US inflation with trace and simultaneous fear conditioning

Two experiments with rat subjects in a conditioned punishment paradigm are reported. These experiments attempted to determine if the events entering into association with the CS following conditioning with informative (forward) and noninformative (simultaneous) CSs were comparable. In Experiment 1, exposure to intense shock alone following trace (ISI = 10 sec) conditioning with moderate shock enhanced the suppressive effects of a 2-sec CS. A similar manipulation following explicitly unpaired CS-US presentations (ISI = 2 min) had no effect. These data were taken as evidence that the CS and US were associated during trace conditioning. Experiment 2 showed that exposure to intense shock following simultaneous conditioning also enhanced suppression to the CS. These results suggested that simultaneous and forward conditioning procedures yield similar forms of associative learning.     

Differential trace conditioning to temporal compounds

Rats were reinforced for responding following the presentation of a light-tone temporal compound, each component having a .5-sec duration separated by a .5-sec empty interval. For different groups, nonreinforced presentations of the compound in the reverse order and either or both of the components separately were included in each session. Results indicated a progressive increase in difficulty as the number of nonreinforced events increased, with behavior being strongly affected by the first component of the compound. Nevertheless, differential performance under the most demanding conditions demonstrate the rat’s ability to acquire a temporal compound discrimination, which suggests an interpretation based on interacting stimulus traces.     

Contextual associations in trace conditioning

Rats were given tone-footshock pairings with a 0-, 10-, or 30-sec trace interval between tone offset and shock onset. Half the rats within each trace interval were tested for their conditioned fear of the tone through a lick suppression procedure; the remaining rats were evaluated for their fear of the background or contextual cues through their avoidance of the compartment in which conditioning had occurred. Less conditioning was observed to the tone with increasing trace intervals. However, conditioned fear of the context increased with increases in the trace duration. The ability of the more predictive stimulus, the tone, to overshadow the contextual cues was determined by the tone’s temporal contiguity with the footshock. The need to incorporate temporal parameters within current theories of conditioning is discussed.     

Temporal encoding in trace conditioning

Conditioned lick suppression in rats was used to explore the role of timing in trace conditioning. In Experiment 1, two groups of rats were exposed to pairings of a CS (CS1) with a US, under conditions in which the interstimulus interval (ISI) that separated CS1 offset and US onset was either 0 or 5 sec. Two additional groups were also exposed to the same CS1→US pairings with either a 0 or a 5-sec ISI, and then received “backward” second-order conditioning in which CS1 was immediately followed by a novel CS2 (i.e., CS1→CS2). A trace conditioning deficit was observed in that the CS1 conditioned with the 5-sec gap supported less excitatory responding than the CS1 conditioned with the 0-sec gap. However, CS2 elicited more conditioned responding in the group trained with the 5-sec CS1-US gap than in the group trained with the 0-sec CS1-US gap. Thus, the CS1-US interval had inverse effects on first- and second-order conditioned responding. Experiment 2 was conducted as a sensory preconditioning analogue to Experiment 1. In Experiment 2, rats received the CS1?CS2 pairings prior to the CS1→US pairings (in which CS1 was again conditioned with either a 0 or a 5-sec ISI). Experiment 2 showed a dissociation between first- and second-order conditioned responding similar to that observed in Experiment 1. These outcomes are not compatible with the view that differences in responding to CSs conditioned with different ISIs are mediated exclusively by differences in associative value. The results are discussed in the framework of the temporal coding hypothesis, according to which temporal relationships between events are encoded in elementary associations.     

Conditioning of simultaneous and serial feature-positive discriminations

Three experiments with rat subjects examined the development of simultaneous and serial feature-positive discriminations in appetitive conditioning. In Experiment 1, reinforced presentations of a simultaneous light-tone compound were intermixed with nonreinforced presentations of either the light or the tone. The compound stimulus acquired conditioned behaviors of a form characteristic of the predictive feature alone; the element common to reinforced and nonreinforced trials did not evoke conditioned behavior. In Experiment 2, reinforced presentations of a serial light-trace-tone compound were intermixed with nonreinforced tone-alone presentations. The light feature stimulus acquired conditioned behaviors characteristic of visual CSs. The tone stimulus, common to reinforced and nonreinforced trials, evoked conditioned behaviors characteristic of auditory CSs, but only when preceded by the light. In Experiment 3, variations in the interval between the light and tone on reinforced trials had little effect on responding to the light CS but substantially altered the pattern of responding to the tone CS. These results suggested that simultaneous and serial feature-positive discriminations may be solved differently. Performance in simultaneous feature-positive discriminations may be determined solely by associations between the feature stimulus and the reinforcer, but performance in serial discriminations may also involve the acquisition of a conditional cue function to the feature.     

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.     

Contextual effects in latent inhibition with an appetitive conditioning procedure

In three experiments, rats received presentations of a diffuse 30-sec stimulus (a light) and of food, and their tendency to enter the food tray was monitored. Experiment 1 showed that when the light was made to signal the delivery of food, the response of entering the food tray increased in frequency during the stimulus. The acquisition of this conditioned response to the light was retarded in subjects that had received preexposure to the stimulus. In Experiments 2 and 3, subjects received preexposure to the stimulus, some in the same context as that subsequently used for stimulus-food pairings and some in a different context. Those experiencing the change of context acquired the response more readily. It is argued that these results demonstrate a latent inhibition effect that is attenuated by contextual change.     

Extinction and retraining of simultaneous and successive flavor conditioning

In three experiments, rats received pairings of flavor conditioned stimuli with polycose unconditioned stimuli, in either a simultaneous or a sequential relation. Both temporal relations produced excellent conditioned increases in consumption of the flavors. Separate presentation of the flavors resulted in extinction in both cases. However, restoring the pairing of the flavor with polycose resulted in reconditioning only with the sequential, not with the simultaneous, relation.     

Temporal coding affects transfer of serial and simultaneous inhibitors

In three experiments with rats, the temporal relationships under which a conditioned inhibitor would transfer its inhibitory potential to an independently trained excitor in a summation test were investigated. Each experiment varied the temporal relationship between the inhibitor and the transfer excitor at test (serial or simultaneous) and, in addition, manipulated either the inhibitor-training excitor (serial or simultaneous), training excitor-unconditioned stimulus (US) (trace or delay), or the transfer excitor-US (trace or delay) temporal relationships. Conditioned inhibition was found only when the no-US expectation evoked by the conditioned inhibitor was temporally aligned with the US expectation evoked by the transfer excitor, independent of whether the inhibitor was trained as a serial or simultaneous signal for US omission. Results are discussed in terms of the temporal coding hypothesis and the comparator hypothesis.     

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.     

Compound conditioning in honeybees: Blocking tests of the independence assumption

Six experiments with color-odor compounds failed to produce convincing evidence of blocking in honeybees even when the possibility of masking by within-compound association could be discounted. The parsimonious assumption that the components of a compound stimulus gain and lose associative strength independently with reinforcement and nonreinforcement of the compounds (which the experiments were designed to challenge) remains tenable for color-odor compounds, although perhaps not for intramodal compounds.     

Posttraining flavor exposure in hungry rats after simultaneous conditioning with a nutrient converts the CS into a conditioned inhibitor

The present study investigated the decrement in nutrient-based conditioned flavor preference found in hungry rats exposed to a flavor following simultaneous flavor–sucrose conditioning while thirsty. Although a significant decrease in preference was found in the experimental group in each experiment, there was no evidence of either spontaneous recovery (Experiment 1) or reinstatement (Experiment 2). In addition, posttraining flavor exposure weakened the original flavor–sucrose association (Experiment 3). These results suggested that the flavor–US association might have been impaired after posttraining flavor exposure. Two further experiments assessed whether the flavor acquired the properties of a net inhibitor, using the retardation and summation tests for conditioned inhibition. Experiment 4 revealed that the flavor suffered retardation when retraining was conducted after the exposure phase. In Experiment 5, the target flavor decreased the preference shown for a different flavor previously paired simultaneously with sucrose when both were presented forming an unreinforced compound in the summation tests. None of these effects was found in a control group, which had received serial flavor → nutrient presentations during training. Together, these results suggest that a flavor simultaneously paired with sucrose acquires the properties of a net inhibitor when it is subsequently presented outside the compound to hungry animals.     

One-trial simultaneous and backward excitatory fear conditioning in rats: Lick suppression, freezing, and rearing to CS compounds and their elements

Three experiments with rat subjects sought to enhance one-trial excitatory simultaneous and backward fear conditioning by using a two-element compound conditioned stimulus (CS) instead of only a single element. During conditioning, experimental groups received a 4-sec CS either coextensively with a 1-mA grid-shock unconditioned stimulus (US) or immediately after US termination. In subsequent tests, CSs evoked more lick suppression and freezing in these groups than in various controls. Compound CSs evoked more lick suppression and freezing than did CS elements, but did so equally for experimental and control groups. Therefore, the use of compounds did not enhance conditioning. Unexpectedly, an explicitly unpaired control in which CS followed US termination by 3 min tended to show more CS-evoked suppression and freezing than did a control in which CS preceded US onset by 3 min. This result raises the possibility that associations between the CS and the training context might engender responding to backward-paired CSs.     

Integration of cardiac responses to serial stimuli after Pavlovian conditioning in rats

The expression of cardiac responses to sequences of two sounds was studied in restrained rats following discriminative trace or delay conditioning. Stimuli paired with a tail shock 10 sec later (CS1) elicited conditioned bradycardia. Unpaired or neutral stimuli (CS0) elicited mostly tachycardia. Rats did not learn to suppress responding to nonreinforced sequences with an interval of 6 sec between sounds. Responses to the second stimulus were significantly augmented following a CS1 stimulus, but not following a CS0 stimulus. Real-time summation of simple responses provided a more complete and quantitative prediction of dual responses than did resetting or facilitation. These results extend the time range over which summation may be observed from less than 2 sec to at least 16 sec. They appear to be inconsistent with models involving competition between unitary representations of stimuli in short-term memory and suggest the existence of multiple stimulus traces with independent time courses.     

Effects of a backward conditioning procedure following acquisition on extinction of conditioned suppression

A one-trial-a-day procedure was used to investigate the effects of US-CS pairings on extinction of conditioned suppression of licking by rats. Following acquisition trials, response suppression was immediately eliminated when US preceded CS, but it reappeared during subsequent CS-alone presentations. Ss that received backward pairings reached a significant level of extinction one trial before Ss that received conventional extinction trials.     

Classical conditioning of an “avoidance” response in goldfish using a linear presentation procedure

The present study examined the nature of the “avoidance” response in goldfish under the linear presentation procedure (Zerbolio, 1981). With this procedure, shuttling behavior occurring during the presentation of the trial stimulus produces either CS? or CS+, and further occurrence of shuttling within the trial interval (10 sec) changes the value of CS from negative to positive, or vice versa. If the fish remains in the compartment when the prevailing cue state is CS? at the end of the interval, shock can be avoided. With this procedure fish responded to the CS+ more than to the CS? and avoided shock. But fish in one of two control groups, in which responses had no effect in changing the cue state from CS+ to CS?, or vice versa, also showed a clear differentiation. The results were generally in line with the view that the “avoidance” response in fish is acquired through classical conditioning. The contribution of classical conditioning to the acquisition of avoidance response is discussed.     

Blocking in eyelid conditioning: Effect of changing the CS-US interval and introducing an intertriai stimulus

Kamin’s three-stage blocking paradigm was investigated in rabbit eyelid conditioning, Two manipulations were examined. A change in the CS-US interval from Stage 1 to Stage 2 did not attenuate blocking. The introduction of a salient stimulus during the intertriai interval in Stage 2 also failed to attenuate blocking. The first result is not consistent with Kamin’s interpretation of the blocking effect in terms of US surprisingness. The second resuit is inconsistent with a prediction based on the Rescorla-Wagner model.     

Flavor-evaluative conditioning is unaffected by contingency knowledge during training with color-flavor compounds

In two experiments, participants inspected and drank a series of drinks, half of which contained sugar and half unpalatable Tween20 (tween). Each sugar and tween drink had a particular flavor and color. Following this training, the flavors of the sugar drinks were assigned higher hedonic evaluations than were those of the tween drinks, even though the participants did not reliably report which flavors had been present in the sugar and tween drinks during training. Moreover, the evaluative conditioning of the flavors was unaffected by whether or not the colors alone had been pretrained to predict the presence of sugar or tween in the drinks. In accord with Baeyens, Eelen, van den Bergh, and Crombez (1990), we conclude that flavor-evaluative conditioning is not mediated by contingency learning.     

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.     

Explaining the effects of relative time in trace conditioning: A preliminary test of a comparator hypothesis

Scalar expectancy theory (SET) predicts that postacquisition manipulations of background expectancy should alter conditioned performance. An experiment was performed to test the application of this hypothesis to an explanation of the “temporal context” effect in trace conditioning. Pigeons were trained on an inhibitory trace conditioning procedure and then subjected to postacquisition manipulations of background expectancy. Nonreinforced exposure to the training apparatus eliminated conditioned withdrawal, exposure to USs under very long interreinforcer intervals slightly weakened conditioned withdrawal, and home-cage confinement had no effect on conditioned withdrawal. These results are discussed in terms of the predictions of SET and the role of background excitation in conditioned inhibition.