Horowitz's (e.g., 1976, 1997; Horowitz, Wilner, Kaltreider, & Alvarez, 1980) formulation of stress response syndromes offers perhaps the most far-reaching and influential social-cognitive model of reactions to trauma. Although inspired by classical psycho-dynamic psychology (notably Freud, 1920), Horowitz's theory is principally concerned with discussing such ideas in terms of the cognitive processing of traumatic information (i.e., ideas, thoughts, images, affects, and so on). Horowitz has argued that the main impetus within the cognitive system for the processing of trauma-related information comes from a completion tendency (Horowitz, 1976): the psychological "need" for new information to be integrated with existing cognitive world models or schemata (Horowitz, 1986).
Horowitz (1986) proposed that, subsequent to the experience of trauma, there is an initial "crying out" or stunned reaction, followed by a period of information overload in which the thoughts, memories, and images of the trauma cannot be reconciled with current meaning structures. As a result, Horowitz suggests, a number of psychological defence mechanisms come into operation to keep the traumatic information in the unconscious, and the individual then experiences a period of numbing and denial. However, the completion tendency maintains the trauma-related information in what Horowitz calls "active memory", causing it to break through these defences and intrude into consciousness in the form of flashbacks, nightmares, and unwanted thoughts as the individual endeavours to merge the new information with pre-existing models. According to Horowitz, this tension between the completion tendency on the one hand and the psychological defence mechanisms on the other causes individuals to oscillate between phases of intrusion and denial-numbing as they gradually integrate the traumatic material with long-term meaning representations. Failures of such processing can mean that the partially processed traumatic information remains in active memory without ever being fully assimilated, thus leading to chronic post-traumatic reactions.
Horowitz's discussion of the processes underlying completion, intrusion, and denial has considerable explanatory power for PTSD phenomenology. His theory indicates clearly the ways in which normal reactions to trauma can become chronic (see Figure 6.8 for a schematic summary of Horowitz's model).
However, Horowitz's model has a number of limitations that are important to highlight. First, Horowitz's formulation seems to struggle to account for epidemi-ological data regarding the frequency of late-onset PTSD (although this might be ascribed to a long period of denial which later breaks down). Second, while Horowitz provides a clear description of the time course of post-traumatic reactions, it seems uncertain that all individuals do experience an initial period of denial, or later oscillations between denial and intrusion. In fact, Creamer, Burgess, and Pattison (1992), in complete contrast, argue for an initial episode of intrusive symptoms. Third, although Horowitz highlights processes such as social support, which, as we have seen above, are clearly important, there is little explanation of how such factors might operate and interact with processes such as completion. Fourth, little credit is given to the power of the individual's attributions and interpretations of the traumatic experience and the effect that these have on outcome. Finally, certain aspects of the theory are under-specified, in particular the concept of "active memory", what form it takes, and how it is related to other mnemonic representation systems (see Dalgleish, 2004).
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