Study of the Relationship Between Hearing Loss and Cognitive Performance at Chronic Exposure to Noise

Abstract

Background: Noise is considered as one of the most significant and dangerous physical factors in work environments, and due to the advancement of industries, it has become a threat to physical and psychological health in the current era. In addition to its undesirable effects on the hearing system, noise can have harmful non-auditory effects that may cause physiological disorders and cognitive impairment. Objectives: This study aimed to investigate the relationship between hearing loss and workers’ cognitive performance in an industrial environment. Methods: A total of 300 individuals were enrolled in this study after their informed consent was obtained, and their compliance with the inclusion and exclusion criteria was confirmed. Based on the sound intensity level, the individuals were classified into two groups of exposure to > 85 dB (n = 196) and ≤ 85 dB (n = 104). To measure the individuals’ occupational exposure at an 8-hour equivalent level based on the ISO 9612: 2009 standard, the Testo device (Model CEL-815) was used with the precision of 0.5 dB. The most common weighting that is used in noise measurement is A-weighting. Like the human ear, this effectively cuts off the lower and higher frequencies that the average person cannot hear. The DANPLEX-AS54 device was also used to check audiometry. To investigate the workers’ hearing performance, two psychological tests, namely Stroop and TOL, were used as well. Results: Hearing loss was higher among workers exposed to a sound intensity level of > 85 dB than those exposed to a sound intensity level of ≤ 85 dB, and this difference was significant in all sound level frequencies (NIHL left ear: for ≤ 85 dB: 25.92 and for > 85 dB: 27.49) (NIHL right ear: for ≤ 85 dB: 27.62 and for > 85 dB: 29.50) (P value < 0.05). The results showed a significant positive relationship between cognitive indicators and hearing loss (P value < 0.05). Moreover, the study of cognitive indicators in the two groups revealed that the mean change of cognitive performance indicators was higher among subjects exposed to a higher sound intensity level (P value < 0.05). Conclusions: The results of this study showed that noise-induced hearing loss in work environments had a significant positive relationship with cognitive indicators. In other words, an increase in the hearing loss level would result in changes in cognitive indicators such as number of errors and response time.