the backward procedure can be at least as effective in weakening an established CR as the traditional CS-alone extinction procedure; but, under other conditions, the backward procedure is less effective and leads to more spontaneous recovery than the CS-alone procedure.     

Reversal learning as a function of changed reward location or changed drive

In two experiments, rats were trained with food in one location (e.g., black alley) and water in another location (white alley) under hunger or thirst. Subsequently, either the locations of the rewards were reversed, or the drive was changed (from hunger to thirst or thirst to hunger). Reversal of instrumental responses took considerably longer when drive was changed and rewards remained in the same locations than when reward locations were reversed. These results were interpreted as indicating that the animal's internal representations of the rewards received in each location transfer when drive is changed. These internal-reward representations interfere with reversal learning by eliciting the responses which were conditioned to them in Phase 1. Because the values of food and water reverse when drive is changed from hunger to thirst or vice versa, it was suggested that the reward representations surviving the drive shift are cognitive representations of the specific events received (food or water), independent of the value of the rewards under either hunger or thirst.     

Contextual control over conditioned responding in an extinction paradigm

Four experiments studied contextual control over rats' freezing to conditioned stimuli (CSs) that had been paired with shock and were then extinguished. In Experiment 1, rats were exposed to a CS A-shock and a CS B-shock pairing in Context C. CS A was then extinguished in Context A, and CS B in Context B. Freezing was renewed when each CS was presented in the context where the other CS had been extinguished. In Experiments 2-4, rats were exposed to a CS A-shock pairing in A and a CS B-shock pairing in B. They were then exposed to Context C where one, both, or neither of the CSs were extinguished, or where both CSs continued to be reinforced. On test, the rats froze more to CS A than to CS B in Context A, and more to CS B than to CS A in Context B, but only if the CSs had been extinguished. Thus, after extinction, rats use contexts to regulate retrieval not only of their memory for extinction, but also of their memory for the original conditioning episode.     

Effect of signaling intertrial unconditioned stimuli in autoshaping

Context-unconditioned-stimulus (US) associations have been suggested as the mediator of the response decrement that occurs when extra USs are added to the intertrial intervals (ITIs) of an otherwise standard Pavlovian conditioning situation. The present autoshaping experiments were concerned with the effect of signaling those extra USs, since such signaling might be expected to lessen their ability to condition the context. Experiments 1 and 2 showed that signaling the ITI USs did reduce their detrimental effects on responding to the conditioned stimulus (CS). To determine whether that reduction was due to an impact of signaling on the target-CS-US association or on performance to the target-CS, Experiment 3 examined responding to differentially trained CSs in a common context, as well as responding to identically trained CSs in differentially trained contexts. Whether the CS was tested in a context of relatively high or low associative strength, more responding occurred to the CS trained with signaled, as compared with unsignaled, ITI USs; further, there was more responding to that CS in the more highly valued context. The pattern of results suggests that contextual value does interact with CS-US learning and may also affect performance to the CS.     

Context Specificity of Excitation and Inhibition in Ambiguous Stimuli

Two experiments examined the susceptibility of excitation and inhibition to contextual change when the conditioned stimulus (CS) was ambiguous using an appetitive conditioning paradigm. In Experiment 1, excitation to a CS was lost with a context switch when inhibition had been learned to the CS in a prior feature-negative (FN) discrimination. Control groups that had received either more or less excitatory conditioning in the absence of inhibitory pretraining showed no loss. In Experiment 2 inhibition was lost with a context switch in a group that had received excitatory and then inhibitory conditioning with the CS. No loss was observed in a group that had not received excitatory pretraining. The results suggest that contexts are especially likely to control performance to ambiguous CSs when they can modulate the second of two learned associations. Results are discussed in terms of their implications for occasion setting and modern conditioning theory.     

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.     

Effect of unconditioned stimulus magnitude on the emergence of conditioned responding

Although unconditioned stimulus (US) magnitude influences conditioning, no experiment has addressed whether it influences a decision point at which the organism first responds (Gallistel & Gibbon, 2000). Two appetitive conditioning experiments with rats confirmed that the rate of food cup entries and proportion of head jerking were related to the number of pellets (US) provided after the conditioned stimulus. In addition, the onset of responding measured by the number of reinforcers to a criterion or by a quantitatively identified change point also reflected US magnitude. Two aversive conditioning experiments also found that the amount and onset of freezing were related to footshock intensity. All experiments identified a trial at which responding increased abruptly in individual subjects. However, the point where the increase occurred was earlier with larger USs.     

Aware and (dis)liking: item-based analyses reveal that valence acquisition via evaluative conditioning emerges only when there is contingency awareness

Evaluative conditioning (EC) refers to changes in the liking of an affectively neutral stimulus (the conditioned stimulus, or CS) following the pairing of that stimulus with another stimulus of affective value (the unconditioned stimulus, or US). In 3 experiments, the authors assessed contingency awareness, that is, awareness of the CS-US associations, by relying on participants' responses to individual items rather than using a global method of assessment. They found that EC emerged on contingency aware CSs only. Of note, whether the CSs were evaluated explicitly (Experiments 1 and 2) or implicitly (Experiment 3) did not make a difference. This pattern supports the idea that awareness of the CS-US associations may be required for valence acquisition via EC.     

Acquisition of superexcitatory properties by an irrelevant background stimulus

Six appetitive conditioning experiments with rats demonstrated that an irrelevant X accompanying a negative patterning discrimination (XA+, XB+, XAB-) acquires extraordinarily high levels of conditioned excitation. Responding to X was similar to that evoked by 2 excitors in combination (Experiment 1) and was greater than responding to a separately reinforced Y (Experiments 2-5). Superexcitatory properties were not acquired by X in the nonpatterning discriminations of Experiments 2-4. Experiment 5 found that A and B, if anything, were weakly excitatory. Making them more strongly excitatory after conditioning did not interfere with retention of the original discrimination (Experiment 6). Results support a counterintuitive prediction of associative theories that, under carefully arranged conditions, irrelevant stimuli may acquire superexcitatory properties.     

Role of conditioned contextual stimuli in reinstatement of extinguished fear

If the unconditioned stimulus (US) is presented independently of the conditioned stimulus (CS) following extinction, the conditioned response may be reinstated to the CS. Three experiments are reported that suggest that reinstatement is mediated by conditioning to contextual stimuli that are present during both US presentation and testing. Shocks presented to rats following the extinction of conditioned suppression reliably reinstated suppression to the CS, but only when they were presented in the context in which testing was later to occur. Reinstatement was also reversed by extinguishing fear to the context through nonreinforced exposure to the context between shock presentation and testing. Reinstatement was obtained in these experiments in spite of procedures that have been used in the past to minimize the influence of context conditioning. Moreover, fear of the context was never detected directly by depressed bar-press rates in the absence of the CS. The results do not support the hypothesis that reinstatement results from an increment in the strength of a memory of the US that has been weakened during extinction. Problems inherent in controlling and detecting levels of context conditioning that may influence behavior toward nominal CSs are discussed.     

Enhancement of food-rewarded instrumental responding by an appetitive conditioned stimulus

Four experiments are reported in which a stimulus (with a minimum duration of 60 s) signalling the delivery of “free” food was presented to rats lever-pressing for food available on a variable interval schedule. It was found that responding was enhanced in the presence of the stimulus when the baseline schedule of reinforcement was lean (Experiment I) and that the enhancement was dependent upon the pairing of the stimulus with free food (Experiments II and III). Experiment IV showed that an enhancement could be found after initial training in which stimulus-food pairings were given to subjects that were not concurrently lever pressing for food. It is argued that these results are consistent with the suggestion that an appetitive conditioned stimulus can energise appetitive instrumental behaviour.     

Contextual control of inhibition with reinforcement: adaptation and timing mechanisms

Four experiments with rats studied the effects of switching the context after Pavlovian conditioning. In three conditioned suppression experiments, a large number of conditioning trials created "inhibition with reinforcement" (IWR), in which fear of the conditional stimulus (CS) reached a maximum and then declined despite continued CS-unconditional stimulus pairings. When IWR occurred, a context switch augmented fear of the CS; IWR and augmentation were highly correlated. Neither IWR nor augmentation resulted from inhibition of delay (IOD): In conditioned suppression, IWR and augmentation occurred without IOD (Experiment 3), and in appetitive conditioning (Experiment 4), IOD occurred without IWR or augmentation. IWR may occur in conditioned suppression because the animal adapts to fear of the CS in a context-specific manner. The authors discuss several implications.