Search

Intrusions are regarded as a 'hallmark' symptom of Post-Traumatic Stress Disorder, yet relatively little is known about their formation and development. This thesis was an experimental examination of potential information processing factors implicated in intrusion development. The thesis begins with an examination of PTSD in the context of intrusions, followed by a review of the main theories of PTSD symptom development and the place of intrusion development within these. Recent theories of PTSD are examined, specifically Dual Representation Theory (Brewin, Dalgleish, and Joseph, 1996), which regards PTSD as a 'hybrid' disorder that involves two distinct yet parallel types of memory encoding one based in part on sensory, visual processing, the other on verbal/narrative based processes, the interaction of which can lead to intrusion development under certain conditions. This thesis attempted to replicate and extend research (Holmes, Brewin, Hennessy, 2004) founded on dual-representation theory, that explored the role of peri-traumatic visuo-spatial and verbal processing in the formation of intrusions based on a trauma analogue film. 40 non-clinical participants were involved either a control condition, or one of two dual-task interference conditions: a visuo-spatial interference condition (involving tapping out a key pattern of a hidden keyboard); and a verbal interference condition (involving counting backwards in threes). Participants were instructed to watch a trauma-analogue film designed to generate intrusions, whilst performing the task they were allocated. Diary measures were taken of subsequent intrusions experienced in the week following exposure to the analogue trauma film. Visuo-spatial interference appeared to significantly disrupt the formation of intrusions, while there was a trend for verbal processing to increase intrusions. The visuo-spatial interference task did not impact on attention to the film, or features of either recall or recognition of film material. For the verbal interference condition, there was also significantly more visual imagery type intrusions, more data driven processes reported, and a reduction in recall memory and attention to film. Increases in state dissociation were also implicated in higher reported intrusions. These findings were discussed in the context of current theories of intrusion formation, and in terms of clinical implications for the assessment and treatment of intrusions in PTSD.

The literature on hypnotizability and dissociation was reviewed in relation to patterns of clinical and non-clinical eating behaviours. Included was a theoretical interpretation of the significantly higher rates of hypnotizability and dissociation in certain eating disordered groups, such as bulimics, compared to age matched controls. However, non-clinical investigations between hypnotizability, dissociation, and problematic eating patterns were focused on in particular. Two principle hypotheses emerged from this review. First, the Socio-Hypnotic hypothesis (e.g. Groth-Marnat & Schumaker, 1990; Frasquilho & Oakley, 1997) suggested that hypnotic suggestibility may influence the internalisation of socio-cultural pressure to be thin. Second, the Dissociative Escape Hypothesis proposes that a vulnerability to experience dissociative phenomena as a potential defence mechanism may lead individuals to disinhibit eating behaviour when faced with aversive cognitions (based on Heatherton & Baumeister, 1991, McManus, 1995; Frasquilho & Oakley, 1997). These hypotheses were framed in terms of a social-cultural model of problematic eating (Stice, 1994). After reviewing the concepts behind the definitions and measurements of hypnotizability, different types of dissociation, dietary restraint, and disinhibited eating, four studies sought to explore associations between these factors within a non-clinical female college student population. Study 1 (n = 40) examined the relationship between types of restraint and non-hypnotic suggestions relating to imagining body size increase and decrease, in the context of body related anxiety, disinhibition of eating, and imagery based suggestibility. Study 2 (n = 87) and Study 3 (n = 123) used correlational and regression techniques to examine relationships between a widely used test of hypnotizability and tests of cognitive and affective dissociation in relation to a number of dietary restraint and disinhibition of eating measures. Study 4 (n = 50) examined differences between restrainers and non-restrainers on a behavioural index of body shape and food concerns based on a Stroop-type paradigm and examined these concerns in relation to dissociation and hypnotizability. The Socio-Hypnotic hypothesis was weakly supported by correlation evidence, though regression analyses revealed more complex effects. While correlations involving dissociation needed to control for depression, different types of dissociation may relate to different features of both disinhibited eating and dietary restraint. These results were summarised and discussed in the final chapter and future research possibilities examined.