Melbourne School of Psychological Sciences - Theses
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ItemPsychological and neurobiological mechanisms underpinning chronic tinnitus( 2017)Chronic tinnitus, the phenomenon of a ringing, buzzing or hissing type sound in the ears or head is a prevalent health condition affecting 10-15% of the general population (Henry, Dennis, & Schechter, 2005a). It can have significant negative effects on an individual’s health and wellbeing and is associated with significant economic burden (Maes, Cima, Vlaeyen, Anteunis, & Joore, 2013; Tyler & Baker, 1983). At present, there is no cure for chronic tinnitus, likely due to the lack of consensus regarding the mechanisms maintaining the presence or impact of chronic tinnitus on individuals experiencing this condition. This thesis aimed to determine if psychological factors, and associated neural networks, could be maintaining awareness of the tinnitus sound and the severity of its impact. To achieve this objective, four studies were conducted utilising meta-analytic, questionnaire, cognitive and neuroimaging techniques. The first study comprehensively and systematically reviewed current literature regarding the psychological functioning of adults with chronic tinnitus. Results suggest that a heterogeneous array of psychological functions may be involved in the experience of chronic tinnitus, particularly emotional and cognitive functions, with meta-analyses providing consistent evidence for a role of reduced emotional wellbeing in both the presence and impact of chronic tinnitus. Study 2 and 3 further investigated the role of emotional and cognitive factors respectively in chronic tinnitus. Specifically, Study 2 investigated possible interactions between psychological factors and the vicious cycle of hypervigilance to the tinnitus sound in a heterogeneous community sample of 81 adults with chronic tinnitus. While analyses replicated the presence of the vicious cycle, this was conditional on the experience of depressive symptoms. Study 3 aimed to determine the contribution of cognitive functioning to chronic tinnitus. Compared to healthy-hearing individuals (n=26) people with chronic tinnitus (n=26) showed significant impairments in cognitive control, inhibitory control and increased symptoms of depression, with depressive symptoms and cognitive control successfully discriminating between people with and without chronic tinnitus. Combined, these studies suggest that disruption of specific large-scale neurocognitive networks proposed to underpin a range of psychological and cognitive symptoms; particularly those associated with depression may also underpin chronic tinnitus. As such, the final study of this thesis investigated the functioning of our stable neurocognitive networks, specifically the cognitive control network, in people with chronic tinnitus (n=15) and matched controls (n=15). While both groups successfully engaged the cognitive control network, the chronic tinnitus group exhibited subtle disruptions to a core node of this network, namely the right middle frontal gyrus, revealing both attenuated activation during cognitive engagement. This region also showed decreased connectivity with a node of the salience network, the right anterior insula, and increased connectivity with nodes of the autobiographical memory network, namely left posterior cingulate cortex and left medial prefrontal cortex. Together, the results of this thesis identify a failure in the process of attention-switching and the associated neurocognitive networks as a core mechanism underpinning the persistent awareness and pervasive impact of chronic tinnitus. This provides a novel framework, the Attention-Switching Model, for investigating both the experience of tinnitus, and potential treatments to help people with chronic tinnitus.
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ItemInvestigating anxiety and depression in adults with low intellectual ability( 2016)Adults with low ability have been routinely excluded from general population research that supports cognitive behavioural therapy for anxiety and depression. Even studies using samples of adults with ability below average exclude potential participants with profound and severe intellectual disability, without testing task-specific capacity. Consequently, little is known about the viability of cognitive models of anxiety and depression amongst adults with low ability. The present study addresses this through four main lines of enquiry: inclusion of all abilities through screening and validity procedures; prevalence of signs and symptoms of anxiety and depression as well as the impact of life stressors on these; cognitions and their specificity for anxiety and depression; and the impact of anxiety and ability on attentional responses to emotional stimuli. A sample of 70 adults from each level of low ability, unselected for signs or symptoms of anxiety and depression, was recruited from community-based disability support services. Participants were screened for general (receptive language) and task-specific abilities, interviewed for symptoms of anxiety and depression and disorder related cognitions then administered a visual-probe task with emotional face stimuli. Informants provided data on signs of mental ill-health, stressful life events and adaptive behaviour. Task-specific validity procedures governed data included for analysis. The inclusionary approach meant participants from all ability levels below average were included. Task-specific screening measures were superior to receptive language in predicting validity on research tasks, especially for participants with severe and profound intellectual disability. Dimensional measurements meant ability variables could be covaried or controlled in most analyses. Mean levels of signs and symptoms were lower than those in available reference studies, as were the rates of clinical level cases. General ability was positively correlated with signs of anxiety and depression but was not related to symptoms. Similarly, the number of life events was correlated with all scales on the measure of signs but not with symptoms of anxiety or depression. The lack of concordance highlights the gap between what informants see and what respondents think and feel. Learning a person’s subjective interpretation of events can help understand their emotions and behaviour. Depressive cognitions uniquely predicted significant variance in symptoms of depression but only ability, rather than anxious cognitions, predicted anxiety symptoms. Cognitive content-specificity for depression bolsters support for the use of cognitive behaviour therapy but further research into the relationship between ability and anxiety is required. The lack of directional bias in selective attention to emotional faces in any of the anxiety or ability groups means cognitive-motivational theory was not supported but future studies should address methodological issues. Attentional control theory was supported but the slowing of emotional face processing caused by high anxiety, but not depression needs replication. Trials of attentional training may be justified to reduce anxiety. Further research into cognitive models of anxiety and depression is urgently needed and future studies should ask theoretical as well as clinical questions.