Dual representation theory

Brewin, Dalgleish and Joseph's (1996) dual representation theory proposes the existence of two distinct memory systems which form qualitatively distinct memories whose retrieval depends on different types of cues. Whilst both systems ordinarily operate in parallel, highly distressing experience can produce disruptions within the system such that one type of memory dominates at the expense of another at event encoding. This produces the distinctive pattern of memory disorders characteristic of PTSD. The original experimental support for this model was drawn from analogue studies cited above, where it was found that taxing the visuospatial load (originally intended to mimic dissociation) had, contrary to prediction, an inhibitory effect of the formation of

subsequent intrusive memories. It was thus reasoned that this finding, in combination with the fact that traumatic memories are often poorly retrieved by verbal cues, pointed to the existence of two types of memory store: one containing verbally accessible memories, the other situationally accessible memories.

The verbally accessible memory (VAM) system encodes our everyday experiences and integrates these within coherent narratives of our lives. Such memories can be accessed through verbal cues, communicated to others through language, edited in memory and drawn upon selectively. The second system, the situationally accessible memory (SAM) store, encodes features of events not consciously encoded but still forming subliminal traces within memory. This offers a more ample, capacious store than verbally accessible memories, yet resists self-cued, intentional retrieval. Instead situational reminders of the original event cue the memory which is retained in an affectively laden, highly vivid form. This draws experimental support from such phenomena as 'inattentional blindness' (Mack and Rock, cited in Brewin et al., 1996) whereby elements of a visual field may be unattended, and not consciously report, but still effect performance on priming tasks and other tests of implicit memory. The stress and anxiety experienced at the time of the traumatic event has the effect of constraining the amount of information that can be registered or attended to at encoding. The

traumatic event is presumed to focus attention on the immediate source of threat to such a degree that other elements are only stored unconsciously.

Brewin, Dalgleish and Joseph originally (1996) proposed that within therapy verbally accessible memories combining the original trauma information combined with states of reduced arousal and new understanding of the event need to be formed which block access to the original memories. Brewin’s revised (2001b) view is framed within the

terms of feature theory such that information (or features of an original stressor)

retained only within the SAM memory system cannot be transferred to VAM structures because of suppression and avoidance behaviours which typify PTSD symptoms. The flashback memory needs to be re-encoded into a format more amenable to general knowledge structures, given a temporal and spatial context, and thereby palliating the sense of threat and alarm which their re-experiencing produces. The quantity of information which the SAM store contains means that a great deal of material needs to be transferred and processed. This calls for often protracted therapeutic treatment.

The trauma reminders encountered within the environment spark a retrieval competition between verbally accessible memories and situationally accessible memories –

successful access to the newly formed VAM of the traumatic event will prevent amygdala activation and the re-experiencing of emotions associated with the event.

This also means that in the future a suitably specific cue may trigger the original trauma memory, which by no means eradicated. Therapy allows verbally accessible memories to be produced which incorporate features from the situationally accessible memory store and which is preferentially accessed.

1.4 6 Summary

The studies so far reviewed in this section have suggested that attending to conceptual and meaningful aspects of an experience constraining visual spatial details of an event may have a protective effect against the formation of intrusive memories; further, and relatedly, post event meaning elaboration and verbal processing can reduce the incidence of analogue PTSD symptoms. The models considered have given such processes as conceptual elaboration, or the formation of verbal accounts, a central role in explaining both how PTSD symptoms arise and how they can be prevented. It must

be stressed however, that such findings and models are intended specifically to account for a particular type of traumatic experience and pathological conditions. Furthermore, they, largely adopt a restricted paradigm (the analogue study) intended to replicate to a lesser degree the effects of a highly distressing event. Their chief focus, too, is on the formation of intrusive memories. Thus much of the evidence reviewed is suggestive, rather than specifying precise mechanisms and processes by which a more global account of emotional processing and memory interactions might be described.

Precisely how the mechanisms and models of memory proposed by these theories map on to general understanding of memory, and emotional processing needs to be

established. The findings do, helpfully, point to a polarity between sensory and

conceptual aspects at encoding and following exposure to materials. This parallels the direction already developed within sections one and two pointing to an association between emotion and sensory memories, and the possibility that a surfeit of sensory encoding might both distort and impede recall.

Certain difficulties persist with the notion of conceptual processing. Within the experimental learning paradigm in which it was originally proposed (Jacoby, 1983;

Blaxton, 1989; Roediger, 1990), it was intimately connected with transfer appropriate processing account of memory. When applied to clinical models, it becomes something of a catch-all for a number of processing styles which might be taken in a broad sense to denote top-down processing (Brewin & Holmes, 2003). Yet, these are far from a homogenous group of processes. They might refer to simply labelling elements of an event, to categorisation, to production of narrative, to interpreting an event in terms of its consequences, or to provide higher-level meaning accounts.

They might all, however, suggest that a recoding and 'processing' of bare sensory data has some protective effect, at least in the type of analogue symptoms here reviewed.

This resonates with multilevel multi representational theories of emotion, (see section 1.1.6) which predict that emotional desynchronies might arise when representations are retained in an analogue format which enables it to access through associative processes emotional responses automatically. In the following section, these considerations will be extended to more wide ranging interactions between conceptual processing of experience and emotional processing.