ReviewContext, ambiguity, and unlearning: sources of relapse after behavioral extinction
Introduction
For at least the last decade, a consensus has been building that extinction, the loss of performance that occurs when a Pavlovian signal or an instrumental action is no longer paired with a reinforcer, does not destroy the original learning. The idea was actually present in Pavlov’s writing (Pavlov 1927) and in that of others who followed him (e.g., Konorski 1948, Pearce and Hall 1980, Wagner 1981. Nonetheless, the notion that extinction causes unlearning is so pervasive that it itself seems difficult to unlearn. Thus, it is second nature to think that exposure therapies are effective at reducing anxiety disorders because they destroy the learning that led to them. Similarly, it seems natural to accept certain assumptions in theories of learning and memory that imply new learning will destroy the old (e.g., McClelland and Rumelhart 1985, Rescorla and Wagner 1972 see McCloskey and Cohen 1989).
Evidence that extinction is not unlearning has been reviewed in other places (e.g., Bouton 1988, Bouton 2000, Bouton and Swartzentruber 1991, Falls 1998, Rescorla 2001. In this article, I briefly summarize and update that evidence in a way that illustrates what I think is the most reasonable alternative to the destruction hypothesis. Extinction does not destroy the first-learned information but instead reflects new learning. The result is that the signal (or instrumental action) acquires a second “meaning” that is available along with the first. In this sense, the current meaning of the signal or action is ambiguous Bouton 1984, Bouton and Bolles 1985. As with other ambiguous stimuli, such as ambiguous words, its current meaning is determined by the current context. Just as the word “Fire!” evokes different reactions in a movie theater and a shooting gallery, an extinguished Pavlovian signal will evoke different reactions in different contexts. The view rejects unlearning, accepts behavioral instability as a potential consequence of extinction, and highlights several possible sources of relapse.
Section snippets
Four mechanisms of relapse
Research on extinction has uncovered at least four phenomena indicating that it does not destroy the original learning. These are summarized in this section and in Table 1. All are potential mechanisms of relapse, and all indicate the importance of context in controlling performance after extinction has occurred. Most of the research has focused on extinction in Pavlovian conditioning, in which a conditional stimulus (CS, e.g., a tone) is first paired with a motivationally significant
Other forms of retroactive interference
The idea that extinction does not destroy the original learning is compatible with a great deal of other research. For example, extinction is just one example of several retroactive interference paradigms in which new learning is introduced to replace old learning (Bouton 1993). Interestingly, the ideas just described may generalize to all examples of interference (Bouton 1993). For example, in “counterconditioning,” a rat might first receive tone–shock pairings and then pairings of the tone
What kinds of cues are contexts?
When one translates animal research into clinical practice, it is natural to ask about the boundaries of the concept or definition of context. As I suggested earlier, it is useful to think that a variety of different background cues might play the role of context in extinction. In fact, research on context effects in both animal and human learning and memory suggests that a wide variety of stimuli might potentially function this way (Table 2). Drugs, for example, can provide salient internal
Conclusion
A large body of research suggests that extinction and retroactive interference do not cause unlearning. It may be tempting to conclude that therapeutic treatments are therefore doomed, but this is not the case. Although it is probably best to assume that the original information is always available, recognition of that fact will promote better, more realistic therapies. The ambiguity framework suggests that the trick will be to develop methods that promote ubiquitous retrieval of the second
Acknowledgements
Preparation of this article was supported by Grant No. RO1 MH64847–01 from the National Institute of Mental Health. The author thanks Laure Pain and Jay Sunsay for their comments.
Aspects of this work were presented at the conference, “Learning and Unlearning Fears: Preparedness, Neural Pathways, and Patients,” held March 21, 2002 in Austin, TX. The conference was supported by an unrestricted educational grant to the Anxiety Disorders Association of America (ADAA) from Wyeth Pharmaceuticals, and
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