Relapse processes after the extinction of instrumental learning: renewal, resurgence, and reacquisition

It is widely recognized that extinction (the procedure in which a Pavlovian conditioned stimulus or an instrumental action is repeatedly presented without its reinforcer) weakens behavior without erasing the original learning. Most of the experiments that support this claim have focused on several "relapse" effects that occur after Pavlovian extinction, which collectively suggest that the original learning is saved through extinction. However, although such effects do occur after instrumental extinction, they have not been explored there in as much detail. This article reviews recent research in our laboratory that has investigated three relapse effects that occur after the extinction of instrumental (operant) learning. In renewal, responding returns after extinction when the behavior is tested in a different context; in resurgence, responding recovers when a second response that has been reinforced during extinction of the first is itself put on extinction; and in rapid reacquisition, extinguished responding returns rapidly when the response is reinforced again. The results provide new insights into extinction and relapse, and are consistent with principles that have been developed to explain extinction and relapse as they occur after Pavlovian conditioning. Extinction of instrumental learning, like Pavlovian learning, involves new learning that is relatively dependent on the context for expression.     

Resistance to extinction and behavioral momentum

In the metaphor of behavioral momentum, reinforcement is assumed to strengthen discriminated operant behavior in the sense of increasing its resistance to disruption, and extinction is viewed as disruption by contingency termination and reinforcer omission. In multiple schedules of intermittent reinforcement, resistance to extinction is an increasing function of reinforcer rate, consistent with a model based on the momentum metaphor. The partial-reinforcement extinction effect, which opposes the effects of reinforcer rate, can be explained by the large disruptive effect of terminating continuous reinforcement despite its strengthening effect during training. Inclusion of a term for the context of reinforcement during training allows the model to account for a wide range of multiple-schedule extinction data and makes contact with other formulations. The relation between resistance to extinction and reinforcer rate on single schedules of intermittent reinforcement is exactly opposite to that for multiple schedules over the same range of reinforcer rates; however, the momentum model can give an account of resistance to extinction in single as well as multiple schedules. An alternative analysis based on the number of reinforcers omitted to an extinction criterion supports the conclusion that response strength is an increasing function of reinforcer rate during training.     

Response-reinforcer relations and resistance to change

Behavioral momentum theory suggests that the relation between a response and a reinforcer (i.e., response-reinforcer relation) governs response rates and the relation between a stimulus and a reinforcer (i.e., stimulus-reinforcer relation) governs resistance to change. The present experiments compared the effects degrading response-reinforcer relations with response-independent or delayed reinforcers on resistance to change in conditions with equal stimulus-reinforcer relations. In Experiment 1, pigeons responded on equal variable-interval schedules of immediate reinforcement in three components of a multiple schedule. Additional response-independent reinforcers were available in one component and additional delayed reinforcers were available in another component. The results showed that resistance to disruption was greater in the components with added reinforcers than without them (i.e., better stimulus-reinforcer relations), but did not differ for the components with added response-independent and delayed reinforcement. In Experiment 2, a component presenting immediate reinforcement alternated with either a component that arranged equal rates of reinforcement with a proportion of those reinforcers being response independent or a component with a proportion of the reinforcers being delayed. Results showed that resistance to disruption tended to be either similar across components or slightly lower when response-reinforcer relations were degraded with either response-independent or delayed reinforcers. These findings suggest that degrading response-reinforcer relations can impact resistance to change, but that impact does not depend on the specific method and is small relative to the effects of the stimulus-reinforcer relation.     

Mathematical principles of reinforcement and resistance to change

Although Killeen's mathematical principles of reinforcement (MPR) apply to the asymptotic rate of a free operant after extended exposure to a single schedule of reinforcement, they can be extended to resistance to change in multiple schedules via alterations in the parameter representing the activating effects of reinforcers. MPR's predictions of resistance to change in relation to reinforcer rate on variable-interval (VI) schedules are empirically correct and agree with behavioral momentum theory (BMT). However, both MPR and BMT encounter problems in accounting for the effects of delayed reinforcement on resistance to change, relative to immediate reinforcement at the same rate. Further problems are raised by differences in resistance to change between variable-ratio (VR) and variable-interval performances maintained by the same reinforcer rate. With both delayed versus immediate reinforcement and variable-ratio versus variable-interval reinforcement, differential resistance to change is negatively correlated with the log ratios of baseline response rates when reinforcer rates are equated. Cases where resistance to change varies despite equated reinforcer rates, and the correlations among behavioral measures, provide challenges and opportunities for both MPR and BMT.     

Stimulus change dis-habituates operant responding supported by water reinforcers

The present experiment examined whether habituation contributes to within-session decreases in operant responding for water reinforcers. The experiment asked if this responding can be dishabituated, a fundamental property of habituated behavior. During baseline, rats’ lever pressing was reinforced by water on a variable interval 15-s schedule. During experimental conditions, rats responded on the same schedule and a new stimulus was introduced for 5 min at 15, 30 or 45 min into the 60-min session. The new stimulus was extinction, continuous reinforcement or flashing lights in different conditions. Rate of responding primarily decreased within the session during baseline. Introducing a new stimulus sometimes suppressed (extinction, continuous reinforcement) and sometimes increased (flashing lights) responding while it was in effect. The new stimulus increased responding after it ended and before it was presented in the session. The results are incompatible with the idea that non-habituation satiety factors (e.g., cellular hydration and blood volume) contributed to within-session changes in responding. These satiety factors should increase with increases in consumption, decrease with decreases in consumption and remain constant with constant consumption of water. Nevertheless, all stimulus changes increased operant responding for water. These results support the idea that habituation contributes to within-session decreases in responding for water reinforcers.     

Reinforcement context and resistance to change

Eight pigeons responded in a multiple variable-interval (VI) schedule in which a constant component always delivered 40rft/h, and an alternated component was either rich (200rft/h) or lean (6.67rft/h) in different conditions. Four tests of resistance to change were conducted in each condition: prefeeding, full extinction, constant-component-only extinction, and response-independent food. Resistance to both prefeeding and full extinction in the constant component varied inversely with the reinforcement rate in the alternated component, but resistance to response-independent food did not. The extinction and response-independent food results were consistent with [J. Exp. Psychol.: Anim. Behav. Proc. 25 (1999) 256] behavioral momentum model. Maintaining reinforcement in the alternated component increased resistance to extinction in the constant component, as predicted by the behavioral momentum model but not accounts of multiple-schedule performance based on [J. Exp. Anal. Behav. 13 (1970) 243] equation. Overall, the momentum model gave a good account of the results with the exception of the prefeeding data. Possible ways to reconcile the prefeeding results with behavioral momentum theory are considered.     

Reinforcer satiation and resistance to change of responding maintained by qualitatively different reinforcers

In previous research on resistance to change, differential disruption of operant behavior by satiation has been used to assess the relative strength of responding maintained by different rates or magnitudes of the same reinforcer in different stimulus contexts. The present experiment examined resistance to disruption by satiation of one reinforcer type when qualitatively different reinforcers were arranged in different contexts. Rats earned either food pellets or a 15% sucrose solution on variable-interval 60-s schedules of reinforcement in the two components of a multiple schedule. Resistance to satiation was assessed by providing free access either to food pellets or the sucrose solution prior to or during sessions. Responding systematically decreased more relative to baseline in the component associated with the satiated reinforcer. These findings suggest that when qualitatively different reinforcers maintain responding, relative resistance to change depends upon the relations between reinforcers and disrupter types.     

Measuring behavioral momentum

The metaphor of behavioral momentum proposes that when ongoing operant behavior is disrupted, changes in response rate are directly related to a force-like aspect of the disruptor and inversely proportional to behavioral mass. Several data sets suggest that differential resistance to change between the components of a multiple schedule satisfies the requirements of a ratio scale and is additive when different disruptors and different dimensions of reinforcement are combined. Differential resistance also provides a basis for scaling force in relation to rate of food presentation between components as a disruptor, and for scaling mass in relation to food rate within a component as a reinforcer. Preference in concurrent chains with terminal links identical to multiple-schedule components also meets the requirements of ratio-scale measurement, is additive when different dimensions of reinforcement are combined, and provides convergent measurement of behavioral mass.     

Extinction under a behavioral microscope: isolating the sources of decline in operant response rate

Extinction performance is often used to assess underlying psychological processes without the interference of reinforcement. For example, in the extinction/reinstatement paradigm, motivation to seek drug is assessed by measuring responding elicited by drug-associated cues without drug reinforcement. However, extinction performance is governed by several psychological processes that involve motivation, memory, learning, and motoric functions. These processes are confounded when overall response rate is used to measure performance. Based on evidence that operant responding occurs in bouts, this paper proposes an analytic procedure that separates extinction performance into several behavioral components: (1-3) the baseline bout initiation rate, within-bout response rate, and bout length at the onset of extinction; (4-6) their rates of decay during extinction; (7) the time between extinction onset and the decline of responding; (8) the asymptotic response rate at the end of extinction; (9) the refractory period after each response. Data that illustrate the goodness of fit of this analytic model are presented. This paper also describes procedures to isolate behavioral components contributing to extinction performance and make inferences about experimental effects on these components. This microscopic behavioral analysis allows the mapping of different psychological processes to distinct behavioral components implicated in extinction performance, which may further our understanding of the psychological effects of neurobiological treatments.     

Quantitative analyses of observing and attending

We review recent experiments examining whether simple models of the allocation and persistence of operant behavior are applicable to attending. In one series of experiments, observing responses of pigeons were used as an analog of attending. Maintenance of observing is often attributed to the conditioned reinforcing effects of a food-correlated stimulus (i.e., S+), so these experiments also may inform our understanding of conditioned reinforcement. Rates and allocations of observing were governed by rates of food or S+ delivery in a manner consistent with the matching law. Resistance to change of observing was well described by behavioral momentum theory only when rates of primary reinforcement in the context were considered. Rate and value of S+ deliveries did not affect resistance to change. Thus, persistence of attending to stimuli appears to be governed by primary reinforcement rates in the training context rather than conditioned reinforcing effects of the stimuli. An additional implication of these findings is that conditioned "reinforcers" may affect response rates through some mechanism other than response-strengthening. In a second series of experiments, we examined the applicability of the matching law to the allocation of attending to the elements of compound stimuli in a divided-attention task. The generalized matching law described performance well, and sensitivity to relative reinforcement varied with sample duration. The bias and sensitivity terms of the generalized matching law may provide measures of stimulus-driven and goal-driven control of divided attention. Further application of theories of operant behavior to performance on attention tasks may provide insights into what is referred to variously as endogenous, top-down, or goal-directed control of attention.