Temporal specificity of extinction in autoshaping

EXPRESS: Determinants of Extinction in a Streamed Trial Procedure

The strength of an association between a cue and its outcome is influenced by both the probability of the outcome given the cue and the probability of the outcome in the absence of the cue. Once an association has been formed, extinction is the procedure for reducing responding indicative of the association by repeated presentation of the cue without the outcome. The present experiments tested whether cumulative frequency and/or cumulative duration of these events affects associative extinction in a streamed trial extinction procedure with human participants. Experiment 1 assessed the effects of parametric manipulations of the frequency and duration of either the cue by itself or cue-outcome coabsence. In Experiment 1, participants proved relatively insensitive to manipulation of the event's duration. In contrast, judgments of the association by participants decreased when the frequency of cue-alone events was increased, even when the durations of those events were decreased so that cumulative exposure to the cue was equated. No effect of either the duration or the frequency of cue-outcome coabsence was observed. Experiment 2 demonstrated that the effect of cue-alone (i.e., extinction trial) frequency generalizes across a wide range of parameters for initial acquisition achieved by cue-outcome pairings. Experiment 3 tested for an interaction between event duration during initial learning and event duration during extinction. Collectively, these results indicate that the cumulative frequency, and not the cumulative duration, of extinction trials as well as the duration of the cue-outcome coabsences between extinction trials controls the effectiveness of an extinction procedure.

BEHAVIORAL AND NEUROBIOLOGICAL MECHANISMS OF PAVLOVIAN AND INSTRUMENTAL EXTINCTION LEARNING

This article reviews the behavioral neuroscience of extinction, the phenomenon in which a behavior that has been acquired through Pavlovian or instrumental (operant) learning decreases in strength when the outcome that reinforced it is removed. Behavioral research indicates that neither Pavlovian nor operant extinction depends substantially on erasure of the original learning but instead depends on new inhibitory learning that is primarily expressed in the context in which it is learned, as exemplified by the renewal effect. Although the nature of the inhibition may differ in Pavlovian and operant extinction, in either case the decline in responding may depend on both generalization decrement and the correction of prediction error. At the neural level, Pavlovian extinction requires a tripartite neural circuit involving the amygdala, prefrontal cortex, and hippocampus. Synaptic plasticity in the amygdala is essential for extinction learning, and prefrontal cortical inhibition of amygdala neurons encoding fear memories is involved in extinction retrieval. Hippocampal-prefrontal circuits mediate fear relapse phenomena, including renewal. Instrumental extinction involves distinct ensembles in corticostriatal, striatopallidal, and striatohypothalamic circuits as well as their thalamic returns for inhibitory (extinction) and excitatory (renewal and other relapse phenomena) control over operant responding. The field has made significant progress in recent decades, although a fully integrated biobehavioral understanding still awaits.

Translations in Stimulus-Stimulus Pairing: Autoshaping of Learner Vocalizations

Stimulus-stimulus pairing (SSP) is a procedure used by behavior analysis practitioners that capitalizes on respondent conditioning processes to elicit vocalizations. These procedures usually are implemented only after other, more customary methods (e.g., standard echoic training via modeling) have been exhausted. Unfortunately, SSP itself has mixed research support, probably because certain as-yet-unidentified procedural variations are more effective than others. Even when SSP produces (or increases) vocalizations, its effects can be short-lived. Although specific features of SSP differ across published accounts, fundamental characteristics include presentation of a vocal stimulus proximal with presentation of a preferred item. In the present article, we draw parallels between SSP procedures and autoshaping, review factors shown to affect autoshaping, and interpret autoshaping research for suggested SSP tests and applications. We then call for extended use and reporting of SSP in behavior-analytic treatments. Finally, three bridges created by this article are identified: basic-applied, respondent-operant, and behavior analysis with other sciences.

Number and time in acquisition, extinction and recovery

We measured rate of acquisition, trials to extinction, cumulative responses in extinction, and the spontaneous recovery of anticipatory hopper poking in a Pavlovian protocol with mouse subjects. We varied by factors of 4 number of sessions, trials per session, intersession interval, and span of training (number of days over which training extended). We find that different variables affect each measure: Rate of acquisition [1/(trials to acquisition)] is faster when there are fewer trials per session. Terminal rate of responding is faster when there are more total training trials. Trials to extinction and amount of responding during extinction are unaffected by these variables. The number of training trials has no effect on recovery in a 4-trial probe session 21 days after extinction. However, recovery is greater when the span of training is greater, regardless of how many sessions there are within that span. Our results and those of others suggest that the numbers and durations and spacings of longer-duration "episodes" in a conditioning protocol (sessions and the spans in days of training and extinction) are important variables and that different variables affect different aspects of subjects' behavior. We discuss the theoretical and clinical implications of these and related findings and conclusions-for theories of conditioning and for neuroscience.

Rescaling of temporal expectations during extinction

Previous research suggests that extinction learning is temporally specific. Changing the conditioned stimulus (CS) duration between training and extinction can facilitate the loss of the conditioned response (CR) within the extinction session but impairs long-term retention of extinction. In 2 experiments using conditioned magazine approach with rats, we examined the relation between temporal specificity of extinction and CR timing. In Experiment 1, rats were trained on a 12-s, fixed CS-unconditional stimulus interval and then extinguished with CS presentations that were 6, 12, or 24 s in duration. The design of Experiment 2 was the same except rats were trained using partial rather than continuous reinforcement. In both experiments, extending the CS duration in extinction facilitated the diminution of CRs during the extinction session, but shortening the CS duration failed to slow extinction. In addition, extending (but not shortening) the CS duration caused temporal rescaling of the CR, in that the peak CR rate migrated later into the trial over the course of extinction training. This migration partially accounted for the faster loss of the CR when the CS duration was extended. Results are incompatible with the hypothesis that extinction is driven by cumulative CS exposure and suggest that temporally extended nonreinforced CS exposure reduces conditioned responding via temporal displacement rather than through extinction per se. (PsycINFO Database Record

Temporal specificity in Pavlovian-to-instrumental transfer

Presentation of a previously trained Pavlovian conditioned stimulus while an organism is engaged in operant responding can moderate the rate of responding, a phenomenon known as Pavlovian-to-instrumental transfer. Although it is well known that Pavlovian contingencies will generate conditioned behavior that is temporally organized with respect to the arrival of the predicted outcome, little work has examined the temporal dynamics of responding during Pavlovian-instrumental transfer. We trained rats using a fixed time 60-sec, fixed time 120-sec, or random time 60-sec schedule in an appetitive Pavlovian task, and found that presentation of the conditioned stimulus potentiated operant responding in a manner that reflected these previously established temporal expectancies. Further, this temporal specificity conformed to the scalar property as seen with other forms of interval timing behavior. Surprisingly, this effect was only seen when the conditioned stimulus was a visual cue, but not when it was an auditory cue. These data suggest that the motivational processes triggered by Pavlovian cues are not static, but fluctuate in strength as a function of temporally specific expectations of reward.

A Rescorla-Wagner drift-diffusion model of conditioning and timing

Computational models of classical conditioning have made significant contributions to the theoretic understanding of associative learning, yet they still struggle when the temporal aspects of conditioning are taken into account. Interval timing models have contributed a rich variety of time representations and provided accurate predictions for the timing of responses, but they usually have little to say about associative learning. In this article we present a unified model of conditioning and timing that is based on the influential Rescorla-Wagner conditioning model and the more recently developed Timing Drift-Diffusion model. We test the model by simulating 10 experimental phenomena and show that it can provide an adequate account for 8, and a partial account for the other 2. We argue that the model can account for more phenomena in the chosen set than these other similar in scope models: CSC-TD, MS-TD, Learning to Time and Modular Theory. A comparison and analysis of the mechanisms in these models is provided, with a focus on the types of time representation and associative learning rule used.

Dentate Gyrus Contributes to Retrieval as well as Encoding: Evidence from Context Fear Conditioning, Recall, and Extinction

Dentate gyrus (DG) is widely thought to provide a teaching signal that enables hippocampal encoding of memories, but its role during retrieval is poorly understood. Some data and models suggest that DG plays no role in retrieval; others encourage the opposite conclusion. To resolve this controversy, we evaluated the effects of optogenetic inhibition of dorsal DG during context fear conditioning, recall, generalization, and extinction in male mice. We found that (1) inhibition during training impaired context fear acquisition; (2) inhibition during recall did not impair fear expression in the training context, unless mice had to distinguish between similar feared and neutral contexts; (3) inhibition increased generalization of fear to an unfamiliar context that was similar to a feared one and impaired fear expression in the conditioned context when it was similar to a neutral one; and (4) inhibition impaired fear extinction. These effects, as well as several seemingly contradictory published findings, could be reproduced by BACON (Bayesian Context Fear Algorithm), a physiologically realistic hippocampal model positing that acquisition and retrieval both involve coordinated activity in DG and CA3. Our findings thus suggest that DG contributes to retrieval and extinction, as well as to the initial establishment of context fear.SIGNIFICANCE STATEMENT Despite abundant evidence that the hippocampal dentate gyrus (DG) plays a critical role in memory, it remains unclear whether the role of DG relates to memory acquisition or retrieval. Using contextual fear conditioning and optogenetic inhibition, we show that DG contributes to both of these processes. Using computational simulations, we identify specific mechanisms through which the suppression of DG affects memory performance. Finally, we show that DG contributes to fear extinction learning, a process in which learned fear is attenuated through exposures to a fearful context in the absence of threat. Our data resolve a long-standing question about the role of DG in memory and provide insight into how disorders affecting DG, including aging, stress, and depression, influence cognitive processes.

Time to rethink the neural mechanisms of learning and memory

Most studies in the neurobiology of learning assume that the underlying learning process is a pairing - dependent change in synaptic strength that requires repeated experience of events presented in close temporal contiguity. However, much learning is rapid and does not depend on temporal contiguity, which has never been precisely defined. These points are well illustrated by studies showing that the temporal relations between events are rapidly learned- even over long delays- and that this knowledge governs the form and timing of behavior. The speed with which anticipatory responses emerge in conditioning paradigms is determined by the information that cues provide about the timing of rewards. The challenge for understanding the neurobiology of learning is to understand the mechanisms in the nervous system that encode information from even a single experience, the nature of the memory mechanisms that can encode quantities such as time, and how the brain can flexibly perform computations based on this information.

Separation of time-based and trial-based accounts of the partial reinforcement extinction effect

Two appetitive conditioning experiments with rats examined time-based and trial-based accounts of the partial reinforcement extinction effect (PREE). In the PREE, the loss of responding that occurs in extinction is slower when the conditioned stimulus (CS) has been paired with a reinforcer on some of its presentations (partially reinforced) instead of every presentation (continuously reinforced). According to a time-based or "time-accumulation" view (e.g., Gallistel and Gibbon, 2000), the PREE occurs because the organism has learned in partial reinforcement to expect the reinforcer after a larger amount of time has accumulated in the CS over trials. In contrast, according to a trial-based view (e.g., Capaldi, 1967), the PREE occurs because the organism has learned in partial reinforcement to expect the reinforcer after a larger number of CS presentations. Experiment 1 used a procedure that equated partially and continuously reinforced groups on their expected times to reinforcement during conditioning. A PREE was still observed. Experiment 2 then used an extinction procedure that allowed time in the CS and the number of trials to accumulate differentially through extinction. The PREE was still evident when responding was examined as a function of expected time units to the reinforcer, but was eliminated when responding was examined as a function of expected trial units to the reinforcer. There was no evidence that the animal responded according to the ratio of time accumulated during the CS in extinction over the time in the CS expected before the reinforcer. The results thus favor a trial-based account over a time-based account of extinction and the PREE. This article is part of a Special Issue entitled: Associative and Temporal Learning.

Facets of Pavlovian and operant extinction

Research on extinction is of fundamental importance in both Pavlovian and operant approaches to the experimental analysis of learning. Although these approaches are often motivated by different empirical and theoretical questions, extinction has emerged as a research area in which common themes unite the two approaches. In this review, we focus on some common considerations in the analysis of Pavlovian and operant extinction. These include methodological challenges and interpretational issues in analyzing behavior during and after extinction. We consider the different roles that theory has played in the development of research on extinction in these preparations and conclude with some attention to applications of extinction.

Acquisition of "Start" and "Stop" response thresholds in peak-interval timing is differentially sensitive to protein synthesis inhibition in the dorsal and ventral striatum

Time-based decision-making in peak-interval timing procedures involves the setting of response thresholds for the initiation (“Start”) and termination (“Stop”) of a response sequence that is centered on a target duration. Using intracerebral infusions of the protein synthesis inhibitor anisomycin, we report that the acquisition of the “Start” response depends on normal functioning (including protein synthesis) in the dorsal striatum (DS), but not the ventral striatum (VS). Conversely, disruption of the VS, but not the DS, impairs the acquisition of the “Stop” response. We hypothesize that the dorsal and ventral regions of the striatum function as a competitive neural network that encodes the temporal boundaries marking the beginning and end of a timed response sequence.

Human fear conditioning and extinction: timing is everything…or is it?

A differential fear conditioning paradigm was used with 107 healthy undergraduate participants to evaluate the effect of conditioned stimulus (CS) temporal properties on fear acquisition and extinction. Two minute duration CSs were used for Day 1 fear acquisition. Participants were randomized to receive either 1, 2, or 4min CS durations during Day 2 extinction. Extinction re-test was examined on Day 3 using the original acquisition CS duration (2min). Findings indicated that participants who were aware of the CS+/unconditioned stimulus (US) contingency (n=52) develop a temporal expectation about when the unconditioned stimulus will be delivered. Although the shorter duration CS resulted in greater fear reduction during extinction, cessation of fear responding at re-test was the same for CS extinction durations ranging from half the CS acquisition duration to twice the CS acquisition duration. Thus, extinction performance did not predict extinction at re-test, which could have important implications for optimizing exposure therapy for anxiety disorders.

Stimulus compounding in interval timing: the modality-duration relationship of the anchor durations results in qualitatively different response patterns to the compound cue

We have previously demonstrated that rats trained on a two-duration peak procedure in which two modal signals (i.e., tone and houselight) predicted probabilistic reinforcement availability at two times (10 s and 20 s) would respond in a scalar manner at a time between the trained durations in response to the simultaneous compound cue (tone + houselight). In these experiments, we evaluated whether this scalar response pattern would remain with greater relative separation between the anchor durations. Results revealed an effect of the modality-duration relationship, such that scalar responding was seen on compound trials in rats trained that the auditory stimulus signaled the shorter duration, whereas the visual stimulus signaled the longer duration, but not in the reverse condition. In rats showing scalar responding on compound trials, post hoc analyses demonstrated that the peak time of compound responding was most accurately predicted by the reinforcement probability weighted average of anchor peak times. In contrast, rats trained that the visual stimulus signaled the shorter duration, whereas the auditory stimulus signaled the longer duration, responded in a highly rightward skewed manner. In these rats, initiation of responding to the compound stimulus appeared to be controlled by the visual stimulus only, whereas response terminations reflected control by both modal stimuli. These latter data provide evidence of separate determinants of response initiation and termination.

Temporal factors control hippocampal contributions to fear renewal after extinction

Fear can be extinguished by repeated exposure to a cue that signals threat. However, extinction does not erase fear, as an extinguished cue presented in a context distinct from that of extinction results in renewed fear of that cue. The hippocampus, which is involved in the formation of contextual representations, is a natural candidate structure for investigations into the neural circuitry underlying fear renewal. Thus far, studies examining the necessity of the hippocampus for fear renewal have produced mixed results. We isolated the conditions under which the hippocampus may be required for renewal. Rats received lesions of the dorsal hippocampus either prior to tone fear conditioning or following extinction. Fear renewal was measured using discrete tone presentations or a long, continuous tone. The topography of fear responding at test was assessed by comparing "early" and "sustained" renewal, where early fear was determined by freezing to the first discrete tone or the equivalent initial segment of a continuous tone and sustained fear was determined by freezing averaged across all discrete tones or the entire continuous tone. We found that following pretraining damage of the hippocampus, early renewal remained intact regardless of lesion condition. However, sustained renewal only persisted in discrete, but not continuous, tone-tested animals. A more extensive analysis of the topography of fear responding revealed that the disruption of renewal was generated when the tone duration at test began to violate that used during extinction, suggesting that the hippocampus is sensitive to mismatches in CS-duration. Postextinction lesions resulted in an overall reduction of fear renewal. This pattern of results is consistent with those observed for contextual fear conditioning, wherein animals display a resistance to anterograde amnesia despite the presence of a strong retrograde amnesia for the same contextual information. Furthermore, the data support a role for the hippocampus in sustaining renewal when the CS duration at test does not match that used during extinction.

Expanding the intertrial interval during extinction: response cessation and recovery

We examined trial spacing during extinction following a human contingency learning task. Specifically, we assessed if an expanding retrieval practice schedule (Bjork & Bjork, 1992, 2006), in which the spacing between extinction trials was progressively increased, would result in faster immediate extinction and less recovery from extinction than uniformly spaced extinction trials. We used an ABB vs. ABA renewal design and observed that, whereas the expanding group extinguished faster during extinction treatment, the expanding and constant groups showed the same level of extinction with an immediate test in the extinction context (ABB) and the two groups showed equivalent ABA renewal at test in the training context. We conclude that the faster extinction observed in the expanding groups could be misleading in clinical treatment, if the therapist used the absence of fear during extinction as the basis for terminating treatment.

Time and Associative Learning

In a basic associative learning paradigm, learning is said to have occurred when the conditioned stimulus evokes an anticipatory response. This learning is widely believed to depend on the contiguous presentation of conditioned and unconditioned stimulus. However, what it means to be contiguous has not been rigorously defined. Here we examine the empirical bases for these beliefs and suggest an alternative view based on the hypothesis that learning about the temporal relationships between events determines the speed of emergence, vigor and form of conditioned behavior. This temporal learning occurs very rapidly and prior to the appearance of the anticipatory response. The temporal relations are learned even when no anticipatory response is evoked. The speed with which an anticipatory response emerges is proportional to the informativeness of the predictive cue (CS) regarding the rate of occurrence of the predicted event (US). This analysis gives an account of what we mean by "temporal pairing" and is in accord with the data on speed of acquisition and basic findings in the cue competition literature. In this account, learning depends on perceiving and encoding temporal regularities rather than stimulus contiguities.

Spacing extinction trials alleviates renewal and spontaneous recovery

Studies of extinction in classical conditioning situations can reveal techniques that maximize the effectiveness of exposure-based behavior therapies. In three experiments, we investigated the effect of varying the intertrial interval during an extinction treatment in a fear-conditioning preparation with rats as subjects. In Experiment 1, we found less fear at test (i.e., more effective extinction) when extinction trials were widely spaced, relative to intermediate or massed extinction trials. In Experiment 2, we used an ABA renewal procedure and observed that spaced trials attenuated renewal of conditioned fear relative to massed trials. In Experiment 3, we used a similar design, but instead of changing the physical context at the time of testing, we interposed a retention interval after the extinction treatment to produce a change in the temporal context. The results showed less spontaneous recovery of fear after spaced than after massed extinction trials. These results suggest that extinction is more enduring when the extinction trials are spaced rather than massed. Although the benefits of spacing trials are small when there is no contextual change from extinction to testing, a change in either physical or temporal context following massed extinction trials leads to a recovery from extinction, which is reduced when the trials are spaced.

A modular theory of learning and performance

We describe a theory to account for the acquisition and extinction of response rate (conditioning) and pattern (timing). This modular theory is a development of packet theory (Kirkpatrick, 2002; Kirkpatrick & Church, 2003) that adds a distinction between pattern and strength memories, as well as contributing closed-form equations. We describe the theory using equations related to a flow diagram and illustrate it by an application to an experiment with repeated acquisitions and extinctions of a multiple-cued-interval procedure using rats. The parameter estimates for the theory were based on a calibration sample from the data, and the predictions for different measures of performance on a validation sample from the same data (cross-validation). The theory's predictions were similar to predictions based on the reliability of the behavior.

Timing of omitted events: an analysis of temporal control of inhibitory behavior

This paper reviews research designed to investigate the temporal control of inhibitory responding using rats as subjects. One area of investigation has focused on the role of temporal variables in conditioned inhibition produced using Pavlov's [Pavlov, I.P., 1927. Conditioned Reflexes. Oxford University Press, London, 430 pp.] procedure. These studies have found that evidence of conditioned inhibition obtained by negative summation testing is strongest when the conditioned inhibitor signals the omission of the unconditioned stimulus (US) at the same temporal location as a transfer excitor signals presentation of the US [e.g., Barnet, R.C., Miller, R.R., 1996. Temporal encoding as a determinant of inhibitory control. Learn. Motiv. 27, 73-91]. Similarly, retardation of acquisition of behavioral control by a previously inhibitory conditioned stimulus (CS) is maximal when the inhibitory CS is paired with the US at the same temporal location as the inhibitor had previously signaled US omission [Burger, D., Denniston, J.C., Miller, R.R., 2001. Temporal coding in condition inhibition: retardation tests. Anim. Learn. Behav. 29, 281-290]. Other lines of research designed to assess the associative structure of temporal control of inhibition [e.g., Denniston, J.C., Blaisdell, A.P., Miller, R.R., 2004. Temporal control in conditioned inhibition: analysis of associative structure of inhibition. J. Exp. Psychol. Anim. Behav. Process. 30, 190-202] are reviewed, as is the assessment of temporal control of inhibition produced through extinction [Denniston, J.C., Miller, R.R., 2003. The role of temporal variables in inhibition produced through extinction. Learn. Behav. 31, 35-48]. These collective observations are discussed in terms of the temporal coding hypothesis [Matzel, L.D., Held, F.P., Miller, R.R., 1988. Reexamination of simultaneous and backward conditioning: Implications for contiguity theory. Learn. Motiv. 19, 317-344].

Resistance to extinction following variable-interval reinforcement: reinforcer rate and amount

Rats obtained food-pellet reinforcers by nose poking a lighted key. Experiment 1 examined resistance to extinction following single-schedule training with different variable-interval schedules, ranging from a mean interval of 16 min to 0.25 min. That is, for each schedule, the rats received 20 consecutive daily baseline sessions and then a session of extinction (i.e., no reinforcers). Resistance to extinction (decline in response rate relative to baseline) was negatively related to the rate of reinforcers obtained during baseline, a relation analogous to the partial-reinforcement-extinction effect. A positive relation between these variables emerged, however, when the unit of extinction was taken as the mean interreinforcer interval that had been in effect during training (i.e., as an omitted reinforcer during extinction). In a second experiment, rats received blocks of training sessions, all with the same variable-interval schedule but with a reinforcer of four pellets for some blocks and one pellet for others. Resistance to extinction was greater following training with the larger (four pellets) than with the smaller (one pellet) reinforcer. Taken together, these results support the principle that greater reinforcement during training (e.g., higher rate or larger amount) engenders greater resistance to extinction even when the different conditions of reinforcement are varied between blocks of sessions.

The pattern of responding after extensive extinction

Extensive extinction greatly reduces response rate and increases the relative frequency of short interresponse times, but does not affect temporal learning or operant response rate. In each of two experiments, 24 rats were trained in a multiple cued interval procedure with three stimuli (noise, light, and clicker) at three intervals (30, 60, and 120 sec). In Experiment 1, after 50 sessions of extinction, response rate decreased from about 25 to 0.5 responses/min, but temporal discriminations were maintained and the initial response gradients in reacquisition had a pattern that corresponded with the original (rather than current) training conditions. In Experiment 2, these results were replicated and extended by examination of the effect of stimulus duration on response patterns during extinction, but its lack of effect on reacquisition. The similarity of the initial performance in reacquisition to the asymptotic performance in acquisition was presumably due to the similarity of context. The individual subject data may be downloaded from www.psychonomic.org/archive.

Resistance to extinction in the steady state and in transition

Three experiments with pigeons explored the constancy of reinforcer omission during extinction conjectured by rate estimation theory. Experiment 1 arranged 3-component multiple variable-interval (VI) schedules with a mixture of food and extinction trials within each session. Reinforcers omitted to an extinction criterion increased with food-trial reinforcer rate. Experiment 2 arranged 3-component multiple VI schedules where components differed in rate or number of reinforcers. Resistance to extinction depended on the training reinforcer rate but not on the number of reinforcers omitted. Experiment 3 replicated the partial-reinforcement extinction effect within subjects in a discrete-trial procedure and found that more reinforcers were omitted in continuous- than in partial-reinforcement trials. A model of extinction based on behavioral momentum theory accounted for all the data.

Context and behavioral processes in extinction

This article provides a selective review and integration of the behavioral literature on Pavlovian extinction. The first part reviews evidence that extinction does not destroy the original learning, but instead generates new learning that is especially context-dependent. The second part examines insights provided by research on several related behavioral phenomena (the interference paradigms, conditioned inhibition, and inhibition despite reinforcement). The final part examines four potential causes of extinction: the discrimination of a new reinforcement rate, generalization decrement, response inhibition, and violation of a reinforcer expectation. The data are consistent with behavioral models that emphasize the role of generalization decrement and expectation violation, but would be more so if those models were expanded to better accommodate the finding that extinction involves a context-modulated form of inhibitory learning.