Search

Competition between contextual occasion setting and associative processes was indicated by experiments with rats using appetitive conditioning. The presence of a discrete predictive stimulus interfered with occasion setting by contextual stimuli. The rats were separated into groups that learned to predict nonreinforcement of an auditory target stimulus based on contextual stimuli (CTX), a visual stimulus that was compounded with the target (CI), or both (CTX+CI). A second auditory target was inconsistently reinforced. The visual stimulus controlled behavior in both the CI and CTX+CI groups, while the contextual stimuli controlled behavior of the CTX group.

The associative status of an explicitly unpaired conditioned stimulus (CS) was investigated in three experiments with rats. With short intertrial intervals, the explicitly unpaired CS acted as a conditioned excitor. The explicitly unpaired CS also acted as a conditioned inhibitor following extinction of the CS or extinction of the contextual cues only. The results may be explained by associations between the CS and context, the context and the unconditioned stimulus (US), context-CS and CS-US or all of the above. Predictions of comparator theories of performance were contradicted by the experimental results.

Competition occurred between inhibitory conditioning to a punctate stimulus and acquisition of negative contextual occasion setting in two experiments using a Pavlovian discrimination procedure with rats. Relative salience of the competing stimuli determined the outcome. The results contradict previous appetitive blocking studies which found no interaction between positive occasion-setters and excitatory stimuli and suggest that higher-order and simple associative memory systems are not independent.

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 [+ or -]) 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 the 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 context's role as a modulator of responding to Stimulus X, it did not appreciably overshadow context's 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., Two experiments were conducted using conditioned lick suppression in water-deprived rats to investigate the effect of excitor salience on Pavlovian conditioned inhibition training. The first experiment used a summation test for inhibition; the second, a retardation test. Bright or dim lights served as high- or low-salience punctate excitors. The high-salience excitor overshadowed the training context, but the low-salience excitor did not. The results are interpreted in terms of the comparator hypothesis.

Two experiments used lick suppression by water-deprived rats to investigate the associative structure underlying the enhancement of negative summation often seen following operational extinction (i.e., X-) of a Pavlovian conditioned inhibitor (A+/AX-). Our expectation was that one consequence of inhibitory training with Stimulus X was X's accruing excitatory strength through mediation by Stimulus A, and that operational extinction of A attenuated this strength. Experiment 1 determined that, following A+/AX- training, operational extinction of X enhanced negative summation even when the same excitor was used both on the summation test and in inhibitory training (i.e., Stimulus). This suggests that the enhanced negative summation arises from extinction of a direct X[right arrow]US excitatory association, which is mediated by A during acquisition but not during subsequent retention. In Experiment 2, the AX compound was extinguished following A +/AX - training. This treatment was intended to maintain the X[right arrow]A association while extinguishing the X[right arrow]US association. Stimulus X was then tested in summation with an excitor other than A. Unlike extinction of X alone, extinction of AX caused no increase in the inhibitory potential of X; however, it produced a decrease in the excitatory value of A. Additionally, Experiment 2 found that the effectiveness of further inhibition training was similar to operational extinction of X in increasing X's inhibitory response potential. These results a consistent with the view that X, as a result of the AX- trials of inhibitory training, comes to possess a direct X[right arrow]US associative link, and that the negative summation potential of an inhibitor is a function of the discrepancy in excitatory associative strengths betweene putative inhibitor and the conditioned excitor used in inhibition training., Two experiments were conducted using lick suppression by water-deprived rats to examine mechanisms causing enhanced negative summation after operational extinction of a Pavlovian inhibitor. Results support the comparator hypothesis, which denies the existence of inhibitory associations, over the model proposed by R.A. Rescorla, in which negative summation is caused by loss of excitatory strength of the inhibitor.

Following A+/X- training (with A, X, and + being a light, tone, and footshock, respectively), rats received extinction of A and the training context, extinction of the training context alone, or no extinction. The inhibitory potential of X was then assessed with conditioned lick suppression in a neutral context using both summation and retardation tests. Extinction of the training context alone and extinction of A and the training context reduced the inhibitory potential of X appreciably and equally. Hence, what is traditionally called differential inhibition appears to depend not on the excitatory value of A but on the excitatory value of the training context. In conjunction with what is known about other inhibitory training procedures, these results suggest that a conditioned inhibitor is a stimulus that has been paired with little or no reinforcement in the presence of an accompanying stimulus that predicts greater reinforcement.

We used summation tests in conditioneed suppression with rats to evaluate the effects of two preconditioning manipulations on the acquisition of associative strength by a backward conditioned inhibitory stimulus (CS-) that followed an unconditioned stimuls (US). Two backward CS-s were establisheed within subjects; onee backward CS- followed a US that was always signaled by a conditioned excitatory stimulus (CS+), a second backward CS- followed a US that was never signaleed. In Experiment 1, prior conditioning of the forward CS+ before backward conditioning enhanced inhibitory conditioning to the backward CS- that followed the signaled US. An opposite effect was observed on the unsignaled trials; backward inhibitory conditioning was impaired by preconditioning of the forward CS+. In Experiment 2, prior conditioning of the context, which involved embedding many USs within the context before backward conditioning, facilitated later inhibitory conditioning with both signaled and unsignaled USs. This geneeral facilitative effect was specific, in Experiment 3, to the preconditioned context and was not evident in a nonpreconditioned context. We conclude that backward inhibitory conditioning with a signaled US is multiply determined by contextual and forward CS+ based inhibitory processing. These data are consistent with the preconditions of Wagner's standard operating procedure (SOP) model, as well as a modified veersion of Miller and Schachtman's comparator hypothesis of response generation.

Water-deprived rats served in a conditioned lick-suppression paradigm designed to asses the associative structure underlying a partially reinforced Pavlovian inhibitor. In all experiments, a Pavlovian conditioned inhibition procedure was used in which Stimulus A was consistently reinforced with footshock, and a simultaneous compound of Stimuli A and X was partially reinforced (25%) with footshock (i.e., A+/AX[+ or -]. Experiment 1 and 2 demonstrated that Stimulus X passed an inhibitory summation test and that postraining extinction of Stimulus A decreased this summative effect. Experiment 3 indicated that Stimulus X passed a retardation test for inhibition and that posttraining extinction of Stimulus A decreased the observed retardation. Experiment 4 provided evidence that posttraining extinction of Stimulus A increased responding to Stimulus X on a direct test for excitation. Thus, extinction of Stimulus A was found to decrease Stimulus X's response potential on retardation and summation tests for inhibition and to increase Stimulus X's reponse potential on a test for excitation. These observations suggest that the associative response potentials of a stimulus are not solely functions of the associative strength of that stimulus. After partially reinforced Pavlovian inhibition training, Stimulus X and Stimulus A appear to have an inverse relationship in influencing associative responding to Stimulus X regardless of whether responding is measured with test for inhibition or excitation.