In the present experiments, we examined the role of within-compound associations in the interaction of the overshadowing procedure with conditioned stimulus (CS) duration, using a conditioned suppression procedure with rats. In Experiment 1, we found that, with elemental reinforced training, conditioned suppression to the target stimulus decreased as CS duration increased (i.e., the CS duration effect), whereas, with compound reinforced training (i.e., the overshadowing procedure), conditioned suppression to the target stimulus increased as CS duration increased. In subsequent experiments, we replicated these findings with sensory preconditioning t and demonstrated that extinction of the overshadowing stimulus results in retrospective revaluation with short CSs and in mediated extinction with long CSs. These results highlight the role of the duration of the stimulus in behavioral control. Moreover, these results illuminate one cause (the CS duration) of whether retrospective revaluation or mediated extinction will be observed.

In two conditioned suppression experiments with rats as subjects, we examined two classes of accounts of spontaneous recovery. One view suggests that spontaneous recovery occurs due to greater temporal instability of inhibitory associations, whereas the other posits that spontaneous recovery occurs due to greater temporal instability of second-learned associations. These accounts diverge in predictions concerning spontaneous recovery when the first-learned association is inhibitory and the second-learned association is excitatory. Using different designs, Experiments 1 and 2 found spontaneous recovery of both excitation and inhibition. The results support the view that spontaneous recovery occurs due to faster waning of second-learned associations. Keywords spontaneous recovery; extinction; conditioned inhibitionSpontaneous recovery is typically defined as the reemergence of conditioned responding to an extinguished conditioned stimulus (CS) with the passage of time since extinction. Because acquisition followed by extinction constitutes a two-phase training regimen, a broader definition of spontaneous recovery is the reemergence of a first-learned association to a CS that subsequently has received contradictory training, with the passage of time since the contradictory training. This latter definition better engages the present discussion; thus, it will be our working definition of spontaneous recovery. Consistent with this definition, spontaneous recovery can also be regarded as an increase in primacy with delay of testing, which has been frequently observed (Konorski & Szwejkoweska, 1952;Postman, Stark, & Fraser, 1968;Wheeler, Stout, & Miller, 2004).In his seminal paper, Bouton (1993) proposed two types of explanations of spontaneous recovery from extinction. One account emphasizes the nature of the learning that happens during extinction, specifically the formation of an inhibitory CS-no unconditioned stimulus (US) association that is superimposed at test onto the previous CS-US excitatory learning (Bouton, 1993;Pavlov, 1927). This account explains spontaneous recovery from extinction of the conditioned response by assuming that the retrievability of the inhibitory memory fades faster over time than that for excitation (which presumably fades very slowly). The other type of explanation suggests that spontaneous recovery is a consequence of sequentially learning two contradictory associations (Bouton, 1993;Spear, 1971). According to this account, the impact of extinction fades with time because extinction is the second-learned association and consequently the more ambiguous of the two experiences (the first being acquisition). Toward differentiating between these two accounts, we noted that they differ in their expectations for spontaneous recovery in situations involving two contradictory learning experiences when the second experience includes reinforcement. If conditioned inhibition fades faster than Mailing Address: Ralph R. Miller, Department of Psychology, State University of New York at Bingham...

Three experiments were conducted to examine the interaction of overexpectation treatment and trial massing using a Pavlovian fear conditioning procedure with rats. In first-order conditioning, Experiment 1 found the overexpectation effect (i.e., decreased conditioned responding to a cue after compound training when the elements were previously reinforced), the trial spacing effect (i.e., decreased responding to a cue when reinforced trials are massed), and a counteraction between overexpectation treatment and trial massing (i.e., an alleviation of the decrement in responding seen with overexpectation treatment or trial massing alone when the two treatments are conjointly administered). Experiment 2 replicated Experiment 1 with the critical treatments embedded within a sensory preconditioning preparation. The overexpectation effect, the trial spacing effect, and the mutual counteraction of overexpectation treatment and trial massing all proved significant. In Experiment 3, either the nontarget conditioned stimulus of overexpectation treatment or the excitatory context resulting from trial massing was extinguished. Results are best explained by the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001). Keywords cue competition; overexpectation; trial massing; counteractionThe overexpectation effect is a decline in conditioned responding to each element of a pair of well-established conditioned stimuli (CSs), originally reinforced elementally (A-US/X-US), observed as a result of their being given further reinforcement in compound (AX-US; Rescorla, 1970). Rescorla and Wagner (1972) provided the first model that could account for overexpectation. This model asserts that overexpectation occurs because the expected unconditioned stimulus (US) based on all cues present is greater than the US that actually occurs during compound conditioning. Because both CS A and CS X are typically trained to asymptote during the initial elemental training, the US expectation based on the sum of the expectations evoked by CS A and CS X when they are paired should be a doubly strong US. According to Rescorla and Wagner, during compound conditioning trials, CS A and CS X should both lose associative strength to the US until the sum of their associative strengths equals the maximum allowable associative strength supportable by the US experienced on each compound trial. This decrement in X-US associative strength results in a loss of conditioned responding to CS X when presented alone on subsequent tests.The extended comparator hypothesis (ECH; Denniston, Savastano, & Miller, 2001) can also account for the overexpectation effect but through a very different mechanism that emphasizes competition at the time of testing rather than at the time of training. The ECH assumes that associations are formed between all stimuli (including outcomes) that are present during training. There are three primary associations: the conventional target stimulus-outcome Correspondence concerning this article should be ad...

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