The Restorative Potential of Natural Soundscapes in Indoor Environments: EEG and Psychological Evidence

Given the considerable time individuals spend indoors, the acoustic characteristics of indoor environments play a crucial role in shaping psychophysiological health. To investigate how various sound types influence subjective perception and neural responses, this study examined five auditory conditions: no sound, traffic noise (TN), environmental noise, birdsong (BS), and water sound (WS). Thirty-eight university students participated in the experiment, during which subjective evaluations-including sound comfort (SCV), sound pleasure (SPV), and sound satisfaction (SSV)-were collected alongside electroencephalogram (EEG) data. EEG analysis included time-frequency and nonlinear dynamic features. Compared with TN, both BS and WS improved subjective perception, with BS increasing SCV, SPV, and SSV by 1.68-2.42 points (p < 0.001) and WS increasing them by 1.95-2.37 points (p < 0.01). Exposure to BS and WS elicited enhanced α and β activity, with power increases of 3.42%-11.05% and 9.61%-13.22% (both p < 0.05), predominantly in the frontal and parietal regions. Furthermore, natural sounds induced neural avalanche dynamics with shorter durations, smaller avalanche sizes, and reduced branching parameters and avalanche critical indices (decreases of 4.94%-8.24% and 15.53%-16.43%, both p < 0.05), indicating closer proximity to the brain's critical state. Compared to traffic noise, the ratio of brain self-stabilisation to synchronisation under natural sound increased by 1.34-1.35 times. Canonical correlation analysis revealed a strong association (r = 0.643) between subjective sound perception and brain activity, highlighting the psychophysiological coupling induced by sound exposure. These findings support incorporating restorative natural sounds into architectural acoustic design. Based on a neuroarchitectural framework, this study proposes an integrated evaluation approach for indoor sound environments, offering insights for enhancing occupant well-being in built spaces.