After decades of widely studying fear habituation as a mechanism of change in exposure therapy, the focus seems to be shifting towards harm expectancy violation through which new non-threat...Show moreAfter decades of widely studying fear habituation as a mechanism of change in exposure therapy, the focus seems to be shifting towards harm expectancy violation through which new non-threat associations are acquired. Expectancy violation has found a more consistent support in modern literature, but it has not yet been sufficiently investigated as a mechanism or a marker of change in exposure, when treating post-traumatic stress disorder (PTSD). Understanding what drives change could facilitate designing effective interventions that would improve exposure outcome, and high dropout or non-response rates, that are often accompanying PTSD treatment. The aim of this master thesis was to explore the relationship between harm expectancy violation, within and between the first two exposure sessions, and change in PTSD symptoms, after these two sessions and post-treatment, as measured by PCL. To put these relationships into perspective, predictive value of fear habituation indices in relation to the outcome was also assessed; and further, it was evaluated whether expectancy violation and habituation act as separate constructs when standing together. Results have shown that early indices of between-session expectancy violation and within-session fear habituation had a significant, though weak, relationship to early treatment outcome, while acting as separate predictors. However, this study has not found any of the early indices of expectancy violation or fear habituation to be indicative of the end-of-treatment outcome. Furthermore, it points to limitations regarding measuring harm expectancies and provides recommendations for future research.Show less