![]() However, to date, no study has investigated the CAP skills in individuals with subjective memory complaints (SMCs). Central auditory processing impairment is now considered the primary auditory impairment associated with an increased risk of AD ( Panza et al., 2018).Ī few studies have previously investigated the CAP skills in individuals diagnosed with MCI ( Idrizbegovic et al., 2013 Edwards et al., 2017) and dementia ( Gates et al., 2011 Golden et al., 2015 Quaranta et al., 2015). These studies have demonstrated that individuals with CAP dysfunction were at a significantly higher risk for incident dementia with hazard ratios ranging from 9.9 (95% CI, 3.6–26.7) to 23.3 (95% CI, 6.6–82.7) ( Gates et al., 1996, 2011). Results from several longitudinal studies suggest that central hearing or CAP skills, in the absence of a severe peripheral hearing loss, are associated with high incidences of cognitive decline and AD dementia ( Gates et al., 2002, 2008, 2011) and may precede cognitive impairments and dementia diagnosis by three to 12 years ( Gates et al., 1996). Together, peripheral hearing loss, cognitive decline, aging, and diminished CAP skills (i.e., decline in speech-in-noise processing, dichotic processing and temporal processing skills, or a combination of all these abilities) contribute to the poor speech understanding skills of older adults ( Humes et al., 2012 Musiek and Chermak, 2013). A typical hearing complaint of older adults is their inability to understand speech, especially in the presence of background noise ( CHABA, 1988). In an 11-year longitudinal study, baseline peripheral hearing loss was associated with the increased risk of incident AD (1.27 times per 10 dB hearing loss).Ĭentral auditory processing (CAP) impairment refers to auditory perceptual difficulties that cannot be explained by impairment in peripheral hearing but refers to the impairment in the central auditory pathway affecting speech understanding such as neural transmission, feature extraction and detecting small gaps in the speech which is crucial in speech discrimination, integrating and separating binaural auditory information ( Humes et al., 2012 Musiek and Chermak, 2013 Fortunato et al., 2016). Evidence from both cross-sectional ( Jayakody et al., 2017) and longitudinal ( Lin et al., 2011a Deal et al., 2016) studies confirmed an increase in the risk of cognitive impairment and incident dementia among older adults with ARHL ( Lin et al., 2011a Deal et al., 2016). Prevalence data indicates that 63% of adults aged 70 years and older have a >25 dBHL speech frequency (4 PTA average of 0.5, 1, 2, and 4 kHz) hearing loss in their better ear ( Lin et al., 2011b). ![]() Age-related hearing loss (ARHL) or presbycusis is a multifactorial disorder affecting hearing acuity that varies from mild to profound and results from lifetime insults to the auditory system ( Gates and Mills, 2005). ![]() Of the potentially modifiable risk factors, untreated hearing loss contributes up to 8% of the modifiable risk factors in mid-life ( Livingston et al., 2020). With no cure or effective treatment currently insight, it is critical to identify those factors that may prevent or delay cognitive decline and dementia in older adults. Current evidence suggests that the self-reported decline in memory or other cognitive functions in the presence of normal performance on neuropsychological measures is associated with an increased risk for future cognitive decline and AD dementia ( Glodzik-Sobanska et al., 2007 Wang et al., 2011 Scheef et al., 2012). The National Institute of Aging-Alzheimer’s Association Work Groups on diagnostic guidelines suggest that the course of AD can be divided into three subsequent stages: (1) the pre-clinical stage of AD (no impairment in cognition on standard assessments and biomarker evidence for AD), (2) mild cognitive impairment (MCI) due to AD (impairment on memory or other domains of cognition on a standard assessment and biomarker evidence for AD), and (3) dementia due to AD (dementia and biomarker evidence for AD plus subtle cognitive decline) ( Jack et al., 2011 McKhann et al., 2011 Sperling et al., 2011 Albert et al., 2013). The neuropathological changes associated with AD, including the deposition of amyloid plaques and neurofibrillary tangles, start 20–30 years before the clinical diagnosis ( Serrano-Pozo et al., 2011). Alzheimer’s disease (AD) is the most common cause of dementia in older adults accounting for 60–80% of all-cause dementia ( Lambert et al., 2014). According to the World Alzheimer Report, the number of people with a dementia diagnosis will rise to 74.7 million in 2030 and 132 million by 2050 ( Prince et al., 2015). With over 47 million individuals living with dementia worldwide in 2015, this syndrome is considered a growing global epidemic in older adults ( Prince et al., 2015).
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