Mechanisms of resurgence of an extinguished instrumental behavior
Published on Jan 1, 2010in Journal of Experimental Psychology: Animal Behavior Processes
· DOI :10.1037/a0017365
A characteristic feature of extinction in both instrumental and Pavlovian conditioning paradigms is the relative fragility of the reduction in behavior that the procedure produces (e.g., Bouton & Swartzentruber, 1991). Indeed, although "unlearning" accounts of extinction are sometimes discussed, and embodied in otherwise powerful models of conditioning (e.g., Rescorla & Wagner, 1972), relatively enduring extinction seems to be the exception, not the rule. Continuing effects of original training on post-extinction performance may be uncovered by a wide range of manipulations, from simply allowing spontaneous recovery via the passage of time, to reinstating pre-extinction behavior via the reintroduction of primary reward or an unconditioned stimulus, to renewing behavior by removing the animal from the extinction context. As different as these procedures appear, the common thread is that all seem to depend upon the failure of what is learned in extinction to generalize beyond the extinction context (Bouton, 2002). Resurgence, a form of relapse that has primarily been examined in instrumental learning tasks, has seen little recent empirical scrutiny. In resurgence, when a previously acquired behavior is no longer rewarded while a second, novel behavior delivers reward, subsequent extinction of that new behavior will result in recovery of the original one. That is, resurgence is a return to performance of the original behavior found when all reward is discontinued (for a discussion of this and other uses of the term "resurgence" see Cleland, Guerin, Foster, & Temple, 2001). This definition is broad enough to capture several potentially heterogeneous phenomena. For example, a resurgence effect was produced when Lindblom and Jenkins (1981) provided unpredicted rewards during extinction of autoshaped keypecking behavior, then at test stopped the novel reward deliveries; when Epstein (1983) rewarded and then extinguished an alternative behavior following extinction of the original one; and when Leitenberg, Rawson, and Bath (1970) first rewarded an alternative behavior during extinction of the original and then stopped rewarding it at test. Although these procedures all induced a recovery of the original behavior when the alternative source of reward was removed or extinguished, they may well have acted via distinct mechanisms. The present experiments explored the form of resurgence first investigated by Leitenberg and colleagues (Leitenberg et al., 1970; Leitenberg, Rawson, & Mulick, 1975; see also Lieving & Lattal, 2003, Experiments 2 and 3), who developed and tested a specific hypothesis to account for the increasing amount of activity on the original behavior at test (Rawson, Leitenberg, Mulick, & Lefebvre, 1977). Their typical experiment employed three phases: (1.) an initial training phase where rats were, for instance, allowed to press one lever (L1) for food reward, (2.) an extinction training phase where L1 presses were not rewarded while presses on a novel, alternative lever (L2) were, and (3.) a test phase in which both levers were presented in extinction. Upon extinction of L2, animals resumed pressing L1 (i.e. resurgence was observed during Phase 3), and during extinction of L1, animals rewarded on L2 pressed L1 much less frequently than control animals not rewarded for L2 presses (i.e. response competition was observed in Phase 2). Based upon the latter finding, Rawson et al. argued that if the number of extinction presses emitted is a critical determinant of the strength of extinction, then animals with an alternative source of reward might have developed much weaker extinction because of response competition. When the distracting reward source was then removed, itself via extinction, these animals would have been able to manifest the relatively more intact acquisition associations in the form of greater L1 pressing. Resurgence thus occurred because animals were functionally prevented, by response competition, from emitting sufficient L1 presses to exhibit robust extinction. Rawson et al. therefore compared resurgence to an explicit response prevention procedure as a determinant of later extinction performance, and found comparable effects of the two treatments. Although this "response prevention" account is difficult to apply to other examples of resurgence, such as Epstein’s (1983) result (in which the first behavior was fully extinguished before the second behavior was trained), it does appear consistent not only with the body of Leitenberg's studies, but also with the effect detected by Lindblom and Jenkins (1981), where free reward could have produced behavior that competed with extinction of L1. The difficulties the response prevention account has with Epstein's (1983) findings suggest that different forms of resurgence may be controlled by different mechanisms. A common mechanism, however, may be involved: key to all resurgence procedures is the introduction of a clear change in background stimuli during both the transition to extinction and the shift to testing. Since extinction learning is highly context-specific (e.g., Bouton, 2004), extinction performance of the original behavior may depend on the continued presence of either the second behavior or its associated reward -- both of which are reduced or removed during the resurgence test. “Renewal” of an extinguished instrumental behavior can be observed when training occurs in one context (i.e., an "A" context), extinction occurs in a different context (i.e., a "B" context), and animals are returned to the training "A" context for test (this is "ABA" renewal -- see e.g., Nakajima, Tanaka, Urushihara, & Imada, 2000; Bouton & Swartzentruber, 1991). It is plausible that "context" may be provided by both the actions the animal performs (e.g., Weise-Kelley & Siegel, 2001) and the reward it earns through that performance (e.g., Bouton, Rosengard, Achenbach, Peck, & Brooks, 1993). An inactive or absent L2 during L1 training could act as Context A, while the establishment of L2 as a source of reward could act as Context B. At the final extinction test, if L2 was present during initial acquisition the animal would return to Context A, or if it was absent the animal would experience a "C" context ("ABC" renewal is well established in Pavlovian conditioning [e.g., Bouton & Bolles, 1979], although demonstrations in instrumental conditioning are currently lacking). Renewal of extinguished performance is thus a direct and general explanation of the return to leverpressing evinced at the resurgence test phase. The present article reports four experiments that examined several questions that remain open about the form of resurgence studied by Leitenberg et al. (1970). All previous demonstrations of resurgence involved an increase in the rate of reward between Phase 1, when L1 was trained, and Phase 2, when L1 was extinguished during concurrent L2 training. Such an increase might produce an L2 that is especially effective at competing with L1, and hence an L2 that is particularly likely to release suppressed L1 pressing when shifted to an extinction contingency. Experiments 1 and 2 therefore asked whether resurgence could occur when Phase 2 reward for L2 pressing was delivered at a rate equal to, or lower than, that experienced during Phase 1 L1 pressing. A second open question was whether resurgence depends on initial reward and extinction of L1. It is conceivable that extinction of L2 might cause an increase in any behavior, regardless of its history of association with reward, because a decline in L2 pressing produces a vacuum in behavior, or because frustration would invigorate any available behavior. Experiment 3 therefore asked whether the resurgence effect is in fact another example of the recovery of a learned-then-extinguished behavior. A third question was whether resurgence depends on the nature of the response contingency employed in Phase 2. Experiment 4 thus examined the effects of the contingency between L2 pressing and reward (which was delivered according to ratio, interval, or noncontingent schedules of reinforcement, with rate matched across treatments). Overall, the results suggest that resurgence can occur over a wide set of conditions, and that response prevention plays little necessary role.
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