Martijn van Teffelen

Impact 181 9 SCIENTIFIC AND SOCIETAL IMPACT The present dissertation aimed to investigate the nature of hostility and how to manipulate it. In a sequence of studies, we examined the validity of hostility, how it can be provoked in laboratory settings, and how increased levels of hostility can be reduced. First, findings revealed that hostility can be structurally divided in cognitive, affective, and behavioral factors. Second, results demonstrated that social exclusion and insult are comparable in terms of impact on hostility, but the personality traits of psychopathy and narcissismdifferentially impact on this relationship. Third, findings revealed that hostile interpretations and aggressive behavior can efficaciously be reduced with therapist provided imagery-enhanced cognitive restructuring (I-CR) and computerized cognitive bias modification for interpretation bias (CBM-I). The present findings have scientific and clinical impact in several ways. First, the result that hostility can be hierarchically structured may in short term provide hostility scholars with more precisely defined dimensions of hostility. Hopefully, this stimulates efforts to develop and test more standardized and precise assessment options for hostility. In the long term, this findingmay contribute to a reduction of conceptual identity confusion that clouds the validity of the hostility construct and provide more precise intervention targets. Second, the finding that social exclusion and insult have equal impact on hostility in the short terms provides first evidence that researchers may interchangeably use social exclusion or insult procedures to experimentally induce hostility. Moreover, the finding that psychopathic and narcissistic traits differentially impact this relation may in the long run provide clinicians with new insights on how to tailor treatment plans for people with clinical levels of hostility. Third, the finding that integratingmental imagery in existing therapist-provided CR enhances its efficacy, in the short term provides scholars and clinicians with a novel procedure that can be used and further tested in scientific and clinical settings. In order to stimulate further efforts of researchers and clinicians in testing and using I-CR, we developed a detailed narrative procedure. This is important, because the technique needs further proof of its’ effectiveness in different samples and independent laboratories. For example, the impact of multiple, or the optimal number of I-CR sessions is unclear. Also, it is not clear whether the technique generalizes to novel everyday situations, or what its efficacy is in people with more extreme levels of hostility. Hopefully, in the long run, I-CR offers a new option for patients (and their social relations) that suffer from the profound negative consequences of hostility. Last, the finding that CBM-I efficaciously reduces hostile interpretations and aggressive behavior in the short term provides the clinical field with a new technique that can be implemented at relative low-cost. Compared to the fields of anxiety and mood disorders, the hostility field lags behind in terms of CBM-I research. With the present study we hope to stimulate research efforts to answer more detailed questions concerning the effects of CBM-I. This includes, for example, investigating the optimal ‘dose’ of CBM-I, or examining the effects of CBM-I when it is offered as an add-on prior to traditional therapist-provided therapy. Taken together, the present findings impact patients, clinicians, and scientists by providing new insights in the nature of hostility, how it can experimentally be provoked and how it can be efficaciously reduced.