Objective As a crucial component of the human living environment, soundscape quality directly impacts users’ environmental experience as well as physical and mental health. Its positive effects in alleviating mental stress, improving emotional states, and facilitating cognitive recovery have been widely recognized. Bird vocalizations, as one of the most distinguishable and positively valenced elements in natural soundscapes, are not only regarded as key acoustic signals in ecological environments but also considered an important medium connecting humans with nature and promoting public mental health. Moreover, avian biodiversity may exert potential impacts on human restorative experiences by regulating the diversity and loudness characteristics of soundscapes. Clarifying the dose-response relationship between the richness of different bird vocalizations and psychological restorative outcomes constitutes a vital step in advancing soundscape design from qualitative description to scientific quantification.
Method Three types of bird vocalizations with varying richness levels were selected as experimental stimuli: continuous singing of a single bird species, alternating calls of 5 bird species, and alternating calls of 9 bird species. A 60-second audio clip was extracted from each group to serve as restorative sound materials for the experiment. Stimuli were compiled and randomly presented via ErgoLAB software. For physiological data collection, electroencephalography (EEG)was employed to provide objective physiological evidence. Psychological data were assessed using the Perceived Restorativeness Soundscape Scale (PRSS)and the Profile of Mood States questionnaire (POMS). A total of 54 healthy adult participants were recruited online. First, participants were fitted with EEG recording equipment and signal calibration was performed. Subsequently, baseline data were recorded under a resting state. After that, participants were exposed to 2 minutes of urban environmental noise stimulation. In the recovery phase, three types of acoustic stimuli with different avian species richness levels were randomly presented, and participants’ physiological and psychological responses were measured. The experimental module structure was consistent across all richness conditions: it began with a 2-minute silent adaptation period, followed by a 1-minute playback of the corresponding bird vocalization stimulus. Upon completion of stimulus playback, participants were required to complete the POMS and PRSS scales.
Results After preprocessing all EEG data, valid data were obtained from 52 participants. Compared with urban noise, the bird vocalization environment significantly enhanced the psychological restorative effect. When comparing the restorative differences among the three bird vocalization groups with varying richness levels, the average relative power of different frequency bands across brain regions was calculated: the 9-species group showed higher α wave power.PRSS and POMS analysis showed that under the single bird species condition, 9 of the 12 PRSS items achieved the highest scores, showing a trend that simplicity is superior to complexity. All negative mood scores of POMS were below 2.1, indicating that the overall negative emotional level in the birdsong acoustic environment was low. The negative emotions increased slightly with a greater number of birds. Combining subjective restorativeness scores and physiological regulatory effects, one bird sound yielded the strongest subjective restoration, while nine bird sounds produced the strongest physiological restoration for the brain, followed by one bird. However, nine or more species resulted in reduced restorative effects due to information overload. Spearman correlation analysis among PRSS, POMS subjective scale scores, and EEG data revealed the following relationships: stronger perceived soundscape compatibility was associated with lower δ wave relative power; greater curiosity about the sound was linked to lower θ wave relative power; higher levels of fatigue experienced by participants correlated with higher α wave relative power; and stronger perceptions of soundscape compatibility and "being away" were associated with higher β wave relative power. Certain EEG physiological indicators were correlated with specific dimensions of subjective perception. A degree of dissociation was observed between some EEG indicators and subjective experiences: high-richness bird vocalizations may be more effective in inducing physiological relaxation in the brain; although they did not trigger negative physiological stress responses, they increased information processing load, leading to a decline in subjective restorative experiences.
Conclusion This study adopted a dual research paradigm combining "objective physiology + subjective experience". By integrating multi-frequency, multi-brain region EEG analysis with standardized scales (PRSS, POMS), it avoided the limitations of a single research perspective and enhanced the reliability and comprehensiveness of the results. Focusing on avian vocalization richness as a key variable, this study systematically explored the differential effects of varying richness levels and attempted to identify specific quantitative ranges, aiming to provide directly applicable parametric basis for landscape design. Future research can be further expanded in the following aspects: expanding the type and scope of samples to include participants of different ages, occupations, and geographical regions to verify the generalizability of the avian vocalization richness effect; extending research scenarios to explore the interaction between scene characteristics and avian vocalization richness in combination with different landscape types, thereby improving the contextual adaptability of research results; and deepening research variables by introducing acoustic indices, bird vocalization types, and other variables to investigate the soundscape restorative effect under the synergistic action of multiple factors.
DownLoad: