A feature positive effect in conditioned suppression

A conditioned suppression experiment with rats studied the development of two discriminations involving two conditioned stimuli, A and X. In one discrimination (AX+/A?), compound presentations of A and X signaled shock and presentations of A alone signaled no-shock. In the other discrimination (A+/AX?), A alone signaled shock and AX signaled no-shock. AX+/A? discriminations were learned more rapidly than their A+/AX? counterparts. These results, which resemble the feature-positive effect of Jenkins and Sainsbury (1969, 1970), are discussed in terms of Rescorla and Wagner’s (1972) theory of conditioning and also in terms of stimulus intensity mechanisms.     

Pavlovian conditioning to contexts that precede the place where shock occurs as measured by freezing and activity suppression in mice

Three experiments were conducted to demonstrate that the place where an organism has been, before the organism is moved to a place with aversive consequences, can also become aversive through classical conditioning. In Experiment 1, two groups of 8 mice were exposed to three different contexts in succession, with a single shock occurring in the third context. The distal context was a putative 3-min conditioned stimulus (CS) for freezing; the second context was a delay manipulation; and the unconditioned stimulus (US) occurred in the proximal context. The group delayed for 15 sec showed significantly more freezing to the distal CS context than did the group delayed for 3 h. In a second experiment, conditioning to the distal context was demonstrated with a discrimination procedure for 8 more mice by using two different distal contexts as CS+ and CS? for the proximal context with shock. On CS+ days, 3 min of exposure to the distal context was followed within 5 sec by placement in the proximal box where shock occurred, whereas on CS? days, exposure to a second distal context was followed immediately by return to the home cage. Very strong differences in freezing between the CS+ and CS? distal contexts were found in all 8 mice after 14 days of conditioning. In a third experiment, the discriminative procedure was repeated for 9 more mice, with two changes. More objective stabilometertype activity measures were substituted for observed freezing, and, in addition to the CS+ and CS? distal context trials, each mouse was also exposed to a third discriminative distal context, which was followed by 15 min in a delay chamber followed by shock in the proximal context. This discrimination procedure with the activity suppression measure again resulted in significant differences between the contexts. The CS+ context and the context followed by a 15-min delay did not differ, but both of them differed from the CS? context.     

Blocking and enhancement of fear conditioning by appetitive CSs

Prior research on Pavlovian-to-instrumental transfer has shown that when a CS previously associated with shock (AvCS+) is presented contingent upon a choice response to a discriminative stimulus for food reinforcement, it facilitates discrimination learning. Conversely, a response-contingent CS previously associated with the absence of shock (AvCS?) retards discrimination learning. To evaluate whether these findings reflect across-reinforcement blocking and enhancement effects, two experiments investigated the effects of appetitively conditioned stimuli on fear conditioning to a novel stimulus that was serially compounded with the appetitive CS during conditioned-emotional-response (CER) training. Although there were no differential effects of the appetitive CSs in CER acquisition, Experiment 1, using a relatively weak shock US, showed that a CS previously associated with food (ApCS+) retarded CER extinction to the novel stimulus, in evidence of enhanced fear conditioning to that stimulus. In addition, Experiment 2, using a stronger shock US, showed that a CS previously associated with the absence of food (ApCS?) facilitated CER extinction to the novel stimulus, in evidence of weaker fear conditioning to that stimulus. These results parallel traditional blocking effects and indicate not only that an ApCS+ and an ApCS? are functionally similar to AvCSs of opposite sign, but that their functional similarity is mediated by common central emotional states.     

Conditioned fear assessed by freezing and by the suppression of three different baselines

Rats received either forward or backward pairings of an auditory CS and shock. They were then tested for conditioned suppression to the CS while barpressing for food, licking a sucrose solution, or being spontaneously active. Behavior was simultaneously observed using a time-sampling method. In each case, forward-conditioned animals exhibited more freezing than controls, and freezing was reliably correlated with suppression of the baseline. These results suggest that the different loss-of-baseline measures of aversive conditioning reflect the amount of defensive behavior evoked by the CS. They also suggest the utility of freezing as an index of conditioning. Freezing assayed by the time-sampling method was comparable to the more conventional indices of conditioning in sensitivity to the effects of conditioning.     

Acquisition and extinction of differential responses to signals paired with shock or shock omission in goldfish: Evidence for truly discriminated avoidance learning

Goldfish trained to discriminate between signals paired with shock (S?) and signals paired with shock omission (S+) with a linear presentation procedure, originally learned (OL) to control the signal state of a shuttle box and showed a decided preference for the S+ signal. In Experiment 1, following OL, groups had one OL signal replaced (S+ or S?), both signals replaced (S+ and S?), or the OL signals reversed (S+ and S? reversed) and were then tested in a transfer training procedure. In transfer, groups with one signal replaced maintained discriminated performance at OL levels; the S+ replaced group was slightly superior to the S? replaced group on the first day of transfer. With both OL signals replaced, discrimination dropped to chance performance levels, whereas, with OL signal shock pairing reversed, discrimination performance dropped below chance levels. In Experiment 2, following OL, extinction procedures consisted of turning off the shocker (0% shock) or of shocking 100% or a random 25% of the trials. A fourth extinction procedure (R,) retained the trial start response-dependent shock-omission contingency, but shock differentiating the S+ and S? signals was eliminated entirely. Extinction of the S+/S? discrimination was measured both during extinction training per se and with reversal retraining of the S+/S? discrimination later. Groups for which the OL S+ was paired with shock during extinction extinguished on both measures, but groups for which the OL S? was paired with shock omission did not extinguish, especially as shown by the reversal test procedure. Theoretical implications and the implications for several conditioning procedures are discussed.     

A test of two methods for extinguishing Pavlovian conditioned inhibition

Two experiments were performed using rats in a conditioned suppression procedure to test two different methods for extinguishing Pavlovian conditioned inhibition. In both experiments, a target stimulus, X, was made inhibitory by giving discrimination training of the form A+ AX?. Then, in Experiment 1, an attempt was made to extinguish the inhibition conditioned to X by presenting nonreinforced occurrences of X, of AX, and of A. Testing for conditioned inhibition took the form B+ BX?. It was found that the extinction procedure did not weaken the inhibitory properties of X. Experiment 2 attempted to extinguish the inhibition conditioned to X by presenting X randomly and independently of the reinforcer, electric grid shock. This procedure appeared to weaken inhibition quickly and permanently.     

Recovery from conditioned suppression to a partially overlapping compound stimulus

In a conditioned suppression paradigm, a partially overlapping compound stimulus signaled occurrences of electric shock. That compound CS consisted of 3 min of continuous illumination of the houselight with three discrete 5-see presentations of a tone superimposed. A .5-sec electric shock was coterminous with each tone presentation. Rats that received this treatment in early conditioning sessions showed considerable recovery from conditioned suppression to the houselight as the experiment progressed. However, the effect was not reversible, and it could not be demonstrated in rats that experienced extensive prior conditioning to the houselight alone. These results are discussed in relation to a hypothesis concerning the modulation of behavioral control exerted by elements of compound stimuli and as they relate to a recent theoretical model for Pavlovian fear conditioning.     

Blocking with serial and simultaneous compounds in a trace conditioning procedure

Blocking of conditioned suppression in rats was studied in three experiments using serial and simultaneous compounds in Pavlovian trace conditioning procedures. Experimental groups were first given trace conditioning trials with a 2-sec stimulus (A) presented at least 60 sec before an electric grid shock US. Next, both experimental and control groups received reinforced trials with a compound stimulus (AB). Both A and B were 2 sec in duration and were presented at least 60 sec before the US. For some groups during AB training, the A stimulus preceded the B stimulus; for others, B preceded A; for still others, A and B occurred simultaneously. Conditioning was subsequently assessed separately to both A and B. The results were as follows: First, varying the interval between the onset of A and the US during A training appeared to produce significantly different levels of conditioning to A but did not detectably affect A’s ability to block conditioning to B. Second, blocking was observed in both simultaneous and serial procedures. Third, in the serial procedure, A blocked conditioning to B whether it preceded B or followed B in the AB compound. Fourth, in tests given after AB conditioning, the experimental and control groups suppressed similarly to A. The relevance of these results to the conditioning model of Rescorla and Wagner (1972) and to Mackintosh’s (1975b) theory of attention are discussed.     

Summation of undetected excitation following extinction of the CER

The effects of compounding two conditioned stimuli (CSs), each of which had been extinguished to varying degrees in different groups of rats given identical acquisition training, was examined within the conditioned emotional response paradigm. Greater suppression to the compound than to the individual CSs was observed following 6, 12, 48, 72, and 96 stimulus extinction trials, although after only 12 extinction trials suppression to the individual stimuli was no longer observed. The amount of compound suppression decreased progressively as the number of extinction trials increased until, after 120 extinction trials on each stimulus, the compound no longer elicited observable suppression. Control group data indicated that the observed summation effect could not be attributed to disinhibition. The possible role of the summation of undetected excitation in studies examining configurai conditioning, avoidance conditioning and reinstatement is discussed briefly.     

Effect of odor preexposure on acquisition of an odor discrimination in dogs

In two experiments, we investigated the impact of odor preexposure treatments on the acquisition of an olfactory discrimination in dogs. In the first experiment, four groups of dogs were each given five days’ odor-exposure treatment prior to discrimination training. Dogs in the exposure group were exposed to anise extract (S+) for 30 min daily. Dogs in the Pavlovian-relevant pairing group received six daily delayed-conditioning trials to the same S+. The Pavlovian-irrelevant pairing group received conditioning trials to almond extract (S'). Dogs in the control group received no pretreatment. All of the dogs were then trained to detect S+ from a background pine odor (an AX-vs.-X discrimination). The Pavlovian-relevant pairing group acquired the odor discrimination significantly faster than all of the other exposure and control groups, and the remaining groups acquired the discrimination at the same rate as the no-exposure control group. In a second experiment, we extended these results to a within-subjects design using an AX-versus-BX discrimination. Six dogs were simultaneously trained on two different odor discriminations, one discrimination in which the S+ was previously Pavlovian conditioned, and one discrimination in which the S+ was novel. All of the dogs learned the odor discrimination with the previously conditioned S+ faster than they learned the novel odor discrimination, replicating the results of Experiment 1, and demonstrating that familiarity in the form of Pavlovian conditioning enhances odor-discrimination training. The potential mechanisms of the facilitated transfer of a Pavlovian conditioned stimulus to discrimination training are discussed.     

Effects of CS preexposure on inhibition of delay

Two experiments examined the effects of preexposure to a stimulus on the subsequent acquisition of conditioned suppression by rats. Variations in the level of suppression within conditioning trials were noted so thatinhibition of delay (taken here to mean less suppression at the beginning of a trial than at the end) could be detected. Inhibition of delay was observed both during the acquisition of suppression and (in Experiment 1) when suppression began to wane with continued postasymptotic training. Preexposure to the to-be-conditioned stimulus retarded acquisition of suppression and slowed the appearance of inhibition of delay both in acquisition and (in Experiment 1) in postasymptotic performance. Experiment 2 demonstrated that inhibition of delay was attenuated during conditioning that followed preexposure in which the stimulus was paired with a weak reinforcer. These results provide no support for the suggestion that preexposure to a stimulus retards later conditioning because it allows the subject to acquire information about stimulus duration that in turn fosters the development of inhibition of delay. Rather, they are compatible with the suggestion that preexposure causes the stimulus to lose associability.     

Higher order occasion setting

Higher order occasion setting with serially presented stimuli was investigated in an appetitively motivated, discrete-trial operant study with rats. Reinforcement of barpressing during an occasion-setting light (a discriminative stimulus) was contingent on immediately preceding second-order occasion setters (i.e., a click train or a buzzer served as a conditional discriminative stimulus). Moreover, the meanings of the clicks and buzzer were themselves indicated by a third-order occasion setter that preceded them (i.e., a white noise acted as a second-order conditional discriminative stimulus). Subjects responded more frequently and had shorter latencies to the first response in the presence of the light on trials during which barpressing was reinforced than on trials during which barpressing was not reinforced. The likelihood that the subjects solved the problem by responding to unique compound stimuli was minimized by the insertion of a 5-sec gap between the different controlling stimuli presented on each trial. Thus, these subjects appear to have mastered a second-order conditional discrimination, which is equivalent to third-order occasion setting if the discriminative stimulus (light) is viewed as a first-order occasion setter. Although the subjects learned to respond appropriately to each of the compound stimuli, differences in responding to specific stimuli were consistent with a higher order feature-positive effect. Some implications of higher order occasion setting are discussed, including the issue of independence between the different levels of occasion setting signaled by a single stimulus.     

Latent inhibition in honeybees

Aversive conditioning was studied in individual honeybees flying back and forth between the hive and the sill of an open laboratory window, where they took sucrose solution from a target so constructed that shock could be delivered while the proboscis was in contact with the solution. During feeding, a conditioned stimulus—substrate vibration or airstream—was paired with brief shock avoidable by interruption of feeding. In Experiment 1, unreinforced preexposure of the conditioned stimulus was found to retard acquisition (latent inhibition). In Experiment 2, which was designed to inquire into the stimulus specificity of the effect, differential conditioning was found to be impaired by unreinforced preexposure of the positive stimulus and facilitated by unreinforced preexposure of the negative stimulus. In Experiment 3, a summation experiment designed to test various alternative explanations of the effect, a preexposed stimulus was found to suppress response to an excitatory conditioned stimulus when the two stimuli were presented together.     

Surprise and blocking: Effects of the number of compound trials

In an experiment on conditioned suppression of licking in thirsty rats, subjects received either one or two trials to a tone-light compound, either preceded or not preceded by four conditioning trials to the light alone. Prior conditioning to the light blocked conditioning to the tone in subjects receiving two compound trials but not in those receiving only one compound trial. The blocking observed in the two-trial groups was abolished either by the addition of an unexpected second posttrial shock 10 sec after the first on each compound trial or by the omission of an expected second, posttrial shock. The comparable operations had no effect on conditioning to the tone in the one-trial group. In this preparation, both blocking and the attenuation of blocking by surprising changes in reinforcement appear to require more than one trial to appear.     

Nonassociative habituation,US preexposure,and backward inhibitory conditioning with signaled and unsignaled USs

In a conditioned suppression experiment, rats received a single, massed session of conditioning in which one backward conditioned inhibitory stimulus (CS-) followed shocks that were signaled by a visual cue, and a second backward CS-followed shocks that were unsignaled. Conditioning was preceded by a preexposure phase in which some groups of rats were preexposed to unsignaled shock, while others were not preexposed and remained in the experimental apparatus in the absence of shock. The groups were further distinguished by whether US preexposure and conditioning occurred in the same or different contexts, and by whether conditioning began immediately or after a 24-h rest period in the home cage. Although the conditioning itself was effective in establishing the visual cue as a conditioned excitor in the nonpreexposed groups, it was not effective in establishing the two backward cues as reliable inhibitors with either signaled or unsignaled USs. After 210 US preexposures, however, the same conditioning sessions did yield conditioned inhibition to both CS-s. A 24-h rest period in the home cage reduced the magnitude of, but did not completely abolish, the facilitative effect of US preexposure on inhibitory conditioning. Other tests demonstrated that US preexposure had retarded excitatory conditioning to the visual cue. This interference with excitatory conditioning was unchanged in magnitude after the 24-h rest period. The facilitative effect of US preexposure on backward inhibitory conditioning, and the interference effect on excitatory conditioning, were both eliminated by a change in context between US preexposure and conditioning. These observations encourage predominantly associative accounts of the effects, but allow for a small nonassociative habituation component.     

Transfer testing after serial feature-ambiguous discrimination in Pavlovian keypeck conditioning

Four experiments were performed to explore modulatory transfer after serial feature-ambiguous (F-A) discrimination (X→A+, A?, X→B?, B+) in Pavlovian keypeck conditioning (autoshaping) with pigeons. Diffuse features were used in the first three experiments, and no modulatory transfer was found: (1) There was no modulatory transfer between two concurrently trained F-A tasks; (2) modulatory transfer to conditioned and then extinguished stimuli was not observed; and (3) responding to the targets (A and B) after their contingencies were reversed was not affected by presentation of their original feature stimulus (X). Transfer between two serial F-A tasks was obtained in the last experiment, in which keylights were used as features, but other evidence indicated that this was due to stimulus generalization between the features. Together, the results strongly suggest that specific target-food occasion setting or configural learning is the underlying mechanism of F-A discrimination.     

Bidirectional heart rate responses in rats associated with excitatory and inhibitory stimuli

Following classical conditioning to a shock-reinforced tone CS (T₁+), heart rate (HR) of three groups of rats was examined in response to a new reinforced tone (T₂+) and a nonreinforced light (L?) CS given during conditioned inhibition (T₂+ vs. T₁L?), discrimination conditioning (T₂+ vs. L?), or explicitly unpaired (T₂/L? vs. US alone) procedures. Decelerative HR reactions occurred to the reinforced T₂+ and T₂+ CSs. To the respective nonreinforced CSs, the conditioned inhibition group displayed diminished but sizable HR deceleration, the discrimination group showed near-zero responding, and the explicitly upaired group showed HR acceleration. Subsequent reversal conditioning to L was retarded in the conditioned inhibition and explicitly unpaired groups relative to the discrimination group. Group differences on combined-cue [T₂/L?) trials were not found. Both the HR responses during inhibitory training and the reversal-conditioning impairments suggest that inhibition may have been established to L? in the conditioned inhibition and explicitly unpaired groups.     

Positive and negative transfer of conditioned aversive stimuli to a conditioned appetitive excitor as a function of aversive US intensity

Rats were given Pavlovian aversive (Av) conditioning in which a weak (0.5-sec, 0.7-mA) or a strong (0.5-sec, 1.4-mA) footshock unconditioned stimulus (US) was presented alone or in a positive, zero, or negative correlation with a flashing-light conditioned stimulus (AvCS+, AvCSo, or AvCS?, respectively). Thereafter, the subjects received Pavlovian appetitive (Ap) conditioning in which the flashing-light CS was positively correlated in a forward order with the delivery of a food US. As anticipated, for subjects that had been trained with the strong shock US, the AvCS+ retarded and the AvCS? facilitated Ap conditioning relative to both the AvCSo and the novel-CS treatments, which did not differ in effect. However, the exact opposite prevailed for the AvCS+ and AvCS? subjects that had been trained with the weak shock US. On the basis of these and other data, we propose an “ABC” model of transfer that stresses the importance of affective, behavioral, and cognitive factors in accounting for the divergent results that are obtained in both Av-to-Ap and Ap-to-Av transfer paradigms.     

One-trial simultaneous and backward fear conditioning as reflected in conditioned suppression of licking in rats

In three experiments, groups of albino rats received one strictly simultaneous pairing of a 4-sec auditory conditioned stimulus (CS) and a 4-sec 1-mA shock unconditioned stimulus (US). Other groups received a backward pairing, in which the US began before the CS, or a forward pairing, in which the CS began before the US. Control groups received only the US or received both the CS and the US but widely separated in time. Later, the CS was presented while the rats licked a drinking tube for water, and CS-elicited suppression of licking was taken as an index of the Pavlovian conditioned response (CR). It was found that groups receiving a single forward or a single simultaneous pairing suppressed more than groups that had received a backward pairing; and the backward groups, in turn, suppressed more than the control groups. It appears, then, that excitatory fear conditioning, as reflected in conditioned suppression of licking in rats, can be produced in a single trial by both backward and simultaneous conditioning procedures.     

Stimulus competition in the absence of compound conditioning

Most associative theories have assumed that stimulus competition occurs only between conditioned stimuli (CSs) that are trained in compound. The present research investigated the possibility of competition between two CSs that were individually paired to the same unconditioned stimulus (US). We used human subjects in an anticipatory suppression analogue to Pavlovian conditioning. Experiment 1 showed that X+ training followed by A+ training resulted in impaired responding to X. This did not occur when A+ training preceded X+ training. Experiment 2 replicated the basic effect and showed that it did not occur when the Phase 2 training consisted of A? instead of A+ nor when the A+ pairings occurred in a second context. Experiment 3 showed that A+ pairings occurring in a second context could still produce the effect when X was tested in the context in which the A+ pairings had occurred, but not when X was tested in a context different from that used for A+ training. Collectively, these results suggest that individually trained CSs may compete with each other when one of those CSs is more strongly activated by the test context than the other one.