Age-related changes in auditory processing in younger and middle-aged adults

Abstract

We live in an aging world, and one of the most common chronic pathological conditions associated with aging is increased hearing difficulties. The Report of the Working Group on Speech Understanding and Aging by the Committee on Hearing and Bioacoustics and Biomechanics (CHABA, 1988) has guided the relevant aging research since its publication. It purposed to investigate the problem in three levels: the peripheral auditory level, the central auditory level, and the cognitive level. Following that, one of the research directions was to examine age effects on the central auditory processing functions; and often the research paradigms focused on comparing younger with older adults. In the older adult group, the high prevalence of declined peripheral hearing and cognitive skills presented as confounding factors. In recent years, scattered studies had shifted to another research paradigm by investigating the possible aging effects on auditory processing functions in younger to middle-aged adults. The objective of the current study is to provide a comprehensive characterization of the auditory processing abilities in younger to middle-aged adults free of the confounding effects of peripheral hearing loss and cognitive decline.

Three pre-studies were conducted prior to the main study in order to construct two Cantonese assessment tools in the auditory processing test battery, and to test-run some of the components in the test battery to gaze the sample size needed. In the main study, altogether 80 younger to middle-aged normal hearing adults participated. They were tested with a comprehensive auditory processing test battery, which included the duration pattern test, Adaptive Tests of Temporal Resolution (ATTR), Cantonese Dichotic Digit Test (CDDT), monaural Cantonese bisyllabic speech in noise test, localization Test, Cantonese Hearing in Noise Test (CHINT), acoustic reflex threshold (ART), Auditory Brainstem Response to complex sound (cABR) and Cantonese Speech, Spatial and Qualities of Hearing Scale (CSSQ). These tests represented a variety of both speech and non-speech tasks that involve different levels/ regions of central auditory nervous system (CANS), and covered different behavioral measures, electroacoustic measures, electrophysiological measures and questionnaire items. Cautions were taken to recruit clinically normal hearing adults, however demographic data found significant “hidden” difference in the participants’ high frequencies hearing thresholds. High frequencies hearing thresholds (HFA) was therefore treated as a covariate in the subsequent data analysis. Hierarchical multiple linear regression or logistic regression were the statistical methods we used to investigate the role of HFA and age on predicting the different AP performances. Results showed that among the nine assessments in the test battery, four of them (i.e. monaural Cantonese bisyllabic speech in noise test, CHINT, cABR and CSSQ) showed significant early age-related changes.

In summary, the current study demonstrated that during early to middle adulthood, some AP abilities did not change with advancing age while some of them showed changes that were correlated to age and/ or high frequency hearing thresholds. We hypothesized that age-related physiological changes in the CANS, together with hidden changes in the peripheral auditory system, are two of the components leading to the early onset hearing difficulties observed in midlife.