Middle Ear Muscle Reflex in Normal-Hearing Individuals with Occupational Noise Exposure.

Objectives: Noise-induced cochlear synaptopathy is studied extensively in animal models. The diagnosis of synaptopathy in humans is challenging and the roles of many noninvasive measures in identifying synaptopathy are being explored. The acoustic middle ear muscle reflex (MEMR) can be considered as a vital tool since noise exposure affects the low-spontaneous rate fibers that play an important role in elicitation of MEMR. The present study aimed at measuring MEMR threshold and MEMR strength. Design: The study participants were divided into two groups. All the participants had normal-hearing thresholds. The control group consisted of 25 individuals with no occupational noise exposure whereas noise exposure group had 25 individuals who were exposed to occupational noise of 85 dBA for a minimum period of 1 year. MEMR threshold and strength was assessed for pure tones (500 Hz and 1000 Hz) and broadband noise. Results: The results showed that the MEMR threshold was similar in both the groups. MEMR strength was reduced in noise exposure group compared to control group. Conclusions: The results of the study suggest that MEMR strength could be used as a sensitive measure in identifying cochlear synaptopathy with careful consideration of the stimulus characteristics.

Effect of Occupational Noise Exposure on Cognition and Suprathreshold Auditory Skills in Normal-Hearing Individuals.

OBJECTIVES: Adverse effects of noise exposure on hearing and cognition are well documented in the literature. Recently, it has becoming increasingly evident that noise exposure deteriorates suprathreshold auditory skills, even though the hearing sensitivity is intact. This condition is termed as cochlear synaptopathy or hidden hearing loss, which is apparent in animal models. However, equivocal findings are reported in humans. This study aimed at assessing the working memory, attention abilities, and suprathreshold hearing abilities in normal-hearing individuals with and without occupational noise exposure. We also explored the relationship between cognitive measures and suprathreshold auditory measures. DESIGN: The study participants were divided into two groups. All the participants had normal-hearing thresholds. The control group consisted of 25 individuals with no occupational noise exposure, whereas the noise exposure group had 25 individuals exposed to occupational noise of 85 dBA for a minimum period of 1 year. Working memory was assessed using auditory digit span (forward and backward), operation span, and reading span. The Erikson flanker test was used to evaluate attention abilities. The suprathreshold hearing was assessed in terms of gap detection thresholds and sentence identification in noise. RESULTS: The results showed that the noise exposure group performed poorly compared to the control group on all auditory and cognitive tasks except the reading span. CONCLUSION: The results of the study suggest that occupational noise exposure may hamper the cognitive skills and suprathreshold hearing abilities of the individual despite having normal peripheral hearing.