The Impact of Cochlear Implantation on Cognitive Function in Adults

Abstract

Background: The association between hearing loss and dementia have been found in past research. As both hearing loss and dementia are more prevalent in late adulthood, this results in a growing attention in age-related hearing loss. Despite the investigation done by numerous studies, a clear consensus of the causal relationship between the two has not been found yet, especially among those with severe-profound hearing loss. Aims: The goal of this study was to explore the potential relationship between hearing loss and cognition in the older adult population. Aims were: to investigate the effect of hearing loss simulation on cognitive performance on normally-hearing individuals; to investigate whether presenting stimuli through different sensory modalities could affect cognitive performance on individuals with and without hearing loss and cochlear implants; and, to investigate the potential effect of severe-profound sensorineural hearing loss on cognitive performance with and without cochlear implants. Methods: In the current study, hearing loss simulation groups were added. Data were collected from 26 participants (10 normally-hearing, 10 normally-hearing with simulated hearing loss at 70dB HL, 4 normally-hearing with simulated hearing loss at 60dB HL, 1 cochlear implant user, and 1 participant with hearing loss). To provide sufficient power for analysis, these findings were combined with data from earlier research (Phase 1) that adopted the same methods as were used for the present thesis (Phase 2) Digit Span and Arithmetic tasks from WAIS-IV were used to assess cognitive performance, presented in auditory and visual modalities. The scores from both modalities were then compared. Phase 1 data have been combined with Phase 2 data for data analysis using IBM SPSS statistical software. This results in a data analysis of 58 participants in total, with data from 32 participants in Phase 1 (11 normally-hearing, 11 cochlear implant users, and 10 participants with hearing loss). Results: There was an interaction between modality (visual or auditory) and cognitive test (digit span or arithmetic) across all groups. This manifested as Digit Span scores being slightly higher in the visual modality while the Arithmetic scores were much higher in visual modality. There was also a significant interaction between modality and hearing group. In the Digit Span test, all groups performed worse in the visual modality except the 70 dB hearing loss simulation group. For the Arithmetic test, all groups performed better in the visual modality. Conclusions: The findings supported the cognitive load and overdiagnosis hypotheses that hearing loss provides a disadvantage in cognitive assessments due to limited cognitive capacity for working memory thus resulting in poor cognitive performance. This also highlights the protective effect of hearing assistive devices from cognitive decline.