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The experiments described in this thesis examined post-extinction recovery phenomena following classical conditioning in the rabbit. The first series of experiments examined the rate of reacquisition to the original conditioned stimulus (CS) and to a cross-modal CS following various amounts of extinction. In both the rabbit nictitating membrane (NM) preparation and rabbit heart rate (HR) conditioning, there was a graded reduction in the rate of reacquisition as a direct function of the number of extinction trials. In the rabbit NM preparation, there was also a graded reduction in the rate of acquisition to a cross-modal stimulus (CSB, e.g., light). However, concurrent recovery of responding to the original, extinguished stimulus (CSA, e.g., tone) during training with a novel, cross-modal stimulus (CSB, e.g., light), appeared uniformly robust even following extensive extinction. The second series of experiments examined the conditions necessary for concurrent recovery to occur in the rabbit NM preparation. The introduction of CSB-US pairings resulted in strong recovery of responding to CSA, while the reintroduction of the US alone failed to result in any discernable reinstatement of responding to CSA. Concurrent recovery was specific to the trained and extinguished CSA, with virtually no generalized responding to a novel cross-modal test stimulus (CSC). However, pretraining with CSB-US pairings significantly reduced the amount of recovery to CSA during subsequent CSB???US pairings. The third series of experiments revealed that concurrent recovery was specific to the extinguished stimulus (CSA) with only moderate generalization to other familiar but untrained stimuli in the same modality as CSA. Together these results indicate that concurrent recovery is not primarily the result of the unmasking of the original CSA-US association. Rather, concurrent recovery appears to be at least partially the result of learning-dependent generalization. However, in order for responding to CSB, to generalize to CSA, CSA must have been paired with the same US which is subsequently paired with CSB. Thus, the CSA-US association must be partially intact for concurrent recovery to occur. A layered network model with multiple hidden units is able to simulate rapid reacquisition, facilitated cross-modal acquisition and concurrent recovery.

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Five experiments with rats were conducted to determine the extent to which associative processes could be used to explain how rats seem able to learn complex CS-US contingencies during Pavlovian conditioning. Rats were exposed to positive, zero and negative CS-US contingencies and conditioned behaviour was compared with predictions derived from both associative models of conditioning and nonassociative normative theories of causal reasoning. A common measure of contingency, Deltap, when used to analyze Pavlovian conditioning requires defining the likelihood of the US in the presence and absence of the CS. Experiments 1 and 2 involved a novel preparation in which, in addition to standard CS presence trials, the absence of the CS was signalled by a second CS, called the trial marker (a lever). Rats were trained to learn relationships in which the CS was either a positive predictor of the US or in which it was unrelated to the US. More conditioned tray entries were observed when the CS signalled an increased likelihood of the US (positive contingency). Consistent with the associative explanations, the trial marker elicited conditioned lever pressing when the CS signalled no change in the likelihood of the US (zero contingency). Experiments 3, 4 and 5 extended the analysis with multiple CSs. These experiments examined whether learning about one CS was determined by its contingency relative to the contingency of other concurrently trained CSs. In experiments 3 and 4 conditioned responding to a moderately predictive CS was determined by its contingency relative to a perfectly predictive CS. Experiment 5 extended this effect to a case in which conditioning was influenced by the presence of a perfect predictor of the absence of the US. Together these results support the hypothesis that relative contingencies determine the strength of conditioned responding. The results are discussed from the perspective of both associative and nonassociative theory.

The experiments described in this thesis examined post-extinction recovery phenomena following classical conditioning in the rabbit. The first series of experiments examined the rate of reacquisition to the original conditioned stimulus (CS) and to a cross-modal CS following various amounts of extinction. In both the rabbit nictitating membrane (NM) preparation and rabbit heart rate (HR) conditioning, there was a graded reduction in the rate of reacquisition as a direct function of the number of extinction trials. In the rabbit NM preparation, there was also a graded reduction in the rate of acquisition to a cross-modal stimulus (CSB, e.g., light). However, concurrent recovery of responding to the original, extinguished stimulus (CSA, e.g., tone) during training with a novel, cross-modal stimulus (CSB, e.g., light), appeared uniformly robust even following extensive extinction. The second series of experiments examined the conditions necessary for concurrent recovery to occur in the rabbit NM preparation. The introduction of CSB-US pairings resulted in strong recovery of responding to CSA, while the reintroduction of the US alone failed to result in any discernable reinstatement of responding to CSA. Concurrent recovery was specific to the trained and extinguished CSA, with virtually no generalized responding to a novel cross-modal test stimulus (CSC). However, pretraining with CSB-US pairings significantly reduced the amount of recovery to CSA during subsequent CSB???US pairings. The third series of experiments revealed that concurrent recovery was specific to the extinguished stimulus (CSA) with only moderate generalization to other familiar but untrained stimuli in the same modality as CSA. Together these results indicate that concurrent recovery is not primarily the result of the unmasking of the original CSA-US association. Rather, concurrent recovery appears to be at least partially the result of learning-dependent generalization. However, in order for responding to CSB, to generalize to CSA, CSA must have been paired with the same US which is subsequently paired with CSB. Thus, the CSA-US association must be partially intact for concurrent recovery to occur. A layered network model with multiple hidden units is able to simulate rapid reacquisition, facilitated cross-modal acquisition and concurrent recovery.

The experiments described in this thesis examined post-extinction recovery phenomena following classical conditioning in the rabbit. The first series of experiments examined the rate of reacquisition to the original conditioned stimulus (CS) and to a cross-modal CS following various amounts of extinction. In both the rabbit nictitating membrane (NM) preparation and rabbit heart rate (HR) conditioning, there was a graded reduction in the rate of reacquisition as a direct function of the number of extinction trials. In the rabbit NM preparation, there was also a graded reduction in the rate of acquisition to a cross-modal stimulus (CSB, e.g., light). However, concurrent recovery of responding to the original, extinguished stimulus (CSA, e.g., tone) during training with a novel, cross-modal stimulus (CSB, e.g., light), appeared uniformly robust even following extensive extinction. The second series of experiments examined the conditions necessary for concurrent recovery to occur in the rabbit NM preparation. The introduction of CSB-US pairings resulted in strong recovery of responding to CSA, while the reintroduction of the US alone failed to result in any discernable reinstatement of responding to CSA. Concurrent recovery was specific to the trained and extinguished CSA, with virtually no generalized responding to a novel cross-modal test stimulus (CSC). However, pretraining with CSB-US pairings significantly reduced the amount of recovery to CSA during subsequent CSB???US pairings. The third series of experiments revealed that concurrent recovery was specific to the extinguished stimulus (CSA) with only moderate generalization to other familiar but untrained stimuli in the same modality as CSA. Together these results indicate that concurrent recovery is not primarily the result of the unmasking of the original CSA-US association. Rather, concurrent recovery appears to be at least partially the result of learning-dependent generalization. However, in order for responding to CSB, to generalize to CSA, CSA must have been paired with the same US which is subsequently paired with CSB. Thus, the CSA-US association must be partially intact for concurrent recovery to occur. A layered network model with multiple hidden units is able to simulate rapid reacquisition, facilitated cross-modal acquisition and concurrent recovery.

The experiments described in this thesis examined post-extinction recovery phenomena following classical conditioning in the rabbit. The first series of experiments examined the rate of reacquisition to the original conditioned stimulus (CS) and to a cross-modal CS following various amounts of extinction. In both the rabbit nictitating membrane (NM) preparation and rabbit heart rate (HR) conditioning, there was a graded reduction in the rate of reacquisition as a direct function of the number of extinction trials. In the rabbit NM preparation, there was also a graded reduction in the rate of acquisition to a cross-modal stimulus (CSB, e.g., light). However, concurrent recovery of responding to the original, extinguished stimulus (CSA, e.g., tone) during training with a novel, cross-modal stimulus (CSB, e.g., light), appeared uniformly robust even following extensive extinction. The second series of experiments examined the conditions necessary for concurrent recovery to occur in the rabbit NM preparation. The introduction of CSB-US pairings resulted in strong recovery of responding to CSA, while the reintroduction of the US alone failed to result in any discernable reinstatement of responding to CSA. Concurrent recovery was specific to the trained and extinguished CSA, with virtually no generalized responding to a novel cross-modal test stimulus (CSC). However, pretraining with CSB-US pairings significantly reduced the amount of recovery to CSA during subsequent CSB???US pairings. The third series of experiments revealed that concurrent recovery was specific to the extinguished stimulus (CSA) with only moderate generalization to other familiar but untrained stimuli in the same modality as CSA. Together these results indicate that concurrent recovery is not primarily the result of the unmasking of the original CSA-US association. Rather, concurrent recovery appears to be at least partially the result of learning-dependent generalization. However, in order for responding to CSB, to generalize to CSA, CSA must have been paired with the same US which is subsequently paired with CSB. Thus, the CSA-US association must be partially intact for concurrent recovery to occur. A layered network model with multiple hidden units is able to simulate rapid reacquisition, facilitated cross-modal acquisition and concurrent recovery.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves 67-70). Also available via World Wide Web.