Examining the relationship between cognitive abilities and auditory-visual cross-modal activation
thesisposted on 28.03.2022, 17:43 by Amanda-Mei Fullerton
Considerable variability exists in speech perception outcomes after cochlear implantation, particularly in adults with post-lingual hearing loss. Electroencephalography (EEG) studies have demonstrated that the extent of cross-modal plasticity (i.e. competitive take-over of the auditory cortex by the visual cortex), measured by the activity of the visual-evoked potential (VEP) activity in the cortical regions, is significantly correlated with performance measures of speech perception-in-noise. This trend is observed in adults with a cochlear implant (CI) and therefore, it is of interest to understand how cross-modal plasticity changes with time in adults with severe-profound hearing loss once audition is restored with a CI. As speech perception in noise is influenced by cognitive and linguistic processes, and hearing loss is strongly associated with ageing and cognition, we need to better understand the role of each in influencing cross-modal activation and plasticity. Therefore, the aim of this pilot study was to assess the relationship between cognition, speech perception (using words and sentences in background noise) and activation of cortical areas, specifically the occipital (visual) and temporal (auditory) cortices, in response to visual stimuli, in older adults with normal hearing. It compared speech perception outcomes and a novel behavioural measure of cognition, Cogstate, (which does not rely on audition) with the P1, N1 and P2 components of the VEP responses, measured using EEG and MEG simultaneously. This study provides normative data for a future longitudinal study, which aims to investigate brain changes following cochlear implantation in older adults with post-lingual hearing loss. Results showed that while no correlations were found between speech and cognitive measures, significant correlations and relationship trends were observed between VEP responses (in both occipital and temporal regions) and speech perception and cognitive measures. While expansion of this cohort is needed to verify these trends, the results support the need to consider cognition as a potential influencing factor in broader topographical cortical representations in adults with hearing loss and/ or a cochlear implant.