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Abstract
The inference-based approach (IBA) has proposed a cognitive model to explain the aetiology and maintenance of obsessive-compulsive disorder (OCD). According to this model, specified reasoning processes lead an individual with OCD to confuse an imagined possibility with an actual probability, a state termed inferential confusion. These reasoning processes include inverse reasoning, in which hypothetical causes form the basis of conclusions about reality, and distrust in one's senses. Empirical evidence for the IBA and these reasoning processes is emerging but has been limited to self-report measures, which do not allow causal inferences. Thus the overarching aim of the current thesis was to explore the role of these reasoning processes in OCD using different methodological strategies, particularly experimental designs. In Study 1, I developed a task-based measure of inverse reasoning and found that performance on this task was associated with OCD symptoms in a large online sample. In Study 2, I used an interpretive cognitive bias modification procedure to train a bias towards inverse reasoning in an undergraduate sample. I found that those trained in inverse reasoning, compared to a control condition, reported more OCD symptoms and were more avoidant of potentially contaminated objects. In Studies 3 and 4, I attempted to replicate and extend previous research suggesting that the distrust of one's senses in OCD may stem from an actual deficit in accessing sensory information. There was insufficient evidence for a clinically significant deficit in OCD when accessing sensory information to accurately produce levels of grip strength and distance judgements. In Study 5, I explored the relationship between the ease of imagining a future situation and the perceived likelihood of this situation in a clinical OCD population. In this thesis I have presented a series of studies that have facilitated significant progress towards our understanding of the role of maladaptive reasoning processes and related processes in OCD. In conclusion, research into these mechanisms warrants continued attention in order to develop and refine techniques for clinical practice that effectively target these processes and reduce the debilitating effects of OCD.