The effects of occupational noise exposure and age on speech perception in noise and self-reported hearing function: An online study in Palestine

Background: Animal research shows that both aging and excessive noise exposure can damage the cochlear hair cells as well as the synapses connecting the inner hair cells with the auditory nerve, while aging has been associated with deficits in central auditory neural processing. Workers in developing countries typically are exposed to unsafe levels of occupational noise throughout their lifespan due to the lack of enforcement of occupational health and safety measures. The effects of occupational noise exposure may be more apparent in the older adult worker population, which may manifest as decreased ability to understand speech especially in noise, tinnitus, and hyperacusis. The current study investigates the effects of occupational noise exposure and aging on: (i) speech-perception-in-noise (SPiN) thresholds, (ii) self-reported hearing ability (iii) the presence of chronic tinnitus, and (iv) severity of self-reported hyperacusis.

Methods: Two hundred and fifty-one worker and non-worker adults (females: 152, age range: 18-70, mean age: 35.1) from the Occupied Palestinian Territories with no past diagnosis of hearing and memory impairments were recruited online. Subjects completed a set of online instruments in Arabic including: an otologic health and demographic questionnaire; the online forward and backward digit span test; a noise exposure questionnaire which evaluates lifetime occupational, recreational, and firearm noise exposure; the Khalfa hyperacusis questionnaire; the speech-spatial and hearing qualities (SSQ12) questionnaire; the tinnitus handicap inventory (THI); and an Arabic online digits-in-noise (DIN) test. In pre-registered analyses, multiple linear regressions were employed to test the study aims (i) (ii) and (iv), while logistic regression was used to evaluate aim (iii). The covariates of recreational noise exposure, the sex of participants and their cognitive function, as reflected by the forward and backward digit span test score and the highest level of formal academic attainment, were accounted for in all the statistical models. Exploratory analyses were performed to determine the effects of occupational noise exposure and age on THI scores.

Results: For participants with at least some occupational exposure, higher exposure was associated with higher DIN thresholds, increased likelihood of tinnitus, and lower SSQ12 scores. However, these results did not survive correction for multiple comparisons. Participants with occupational noise exposure had a significantly greater severity of hyperacusis compared to those with no occupational exposure, after correction for multiple comparisons. Age was a significant predictor of DIN threshold and SSQ12 score after correction. In exploratory analyses, neither occupational noise exposure nor age significantly predicted the severity of chronic tinnitus as reflected by the THI scores.

Conclusions: The present preliminary data, derived using online instruments, provide evidence that aging results in poorer SPiN, and poorer self-reported hearing ability, in Palestinian adults with no past diagnosis of hearing impairment. Occupational noise exposure increases the risk of more severe hyperacusis.