Available online 9 December 2023, 107879

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This series of experiments examined the effects of extinction and an explicitly unpaired treatment on the ability of a conditioned stimulus (CS) to function as a reinforcer. Rats were trained to lever press for food, exposed to pairings of a noise CS and food, and, finally, tested for their willingness to lever press for the CS in the absence of the food. Experiment 1 provided a demonstration of conditioned reinforcement (using controls that were only exposed to unpaired presentations of the CS and food) and showed that it was equivalent after one or four sessions of CS-food pairings. Experiments 2 and 3 showed that, after one session of CS-food pairings, repeated presentations of the CS alone reduced its reinforcing properties; but after four sessions of CS-food pairings, repeated presentations of the CS alone had no effect on these properties. Experiment 4 showed that, after four sessions of CS-food pairings, explicitly unpaired presentations of the CS and food completely undermined conditioned reinforcement. Finally, Experiment 5 provided within-experiment evidence that, after four sessions of CS-food pairings, the reinforcing properties of the CS were disrupted by explicitly unpaired presentations of the CS and food but spared by repeated presentations of the CS alone. Together, these findings indicate that the effectiveness of extinction in undermining the reinforcing properties of a CS depends on its level of conditioning; and that, where extinction fails to disrupt these properties, they are successfully undermined by an explicitly unpaired treatment. They are discussed with respect to findings in the literature on Pavlovian-to-instrumental transfer; and the Rescorla-Wagner model, which anticipates that an explicitly unpaired treatment will be more effective than extinction in reversing the effects of conditioning.

Section snippetsExperiment 1

Experiment 1 had two aims. The first was to demonstrate the conditioned reinforcing properties of a CS using an adaptation of the protocol developed by Miles (1956) and others (e.g., Egger and Miller, 1962). The second was to examine whether these properties vary with the amount of Pavlovian training. Instrumental training and Pavlovian conditioning were conducted separately to prevent confounding of the stimulus-food and the food reinforced response-stimulus associations that had been present

Experiment 2

A minimally trained CS, like an extensively trained one, is able to control the selection of an instrumental response with which it shares the same outcome (Delamater & Oakeshott, 2007). However, extinction differentiates these two cases: whereas extinction leaves intact the ability of an extensively trained CS to control such responses (Delamater, 1996), extinction removes this ability in the case of a minimally or weakly trained CS (Delamater, 2012, Delamater et al., 2017). The present

Subjects

The subjects were 32 female rats of the same strain and obtained from the same source as in Experiment 1. They were approximately 3 months old and weighing an average of 238 g (ranging from 181-279 g) at the start of the experiment. The rats were housed and maintained in the same manner as in Experiment 1 with 8 females per tub.

Apparatus

The apparatus and stimuli were those used in Experiment 1.

Procedure

Rats were randomly allocated to four groups (n = 8). Magazine training on days 1-2, and instrumental training

Experiment 3

The previous experiment demonstrated that extinction of a minimally trained CS reduced its ability to act as a conditioned reinforcer for an instrumental response and its ability to elicit magazine visits. Therefore, a natural question is whether extinction will have a similar effect on a more extensively trained CS. As noted, extinction has been shown to spare (instead of destroy) outcome-selective PIT when the CS is well trained (Delamater, 1996). Thus, the following experiment assessed the

Experiment 4

The previous experiment showed that that an extensively trained CS retains its ability to act as a conditioned reinforcer for an established instrumental response even when extinction has removed its ability to elicit magazine visits. Another way to cause a CS to lose its ability to elicit responses is to replace the positive contingency that generated the conditioned responses with a negative contingency. Here, as in extinction, the CS is presented in the absence of the US. However, unlike in

Experiment 5

The previous experiment showed that shifting rats from paired to unpaired presentations of the noise and food pellets reduced the conditioned reinforcing properties of that CS. This is in contrast to the results of the previous experiments which showed that, following the same amount of Pavlovian conditioning, extinction spares the conditioned reinforcing properties of the CS. It is, however, important to note that the two treatments were administered in different ways: extinction consisted in

General Discussion

This series of experiments examined whether extinction of a Pavlovian CS reduces its effectiveness as a conditioned reinforcer. Each experiment involved a minimum of three stages. We note that only female rats were used, and thus, sex differences were not examined and may exist. In stage 1, rats were trained to lever-press for food. In stage 2, they were exposed to presentations of an auditory stimulus (a white noise) and food while the lever was retracted. Finally, rats were tested with access

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by an Australian Government Research Training Fellowship awarded to NGWK, an Australian Research Council Discovery Project awarded to RFW and NMH (DP200102969) and an Australian Research Council Future Fellowship awarded to NMH (FT190100697).

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