thesis

Auditory Scene Analysis in Alzheimer's disease

Abstract

This thesis explores the behavioural and neuroanatomical picture of Auditory Scene Analysis (ASA) in Alzheimer’s disease (AD). Central auditory dysfunction is an understudied symptom of AD and there has been little connection between the neuropathological profile of the disease, its relationship to generic ASA functions, and real-world listening situations. Utilising novel neuropsychological batteries alongside structural and functional imaging techniques, this thesis aims to bridge this gap through investigations of auditory spatial, speech in noise, and (as a specialised auditory scene) music processing. Spatial location discrimination and motion detection of sounds was impaired in both typical AD and posterior cortical atrophy; this was associated with atrophy in right inferior parietal and posterior medial regions. A functional imaging investigation of auditory spatial processing in typical AD revealed abnormalities in posterior medial cortical areas when sounds were changing in location. Functional imaging of an everyday auditory scenario (hearing one’s own name over background babble) highlighted alteration in a right inferior parietal region. Novel neuropsychological tasks assessing components of musical ‘scenes’ found that global aspects of pitch pattern processing were impaired in both the typical and language variant of AD while local aspects were preserved; both global and local forms of temporal processing were also intact. These patients also exhibited diminished tonality perception and musical stream segregation based on familiar templates. These investigations delineate reduced ASA capacity in a number of components that make up everyday auditory scenes. This has real world implications for both typical AD and its rarer phenotypes. Furthermore, ASA dysfunction may inform us about network breakdown, network function, and sources of phenotypic similarity in AD

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