Understanding cognitive behaviour therapy: A retrieval competition account

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Behaviour Research and Therapy 44 (2006) 765–784 www.elsevier.com/locate/brat

Understanding cognitive behaviour therapy: A retrieval competition account Chris R. Brewin University College London, London, UK Received 14 October 2005; received in revised form 3 February 2006; accepted 10 February 2006

Abstract Vulnerability to emotional disorders is thought to lie in memory representations (e.g. negative self-schemas) that are activated by triggering events and maintain negative mood. There has been considerable uncertainty about how the influence of these representations can be altered, prompted in part by the development of new metacognitive therapies. This article reviews research suggesting there are multiple memories involving the self that compete to be retrieved. It is proposed that CBT does not directly modify negative information in memory, but produces changes in the relative activation of positive and negative representations such that the positive ones are assisted to win the retrieval competition. This account is related to the treatment of common symptoms typical of emotional disorders, such as phobic reactions, rumination, and intrusive images and memories. It is shown to provide a parsimonious set of principles that have the potential to unify traditional and more modern variants of CBT. r 2006 Elsevier Ltd. All rights reserved. Keywords: CBT; Treatment; Memory; Retrieval; Intrusion; Rumination

Introduction The foundations of cognitive-behaviour therapy (CBT) have been the challenging and modification of irrational ways of thinking and dysfunctional ways of behaving. Its procedures formalised in detailed treatment manuals and its outcome evaluated in randomised controlled trials, CBT has been extremely successful and is now a favoured therapy for a wide variety of conditions (e.g. Hollon & Beck, 2003; Roth & Fonagy, 2005). What is still controversial is how it brings about change, and whether the different types of procedure used in CBT utilise similar mechanisms. In this article I review the theoretical basis of CBT and propose that it should be understood in the context of multiple representations in memory, some positive and some negative, that compete for retrieval. In the acute phase of an emotional disorder negative representations are highly accessible, with intrusive memories, self-depreciating interpretations, and ruminative thoughts dominant. CBT procedures involve the selection and creation of alternative representations that are assisted to

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win the retrieval competition and restore more positive mood states. This approach is evaluated against several criteria such as utility and parsimony, and the wide-ranging clinical implications discussed. Why, if CBT is so successful, is it necessary to question its theoretical basis? First, therapeutic techniques such as desensitisation or exposure were based on behaviourist theories that have largely been superseded by more sophisticated approaches to associative learning in animals and humans (Mineka & Zinbarg, 2006). Similarly, the philosophy of cognitive therapy is largely rooted in the assumptions of the 1960s and 1970s. It is now possible to draw on a much more extensive empirical and theoretical understanding of learning and cognition than was available at that time. Second, reviews have concluded that CBT, while effective, does not always lead to clinical improvement and does not always protect successfully treated patients against relapse (Robinson, Berman, & Neimeyer, 1990; Roth & Fonagy, 2005). Hence, by clarifying the mechanisms by which CBT brings about change, it may be possible to improve outcomes. The third reason is that cognitive therapy is itself developing in new directions. There is a greater emphasis on metacognitive interventions that attempt to change a person’s relationship to their negative thoughts rather than directly challenge the content of those thoughts (e.g. Hayes, Strosahl, & Wilson, 1999). Other interventions seek to introduce positive distortions into cognitive processes, for example by manipulating imagery (e.g. Hackmann, 1998; Smucker, Dancu, Foa, & Niederee, 1995). These approaches appear on the face of it to be challenging some of the original assumptions of CBT. Fig. 1 presents a generic version of the cognitive model of emotional disorder underlying CBT, adapted from Beck (1976), Beck, Emery, and Greenberg (1985), Foa and Kozak (1986), Harvey, Watkins, Mansell, and Shafran (2004), Wells (1997), and others. Over the years the generic model has been developed and applied to various disorders including depression (Beck, Rush, Shaw, & Emery, 1979), panic disorder (Clark, 1986), posttraumatic stress disorder (PTSD: Ehlers & Clark, 2000; Foa & Rothbaum, 1998), hypochondriasis (Warwick & Salkovskis, 1990), obsessive-compulsive disorder (OCD: Salkovskis, 1985), generalised anxiety disorder (Riskind, 2005), and social phobia (Clark & Wells, 1995). Although many of these models focus primarily on the different maintaining processes, they generally assume that previous adversity produces vulnerability in the form of negative representations of the self and the world (the most widely used term for such representations being ‘negative schemas’). Triggering events lead not only to negative mood states but, in

Causal Factors

Consequences

1. Vulnerability Negative life experiences (particularly if uncontrollable, repeated etc.)

Formation of latent representations in memory (associations, episodic memories, schematic knowledge) summarising experiences with negative mood

2. Onset Negative experiences in later life

Experience of negative mood Activation of inaccurate or inappropriately generalised representations. Experiencing of intrusive thoughts, images, impulses etc.

3. Maintenance Interactions (e.g., vicious circle) between mood and processes such as selective attention, selective memory, selective interpretation, reasoning bias, avoidance, safety behaviours, thought suppression, metacognitive beliefs, etc.

Persistence and exacerbation of negative thoughts and behaviours

Fig. 1. A generic cognitive-behavioural model of emotional disorder.

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interaction with these representations, to the intrusion of negative thoughts and images that prolong negative mood. Altering the processes that maintain these thoughts and images improves mood immediately but, in the longer term, must also reduce the likelihood of problematic representations being activated in future. The focus of this article is on the critical issue of how overcoming behavioural and cognitive avoidance, challenging negative thoughts, or modifying maintaining processes affect the memory representations that carry vulnerability to future episodes of disorder. Barber and DeRubeis (1989) discussed this in the context of cognitive therapy for depression. Their accommodation model corresponds to the widely accepted view (Beck et al., 1979; Foa & Kozak, 1986) that therapy modifies the structures in memory that give rise to negative beliefs. That is, successfully correcting irrational thinking or behaviour directly alters the content of the schemas that carry vulnerability and reduces the risk of relapse. In contrast, their activation– deactivation model proposes that therapy does not change structures in memory but leads to the deactivation of negative memories and the activation of positive ones.1 These models have been further elaborated by Kwon and Oei (1994). Brewin (1989) proposed more specifically that it is the creation of competing memories in therapy that deactivates or blocks access to problematic representations. Thus, both Brewin (1989) and Barber and DeRubeis (1989) were concerned with whether problematic memory representations were directly modified or simply deactivated. This apparently simple question has important implications for understanding and designing interventions within CBT. Before proceeding further, it is important to consider whether the structures in memory that carry vulnerability are all of the same kind. Whereas the original proponents of behaviour therapy argued that behaviour is mainly under the control of associations that are not consciously accessible, cognitive therapists have tended to argue that the memory structures controlling behaviour are explicit and knowable. Work in social, cognitive, and neuropsychology (e.g. Berry & Broadbent, 1984; Nisbett & Wilson, 1977; Poldrack & Packard, 2003; Squire, 2004) has strongly supported the view that knowledge can be stored both in a form that is open to conscious inspection and in a form that is consciously inaccessible but gives rise to products in the form of moods, impulses, and intuitions. There are now several influential multi-level memory theories of psychopathology (e.g. Brewin, 1989, 1996; Power & Dalgleish, 1997; Teasdale & Barnard, 1993), all of which draw attention to the importance of representations of events that exceed the limits of conscious processing and the implications this has for therapeutic intervention. Other memory theorists (e.g. Brown & Kulik, 1977; Johnson & Multhaup, 1992; Pillemer, 1998) have made a strong case for the existence of parallel representational systems for images and conceptual knowledge. The image-based system is thought to be highly efficient in capturing sensory experience, requiring few if any attentional resources. Image retrieval is an automatic process, triggered by relevant cues. In contrast, the conceptual system requires considerable attentional resources but enables the storage of representations that can be flexibly retrieved and utilised for planning and other forms of complex thought. Recent research confirms early clinical observations (Beck, 1970; Beck, Laude, & Bohnert, 1974) that many disorders are characterised not only by negative thoughts but by distressing, intrusive images (e.g. health anxiety: Wells & Hackmann, 1993; agoraphobia: Day, Holmes, & Hackmann, 2004; and social phobia: Hackmann, Clark, & McManus, 2000). Likewise, negative thoughts frequently accompany the intrusive memories that are characteristic of PTSD (Reynolds & Brewin, 1998). Some theories of posttraumatic stress disorder (Brewin, Dalgleish, & Joseph, 1996; Dalgleish, 2004) have proposed that different representational systems underpin the negative images and negative beliefs, and require different types of intervention. Despite the fact that they are often considered (and delivered) together under the umbrella of CBT, behaviour and cognitive therapy have traditionally been thought to be based on different underlying principles. In the next sections they are therefore discussed in turn, paying particular attention to the role of memory representations. I then present evidence from social and clinical psychology that is relevant to the existence of multiple representations and the processes that determine which of them will come to mind. Finally, I shall propose and evaluate a retrieval competition account of CBT and discuss how it can provide theoretical integration for a broad range of alternative therapeutic procedures.

1

Barber and DeRubeis’s (1989) third model, the compensatory skills model, was couched in terms of maintaining processes rather than in terms of memory structures, and as such is not in competition with the other two.

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Principles of behaviour and cognitive therapy Behaviour therapy According to the associationist perspective, the behaviour of persistently anxious people is guided by rules automatically abstracted from threatening experiences using principles such as contiguity, contingency, and similarity. For the original proponents of behaviour therapy (e.g. Wolpe, 1973) these rules took the form of conditioned associations that drove behaviour independently of conscious beliefs. Individuals were aware of the kind of stimuli that produced emotional reactions, but not of the rules themselves. The paradigm case was the acquisition of a phobia from a brief exposure to a threatening situation. By a process of stimulus generalisation situations that were similar but not identical to the original one could come to elicit the phobic symptoms, allowing the conditioned response to become gradually more and more detached from the circumstances of the original threat. Lang (1979) reformulated conditioning theory by positing that threatening situations created a ‘‘fear memory’’ of the learning episode consisting of stimulus, response and meaning information. Fear memories were held to be exceptionally stable, coherent, and likely to be retrieved by relevant environmental cues, resulting in a reinstatement of the person’s original fearful reaction. These ideas have been applied in a somewhat adapted form to other disorders such as PTSD (Foa & Rothbaum, 1998). For behaviourists such as Wolpe, verbal interventions were thought to be ineffective for phobias based on conditioned associations, although they acknowledged their potential value for cognitively based fears (Wolpe, Lande, McNally, & Schotte, 1985). The most effective treatment was found to be repeated and prolonged exposure to the unreinforced phobic stimulus (Roth & Fonagy, 2005). Exposure is typically conducted within a structured context emphasising safety, personal control, and sustained attention to the phobic stimulus. This usually leads to a fairly rapid reduction in anxiety, which it has been suggested is brought about by habituation. Although the steps demanded by the treatment are deliberate, the processes by which change occurs are predominantly automatic and do not require explicit logical or causal thinking. Exposure, which remains a central part of treatment for phobias, PTSD, and OCD, has traditionally been regarded as an example of associative learning in that it attempts to produce new patterns and regularities involving the same elements that were part of the fear-inducing experience. Contemporary cognitive theorists (e.g. Evans, 2004; Epstein, 1994; Kahneman, 2003; Sloman, 1996) similarly describe a type of reasoning that is associative and automatic, making use of basic principles such as the similarity between elements or the closeness of two elements in time. It searches for and bases conclusions on patterns and regularities between elements such as images and stereotypes. The neural systems underlying this form of thought have the capacity to process large amounts of information in parallel, but are relatively inflexible. Conclusions are experienced as preferences, emotions, images, impulses, or intuitions that may be hard to explain or put into words. The most influential recent formulation of how the memories of phobic patients are changed was put forward by Foa and Kozak (1986), who proposed that confronting the patient with their feared situation, whether in imagination or in vivo, first activated the memory, resulting in the experience of fear. Corrective information was then incorporated into it in the form of the experience of habituation to threat cues that occurred within or between therapeutic sessions. Later exposure to the phobic stimulus resulted in the activation of this modified memory, with its accompanying lower levels of arousal. This is an example of Barber and De Rubeis’s (1989) accommodation model. Although widely accepted, empirical support has been equivocal. For example, two studies have supported the predicted relationship of therapeutic response to the initial activation of fear, and two studies did not support it once initial symptom severity or subsequent habituation were controlled. In two studies improvement in PTSD symptoms was related to reductions in levels of fear between treatment sessions but not to reductions in fear within sessions. It is not clear, however, that the between-session reductions in fear were actually produced by habituation rather than by some other mechanism such as reappraisal (see Brewin & Holmes, 2003, for a more detailed review). Another source of understanding the changes in underlying representations brought about by exposure comes from animal models of aversive learning. Conditioned fear reactions to a stimulus are produced which can then be extinguished by re-presenting the stimulus to the animal numerous times in the absence of the noxious experience. Initially it was thought that extinction was a form of unlearning, in which the conditioned

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associations that had been created were systematically weakened (another example of the accommodation model). However, there is ample evidence that conditioned fear reactions in animals can be easily reinstated or renewed following successful extinction, for example by re-exposing animals to the unconditioned stimulus or by placing them into a new context and re-presenting the conditioned stimulus (Bouton & Moody, 2004; Jacobs & Nadel, 1985). The implication drawn by these researchers is that during extinction the original associations are not being unlearned but that the animal is acquiring new learning which can under certain conditions take precedence over the original memories. It has been proposed that new hippocampally dependent memories compete for retrieval with the original learned associations and, if they take precedence, exercise inhibitory control over the amygdala either through direct connections between the two structures or via the projection of the hippocampus to the prefrontal cortex (Brewin, 2001; LeDoux, 1998). These pathways have the capacity to inhibit the activation of the amygdala when the person or animal is in a context associated with safety, but in unfamiliar contexts where there are no safety cues or in contexts associated with threat no inhibition takes place and the original fear response returns. According to LeDoux (1998), conditioned emotional reactions are probably indelible but are inhibited when new learning indicates that they are no longer relevant.2 Similarly, the return of fear has been demonstrated in human participants who have undergone extinction of conditioned fear (Hermans et al., 2005; Vansteenwegen et al., 2005) or successful treatment for phobias and anxiety disorders (Mineka, Mystkowski, Hladek, & Rodriguez, 1999; Mystkowski, Mineka, Vernon, & Zinbarg, 2003; Rachman, 1989). In other words, this research strongly favours the hypothesis that new learning deactivates problematic representations rather than directly changing them. It also raises questions about the processes that determine the relative accessibility of the different representations. For example, it draws attention to the match between potential environmental triggers and the content of competing memory representations, and suggests that contextual cues will be important in determining which of a set of relevant memories is retrieved. Cognitive therapy According to the founder of cognitive therapy, Aaron Beck, and his colleagues, the aim of this type of therapy is to bring about positive changes in erroneous cognitions, in maladaptive information processing strategies, and in one-sided memory structures. In contrast to the associationist views of conditioning theorists, this approach is primarily rationalist in its formulation of patients’ thinking as (a) open to conscious inspection, (b) in need of correction to achieve consistency with logical and empirical standards, and (c) in its choice of interventions such as Socratic questioning, behavioural experimentation, and systematic data gathering and analysis (Beck et al., 1979). Although the extent to which cognitive therapy identifies psychopathology with irrationality may have been somewhat exaggerated, a recent exposition of the underlying theory does claim that information processing differs in depression by virtue of the presence of systematic errors and that therapy promotes constructive, reality-based reasoning (Clark, Beck, & Alford, 1999). Cognitive therapy was originally applied to depression, a disorder that encompasses a negative response to a wide variety of adverse circumstances (unlike the much more circumscribed specific phobia). Because of the focus on the way depressed people think, not just on how they behave, cognitive therapy has always made a distinction between memory representations and their products. The intrusive cognitions and thinking styles associated with psychopathology are thought to arise from the existence of various kinds of semi-permanent memories that represent a synthesis of previous life experiences in an abstracted form. Repeated experiences are believed to result in the formation of a ‘‘schema’’, a form of semantic memory that describes the qualities associated with the self. For example, the model proposes that depressed people possess negative ‘‘schemas’’ about the self that contain absolute beliefs of the kind ‘‘I am unlovable’’ or ‘‘I am incompetent’’ as well as conditional beliefs (basic assumptions) of the kind ‘‘If I am not a success my life is 2

Ledoux’s views about the indelibility of memory have been modified to take into account observations concerning reconsolidation processes (see Brewin, 2005, for a review).

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meaningless’’. The schema is a theoretical structure that not only reflects past experience but also is involved in organising and structuring new experiences, particularly ambiguous ones. The content usually reveals a thematic connection either to a failure to achieve a desired goal or to some kind of interpersonal loss or rejection (e.g. Beck, 1983; Blatt, 2004; Hammen, 1997). These structures are believed to remain latent until activated by the onset of negative mood or by negative life events. The standard account of how cognitive therapy works (Beck et al., 1979) focuses on the challenging of negative thoughts and the modification of the content of basic assumptions and schemas (corresponding to Barber and De Rubeis’s, 1989, accommodation model). After determining the content of these knowledge structures, therapists attempt to change the semantic information they contain by reinterpreting the meaning of significant autobiographical episodes occurring in the past, present, and future. As indicated above, this is achieved by a combination of verbal and behavioural techniques that challenge prior knowledge. Behavioural tasks and experiments are set, not because (as in behaviour therapy) it is intended they will bring about change automatically through associationist principles, but because they will yield information that will challenge beliefs and assumptions. Interventions are conducted both in therapy sessions and through homework assignments, with emphasis being placed on the necessity of practising challenges to established ways of thinking. These challenges then assist more even-handed information processing that properly incorporates positive information into memory representations and hence into the generation of future interpretations and expectations. In contrast to the reliance of behaviour therapy on implicit, associative processes, cognitive therapy appears to draw mainly on explicit, verbal reasoning. This corresponds to contemporary notions of a form of reasoning that is conscious, rule-based, and deliberate, and tries to describe the world in conceptual terms by capturing a structure that is logical or causal (e.g. Evans, 2004; Epstein, 1994; Kahneman, 2003; Sloman, 1996). The neural systems underlying this form of thought, unlike those underlying associative reasoning, have a very limited capacity but are extremely flexible. Conclusions arrived at are typically verbalisable. Hollon and Garber (1988) suggested that depressed patients might have to acquire a facility for logical reasoning that was superior to that of the majority of the population. Cognitive therapy does not only rely on logical reasoning, however. As noted by Hollon and Garber (1988), Beck and his colleagues have always recommended metacognitive strategies that involved changing patients’ relationship to their thoughts, for example by ‘‘distancing’’ themselves and observing their mental processes more dispassionately. These strategies may utilise an associative process whereby the same distressing mental contents are progressively paired with more detached, less emotional mental states. Also, various methods of working with imagery have been suggested for anxiety disorders (Beck et al., 1985). These procedures are more experiential and do not necessarily involve explicit verbal challenges. Consistent with the return of fear in anxiety disorders, patients successfully treated for their depression with cognitive therapy are also prone to relapse (Roth & Fonagy, 2005). Applying the same logic that was used above in relation to behaviour therapy suggests that cognitive therapy, like exposure to a frightening stimulus, does not work by altering an underlying negative representation but by creating or strengthening competing positive representations. In support of this idea, the tendency for people who have recovered from or are vulnerable to depression to endorse negative depressogenic beliefs can be manipulated experimentally. Under normal conditions, these individuals tend to endorse positive beliefs and are indistinguishable from never depressed or non-vulnerable controls. If a negative mood is temporarily induced (Miranda, Gross, Persons, & Hahn, 1998; Miranda & Persons, 1988; Miranda, Persons, & Byers, 1990; Teasdale & Dent, 1987), or stressful life events intervene (Miranda, 1992), they revert to endorsing negative beliefs typical of the currently depressed. Persons and Miranda (1992) articulated a mood-state hypothesis to account for their findings. As they noted, it was very much in line with previous suggestions (e.g. Beck et al., 1979; Ingram, 1984; Riskind & Rholes, 1984; Teasdale, 1988) concerning depressive vulnerability. They proposed that negative beliefs remained latent and inaccessible to self-report until activated by stressful events or a negative mood. More recently, Wenzlaff and Bates (1998) found that whereas recovered depressed patients typically completed sentences using positive words, similar to the never depressed, they could be induced to complete them using negative words by temporarily imposing a cognitive load. Wenzlaff and Bates interpreted these results to mean that in order for the recovered depressed to maintain positive beliefs in consciousness they have to effortfully

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suppress competing negative beliefs. If the efficiency of this suppression is reduced by having to attend to a second task, the negative beliefs once again become accessible. There are thus theoretical and empirical reasons for believing that the depressed have access to a variety of memory representations, some positive and some negative, with circumstances dictating which are retrieved from moment to moment. Consistent with this, currently depressed individuals do report both positive and negative thoughts (Kendall, Howard, & Hays, 1989), evaluate themselves both positively and negatively in different areas of their life (Brown, Andrews, Bifulco, & Veiel, 1990), and distinguish the predominantly negative traits that characterise their current view of themselves from more positive traits that characterise them at other times in their lives (Brewin, Smith, Power, & Furnham, 1992). There is now strong support for the idea that the activation of competing memory representations is closely involved in depressive vulnerability, relapse, and recurrence (Scher, Ingram, & Segal, 2005). The representations available to the depressed are not just distinguished by their valence, and do not appear just to consist of general self-representations summarising past experience or conditional assumptions. Depressive thinking is also characterised by the intrusion of image-based personal memories largely involving accidents and injuries to the self or close others, physical and sexual assaults, and interpersonal difficulties including loss and rejection (Brewin, Hunter, Carroll, & Tata, 1996), and if these memories are frequent a less favourable outcome to the depressive episode is likely (Brewin, Reynolds, & Tata, 1999). These findings all emphasise the variety and significance of representations that may be competing for retrieval during an episode of depression. Summary Behaviour therapy involves procedures such as exposure that rely on a form of associative reasoning to overcome the effects of prior learning that is not directly accessible to consciousness. Exposure produces new memory representations that compete with this prior learning and inhibit its effects. Cognitive therapists, in contrast, have usually assumed that relevant memory representations are available to conscious inspection and that their content can be altered by a process of logical or causal reasoning. There is evidence that individuals with emotional disorders have access to a variety of relevant representations including semantic and episodic memories. There are theoretical and empirical reasons to believe that these representations remain available after recovery from an acute episode of disorder and can be accessed under appropriate conditions. Previous research on multiple representations and retrieval competition As we have seen, the idea that representations in memory compete for retrieval, with negatively valenced structures being latent but winning the retrieval competition in the presence of stressful life events or negative mood, is consistent with Beck et al.’s (1979) original diathesis-stress conceptualisation of depression and with the theoretical position of numerous other authors concerned with vulnerability, relapse, and recurrence in emotional disorders. What is being proposed here is simply that the same principles underlie how CBT works. To date the standard account of therapeutic change involves the direct modification of memory representations, and an activation/deactivation or retrieval competition account has been less often considered as a possibility (for exceptions see Barber & DeRubeis, 1989; Brewin, 1989, 1996, 2001, 2003; Foa & McNally, 1996; Kwon & Oei, 1994). Other areas of psychology, however, have produced research on multiple representations and retrieval competition. A full review of this literature is beyond the scope of this article, and I will confine myself to those aspects most relevant to involuntary memory and psychotherapy processes. An assumption prevalent at the time CBT was first formulated concerned the existence of a unitary and enduring personality structure (Cantor, Markus, Niedenthal, & Nurius, 1986). Since then several lines of research in social and cognitive psychology have greatly modified theoretical understanding of the way in which the self is represented in memory. Markus and Wurf (1987) claimed that there are close parallels between the organisation of semantic knowledge about the world and semantic knowledge about ourselves. Information in memory about the self is thought to be organised as a set of multiple, related memory records

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that capture important episodes and relationships. These overlapping records preserve some consistent features of the self but also contain information relating to the self at different ages and in the performance of different roles. They span the whole range of success and failure, stability and change, attachment and loss, acceptance and rejection. Importantly, selves can be based on wishes or aspirations (possible selves: Markus & Nurius, 1986). Strauman and Higgins (1988) presented evidence that depression is associated with a large discrepancy between the person we think we actually are and the person we would ideally like to be, whereas anxiety is associated with a perceived failure to be the person we think we ought to be. Other recent research suggests that both anxiety and depression are strongly related to feeling too close to a feared or undesired self and striving to avoid experiencing it (Carver, Lawrence, & Scheier, 1999), a phenomenon which appears particularly relevent to OCD (Ferrier & Brewin, 2005). Thus, self-representations do not appear to consist only of summaries of past experience. Knowledge about the self consists at least in part of imaginative constructions that may be only partly rooted in reality. Similarly, in decision-making, people routinely model possible scenarios in order to select the optimal behavioural choices (Evans, 2004). Faced with negative outcomes, they frequently engage in counterfactual thinking of the form ‘‘What if I had not done Xy’’ These developments confirm Beck et al.’s (1979) observations about the importance of conditional assumptions and emphasise that memory representations are not just concerned with summarising the past but with attempting to predict the future (see also Barsalou, 2003). In numerous contexts where a task involves selection among alternative representations it has been widely assumed that a process of retrieval competition decides which of the representations will enter conscious awareness (Anderson, 1974; Anderson, Bjork, & Bjork, 1994; McGeoch, 1942). The idea that representations compete for access via a shared retrieval cue has been used, in particular, to explain the phenomenon of interference, in which the ability to recall an item is impaired by the existence of a related item. For example, the failure to retrieve the name of a distant acquaintance may be frequently accompanied by persistently intruding unwanted names that are similar to the target name. Those items in memory with stronger associations to the retrieval cue are generally held to be more likely to win the retrieval competition and be recalled to mind. Interference effects are ubiquitous in psychology, and have been found in studies of word meanings, semantic memories, episodic memories, memory for visual stimuli, motor skills, and animal conditioning (Anderson & Neely, 1996). What is perhaps unique about the self is the potential for inconsistency and hence competition among alternative records containing contradictory information relating, for example, to the self and to relationships with important attachment figures. Just as simple words such as ‘‘bank’’ can have more than one meaning attached to them, so the same is true of our concepts of ourselves and others, only to an infinitely greater extent. Autobiographical memory is thought to be organised hierarchically, with different types of representation corresponding to life themes, specific episodes, and detailed event memory (Conway & Pleydell-Pearce, 2000). At any one time a small subset of these representations is active in working memory (Andersen & Chen, 2002; Cantor et al., 1986), suggesting that they compete for retrieval as a ‘working self’ in the same way as do other items in memory (Conway & Pleydell-Pearce, 2000). In clinical disorders such as depression it appears that there is not only evidence for intrusive thoughts, but a strong tendency for records containing negative information about the self, negative images, and negative episodic memories to be retrieved involuntarily in preference to corresponding positive records. There are several explanations, described by Anderson and Neely (1996), that attempt to account for the tendency of some representations to keep coming to mind in preference to their competitors. The occlusion approach proposes that the greater associative strength of some items blocks the retrieval of other items. If retrieval is blocked for long enough, search efforts may be abandoned and eventually the item may be forgotten. The unlearning approach proposes that the association between a cue and a previously learned item becomes weaker when a new association is formed between that cue and a different item. The weakening of the association leads eventually to forgetting. The attentional focus approach proposes that retrieval can be viewed as a kind of selective attention to certain kind of internal items in memory. The act of retrieval strengthens levels of activation of relevant items and decreases levels of activation of competing but unwanted items. The distinction between unlearning, on the one hand, and occlusion or attentional focus on the other, is clearly

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related to the distinction between direct modification versus activation/ deactivation of memory contents as potential mechanisms of therapeutic change. The current level of activation of competing representations will depend on a number of processes, primarily frequency of rehearsal. Recall that leads to elaborative rehearsal, in which memory contents are deeply semantically processed (for example in relation to the self), is likely to make those representations highly accessible (Baddeley, 1990). For example, recall of a relationship break-up that is then related in detail to negative qualities of the self will have a high probability of occurring again. Moreover, rehearsal of one memory leads automatically to reduced activation of other related memories (retrieval-induced forgetting: Anderson et al., 1994). Thus, recall of a negative memory concerning the self may automatically reduce the accessibility of competing positive memories, and vice versa. Another important factor is the nature of the cues present at recall, as described by the encoding specificity principle: ‘‘The probability of successful retrieval of the target item is a monotonically increasing function of informational overlap between the information present at retrieval and the information stored in memory (Tulving, 1979, p. 408). This principle forms a core aspect of several theories of depression that posit a vicious circle whereby negative mood leads to the retrieval of negative memories, which in turn enhance negative mood (e.g., Ingram, 1984; Teasdale, 1988). In addition to rehearsal, it has long been known that the encoding of unusual or distinctive features makes retrieval more likely if some of those features are available when the time comes to recall what has been learned. For example, in trying to learn a word paired with train (such as train–cloud) it is will probably be easier to remember cloud if you form a bizarre image of a train flying through the air above the clouds. More recent evidence goes further in showing that the encoding of unique features with the target memory improves retrieval even when these features are not available at recall. Even general reminders or cues can access these distinctive encodings (Hunt & McDaniel, 1993; Hunt & Smith, 1996). In cases where there are several memories competing for retrieval, the more a target memory is made distinct from potential competitors, the more those competitors are suppressed each time the target memory is retrieved (Anderson, Green, & McCulloch, 2000). Finally, there is evidence in the general population for a pervasive memory bias favouring the retrieval of positive over negative autobiographical memories (Walker, Skowronski, & Thompson, 2003). In the absence of other influences, positive memories appear to enjoy a retrieval advantage. Although such a bias may not be evident in conditions such as depression, it is possible that they become important during psychotherapy, as positive competitors are developed and rehearsed. Summary The idea that there may be multiple representations of an object that compete for retrieval is very common in psychology, particularly in relation to the self. Self-representations consist of semantic and episodic memories, as well as imagined, wished for, and feared elements. Theories of retrieval competition have similarities to the proposed mechanisms put forward to explain the success of CBT (e.g. Barber & DeRubeis, 1989; Brewin, 1989). Successful retrieval is likely to depend on rehearsal, the cues present at recall, and the distinctiveness and valence of the to-be-remembered item. Specification and evaluation of a retrieval competition account of CBT According to a retrieval competition account of CBT, the purpose of therapy is to alter the relative accessibility of memory representations containing positive and negative information, particularly when patients are faced with challenging situations. It is assumed that potentially there are multiple relevant knowledge structures, some dominated by sensory features (e.g. episodic memories, images), some dominated by somatic and motor responses, and some predominantly verbal and conceptual, ranging from concrete summaries of experience to abstract, hypothetical constructs. The account does not specify the architecture of these structures but does not assume that their content is necessarily consciously accessible. However, it is assumed that in the presence of external or internal cues all these representations compete, with success

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depending on established factors likely to affect involuntary retrieval, i.e., level of activation, encoding specificity, distinctiveness, and valence. Therapists, it is suggested, help the individual to create or strengthen competitor representations in which cues that previously led to the retrieval of negative memories are now combined with positive elements. This is shown in simplified form in Fig. 2. Before therapy, only negative representations enjoy a high level of activation. Following therapy, it is positive representations that are highly activated. Some of these representations are indirect competitors (P1, P3). Others (P6, P8) are direct competitors that have been created to have similar features to the original negative representations. These negative representations (N6, N8) remain available but at a low level of activation. The direct competitors can be created using either logical or associative forms of human reasoning as described above. In those cases where negative cues resulted in the retrieval of generalised negative representations, for example concerning the self, the new competitors will need to be associatively linked with generalised positive representations in memory. Further, therapists must help to ensure that positive representations win the retrieval competition when the person is once again confronted with those cues. If there are no preexisting memory representations containing positive information about the self that are sufficiently well-developed or stable to compete effectively with currently active structures containing negative information, then longer-term therapy aimed at establishing and elaborating such structures is assumed to be necessary. This would correspond to what have been called ‘‘schema-focused’’ variants of CBT that have been applied to individuals with long-standing problems in social adjustment or chronic psychopathology dating from early childhood (Padesky, 1994; Young, 1990).

PRE-THERAPY Representations

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P2

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Legend P1 etc. = positive representations N1 etc. = negative representations P6 etc. = newly constructed positive representations = weak activation = strong activation Fig. 2. The effect of therapy on the retrieval competition process.

P8

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This account differs from the standard rationale for CBT described above in several key aspects. First, its underlying philosophy is explicitly constructivist rather than rationalist. That is, it does not require that patients’ thinking is initially distorted or that the positive elements it seeks to introduce are in any sense more reasonable or logical. Rather, it is the valence of these elements and the ability of the new representations to compete effectively for retrieval that are seen as critical. Second, preexisting negative representations are assumed to be permanent and available, even after successful therapy, to be accessed by the right combination of retrieval cues. Therapists should, therefore, explain the role played by unwanted memory representations and teach strategies for limiting their activation. The third key aspect is to emphasise the potential role of associative processes in the strategic formation of competitor representations. As noted by Teasdale and Barnard (1993), the lack of clear-cut, replicable effects in psychotherapy research means that it is rarely possible to provide a definitive proof that a given theory is right or wrong. Rather, theories must be judged by a variety of criteria such as their adequacy in explaining existing observations, their ability to generate testable predictions, and their parsimony in requiring the fewest assumptions. In the remainder of this section I will evaluate the account against these criteria. Adequacy to explain existing observations Behaviour therapy In the exposure methods used in the treatment of phobia patients are asked to vividly imagine or actually revisit the frightening situation, staying with the image or situation long enough for anxiety to reduce. This is repeated until there appears to be little arousal of anxiety to the original situation. According to current theory, these procedures result in the incorporation of corrective information (habituation) into the original fear memory (Foa & Kozak, 1986). Faced with the reality that fear often returns despite successful treatment (Rachman, 1989), behaviour therapists have traditionally been encouraged to extend exposure work to related situations, for example desensitising a person bitten by a wolfhound to other large dogs as well. The rationale for this was to prevent stimulus generalisation, the tendency of the original association to be evoked by a related stimulus. If the original fear memory has been corrected, however, it is not clear why an encounter with other large dogs should result in a return of fear. From a retrieval competition perspective, the behaviours that therapists have their patients perform, whether in vivo or in imagination, are creating additional detailed representations of encounters with the feareliciting situation. The new representations differ, however, in that they incorporate a positive context involving, for example, free choice, comparative safety, or a belief in at least partial self-efficacy, rather than a negative context involving compulsion, fear, or helplessness. The fact that empirical data on the importance of habituation are inconsistent (e.g. Brewin & Holmes, 2003 is explained by habituation being one of several possible positive elements rather than as being critical in mediating change. Within these new representations, therefore, positive elements are automatically associated with features of the original situation. A number of factors will potentially give the new representations a retrieval advantage: Rehearsal will increase their level of activation and reduce the activation of the original representation, deliberate self-exposure in a therapeutic context will help to make them distinctive, and the reduction in experienced anxiety will give them a positive valence. Avoidance is seen as a critical process in many different types of psychopathology (e.g. Borkovec, Ray, & Stober, 1998; Hayes, Wilson, Gifford, Follette, & Strosahl, 1996). It is also seen as critical to successful therapy. For example, it has been argued that exposure is only effective if the patient attends fully to the frightening image or situation and does not exercise cognitive avoidance by distracting themselves or omitting to attend to the most frightening aspects (Foa & Kozak, 1986). From a retrieval competition perspective, the effect of cognitive avoidance is to create a representation that is impoverished in important areas and that will not compete for retrieval so effectively with the original representation in the presence of phobic cues. The encoding specificity principle requires that the new representation, if it is to be effective, must incorporate all the elements that characterise the original memory. The observations of the return of fear are explained by hypothesising that from time to time any recovered patient may be exposed to a particularly potent combination of phobic cues that, together perhaps with a corresponding mood state, result in the original representation temporarily winning the retrieval competition and reinstating a fearful reaction.

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Cognitive therapy This requires the therapist to identify negative thoughts and assumptions, to assess their evidential base, and to challenge them both logically, by considering the evidence that alternative beliefs are more likely to be correct, and empirically, by collecting new data that are relevant to deciding between positive and negative beliefs. Problematic situations are repeatedly analysed, with the aim of coming to a new causal understanding of the role of thoughts in determining negative mood. The standard account reviewed above is that these procedures result in corrective information being incorporated within the original negative representations. From a retrieval competition perspective, these procedures are resulting in the creation of new representations in which negative thoughts and events are associated with more positive mood and with positively valenced material such as contrasting memories of past successes, more realistic standards, or the experience of acceptance by the therapist. These representations are themselves associatively linked to knowledge structures in memory containing positive information about the self. As with behaviour therapy, the effectiveness of the new competitors is enhanced by the rehearsal that is part of the therapy. In addition alternative ways of thinking and analyzing situations suggested by therapists, which often come as a revelation to patients, contribute to the distinctiveness and positive valence of the new representations. As a result, brief episodes of negative mood may in future result in more positive rather than negative thinking (see Segal, Gemar, & Williams, 1999). As is the case for behaviour therapy, more adaptive representations created by patients are only likely to win the retrieval competition if they contain the same elements as the most negative thoughts and images. This requires the therapist to ensure that there are no outstanding negative experiences or sources of evidence that are not included in the new constructions. To take a simple example, patients may become convinced through therapy that behaviour which they have regarded as evidence of their inherent weakness (such as lack of motivation to return to work) can be plausibly interpreted as a symptom of depression and that a more appropriate view of themselves is as temporarily less robust because of illness rather than as characterologically weak. As a result, reminders of their failure to return to work may no longer result in a positive self-representation being replaced by a negative one, and mood may improve. The new selfrepresentation may not, however, include other behaviours such as irritability with family members that are still regarded as evidence of weakness. In situations involving irritability, therefore, the representations of weakness are more likely to win the retrieval competition. Several disorders, including depression, are likely to involve the deliberate and repeated reinstatement of negative thinking about symptoms or problems, a process known as rumination. For example, NolenHoeksema (1991) has identified the ruminative response style, a habitual tendency to deliberately pay attention to, evaluate, or speculate on the meaning of events and symptoms in the sufferer’s life. Rumination is a process that is theoretically distinct from the existence of negative thoughts and beliefs, and describes one particular way of responding to them. There is evidence that the depressed may be characterised not so much by the content of their negative thoughts as by their tendency to ruminate on rather than disengage from them (Spasojevic & Alloy, 2001). Recognition of the importance of rumination draws attention to the problem of retrieving related and more adaptive representations in memory. Ruminators may have few associative links between their negative thoughts and other memory contents, so that it is hard to break out of the cycle of thinking. Therapy may create new competitors in memory that are equally powerfully activated by the entry of ruminative thoughts into consciousness. Generation of testable predictions One major implication that distinguishes a retrieval competition account from standard models of CBT is that anxious and depressive reactions, including successfully treated negative cognitions, should be capable of returning even after successful therapy, provided sufficient triggers are present. The evidence for the return of anxiety and depressive symptoms is strong and has already been reviewed. However, it has yet to be shown that relapse following CBT is accompanied by a return of the same negative cognitions that were successfully treated in therapy. This is a critical prediction for the retrieval competition position. Previous work has shown that CBT for depression makes individuals less vulnerable to negative thinking when given a mood induction (Segal et al., 1999), and over the next few months weakens the degree of association between subsequent

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depressive mood and negative thinking (Beevers & Miller, 2005). Future research could usefully focus on documenting whether specific negative cognitions that are no longer intruding by the end of treatment with CBT nevertheless begin to intrude once more in the context of a later relapse. A second implication is that therapeutic procedures based on associative principles should be as effective for conditions such as depression as they are for simple phobias. Theoretically, it should be possible to create new representations without any logical analysis of the evidence underpinning negative beliefs. Some types of narrative therapy are explicitly focused on enriching positive stories and life themes concerning the self that are currently overshadowed by dominant negative stories and themes. This is achieved in large part by drawing on positive autobiographical memories, and encouraging patients to generate their own associations to these so that they become firmly linked to important values and goals (White & Epston, 1990). According to a retrieval competition account, the alternative target representations created only have to be positive, highly memorable, and attention-grabbing in the presence of negative cues. They are not required to be more consistent with the facts, more rational, or even physically possible. In imagery rescripting (Arntz & Weertman, 1999; Hackmann, 1998), for example, intrusive autobiographical memories or images are first vividly called to mind and then deliberately rescripted so that they result in a positive outcome. For example, Smucker et al. (1995) described treating survivors of child sexual abuse suffering from PTSD by having them imagine their adult self enter the remembered scene of abuse, protecting and comforting their child self. This approach was subsequently adapted and applied to industrial accident victims with PTSD (Grunert, Smucker, Weis, & Rusch, 2003) and to an individual with bulimia nervosa (Ohanian, 2002). To date imagery rescripting has mainly been applied to relatively small numbers of patients with trauma histories. It is claimed that significant improvement has been achieved with a single session or a small number of sessions. A larger study using a related technique involved a randomised controlled trial conducted with sexual assault survivors suffering from PTSD and chronic nightmares (Krakow et al., 2001). Patients received three sessions of imagery rehearsal therapy, in which they described the content of their nightmares and rescripted them to contain a desired outcome. This procedure significantly reduced nightmare frequency, sleep disturbance, and PTSD symptoms relative to the control group. Several other techniques have recently been developed that address verbal thoughts as well as images. None of them explicitly engage in a logical analysis of the validity of negative beliefs, the critical element of CBT. Instead, they focus on overcoming avoidance of mental products, and then pairing those products with positive emotions, mental states, or images. For example, mindfulness-based cognitive therapy (MBCT: Segal, Williams, & Teasdale, 2002) has been applied to depressed patients in remission. The basic premise of MBCT is that it is not the presence of negative thoughts that is pathogenic, but the individual’s tendency to become emotionally involved with them and draw negative inferences about the self. Teasdale, Moore, Hayhurst, Pope, Williams, and Segal (2002) demonstrated that metacognitive awareness, a cognitive set in which negative thoughts/feelings are experienced simply as mental events rather than as the self, was lower in recovered depressed patients than controls, and that patients with more metacognitive awareness were less likely to relapse. Rather than challenging negative thoughts, patients are taught mindfulness meditation skills (Kabat-Zinn, 1990), and encouraged to observe their thought processes in a dispassionate way instead of reacting emotionally to them. MBCT has succeeded in reducing relapse rates in individuals with a history of three or more previous episodes of depression (Ma & Teasdale, 2004; Teasdale, Segal, Williams, Ridgeway, Soulsby, & Lau, 2000). A related procedure derived from behavioural principles is acceptance and commitment therapy (ACT: Hayes et al., 1999). Based on evidence that psychopathology is frequently linked to attempts to control or suppress negative intrusions such as thoughts and images (Hayes et al., 1996), and to lack of psychological flexibility (Hayes, Luoma, Bond, Masuda, & Lillis, 2006), patients are taught instead to fully experience and accept all mental events, just noticing them rather than treating them as either true or false, and to identify and focus on actions directed toward valued goals. ACT is viewed as a constructive therapy, in the sense that it is assumed therapists are only able to add new behaviours or representations, not to take problematic ones away (Hayes & Wilson, 2003). Preliminary trials have provided encouraging evidence that these methods may be helpful for disorders and problematic behaviours as diverse as depression, agoraphobia, social phobia, smoking, polysubstance abuse, chronic stress and pain, and mathematics anxiety (see Hayes, Luoma, Bond, Masuda, & Lillis, 2006, for a review).

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More recently, Gilbert (Gilbert, 2005; Gilbert & Irons, 2004) proposed that individuals high in self-criticism might have little experience at calming or soothing themselves and could benefit from interacting in their imagination with a compassionate other. Like MBCT and ACT reviewed above, Gilbert’s ideas involve greater acceptance of negative thoughts, but in this case the thoughts are paired not with self-acceptance but with imagery involving acceptance, compassion, and forgiveness. One possibility is to involve an entirely fictitious creation such as a ‘‘perfect nurturer’’ (Lee, 2005). Numerous case examples of this kind of work have been described and the relevant procedures described (Gilbert & Irons, 2005; Hackmann, 2005; Lee, 2005). Although not yet empirically tested to the same extent as MBCT and ACT, the underlying principles have a great deal of similarity, the main difference being the opportunity to increase the positive valence of the newly constructed representation by building in an interpersonal dimension. A third implication of the retrieval competition account is that simply teaching individuals methods of permanently disengaging their attention and disrupting the continued processing of negative representations may be sufficient to produce a lasting reduction in symptoms. One approach that seeks to help patients achieve this is attention training (e.g. Papageorgiou & Wells, 2000). Over the course of a small number of treatment sessions patients are taught to switch attention between a number of sounds present in the room where they are sitting, and to practise holding one or more sounds in focal attention at one time. As part of this metacognitive therapy patients’ opinions about rumination may also be explored, and any beliefs about rumination being helpful to them are challenged. Critically, however, intrusive negative thoughts or images or the assumptions underlying them are not subjected to logical or empirical scrutiny. There is encouraging evidence from several small-scale studies that these procedures may be able to bring about lasting symptomatic relief in a number of disorders including depression (Papageorgiou & Wells, 2000), posttraumatic stress disorder (Wells & Sembi, 2004), panic and social phobia (Wells, 1990; Wells, White, & Carter, 1997), and hypochondriasis (Papageorgiou & Wells, 1998). Parsimony As already noted, a retrieval competition account of CBT has some benefits in parsimony as it is extending to the understanding of treatment ideas that have gained widespread acceptance in explaining the onset and recurrence of depressive episodes (e.g. Scher et al., 2005). A further aspect of parsimony is that the same explanation is applied both to behaviour therapy techniques such as exposure and cognitive therapy techniques such as the challenging of negative thoughts and assumptions. At present the former tend to be explained in terms of associative principles and the latter in terms of logical reasoning. What is being proposed here, however, is that associative and logical reasoning have the same outcome, the creation of more positive competitor representations. Logical reasoning is thus one particular means to an end rather than a necessary part of CBT. Extending this point further, the more recent developments in CBT reviewed in the previous section may be regarded as contradicting the standard account of CBT in that they do not engage logically with the content of intrusive images and beliefs, and may even involve the creation of imaginary mental products that bear no relation to reality. Instead, they are all characterised by a metacognitive perspective in which a change is sought in the way individuals respond to their upsetting intrusions. This has led to MBCT, ACT, and related interventions being referred to as a ‘‘third wave’’ of cognitive-behaviour therapy, distinct from the behavioural and cognitive therapies that preceded them (Hayes, 2004). Although we have yet to discover whether these new techniques are as effective as traditional CBT, the fact that they work at all poses important conceptual questions about the principles underlying successful therapy. It is possible, of course, that the effectiveness of these different techniques is due to completely different principles to those underlying CBT. It is an important principle of scientific reasoning, however, that the simplest explanation that accounts for the greatest number of observations is preferred to more complex explanations. Both older and newer variants of CBT appear to be largely consistent with the principles of a retrieval competition approach that suggests negative representations can be deactivated by creating or strengthening more positive alternatives using either logical or associative reasoning. In this way the new developments can be construed as suggesting the possibility of a technical advance in therapists’ armoury without necessarily challenging the underlying principles on which CBT is based.

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Summary The retrieval competition approach relies on a relatively small set of principles that are familiar from other areas of psychology. It suggests that procedures used by behaviour and cognitive therapists, although often differing in the mode of reasoning they employ, all have the aim of strengthening competitor representations in memory that are positive rather than negative in valence. The theory provides an integrated and parsimonious approach to understanding vulnerability, response to treatment, and relapse, as well as generating unique predictions. Further, it suggests that new forms of CBT that appear to diverge from standard CBT may in fact share similar underlying mechanisms. Conclusions Despite the success of CBT there has for some time been uncertainty about the basic principles that underlie it. The very general nature of the scientific questions concerning psychotherapy, the difficulty in accurate measurement of theoretical constructs, and the impossibility of exerting strict experimental control, all militate against designing critical studies that convincingly favour one theoretical explanation over another. In this field, therefore, alternative scientific criteria for choosing between theories have been employed and will continue to be employed. These include face validity, parsimony, consistency with available observations and the psychological knowledge base, ability to generate testable predictions, and utility in suggesting novel treatment approaches. Judged by these criteria, a retrieval competition account brings the explanation of treatment response more closely into line with well-established theoretical views of the onset and recurrence of disorders such as depression. It has the potential to unify traditional CBT with newer therapeutic developments in an extremely parsimonious way by drawing on a small set of well-established principles concerning learning and memory. One implication of these developments is to change the way cognitive therapists may construe the importance of reasoning and logical thinking. According to the argument made in this article, analytic or logical thought is effective at helping patients come to associate negative beliefs and experiences with more positive conclusions and mood states. It may well be that the kind of verbal and behavioural disputation and evidence gathering that is so much a part of traditional CBT is a uniquely powerful way of achieving this. There is now evidence that cognitive therapy does have a specific effect in breaking the link between affect and cognition in recovered depressed patients, so that negative mood induction is less likely to reactivate negative beliefs and assumptions (Beevers & Miller, 2005; Segal et al., 1999). Our review strongly suggests, however, that associative reasoning also has a part to play in the development and treatment of psychopathology. For example, imagery rescripting may be valuable in treating all those disorders, such as depression, health anxiety, agoraphobia, and social phobia, in which intrusive images and memories are common. Only time will tell whether these new techniques prove to be as effective as traditional verbal methods. Many contemporary theories of human and animal cognition (e.g. Gold, 2004; Kesner & Rogers, 2004; Poldrack & Packard, 2003; Squire, 2004) favour the idea that learning is a constructive process, constantly producing new representations that can collaborate or compete with existing memories for control of behaviour. Consistent with this, some theorists from cognitive-behavioural backgrounds have argued that a more explicitly constructivist philosophy emphasising the creation of new representations and behaviours is more appropriate than a strictly rationalist philosophy that emphasises the correction of distorted cognitions (Hayes, 2004; Mahoney, 1993; Meichenbaum, 1993). As we have seen, cognitive therapy has always included constructivist elements, but these have tended to be overshadowed in many writings by the rationalist elements. A retrieval competition account allows for the generativity that is a strength of constructivist therapies, while also giving due weight to the value of logical thought. According to this approach the rationalism of traditional CBT is not an essential part of the therapy but rather a particularly successful method for constructing enduring alternative representations that are both positive and memorable. The arsenal of imaginative behavioural experiments recently documented by Bennett-Levy et al. (2004), for example, help to create striking experiences that not only reveal new causal relations but also readily come to mind when patients are faced with an uncertain outcome. The strengths of CBT lie in the appeal of its core model to both

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therapists and patients, its teachability, and its highly structured methods. Clinical trials comparing the efficacy of traditional methods using logical reasoning with methods based purely on associative principles would be potentially very informative. The most important benefit a retrieval competition account can offer, however, is to assist practitioners to think more creatively about their practice and to respond more flexibly to patients who fail to respond to the standard techniques of CBT. The analysis of patients’ thinking could routinely include assessment of different kinds of representation, including images and personal memories in addition to intrusive thoughts and beliefs. It is possible that images and memories may simply be found to support or provide evidence for negative beliefs, but equally there is evidence that they may be important in their own right (Brewin et al., 1999). In this case, rather than offer a standard treatment package for a specific condition, CBT could develop in the direction of specific subcomponents of treatment aimed at the particular symptoms exhibited by an individual patient. If it is unnecessary for negative thinking to be corrected, only disengaged from, there are a variety of methods that may now be considered within an overall CBT framework. Recent developments have suggested that associative reasoning may be a more powerful tool than has hitherto been suspected, and methods such as rescripting of intrusive memories or images, use of compassionate imagery, mindfulness-based cognitive therapy, and acceptance and commitment therapy, have opened up new possibilities for exploiting what it has to offer. Of particular theoretical interest is the question of whether these procedures also bring about change in the verbal meaning of intrusive thoughts, images, and memories, even without addressing them directly. An alternative possibility is that rescripting or metacognitive therapies create new retrieval targets through association or enhanced attentional control, and that this is sufficient to compete with the original representations. The empirical study of exactly what kinds of associative or procedural modifications are best at generating effective competitors could do much to increase the current effectiveness of CBT. Regardless of which specific methods turn out to be most effective, a soundly based theory is needed to guide CBT in the most productive direction and to ensure that it remains committed to empirically testable assumptions and methods. Acknowledgments I am very grateful to Allison Harvey, Philip Spinhoven, and Mark Williams for comments on earlier drafts of this article. References Anderson, J. R. (1974). Retrieval of propositional information from long-term memory. Cognitive Psychology, 5, 451–474. Anderson, M. C., Bjork, R. A., & Bjork, E. L. (1994). 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