Intrusive memories, or intrusions, are involuntary recollections relating to events that appear, apparently spontaneously, in consciousness (e.g. Brewin and Saunders, 2001, Davies and Clark, 1998b, Halligan et al., 2002, Holmes et al., 2004 and Schlagman et al., 2007). Intrusions can be contrasted with the deliberate recollection of events or repeated verbal rumination over such events. Whilst intrusions can take the form of either sensory mental images or verbal thoughts our main interest is to understand mental imagery based intrusions (i.e. those which have a sensory component such as mental picture or sounds). This focus mirrors both clinical phenomenology and also healthy autobiographical memories for emotional events. Several studies have suggested that emotional memories typically take the form of mental images irrespective of whether such memories are intrusive or deliberately recalled (Arntz et al., 2005 and Conway, 2001) and, conversely, imagery seems to have a special impact on emotion (Holmes & Mathews, 2005).
Intrusive memories occur often in everyday life with studies in non-clinical populations suggesting that their frequency is approximately 2–4 a day (Berntsen, 1996) or 1–5 a day (Mace, 2005), although they occur less frequently than verbal thoughts (Brewin, Christodoulides & Hutchinson, 1996). However, these common, unsolicited recollections typically present no concern for the experiencer and can give rise to positive as well as negative affect. In contrast, the vivid re-experiencing of excerpts from a traumatic event can be extremely distressing and form one of the three key symptoms for diagnosis of post-traumatic distress disorder (PTSD; American Psychological Association [APA], 1994). There is also considerable evidence implicating intrusive image-based memories in psychological disorders other than PTSD such as: social phobia (Hackmann et al., 2000 and Hirsch et al., 2003); depression (Kuyken and Brewin, 1994, Kuyken and Brewin, 1999 and Reynolds and Brewin, 1999); psychosis (Morrison et al., 2002); agoraphobia (Day, Holmes, & Hackmann, 2004); and cravings in substance misuse (Kavanagh, Andrade, & May, 2005). See Holmes and Hackmann (2004) for further examples. Steel, Fowler, and Holmes (2005) suggested that similar cognitive information-processing mechanisms may be involved in the creation of intrusive memories irrespective of disorder. Psychopathological intrusions can be viewed as an extension of a continuum from our common, everyday intrusions (see Holmes, 2004).
The factors that determine whether a memory becomes intrusive need to be understood. The clinical literature indicates that peri-traumatic factors (i.e. processes during encoding of trauma), such as dissociation, are the best predictors of later PTSD symptoms compared to other factors such as demographics or trauma type (see the meta-analysis by Ozer, Best, Lipsey, & Weiss, 2003). However, as argued by Candel and Merckelbach (2004) a limitation of many “peri-traumatic” clinical studies is heavy reliance on retrospective reports of reactions during trauma. Such methodology has important limitations since people in general, and PTSD patients in particular, find it difficult to give accurate descriptions of past emotional states. Prospective designs are therefore warranted, however it is clearly unethical to deliberately expose research participants to real trauma. To circumvent this, some studies have adopted ingenious paradigms such as testing trainee firefighters prior to their exposure to a real fire (Bryant & Guthrie, 2005), or using analogues of high anxiety situations such as volunteer sky divers (Sterlini & Bryant, 2002). Another analogue approach, the trauma film paradigm, offering laboratory control, has emerged in the quest for prospective methodologies.
The trauma film paradigm involves showing non-clinical participants short films which contain scenes depicting stressful or traumatic events. In this context, a traumatic event is defined as actual or threatened death or serious injury to the body or self (APA, 1994). Strictly speaking, these films might best be referred to as “films with traumatic content” since they do not necessarily induce an “intense emotional reaction” as required by the diagnostic criteria for trauma. However, for brevity we use the term “trauma films”.
