Psychophysiological Responses to Medium Levels of Occupational Noise: An Exposure–Response Relationships

Medium noise levels are very common in work environments, and few studies have addressed their effects. This study aims to investigate the effects of real noise levels from four types of workplaces on psychophysiological responses. Thirty-one normal hearing male subjects were recruited. They were asked to judge the noise annoyance (NA) and noise-induced subjective load (NISL) of four occupational environments involved cognitive functions; closed office rooms (CO:57.8–65.2 dB(A), open-plan offices (OPO:65–71.8 dB(A), control rooms (CR:68.7–75 dB(A), and industrial noise (IN:75.5–81 dB(A). Meanwhile, the electrodermal activity (EDA), heart rate (HR), and respiration rate (RR) were monitored throughout the experiments. The saliva cortisol of subjects was also analyzed before and after each trial. The results were evaluated in the view of impact of noise and moderating factors using linear and mixed models, and a dose–response relationship was found for each response. The results showed that the NA were rated 26.5%, 39.5%, 53%, and 72.2%, in the CO, OPO, CR, and IN, respectively, and NISL increase in levels ≥ 65 dB(A)(OPO). In addition to subjective effects, the medium levels of occupational noise can significantly affect the physiological responses in view of the moderating factors. In total, the EDA and RR responses increased, whereas HR initially increased and then decreased. According to the regression models, it seems that medium levels of occupational noise have significant and linear effects on EDA, RR, and HR in levels ≥ 60 (CO), ≥ 65 (OPO), and ≥ 69 dB(A) (CR), respectively. Moreover, the levels range of 60–70 dB(A) (CO and OPO) can increase mean of cortisol level more than the levels range of 70–80 dB(A) (CR and IN).