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Abstract
This thesis aimed to investigate the mechanisms underlying the construct of Intolerance of Uncertainty (IU), in terms of cognitive bias and negative affect. Experiments 1 and 2 examined appraisal dimensions in relation to positive, negative, and ambiguous scenarios across various life domains. In addition, written feedback was used to manipulate task-related uncertainty. Findings indicated that high levels of IU were associated with greater concern and greater estimates of probability and cost of negative outcomes in response to all three scenario types. The biggest between-group difference in concern was observed for the positive scenarios. High levels of IU were associated with lower confidence in problem-solving abilities, particularly in response to ambiguous situations. The uncertainty manipulation did not elicit a strong effect on high IU participants, possibly due to ceiling effects for their ratings of concern, probability, and cost. Similar patterns of manipulation results were observed in a sample of participants with clinical generalised anxiety disorder (GAD). IU was found to share a robust association with rumination, though only IU predicted appraisal biases in GAD. Appraisal bias in response to ambiguous situations was further examined in Experiments 3, 4, and 5 using a modified covariation bias paradigm. IU was associated with enhanced threat appraisal bias and negative affect. Importantly, uncertainty about the occurrence of a negative outcome was more likely to be perceived as threatening if information required for calibrating the relative probability of a negative outcome was unavailable (ambiguous threat). The final experiment examined IU across anxiety disorders. Findings showed that IU was not specific to GAD, though it was more elevated in GAD and obsessive-compulsive disorder, relative to social anxiety disorder, panic disorder with/without agoraphobia, and hoarding disorder. Collectively, findings converge on the conclusion that IU is associated with enhanced threat appraisal bias and negative affect in response to ambiguous situations. Furthermore, the association of IU with a number of anxiety disorders is consistent with the notion that IU may be a shared factor in anxiety psychopathology. These conclusions have important clinical implications for further advancing the treatment for pathological worry/GAD, and for the broader anxiety psychopathology.