Nicholas J. Grahame

Latent inhibition as a performance deficit resulting from CS—context associations

Treatments that attenuate latent inhibition (LI) were examined using conditioned suppression in rats. In Experiment 1, retarded conditioned responding was produced by nonreinforced exposure to the CS prior to the CS-US pairings used to assess retardation (i.e., conventional LI). In Experiment la, retarded conditioned responding was induced by preexposure to pairings of the CS and a weak US prior to retardation-test pairings of the CS with a strong US (i.e., Hall-Pearce [1979] LI). Both types of LI were attenuated by extensive exposure to the training context (i.e., context extinction) following the CS-US pairings of the retardation test. Experiment 2 examined the specificity of the attenuated LI effect observed in Experiment 1. After preexposure to two different CSs in two different contexts, each CS was paired with a US in its respective preexposure context. One of the two contexts was then extinguished. This attenuated LI to a greater degree for the CS that had been trained in the extinguished context. Experiment 3 differentiated the roles in LI of CS-context associations and context-US associations. Following preexposure to the CS in the training context, LI was reduced by further exposure to the CS outside the training context. This observation was interpreted as implicating the CS-context association as a factor in LI. Thus, the results of these experiments suggest that LI is a performance deficit mediated by unusually strong CS-context associations. Implications for Wagner’s (1981) SOP model and Miller and Matzel’s (1988) comparator hypothesis are discussed.

Temporal encoding as a determinant of blocking.

A blocking paradigm with rats was used to evaluate whether different temporal information is encoded in simultaneous rather than forward associations. During Phase 1, the blocking conditioned stimulus (CS) was simultaneously or forward paired with an unconditioned stimulus (US). During Phase 2, the pretrained CS occurred in compound with a novel target CS that was paired in a simultaneous or forward manner with the US. Forward pretraining resulted in more blocking of a forward than a simultaneously trained target CS, and simultaneous pretraining resulted in more blocking of a simultaneously than a forward trained target CS. Thus, greater blocking occurred when the blocking and blocked CSs had the same temporal relation to the US. The results support the temporal coding hypothesis and question the necessity of predictive information in blocking.

Context as an occasion setter following either CS acquisition and extinction or CS acquisition alone.

Abstract Three experiments used conditioned lick suppression with rats in order to investigate the necessary conditions for obtaining occasion setting by context. Experiment 1 sought occasion setting by context as a product of conditioned-stimulus (CS) excitatory training only. Associative summation of the CS and context was observed, but no difference in responding inside versus outside the CS training context was found after devaluing direct context-unconditioned stimulus (US) associations and controlling for both familiarization and generalization decrement between training and nontraining contexts. In Experiment 2, two stimuli were conditioned in separate contexts, and subsequently each CS was or was not extinguished either in the same context in which it had been trained or in the training context of the other CS. This procedure equated the associative values of the two contexts during acquisition, extinction, and testing. No occasion setting by context was seen either with or without extinction of the CSs. In Experiment 3, a renewal paradigm was used in which a single CS was trained in context A and extinguished in Context B. Testing showed renewed responding to the CS in Context A. A context-CS summation test using an unambiguous CS trained in a third context found Contexts A and B to be equally excitatory. We hypothesize that the lack of occasion setting in Experiment 2, in contrast to that of Experiment 3, resulted either from extinction of the positive occasion-setting properties of the two contexts as a consequence of their both being sites of CS extinction or a failure of a contextual occasion setter to carry information about the particular stimulus qualities of a given CS with which it was conditioned (i.e., occasion setters act on US representations, not particular CS-US associations).

Responding to a conditioned stimulus depends on the current associative status of other cues present during training of that specific stimulus

The comparator hypothesis is a response rule stating that responding to a Pavlovian conditioned stimulus (CS) reflects the associative strength of the CS relative to that of other cues (comparator stimuli) that were present during CS training. Thus, modulation of the associative strength of a CSs comparator stimulus should alter responding to that CS. These studies examined the stimulus specificity of this effect using within-subjects designs. Rats were trained on 2 CSs, each with a unique comparator stimulus, to determine the degree to which posttraining extinction of the comparator stimulus for one CS influences responding to the other CS. Using negative contingency (Experiments 1 and 2), overshadowing (Experiment 3), and local context (Experiment 4) preparations, stimulus specificity was observed. In each case, posttraining extinction of the comparator stimulus for one CS had greater impact on responding to that CS than on responding to the alternate CS.

Trial spacing effects in pavlovian conditioning: A role for local context

Two conditioned lick-suppression experiments with rats were conducted in order to replicate and extend findings by Ewing, Larew, and Wagner (1985). Ewing et al. observed that excitatory responding to a CS paired with a footshock US was attenuated when the ITIs thatpreceded each CS-US trial were short (60 sec) relative to when they were long (600 sec). This effect was isolated in the influence of the preceding ITI because the preceding ITI was consistently short for one CS and consistently long for a different CS, while the following ITIs were equally often short and long for both CSs. Ewing et al. interpreted this finding in the framework of Wagner’s (1981) SOP model. Experiment 1 replicated this trial-spacing effect and demonstrated a similar effect under conditions in which thefollowing ITI was consistently short for one CS and consistently long for a different CS, while the durations of preceding ITIs were equally often short and long for both CSs. Experiment 2 revealed that the detrimental effect of a short preceding or a short following ITI could be alleviated by extinguishing the conditioning context after CS-US training. The latter observation indicates that the trial-spacing effect is not mediated by a failure of a CS trained with a short ITI to enter into excitatory associations with the US, a conclusion that is not wholly consistent with the SOP model. Finally, we suggest that short pretrial and short posttrial ITIs may enhance the excitatory value of local context cues that modulate responding to a CS.

Local context and the comparator hypothesis

Abstract“Comparator” accounts of associative conditioning (e.g., Gibbon & Balsam, 1981; Miller & Matzel, 1988) suggest that performance to a Pavlovian CS is determined, by a comparison of the US expectancy of the CS with the US expectancy of general background cues. Recent research indicates that variation in the excitatory value of cues in the local temporal context of a CS may have a profound impact on conditioned responding to the CS (e.g., Kaplan & Hearst, 1982), implicating US expectancy based on local, rather than overall, background cues as the critical comparator term for a CS. In two experiments, an excitatory training context attenuated responding to a target CS. In Experiment 1, the context was made excitatory by interspersing unsignaled USs with target CS-US trials. In this case, posttraining extinction of the conditioning context restored responding to the target CS. In Experiment 2, the target CS’s local context was made excitatory by the placement of excitatory “cover” stimuli in the immediate temporal proximity of each target CS-US trial. In this experiment, posttraining extinction of the proximal cover stimuli, not extinction of the conditioning context alone, restored responding to the target CS. An observation from both experiments was that signaling the otherwise unsignaled USs did not appear to influence the associative value of the conditioning context. The results are discussed in relation to a local context version of the comparator hypothesis and serve to emphasize the importance of local context cues in the modulation of acquired behavior. Taken together with other recent reports (e.g., Cooper, Aronson, Balsam, & Gibbon, 1990; Schachtman & Reilly, 1987), the present observations encourage contemporary comparator theories to reevaluate which aspects of the conditioning situation comprise the CS’s comparator term.

Pavlovian conditioning in multiple contexts: Competition between contexts for comparator status

Water-deprived rats were used to investigate the effects of training a CS in more than one context on conditioned lick suppression. In each experiment, partial reinforcement of the CS was intermingled with unsignaled presentations of the US. In Experiment 1, subjects were either trained in one context alone, trained consecutively in two contexts (such that all training in one context occurred prior to any training in the second context), or trained alternately in two contexts. Following training, the first context, the second context, or neither context was extinguished. Testing of the CS occurred in a third (neutral) context. To the extent that either training context became established as a comparator stimulus for the CS, the comparator hypothesis (Miller & Matzel, 1988) predicts an increase in excitatory responding to the CS following extinction of that context. Subjects trained in a single context exhibited appreciable fear of the CS only when the CS’s training context had been extinguished. Additionally, subjects trained consecutively in the two contexts showed increased fear of the CS following extinction of the second, but not the first training context (i.e., a recency effect). Subjects trained alternately in the two contexts showed no increased fear of the CS as a result of either context alone being extinguished. In Experiment 2, subjects trained alternately in two contexts showed increased fear of the CS only when both training contexts were extinguished, suggesting that both training contexts had become comparator stimuli. These data indicate that multiple training contexts can either compete or act synergistic-ally in modulating responding to a Pavlovian trained CS as a function of the order of training in the different contexts.

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.

Overshadowing-like effects between potential comparator stimuli: Covariation in comparator roles of context and punctate excitor used in inhibitory training as a function of excitor salience

Abstract Water-deprived rats served in a conditioned lick suppression paradigm designed to probe the associative structure underlying a partially reinforced Pavlovian inhibitor (i.e., A + AX ± ) when Stimulus A (a flashing light) was either of high or low salience. Following inhibition training, subjects received either extinction of A, extinction of the training context alone, or remained in their home cages. The inhibitory potential of Stimulus X (white noise) was then assessed in a neutral context using both a summation test with an excitor other than Stimulus A (Experiment 1) and a retardation test (Experiment 2). When A was of high salience, the inhibitory potential of Stimulus X was directly related to the excitatory value of A and not the excitatory value of the training context. But when A was of low salience, the inhibitory potential of X was directly related to the excitatory value of the training context rather than the excitatory value of A. Although the high salience A, relative to the low salience A, overshadowed the contexts role as a modulator of responding to Stimulus X, it did not appreciably overshadow contexts potential to directly elicit conditioned responding; thus, a dissociation was seen in the ability of a punctate CS to overshadow a context as a function of the behavioral index of overshadowing. These results are discussed in the framework of the comparator hypothesis.

Local time horizons in Pavlovian learning.

Responding to a conditioned stimulus (CS) is impaired if the CS is trained in the presence of excitatory local context cues. Four lick suppression experiments with rats explored whether this local context effect arises from the influence of excitatory cues that precede or that follow a reinforced target CS. Pretrained nontarget stimuli served as local context cues that occurred (a) immediately before and after the target CS trial, (b) immediately before or after the target CS trial, or (c) only before or after the target CS trial with varying intervals between the nontarget stimulus and target CS. Results indicated similar control over responding to the target CS by the preceding and following nontarget cues. This outcome implies a symmetrical window of memory integration (local time horizon) for a Pavlovian CS. Possible mechanisms underlying the detrimental effect of embedding a CS in an excitatory local context are discussed.