# Experimental Investigation of Task Performance and Human Vigilance in Different Noise Environments
## 4 Discussion  
The main purpose of this study was to explore the effects of noise exposure and mental workload on task and vigilance performance. The results indicated that increased noise sharpness had a detrimental effect on performance of the TRA subtask. In addition, higher sound pressure level and sharpness could impair human vigilance, as indicated by the lower mean sample entropy of HRV and worse PVT metrics. Therefore, a reduction in noise sharpness was also important for improving performance during task execution. Changes in noise exposure conditions may affect the subjective mental workload. [PERSON] et al. [32] evaluated five occupational noise indicators of open-pit miners in  
Figure 7: Boxplots of the interactive effects of noise condition and mental workload on MATB task performance. (**a**) Overall performance. (**b**) SYS performance. (**c**) TRA performance. (**d**) RES performance (\({}^{\#}\)\(p\) < 0.1; \({}^{\star\bullet}\)\(p\) < 0.01). the United States Midwest with 15 subjects. The results showed that the risk of mental workload increased from a sound pressure level of 80 dB(A). It was suggested that noise exposure at high sound pressure levels could be an independent risk factor for a high mental workload. In addition, [PERSON] et al. [33] investigated mental load and cognitive ability under five noise conditions: a quiet environment (54 \(\pm\) 0.3 dB(A)), closed office (64 \(\pm\) 0.4 dB(A)),), open office (68 \(\pm\) 0.8 dB(A)), control room (73 \(\pm\) 0.3 dB(A)), and industrial place (80 \(\pm\) 0.1 dB(A)). By testing 31 subjects on their cognitive performance and NASA-TLX scale scores under different noise conditions, they found that the higher the sound pressure level, the greater the perception of mental workload level. In our study, we did not find any significant effect of sound pressure level on subjective mental workload. However, the subjective mental workload was slightly increased with higher noise sharpness. The impact of noise on task performance remains controversial [34]. [PERSON] et al. [35] collected the performance indicators of 192 subjects under two noise conditions (95 dB(A) intermittent aircraft noise vs. quiet), and the results confirmed that performance under the noise condition was better than that of the quiet condition. However, [PERSON] et al. [33] showed that an increase in sound pressure level led to increases in errors in job performance. In our study, different noise exposure conditions had no significant impact on overall MATB task performance. However, it was found that TRA performance was significantly lower under N75-S2 than under N85-S1. The difference in the results of noise effects on task performance may be related to task difficulty. TRA is a subtask with the least cognitive challenge in MATB [20], which is more likely to be affected by deteriorating noise exposure. Meanwhile, participants may be more distractable during task processing at low workload demands [36]. At this time, an increase in noise sharpness may lead to narrowed attention of the subjects, causing them to ignore the lower difficulty TRA subtask and focus on the more complex SYS subtask [8]. This suggests that an increase in noise sharpness could narrow attentional focus, inducing participants to concentrate on the more complex tasks. In an experimental study conducted by [PERSON] et al. [37], 112 participants were exposed to aircraft noise for nine consecutive nights in a laboratory, while 64 participants were tested in an airport for nine consecutive nights. The experimental results showed that the sound pressure level could increase the PVT response time of operators in both the laboratory and airport. Our results also confirmed that severe noise exposure could impair human vigilance, which was manifested in worse PVT performance and longer response times.