Abstract
The correlation between sound and psychophysiological health is complex. This study explores effects of various sound pressure levels (SPLs) on psychophysiological responses, utilizing dynamic features of neural activity. Two sound types (traffic noise and spring water sound) and five SPLs (40, 45, 50, 55, and 60 dBA) were tested, with no sound serving as the control condition. The electrocardiography (ECG) and electroencephalogram (EEG) of 38 young college students were collected. The results indicate that spring water sound (SWS) significantly enhances sound perception, with sound comfort votes (SCV) and sound pleasure votes (SPV) increasing by 0.10-0.95 and 0.05-1.10, respectively. SWS facilitated parasympathetic nervous system comfort. Compared to the no sound, as SPLs increased, LF/HF decreased (by 0.07-0.41), and SDNN increased (by 8.85-18.56 ms), whereas traffic noise (TN) exhibited the opposite trend. For brain oscillatory activity, α, θ, and β power-associated with stress recovery-initially increased and then decreased with rising SPLs under spring water sound exposure. At 50 dBA SWS, effective delay duration, linked to comfort, peaked at 284.78 ms. Conversely, the α power and τe for TN diminished with increasing SPLs. The left frontal-parietal and right occipital lobes exhibited the highest sensitivity (p < 0.01). SWS exposure reduced the avalanche critical index (ACI) by 4.78-17.29% compared to no sound, enhancing brain comfort, while TN increased the ACI by 2.28-29.37%. The 50 dBA SWS showed the greatest improvement in brain comfort, being 1.74 times higher than that of TN. Furthermore, compared to no sound, brain power loss was lower for 52.63-63.16% of participants exposed to 50-60 dBA SWS. This study provides a methodology for soundscape evaluation and enhances understanding of how brain activity changes under sound exposure can improve the indoor acoustic environment.