The effects of extinction and an explicitly unpaired treatment on the reinforcing properties of a Pavlovian conditioned stimulus.

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.

Prediction error determines how memories are organized in the brain.

How is new information organized in memory? According to latent state theories, this is determined by the level of surprise, or prediction error, generated by the new information: a small prediction error leads to the updating of existing memory, large prediction error leads to encoding of a new memory. We tested this idea using a protocol in which rats were first conditioned to fear a stimulus paired with shock. The stimulus was then gradually extinguished by progressively reducing the shock intensity until the stimulus was presented alone. Consistent with latent state theories, this gradual extinction protocol (small prediction errors) was better than standard extinction (large prediction errors) in producing long-term suppression of fear responses, and the benefit of gradual extinction was due to updating of the conditioning memory with information about extinction. Thus, prediction error determines how new information is organized in memory, and latent state theories adequately describe the ways in which this occurs.

Latent inhibition is facilitated when a target stimulus is preexposed in compound with a nontarget stimulus, but only when the two stimuli coterminate: A test of the Hall-Rodriguez theory.

The Hall-Rodriguez (Hall & Rodriguez, 2010) theory predicts that latent inhibition can be facilitated when a target stimulus is preexposed in compound with a second, nontarget stimulus: specifically, latent inhibition will be facilitated when the target coterminates with the second stimulus in preexposure, but facilitation will fail to occur when the two stimuli do not coterminate. The present study tested these predictions. In each experiment, rats were preexposed to a 30 s target stimulus alone or in compound with a second stimulus across its final 10 s, or they were preexposed to the context. All rats were then exposed to pairings of the target stimulus and foot shock, and finally, tested for freezing to the target. Experiment 1 demonstrated standard latent inhibition. Experiment 2 provided evidence that preexposure to a 30 s auditory target stimulus, in compound with a visual stimulus across its final 10 s, produced facilitated latent inhibition. Experiment 3 demonstrated that the latent inhibition was also facilitated when each 30 s presentation of a target visual stimulus was compounded with an auditory stimulus across its final 10 s. Experiment 4 showed that facilitation did not occur when each 30 s presentation of the target was compounded with a second stimulus across its initial 10 s, while Experiment 5 found that latent inhibition of the target was impaired when each of its 30 s presentations terminated in the onset of a second (10 s) stimulus. These findings are consistent with the predictions of the Hall-Rodriguez theory. They confirm that the facilitation of latent inhibition depends on coterminations of target and nontarget stimuli in preexposure and, more generally, that the impact of a second stimulus on latent inhibition to a target depends on their temporal relation in preexposure. (PsycInfo Database Record (c) 2021 APA, all rights reserved).