Age-related hearing loss and neurocognitive function: Normal and pathological processes in cognitive ageing

Abstract

This thesis investigates age-related hearing loss (ARHL) as a potential biomarker and risk factor for cognitive decline and dementia. Two reviews were conducted to examine the evidence for an association in the epidemiological and experimental literature. Both reviews found sufficient support for an association and, in particular, a mechanistic association whereby ARHL affects cognitive function. Based on these two reviews, a hypothetical model termed Neurocognitive Implicit-Explicit Asymmetric Decline (NIEAD), whereby ARHL mechanistically causes cognitive decline, was posited. This model postulates that ARHL will be associated with decline in implicit or bottom-up cognitive processes but relative maintenance in explicit cognitive processes. This hypothesis was assessed in three studies in which a sample of older adults with hearing loss was compared to a control group using indices of implicit and explicit function. The results from these studies indicated support for this model. The overall conclusion of this thesis is that further research is warranted into the association between ARHL and cognitive ageing.