Intrusive mental experiences occur within posttraumatic stress disorder (PTSD) and some psychotic disorders. Similarities in the phenomenology and content in the intrusions of both disorders have been noted. Currently there is little understanding of any common etiology in terms of information-processing styles. This study investigated predictors of analogue posttraumatic intrusive cognitions within a nonclinical sample, including schizotypy, dissociation, and trauma history. Forty-two participants watched a trauma video and recorded trauma-related intrusions occurring for 1 week. More reported intrusive experiences were associated with high positive symptom schizotypy. Our findings are discussed in relation to the possible role of trauma-related intrusions within psychotic disorders.
Individuals who have been exposed to traumatic events frequently report experiencing trauma-related intrusive images. These images are often distressing and if maintained may be associated with a clinical diagnosis of posttraumatic stress disorder (PTSD;American Psychiatric Association, 1994). The diagnostic criteria for PTSD include exposure to an event involving actual or threatened death or serious injury or threat to the physical integrity of self or others in which the person experienced intense fear, helplessness, or horror (American Psychiatric Association, 1994). The response to the event is characterized by recurrent and intrusive distressing recollections of the event and avoidance of stimuli associated with the trauma and physical hyperarousal. Thus, a hallmark of PTSD is intrusive memories of particular moments of a trauma, which can be experienced as happening in the present, are associated with high affect, and contain a sense of current threat (Brewin and Holmes, 2003;Ehlers and Clark, 2000;Gray et al., 2001). It is the occurrence of intrusive trauma-related memories that form the focus of the current study.
Dissociation is characterized by a sense of derealization, depersonalization, explicit memory loss, and emotional numbing (Foa and Hearst-Ikeda, 1996) and is considered to be a defensive response that may serve a functional role during intense distress (van der Kolk et al., 1996). However, dissociation during trauma—that is, peritraumatic dissociation (Shalev et al., 1996) and high trait dissociation (Murray et al., 2002)—have been associated with an increased level of PTSD symptoms.
Traumatic and other stressful life events may not only act as a trigger for PTSD but also have been argued to act as a trigger for psychotic episodes within biologically vulnerable individuals (e.g., Zubin and Spring, 1997). Schizophrenia is a form of psychotic disturbance that is diagnosed on the basis of a range of symptoms including delusional beliefs, hallucinations (both auditory and visual), and thought disorder along with social withdrawal and a lack of affect (American Psychiatric Association, 1994). The concept of schizotypy is a relatively recent development in which it is argued that schizophrenic symptomatology exists in milder forms within nonpatient populations. Differing theoretical approaches have been taken towards the conceptualization of schizotypy. While some researchers suggest schizotypy to be taxonic (e.g., Lenzenweger and Moldin, 1990), the current research adopts a fully dimensional model of schizotypy (Claridge, 1997) in which psychotic personality traits are considered to be part of normal individual differences. Within this perspective, an extreme manifestation of ‘schizotypal’ personality traits represents one of a range of factors that may predispose an individual to psychotic illness. These personality traits have been measured using a range of schizotypal personality questionnaires, such as the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE;Mason et al., 1995). Unlike the scales previously developed by Chapman and colleagues (e.g., the Perceptual Abberation Scale, Chapman et al., 1978), the O-LIFE is not specifically intended to measure mild first rank symptoms of schizophrenia but is derived from a variety of schizotype scales and is designed to reflect a fully dimensional model of schizotypy.
Support for such a model comes from reports of similarities in performance between positive symptom schizophrenic patients and individuals who score above the mean on positive symptom schizotypy scales, such as the Unusual Experiences subscale of the O-LIFE, within a range of experimental tasks (e.g., Steel et al., 1996; 2002). Within the concept of schizotypy adopted by the current study, it is argued that schizotypal personality traits can be associated with information-processing styles. Further, both occur within a continuum. Consequently, it is predicted that evidence of an information-processing style associated with high-scoring positive schizotypes would generalize to patients with psychosis and vice versa.
When considering the possibility of traumatic events acting as a trigger for both PTSD and psychosis, it is of interest to note that the symptoms associated with both disorders contain some phenomenological similarities. For example, hallucinations are often experienced as involuntary intrusions associated with high affect (Nayani and David, 1996), as are the intrusions associated with PTSD. Morrison et al. (2002) report a case series of patients with delusions and/or hallucinations who also experienced symptom-related recurrent intrusive images. The content of these intrusions was also linked to traumatic events that had been experienced by the patient, e.g., being assaulted.
Consistent with these observations, intrusive experiences have also been incorporated within two recent psychological accounts of psychotic symptoms (Hemsley, 1994;Morrison, 2001). Morrison (2001) argues that hallucinations and delusions may be conceptualized as the product of idiosyncratic appraisals of intrusive experiences. Further, the cultural unacceptability of these appraisals determines the psychiatric diagnosis. For example, a person may have an intrusive memory image yet interpret it as telepathy and a sign that the devil is communicating with him/her. However, Morrison’s model does not address how intrusive experiences may develop before their appraisal. Hemsley (1994) places a greater emphasis on an individual’s information processing style and consequently on how intrusions might arise. It is argued that both individuals suffering from acute schizophrenia and high scoring positive schizotypes exhibit a relatively weakened ability to integrate information within a temporal and spatial context (Jones et al., 1991;Steel et al., 2002), resulting in the occurrence of intrusive experiences. However, there has to date been no experimental investigation of the development of trauma-related intrusions in relation to either people diagnosed with a psychotic disorder or an analogue population categorized on the basis of a schizotypy questionnaire.
Recent research has led to a growing interest in the overlap between PTSD and psychotic intrusions. A question of interest is why some traumatized individuals develop PTSD symptoms, such as clear trauma-related intrusions, while others develop hallucinations or delusional beliefs. Although a traumatic event may serve as a trigger for a range of intrusive experiences, little is known about the individual differences that may determine the phenomenology of trauma-related intrusions. Given the associated treatment implications, it would seem to be an important area in which to develop our understanding.
To study trauma-related intrusions within the field of PTSD, researchers have used the stressful film paradigm. This paradigm creates an analogue trauma after which intrusions can be studied within a prospective design. Participants watch a traumatic film and then monitor the number of intrusions of the film experienced during the following week. Thus, the paradigm enables researchers to control exposure to a traumatic event meeting diagnostic criteria, while ensuring that the recorded intrusions are directly related to the content of the event. The reported intrusions have been shown to arise spontaneously and be somewhat distressing (Holmes et al., 2003 ‡) and possess phenomenological properties consistent with a clinical presentation of PTSD. Using such a methodology, various predictors of intrusion vulnerability have been identified. These are increased state dissociation during the film (Holmes et al., 2003 ‡), increased negative mood and thought suppression (Davies and Clark, 1998), increased worry after the film (Butler et al., 1997), and focusing on the sensory and perceptual aspects of the film rather than its meaning (Halligan et al., 2002). Such research has contributed to the development of cognitive models of PTSD and associated treatment interventions (Ehlers and Clark, 2000;Brewin, 2001;Brewin and Holmes, 2003).
While the use of an analogue design has inherent limitations, within trauma research it enables control over the content of the traumatic event, along with the measurement of pretrauma characteristics and immediate posttrauma reactions. One advantage of using analogue studies within schizophrenia research is that it allows data to be interpreted without the contaminating effect of a generalized performance deficit normally present within a patient population (Nuechterlein, 1977). Overall, the stressful film paradigm provides a methodological window and is supported by related findings using clinical populations and real trauma exposure (e.g., Murray et al., 2002).
The current study aims to employ the stressful film paradigm to explore the relationship between trauma-related intrusions and individual differences in positive schizotypy. However, given that individuals who score highly on positive symptom aspects of schizotypy also tend to score high on trait dissociation, as measured by the Dissociative Experiences Scale (DES;Merckelbach et al., 2000;Startup, 1999), the current study investigates the development of intrusions within a nonclinical sample, rated on both schizotypy and dissociation scales. On the basis of Hemsley’s (1994) theoretical model, we suggest that individuals scoring high on positive schizotypy may have an information-processing style that makes them vulnerable to having intrusive mental experiences of trauma. It is therefore hypothesized that participants scoring high on the positive symptom schizotypy scale of the O-LIFE (Unusual Experiences) will report a higher number of intrusions than low scorers. Also, consistent with previous research (Holmes et al., 2003;‡ Murray et al., 2002), it is predicted that a higher level of trait and peritraumatic dissociation will be associated with increased intrusions. A self-report measure of the number of traumatic events individuals have experienced in their lifetime will also be completed. Given that a number of variables are predicted to be associated with more frequent intrusions and that positive schizotypy and trait dissociation exhibit a high level of covariance, a multiple regression analysis will be used to determine the relative strength of prediction of these variables.
*MRC Cognition and Brain Sciences Unit, Cambridge, United Kingdom;
†Department of Psychiatry and Behavioural Sciences, University College London, Holborn Union Building, Archway Campus, London, N19 5LW, United Kingdom.
This work was supported in part by Camden and Islington Mental Health and Social Care Trust, and Wellcome Grant 062 452.
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