Schoof, T; (2014) The effects of ageing on the perception of speech in noise. Doctoral thesis , UCL (University College London).

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Abstract

The primary aim of this thesis is to answer the question why older adults often experience increased difficulties understanding speech in the presence of background noise, even in the absence of hearing impairment. The potential contribution of age-related declines in subcortical auditory processing, as measured by the auditory brainstem response (ABR) and the frequency following response (FFR), (spectro)temporal, and cognitive processing is explored. The data showed that older adults who fit strict criteria of normal hearing do not necessarily experience increased difficulties in the perception of speech in the presence of steady-state or amplitude-modulated noise. They only performed more poorly in the presence of two-talker babble. Older adults with slightly poorer hearing, however, did experience increased difficulties understanding speech in steady-state noise. The data furthermore showed age-related declines in subcortical auditory processing, working memory, processing speed, and sensitivity to spectro-temporal modulations. The normal-hearing older adults showed no age-related declines in behavioural measures of envelope or temporal-fine structure processing. These findings suggest that auditory neuropathy and cognitive declines associated with ageing do not necessarily lead to increased speech in noise difficulties. Normal-hearing older adults did not experience increased difficulties understanding speech in the presence of noise maskers, despite declines in subcortical auditory processing and cognition. Moreover, when the older adults did perform more poorly, this could not be explained by auditory neuropathy, cognitive declines, or reduced spectro-temporal modulation sensitivity. This thesis furthermore explores the effects of masker modulation type and sentence complexity on the fluctuating masker benefit. The results indicated that contextual information plays a greater role in dip listening than in the perception of speech in steady-state noise. Lastly, a new technique is proposed to more rapidly collect the FFR. Recording times can significantly be reduced by presenting stimuli continuously and averaging across a single cycle of the response.

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