Martijn van Teffelen

Chapter 4 80 Imagery ability Imagery ability was assessed with the 35-item Questionnaire upon Mental Imagery (QMI) (Sheehan, 1967). Participants are, for example, asked to think of seeing ‘the sun sinking below the horizon’. Then participants rate how vividly they can see the image on a 7-point Likert scale ranging from 1 (perfectly clear and vivid) to 7 (no image present at all). The QMI possesses good internal consistency (Evans & Kamemoto, 1973) –in the present study α = .96– and adequate convergent validity (Sheehan, 1967). Hostility Different aspects of hostility were measured with the following five scales. First, the Social Information Processing-Attribution and Emotional response Questionnaire (SIP-AEQ) (Coccaro et al., 2009) measures hostile interpretation bias (i.e., the tendency to interpret emotionally ambiguous stimuli in a hostile way) and is scored on a 4-point Likert scale ranging from 0 (not likely at all) to 3 (very likely). Second, the voodoo doll task (VDT) measures behavioral aggression by counting the number of pins inserted in a doll (DeWall et al., 2013). Third, the 10-item State Trait Anger Expression Inventory-2 trait anger subscale (STAXI-2T) (Spielberger, 1999) measures affective aspects of hostility and is scored on a 4-point Likert scale ranging from 1 (not at all) to 4 (very much). Fourth, the 8-item Aggression Questionnaire (AQ) hostility subscale (Buss & Perry, 1992) measures cognitive aspects of hostility and is scored on a 5-point Likert scale ranging from 1 (extremely uncharacteristic of me) to 5 (extremely characteristic of me). Last, the Forms of Aggression questionnaire (FOA) (Verona et al., 2008) measures behavioral aspects of hostility and is scored on a 5-point Likert scale ranging from 1 ((almost) never) to 5 ((almost) always). Note that in the current study participants were asked to indicate how often each behavior occurs in general instead of ‘when angry’, as is the case in the original FOA. All scales have shown good reliability – in the present study α ’s range from .73 to .88– and adequate validity (Coccaro et al., 2009; DeWall et al., 2013; Hornsveld et al., 2009; Lievaart et al., 2016; Verona et al., 2008). Emotional stressor In the second session all participants engaged in an imagery-interview, following Hackmann et al. (2000). In this interview, participants were asked to form a mental image from the autobiographical event discussed in session one with their eyes closed as if it was happening now. The imagery-interview served as an emotional stressor to examine the sustainability of obtained effects at measurement 6 (M6). Therapists and Treatment Integrity To ensure treatment integrity three master-level clinical psychology students with clinical experience were extensively trained in the treatment protocol by the fourth author, a licensed clinical psychologist (E.M.) who is an expert in applying both imagery and