Outcome-selective effects of intertrial reinforcement in a Pavlovian appetitive conditioning paradigm with rats

The outcome-selective effects of presenting intertrial unconditioned stimuli (USs) in a rat appetitive conditioning paradigm were examined in two experiments. In both experiments, two stimuli were paired with different outcomes, while one of these outcomes was also presented in the intertrial interval (A+, B*, +). Two measures of learning, stimulus-elicited magazine approach and Pavlovian-to-instrumental transfer, were used to examine these effects. The presence of freely occurring outcomes in the intertrial interval (ITI) was observed to interfere more with the learning of a new association (Experiment 1) and to degrade more an already established association (Experiment 2) when the conditioned stimulus had been paired with the same outcome as that occurring in the ITI. An outcome-selective effect of ITI USs distinguishes among accounts of contingency based on general performance, attentional, and motivational mechanisms from those based on more specific associative mechanisms. Overall, the data highlight the importance of specific encoding processes in the analysis of associative learning.     

The effects of variations in the interpellet interval on wheel running in the rat

Three rats were given access to a running wheel during spaced food deliveries. As the interpellet interval increased, the overall amount of running increased, the rate of running neither systematically increased nor decreased, and the locus of maximal running occurred later in the interpellet interval. Both the overall amount and the temporal distribution of running exhibited considerable within-schedule changes during successive exposures to the different schedules. These data are discussed in terms of Staddon’s (1977) assignment of behavior into different functional classes, that is, schedule-induced and facultative.     

On the nature of CS and US representations in Pavlovian learning

A significant problem in the study of Pavlovian conditioning is characterizing the nature of the representations of events that enter into learning. This issue has been explored extensively with regard to the question of what features of the unconditioned stimulus enter into learning, but considerably less work has been directed to the question of characterizing the nature of the conditioned stimulus. This article introduces a multilayered connectionist network approach to understanding how “perceptual” or “conceptual” representations of the conditioned stimulus might emerge from conditioning and participate in various learning phenomena. The model is applied to acquired equivalence/distinctiveness of cue effects, as well as a variety of conditional discrimination learning tasks (patterning, biconditional, ambiguous occasion setting, feature discriminations). In addition, studies that have examined what aspects of the unconditioned stimulus enter into learning are also reviewed. Ultimately, it is concluded that adopting a multilayered connectionist network perspective of Pavlovian learning provides us with a richer way in which to view basic learning processes, but a number of key theoretical problems remain to be solved, particularly as they relate to the integration of what we know about the nature of the representations of conditioned and unconditioned stimuli.     

Sensory-specific associations in flavor-preference reversal learning

In two experiments, we examined the effect of reversal learning on the status of initially learned associations. In Experiment 1, thirsty rats were first taught to associate one flavor with sucrose and another flavor with Polycose. These relations were then reversed in a subsequent phase. One of the nutrients was then devalued by being paired with lithium chloride. The results of a two-bottle flavor-choice test revealed that the most recently learned associations governed performance. In Experiment 2, we aimed to discern whether the initially learned associations in Experiment 1 were weakened or masked by reversal learning. In order to address this question, either a 1-day (Group Immediate) or a 21-day (Group Delayed) retention interval was interpolated between the reversal and devaluation phases. Subsequent flavor-choice tests revealed that Group Immediate avoided the flavor most recently associated with the devalued nutrient but that Group Delayed avoided the flavor that was initially associated with the devalued nutrient. These findings suggest that the second-learned associations do not erase, but transiently mask, the first-learned associations, which subsequently recover over a retention interval. These results suggest a parallel in the mechanisms of extinction and reversal learning.     

Conditioned inhibition in taste aversion learning: Testing methodology and empirical status

Learning & Behavior - Several assays were used in assessing conditioned inhibition within a taste aversion procedure. Following Pavlovian conditioned inhibition training, in which one taste was...     

Partial reinforcement and latent inhibition effects on stimulus–outcome associations in flavor preference conditioning

Two experiments with thirsty rats explored the harmful effects of non-reinforced exposures to a flavor cue in the control by sensory-specific flavor–sucrose associations in a conditioned flavor preference paradigm. Experiment 1 demonstrated that rats learned to prefer a flavor cue that was consistently paired with sucrose over one that was paired with sucrose the same number of times but was also presented without sucrose on other occasions. However, rats for which sucrose was devalued following the conditioning phase preferred the partially reinforced flavor cue over the consistently reinforced flavor, suggesting that non-reinforcement weakened the ability of that flavor cue to evoke a specific representation of sucrose during the preference test. Experiment 2 demonstrated comparable effects of non-reinforcement in a latent inhibition procedure, although relatively more non-reinforced pre exposures to the flavor, in conjunction with fewer flavor–sucrose pairings, were required to see the effect. Together, the results suggest, as is often found with more traditional learning paradigms, that non-reinforcement of a flavor cue has deleterious effects on preference learning and/or performance.     

A reevaluation of the CS− hypothesis for schedule-induced polydipsia under intermittent schedules of pellet delivery

Lashley and Rosellini (1980) have recently suggested that schedule-induced polydipsia (SIP) is determined by the occurrence of absolute periods within schedules of periodic food delivery which are associated with a low probability of food delivery, that is, CS? periods. To assess this hypothesis, SIP was examined in the present experiments under three schedules—fixed time, variable time, and random time (RT)—which differed in probability of occurrence and/or duration (Experiment 1), and under a range of RT schedules in which the CS? period was systematically varied by changing the interpellet interval (Experiment 2). In both experiments, the level and temporal distribution of SIP did not seem to be related to the absolute period associated with the absence of food. Instead, SIP was more systematically related to the average length of the interpellet interval and, therefore, to the average period associated with no food. It was suggested that drinking under intermittent schedules of pellet delivery, that is, SIP, is determined by an average CS? period and not by an absolute period associated with the unavailability of food.     

Effects of several extinction treatments upon the integrity of Pavlovian stimulus-outcome associations

Pavlovian-to-instrumental transfer tests were used to assess the sensitivity of Pavlovian stimulus-outcome (S-O) associations to various extinction treatments in four appetitive conditioning experiments with rats. In Experiment 1, simple nonreinforcement of a stimulus was shown to have little impact on the ability of that stimulus to display outcome-specific transfer of control. Extinguishing a stimulus by pairing the stimulus with an alternative reinforcement in Experiment 2 also had no detectable effect on the S-O associations as assessed with the outcome-specific transfer measure. The third and fourth experiments, respectively, examined the impact of postconditioning exposures to random and explicitly unpaired S-O contingencies upon previously learned S-O associations. These treatments, as well, had no detectable harmful effects upon the integrity of the S-O associations. In contrast to the consistent failures of various extinction treatments to influence the ability of stimuli to display outcome-specific transfer, these treatments often did reduce the strength of conditioned responding initially trained to these stimuli. These results support the view that extinction entails the preservation of S-O associations as well as the parallel development of inhibitory stimulus-response associations. Other notions of extinction are also discussed.     

Selective reinstatement of stimulus-outcome associations

In two experiments, the possibility of outcome-selective reinstatement of conditioned responding was examined. Evidence for outcome-selective reinstatement of previously extinguished appetitively conditioned magazine responses by rats was observed in both Pavlovian (Experiment 1) and discriminated instrumental conditioning (Experiment 2) procedures. In both experiments, stimulus-elicited magazine responses occurred more in the presence of a stimulus whose reinforcer was reinstated than they did in the presence of another stimulus whose reinforcer was not reinstated. This effect was observed after both brief and extensive amounts of extinction. Outcome-selective reinstatement of instrumental leverpressing, however, was not observed, although nonselective reinstatement of magazine responding and leverpressing was obtained in Experiment 2. Overall, the data from these studies challenge existing theories of reinstatement, and they provide additional evidence of the importance of outcome-specific processes in the control of learned performance.     

An associative analysis of instrumental biconditional discrimination learning

Three different techniques were employed to analyze the associative structures mediating performance on an instrumental biconditional discrimination. In all three experiments, rats were trained concurrently on two tasks in which different stimuli signaled which one of two responses would be followed by reward. In each task, one response was rewarded in one stimulus and the other response was rewarded in the other stimulus. Correct responses earned pellets in one task and sucrose in the other task. The transfer procedure was used in Experiment 1A to identify whether or not an association developed between a biconditional discriminative stimulus and its instrumental outcome. Evidence was obtained that a biconditional cue elevated preferentially a new response trained with the same outcome. Experiments 1B and 3 examined the potential contribution of this stimulus-outcome association to biconditional performance by training the biconditional cues as signals (S-s) for the nonreinforcement of a different response. There was no evidence that this operation interfered with the ability of a biconditional cue to control performance of its correct response. In Experiments 1B and 2, the value of the instrumental outcome was reduced in an attempt to assess the contribution of stimulus-response associations to performance on the biconditional discrimination. The results of Experiments 1B and 2 reveal that correct responses were depressed following devaluation of the outcome used to train them, suggesting that learning about the response-outcome relation occurs. The implications of these results for binary and hierarchical models of instrumental learning are discussed.