*Article* **Effects of Soundscapes on Human Physiology and Psychology in Qianjiangyuan National Park System Pilot Area in China**

**Peng Wang <sup>1</sup> , Youjun He <sup>1</sup> , Wenjuan Yang <sup>1</sup> , Nan Li 2,3 and Jiaojiao Chen 2,\***


<sup>3</sup> China Eco-Culture Association, Beijing 100102, China

**\*** Correspondence: cjj@icbr.ac.cn

**Abstract:** The development of China's national parks is still in the initial stage, and few scholars have studied the effects of soundscapes on human physiology and psychology from the perspective of the auditory senses in national parks. In this study, the Qianjiangyuan National Park System Pilot Area was taken as the research subject, physiological indicators of subjects were collected through a biopAC-MP150 multi-channel physiological instrument data platform, and the subjective psychological response of soundscapes was measured using a Likert scale. The results showed that the sound of water had the most significant effect on the heart rate and respiratory rate of the subjects. Agricultural sound had the greatest impact on the skin conduction levels, while conversation had the least overall impact on human physiology. There were significant differences in comfort, excitement, and significance among the different soundscapes (*p* < 0.001). The sounds of insects are more likely to elicit feelings of comfort and excitement, while the sounds of birds are more likely to arouse curiosity. No significant correlation was observed between the physiological indices and psychological indices. The study on the effects of different soundscapes on human physiology and psychology in China's national parks will provide a basis for the decision makers of national parks to formulate more effective planning, design, and management policies regarding soundscapes.

**Keywords:** soundscape; national parks; human physiology; human psychology

## **1. Introduction**

The concept of soundscapes was first proposed by Raymond Murray Schafer, a Canadian musician and environmentalist [1], known as "the pioneer of acoustic culture research". The soundscape emphasizes the perception and understanding of the sound environment by individuals or society [2,3]. Although the acoustic environment and landscape have the same acoustic source components, there are some differences between them. Acoustic environment, which is mainly defined by the physical properties of sounds, refers to the sound produced by various creatures in the environment or venue for communication purposes. In contrast, a soundscape is mainly defined by human perception, human experience, and sound reconstruction. The essence is the interaction between human and the acoustic environment [4]. Under the influence of physical attributes, the perceptual features of various types of soundscapes are obviously different. Chen et al. believed that pleasure is a comprehensive index to measure the perceptual features of a soundscape, and pointed out that the factors determining pleasure mainly included physical attributes, visual scenes, humanistic value, and individual characteristics [5]. Based on existing research results [6–9], it can be seen that a soundscape with more natural elements such as birdsong and water sound provides a higher overall pleasure, while that with more noise elements such as traffic and machinery offer a lower overall pleasure. The prevailing theory of soundscape stems from two sources. First, the cultural needs of humans require an auditory input to generate different aesthetic feelings. People's perception of the landscape does not depend

**Citation:** Wang, P.; He, Y.; Yang, W.; Li, N.; Chen, J. Effects of Soundscapes on Human Physiology and Psychology in Qianjiangyuan National Park System Pilot Area in China. *Forests* **2022**, *13*, 1461. https://doi.org/10.3390/f13091461

Academic Editors: Xin-Chen Hong, Jiang Liu and Guang-Yu Wang

Received: 30 August 2022 Accepted: 6 September 2022 Published: 11 September 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

solely on vision, but also on the overall sensory responses such as taste, sight, hearing, touch, and smell. An overemphasis on vision comes at the expense of other sensory organs. Second, agricultural sounds and traffic noises of the industrial age have triggered the desire to focus on the acoustic environment, and social development has created a closer relationship between humans and nature. Contemporary soundscape research has mainly focused on related theories and methods of the International Organization for Standardization (ISO). In 2014, 2018, and 2019, the ISO issued the International Standards for soundscapes, which specify the definition, data acquisition, and evaluation standards of soundscapes [3,10,11]. According to the definition of the ISO, a soundscape is an acoustic environment as perceived or experienced and/or understood by a person or people, in context. As a whole, the relationship between soundscape and the human body is very close [12].

Studies on the soundscape of national parks began in the late 1970s in the United States. The National Park Service (NPS, USA) established the Natural Sounds and Night Skies Division (NSNSD), which is committed to protecting, maintaining, and restoring the soundscapes of national parks. The protection and management of soundscapes emphasize the silence of nature or wilderness. The management and control of soundscapes in national parks have focused on the noise caused by human interference [13]. Park et al. constructed a data model of a soundscape and pedestrian space in Rocky Mountain National Park, and found that 49.6% of the tourist group enjoyed natural sounds for 15 min if the sound was below the 35 dB noise threshold [14]. Marin et al. adopted the dose–response method to analyze the relationship between the tourists' motivation to visit national parks and the degree of acceptance of different sounds, revealing that the acceptance of tourists grew with the quietness of the environment [15]. Beal et al. investigated the perception of noise by campers in Australia's Queensland National Park and reported that agricultural sound was the most unacceptable sound type to humans [16].

In recent decades, the number of people with suboptimal health has rapidly increased; therefore, there is an increasing desire for access to nature and more outdoor space, especially during the COVID-19 lockdown period. A growing number of researchers have turned their attention to the relationship between natural soundscapes and people's health. Hume and Ahtamad studied the influence of different soundscapes on people's moods and emotional stimulation. They reported that sounds with a positive perception affected the respiratory rates, while sounds with a negative perception impacted the electrical activity of the skin. This direct relationship between pleasantness and respiratory rate response is greater in males than in females. The electromyography readings increased in both males and females with unpleasant sound clips [17]. Medvedev et al. investigated the effects of soundscapes on the physiological indices after stress stimulation and a rest period, confirming that the sound environment had a positive effect on people's health and well-being [18]. Erfanian et al. summarized the psychophysiological implications of soundscapes. They found that although some studies found a link between the physiological effect of soundscapes and perceptual attributes, most of the research merely focused on one or two physiological reactions. Unfortunately, this link has not been fully verified [19]. Wang et al. studied the impact of soundscape perception behavior on vision and confirmed that sound frequency, sound preference, and auditory satisfaction had an impact on visual perception [20]. Li et al. used heart rate (HR), heart rate variability (HRV), and other indices to explore the tendency of the physiological indices and subjective recoverability in environmental audio–visual interaction [21]. Such studies have paved the way for future research on soundscapes and human physiology and psychology.

China did not establish national parks until relatively recently, so national parks are still an original concept in this country. There are few studies on the health benefits of soundscapes, and most related soundscape studies are conducted in urban areas such as parks, campuses, and urban forests [22]. For example, Zhang et al. selected three types of urban forests and analyzed the ecological health functions of urban forests through the continuous monitoring of six environmental indices: temperature, relative air humidity, wind speed, CO<sup>2</sup> concentration, air negative oxygen ion concentration, and noise [23]. Weng et al. invited 30 college students to participate in audiovisual evaluations in the campus landscape of the Fujian Agriculture and Forestry University in order to explore the impact of the green soundscape on mood and attention [24]. Yang et al. examined the differences in the psychology of tourists with different voice preferences, who visited the ancient town of Lijiang [25]. Chen et al. studied the health care benefit of sound in forest therapy. By analyzing human psychology and emotional state in forest sound, they believed that birdsong, water sounds, and sounds of wind blowing leaves could exert a high positive impact on human psychology [26]. Song et al. selected two environments, urban and forest, and confirmed that forest sound therapy had a moderating effect on the negative emotions of tired working ladies, and forest sound could alleviate fatigue symptoms, but the effect of short-term forest recuperation was limited [27]. However, few scholars have studied the effects of soundscapes on human physiology and psychology from the perspective of auditory senses in national parks.

Therefore, in order to better reveal the effects of different types of soundscapes in the national park on the human body, by taking the Qianjiangyuan National Park System Pilot Area (hereinafter referred to as the system pilot area) as the research subject, two research questions were proposed: (1) Are there any differences in the physiological and psychological effects of different soundscapes on the public in system pilot areas? (2) What are the effects of soundscapes on public physiology and psychology in the system pilot areas? By analyzing the changes in the physiological indices and the data of the psychological indices, this study explored the association of soundscapes with human physiology and psychology in the system pilot area. The results will further reveal the differences in the physiological and psychological effects of various soundscapes and provide new insights for the evaluation and restorative soundscape planning and design of national parks. In addition, this study could help managers master the benefits of soundscapes in various regions, and provide theoretical support and data basis for the management of ecosystems in the future by soundscape analysis and ecological acoustic methods.

#### **2. Materials and Methods**

#### *2.1. Target Area*

As one of the 10 pilot areas of the national park system in China, the system pilot area covered three regions: the Gutian Mountain National Nature Reserve, the Qianjiangyuan Provincial Scenic Area, and the Qianjiangyuan National Forest Park. Located in Western Zhejiang Province (East longitude 118◦010–118◦370 , North latitude 28◦540–29◦300 ), the target area lies at the junction of Zhejiang, Anhui, and Jiangxi. With a land area of approximately 252.38 km<sup>2</sup> , it can be divided into four functional areas: core protection area, ecological conservation area, recreational exhibition area, and traditional use area (Figure 1). Among them, the acreage of the core protection area, ecological conservation area, recreational exhibition area, and traditional use area is 72.33 km<sup>2</sup> , 135.80 km<sup>2</sup> , 8.12 km<sup>2</sup> , and 36.13 km<sup>2</sup> , respectively.

The system pilot area is a typical vegetation transition zone between South China and North China, which has complex terrains, dense forests, and crossed river valleys. It is home to some ancient and extensive low-elevation, mid-subtropical, evergreen, broadleaved forests, which are rare throughout the world. This area covers four towns (Suzhuang, Changhong, Hetian, and Qixi) and 72 natural villages (19 administrative villages), with a total population of 9744 [28].

**Figure 1.** Status of the system pilot area. Note: Land use data from the Resources and Environmental Science and Data Center, Chinese Academy of Sciences (https://www.resdc.cn/, accessed on 3 Septembe 2022). Functional zoning data were obtained from the Qianjiangyuan National Park **Figure 1.** Status of the system pilot area. Note: Land use data from the Resources and Environmental Science and Data Center, Chinese Academy of Sciences (https://www.resdc.cn/, accessed on 3 September 2022). Functional zoning data were obtained from the Qianjiangyuan National Park Administration.

## *2.2. Method and Process*

Administration.

#### The system pilot area is a typical vegetation transition zone between South China 2.2.1. Sound Collection and Material Selection

and North China, which has complex terrains, dense forests, and crossed river valleys. It is home to some ancient and extensive low-elevation, mid-subtropical, evergreen, broadleaved forests, which are rare throughout the world. This area covers four towns (Suzhuang, Changhong, Hetian, and Qixi) and 72 natural villages (19 administrative villages), with a total population of 9744 [28]. *2.2. Method and Process*  2.2.1. Sound Collection and Material Selection The existing physiological test equipment is not suitable for outdoor use due to changeable terrains, large altitude difference, a forest coverage rate of 81.7%, and a complex natural environment. Therefore, this study used audios for indoor physiological and psychological tests to exclude natural conditions (basic conditions of the transformation and formation of natural factors rather than human factors such as terrains, climates, etc.) and other factors (human interference factors for outdoor experiments such as heavy equipment). The audios used in this study were obtained on sunny and breezy days from September to November 2020, and the audio data were acquired at 8:00–10:30 and 15:00– 17:00. A Sony PCM m 10 recording pen was placed on a tripod 1.5 m above the ground. The microphone was kept vertical to the main wind direction of the recording. The typical sampling method was used in the system pilot area to ensure the representativeness of the soundscape in light of factors such as forests, rivers, other ecosystems, bird biodiversity, community distribution patterns, and recreational spaces. The data were collected along the public recreational route, taking into account the typical ecological areas and important public living places. Fifty-three typical areas were selected as sample plots for The existing physiological test equipment is not suitable for outdoor use due to changeable terrains, large altitude difference, a forest coverage rate of 81.7%, and a complex natural environment. Therefore, this study used audios for indoor physiological and psychological tests to exclude natural conditions (basic conditions of the transformation and formation of natural factors rather than human factors such as terrains, climates, etc.) and other factors (human interference factors for outdoor experiments such as heavy equipment). The audios used in this study were obtained on sunny and breezy days from September to November 2020, and the audio data were acquired at 8:00–10:30 and 15:00– 17:00. A Sony PCM m 10 recording pen was placed on a tripod 1.5 m above the ground. The microphone was kept vertical to the main wind direction of the recording. The typical sampling method was used in the system pilot area to ensure the representativeness of the soundscape in light of factors such as forests, rivers, other ecosystems, bird biodiversity, community distribution patterns, and recreational spaces. The data were collected along the public recreational route, taking into account the typical ecological areas and important public living places. Fifty-three typical areas were selected as sample plots for sound collection, and the samples were marked as T1, T2, T3...T53. The sound collection was repeated three times in each plot for a duration of 20–30 s. Among the 53 samples, T6, T11 and T32 had the largest sound levels, which were 70.71 dB(A), 66.9 dB(A), and 62.64 dB(A), respectively. T12, T16, T25, and T52 had the smallest sound levels, which were all 30 dB(A). According to the geographical coordinates of the samples, the Kriging interpolation method was used to generate a spatial distribution map of the sound pressure levels in ArcGIS (Figure 2). Considering the various sound interference factors, the selected sound material was clipped to about 10 s.

sound collection, and the samples were marked as T1, T2, T3...T53. The sound collection was repeated three times in each plot for a duration of 20–30 s. Among the 53 samples, T6,

T11 and T32 had the largest sound levels, which were 70.71 dB(A), 66.9 dB(A), and 62.64 dB(A), respectively. T12, T16, T25, and T52 had the smallest sound levels, which were all 30 dB(A). According to the geographical coordinates of the samples, the Kriging interpolation method was used to generate a spatial distribution map of the sound pressure levels in ArcGIS (Figure 2). Considering the various sound interference factors, the selected

**Figure 2.** The spatial distribution of sound levels in the soundscape of the system pilot area. **Figure 2.** The spatial distribution of sound levels in the soundscape of the system pilot area.

2.2.2. Selection of Study Participants 2.2.2. Selection of Study Participants

sound material was clipped to about 10 s.

Previous studies have shown that college students are ideal subjects for participating in landscape evaluations [29,30]. In this study, 96 undergraduates, M.A students, and PhD students from the School of Economics, School of Humanities and Arts of Renmin University of China and the Chinese Academy of Forestry were randomly chosen as volunteers for the experiment. Due to sensor failures and the participants' last-minute withdrawals, 64 volunteers (25 males and 39 females) participated in the experiment. Specifically, 26 undergraduate students, 34 master students, and four doctoral students who studied ecology, forestry, art, design, economics, finance, and literature, etc. were involved. The age bracket was mainly between 21 and 25 (Table 1). To ensure the validity of the physiological monitoring and psychological response data, the study participants were asked about their physical conditions, and their answers were recorded before the start of the experiment. Previous studies have shown that college students are ideal subjects for participating in landscape evaluations [29,30]. In this study, 96 undergraduates, M.A students, and PhD students from the School of Economics, School of Humanities and Arts of Renmin University of China and the Chinese Academy of Forestry were randomly chosen as volunteers for the experiment. Due to sensor failures and the participants' last-minute withdrawals, 64 volunteers (25 males and 39 females) participated in the experiment. Specifically, 26 undergraduate students, 34 master students, and four doctoral students who studied ecology, forestry, art, design, economics, finance, and literature, etc. were involved. The age bracket was mainly between 21 and 25 (Table 1). To ensure the validity of the physiological monitoring and psychological response data, the study participants were asked about their physical conditions, and their answers were recorded before the start of the experiment.


**Table 1.** The demographic characteristics of the study participants.

## 2.2.3. Classification of Forest Soundscapes

This study investigated the types of soundscapes spanning the sounds of birds, insects, running water, and wind-blown leaves to mixed natural sounds as well as unnatural sounds such as footsteps, conversations, frolicking, agricultural sounds, and traffic sounds. To classify soundscapes, the authors consulted nine experts in ecology, acoustics, landscape architecture, humanities, etc. The classification was repeated three times to ensure the accuracy of the identification of the sound sources. When multiple sounds were superimposed, the loudness, frequency, and duration of the sound determined its final classification.

After consultation, the sound landscape of the system pilot area was finally divided into three types: natural sounds, artificial sounds, and mixed natural and artificial sounds (Table 2). Among them, natural sounds mainly include insect sounds, bird sounds, water sounds, and mixed natural sounds.

**Table 2.** The classification of soundscapes.


2.2.4. Selection of Physiological and Psychological Indices

Selection of the physiological indices. The physiological indices include heart rate, respiratory rate, and skin conductance level. They were measured by a BIOPAC physiological multi-conductance meter (model MP150) manufactured by the BIOPAC company in the United States. The modules for collecting electrical signals included electrocardio (ECG), electroencephalogram (EEG), electrogastrogram (EGG), electromyography (EMG), electro-oculogram (EOG), and electroretinogram (ERS), etc. The heart rate is the number of pulse beats per minute. A change in heart rate reflects the activity level of the sympathetic nervous system and the parasympathetic nervous system. When an individual is in a state of rest or relaxation, the function of the parasympathetic nervous system increases, and the heart rate slows down. When an individual is in a state of excitement or stress, the excitability of the sympathetic nervous system increases, that of the parasympathetic nervous system decreases, and the heart rate increases. In a natural environment, an increase in the heart rate of the subjects indicates that the subject is excited and happy [31]. The respiratory rate is the number of breaths per minute, and studies show that this index is affected by the environment. When a person is in a pleasant or unpleasant mental state, their respiratory rate is significantly different from the norm [31]. Electrical skin activity refers to changes in the function of the sweat glands of the skin, reflecting the activity of the sympathetic nerves. This activity is used as an index of emotional and cognitive loading [32]. The increased secretion of the sweat glands increases the electrical conductivity and the skin conductance levels. The skin conductance levels decrease when a person is mentally relaxed [33]. In general, the heart rate and skin conductivity reflect the human body's autonomous activities, and both are affected by the environment. A person's respiratory rate is significantly different when the human body is in either a happy and unhappy state. As the above physiological indices provide insight into the potential physiological and psychological processes of subjects, they are important indices of emotional stimulation.

Selection of the psychological indices. ISO 12913 (2014, 2018, 2019) provides eight adjective attributes for the evaluation of a soundscape-based pleasantness and eventfulness model. Referring to the existing research results [31,32,34,35], combined with the Profile of Mood State (POMS), the scale was compiled by Grow J.R. and revised by Professor Zhu Beili of East China Normal University in 1994 [36]. Finally, the comfort, excitement, and distinctiveness of a certain sound were selected as the evaluation indices. The Likert scale (5, 4, 3, 2, 1) was used for the evaluation. Before scoring the subjects' psychological state, the staff explained the process to the subjects. As the subjects were well-educated college students, they had a good understanding of the scoring method of the Likert scale. To prevent the recent psychological state of the subjects from affecting the objectivity of the research results, all subjects were measured using the SCL-90 scale, which is a popular tool for assessing the college students' mental health [37]. The results show that the scores of each factor of the test group were at the normal level, indicating that the recent mental health status of the test group was good. Hence, the subjects in the test group were suitable for this sound test.

#### *2.3. Process*

This research experiment was carried out in the Standard Laboratory of the Chinese Academy of Forestry. One staff member and one participant entered the laboratory during each experiment. The laboratory experiment was conducted on sunny days from December 2020 to January 2021 at 8:00–10:00 and 15:00–17:00 to minimize the influence of external noise. The laboratory's sound insulation effect ensured that the whole process of the experiment was quiet and the indoor temperature was kept between 18 ◦C and 22 ◦C. The experiment adopted a ThinkPad X1 laptop (screen size: 14 inches; manufacturer: Lenovo; location: Shenzhen, Guangdong, China) and a JBL-FLIP6 speaker (power was 20–40 W, and the vocal channel was 2.0; manufacturer: Harman; location: Dongwan, Guangdong, China). As the experiment was in the peak of the COVID-19 epidemic, this study did not use conventional earphones, but used speakers to play soundscape samples given the disinfection requirements of epidemic prevention and control, and the large number of subjects (96 subjects). The volume of the loudspeaker was consistent with the sound level dB(A) monitored by field recording. The laboratory temperature was between 20 ◦C and 25 ◦C, and the relative humidity was 51%–56% RH.

The process of the research experiment consisted of four stages (Figure 3): preparation and introduction, pre-investigation, data collection, and subjective evaluation. During the first stage, participants provided their name, gender, age, college, major, hometown, and other basic information before the test. The participants were asked about their physical condition, especially their mental health, medication, and hearing. Then, they were briefly informed of the content and procedures of the research experiment, which helped to reduce any stress and increase their acceptance of the proceedings.

**Figure 3.** A schematic diagram of the experiment flow. **Figure 3.** A schematic diagram of the experiment flow.

In the second stage, participants had physiological sensors with disposable electrode pads attached to their skin after it was sanitized with alcohol and saline. During the data In the second stage, participants had physiological sensors with disposable electrode pads attached to their skin after it was sanitized with alcohol and saline. During the data collection period, they were asked to remain relaxed and still and refrain from talking.

During the first stage, participants provided their name, gender, age, college, major, hometown, and other basic information before the test. The participants were asked about their physical condition, especially their mental health, medication, and hearing. Then, they were briefly informed of the content and procedures of the research experiment, which helped to reduce any stress and increase their acceptance of the proceedings.

collection period, they were asked to remain relaxed and still and refrain from talking. In the third stage, the sound materials were supplemented with a photo of the landscape. In order to highlight the typicality and representativeness of the sound sample, this study seamlessly connected and scrolled the samples of 10 s, with a total duration of 60 s. The playback mode was seamless rolling playback, and the experimental time was controlled by the subjects. There was a silent sample between every two sound samples. The baseline data were the physiological data of the silent samples, with the time controlled In the third stage, the sound materials were supplemented with a photo of the landscape. In order to highlight the typicality and representativeness of the sound sample, this study seamlessly connected and scrolled the samples of 10 s, with a total duration of 60 s. The playback mode was seamless rolling playback, and the experimental time was controlled by the subjects. There was a silent sample between every two sound samples. The baseline data were the physiological data of the silent samples, with the time controlled by the subjects.

by the subjects. In the fourth stage, participants evaluated the psychological indices (comfort, excite-In the fourth stage, participants evaluated the psychological indices (comfort, excitement, and distinctiveness) of the sound based on their own subjective judgement.

#### ment, and distinctiveness) of the sound based on their own subjective judgement. *2.4. Data Processing and Analysis*

*2.4. Data Processing and Analysis*  All data collected in this study were analyzed by Microsoft Excel 2010 and IBM SPSS Statistics 21. Physiological data, which were defined as the physiological data of the audio samples minus the physiological data of previously silent samples, were analyzed and exported using the BIOPAC-MP150 platform. The main statistical methods were one-way ANOVA and multiple comparisons. Psychological data came from the questionnaire sur-All data collected in this study were analyzed by Microsoft Excel 2010 and IBM SPSS Statistics 21. Physiological data, which were defined as the physiological data of the audio samples minus the physiological data of previously silent samples, were analyzed and exported using the BIOPAC-MP150 platform. The main statistical methods were one-way ANOVA and multiple comparisons. Psychological data came from the questionnaire survey. In order to ensure the quality of the data, the authors conducted a reliability and validity analysis.

vey. In order to ensure the quality of the data, the authors conducted a reliability and validity analysis. The results showed that Cronbach's alpha was 0.756, falling between 0.6 and 0.8, which suggested the internal consistency of the data. The results of the Kaiser–Meyer– Olkin (KMO) and Bartlett's test of sphericity were obtained by factor analysis. The KMO was 0.666, close to 0.7. The chi-square value of Bartlett's test of sphericity was 2600.654, and the degrees of freedom were 3, which were significant at the 95% or even 99% confi-The results showed that Cronbach's alpha was 0.756, falling between 0.6 and 0.8, which suggested the internal consistency of the data. The results of the Kaiser–Meyer– Olkin (KMO) and Bartlett's test of sphericity were obtained by factor analysis. The KMO was 0.666, close to 0.7. The chi-square value of Bartlett's test of sphericity was 2600.654, and the degrees of freedom were 3, which were significant at the 95% or even 99% confidence level, respectively, and indicated the high effectiveness of the data. In addition, a Pearson correlation analysis was used to study the correlation between the variables.

#### dence level, respectively, and indicated the high effectiveness of the data. In addition, a **3. Results**

#### Pearson correlation analysis was used to study the correlation between the variables. *3.1. Effects of Different Soundscapes on Human Physiology*

#### 3.1.1. Effects on Heart Rate Changes

Differences in the heart rate of the subjects were observed between different types of soundscapes in the system pilot area (Table 3). Through a single-factor analysis of variance, significant differences were observed between the subjects' heart rate data for the seven soundscapes (*p* < 0.05). Compared with the silent environment, the heart rates of the participants increased by 1.28 bpm, 1.62 bpm, 2.45 bpm, 2.43 bpm, 0.59 bpm, 2.15 bpm, and

1.65 bpm, respectively, when they listened to sounds of insects, birds, water, mixed natural sounds, conversations, agricultural sounds, and mixed natural and unnatural sounds. Overall, the subjects' heart rates showed the largest increase when they heard water sounds and mixed natural sounds and the smallest increase when they heard conversations.


**Table 3.** A comparison of the physiological indices of the subjects for different soundscapes.

Note: \* represents the significant difference at the level of 0.05. Data = mean ± SD (standard deviation). Data with different letters in the same column are significantly different.

#### 3.1.2. Effects on Human Skin Conductance Level Changes

The skin conductance of the subjects responded differently to different types of forest soundscapes in the pilot area (Table 3). Compared with the silent environment, their skin conductance level decreased by 3.51 µs, 3.60 µs, 3.68 µs, 4.14 µs, 2.98 µs, 4.27 µs, and 3.81 µs when they listened to sounds of insects, birds, water, mixed natural sounds, conversations, agricultural sounds, and mixed natural and unnatural sounds, respectively. Overall, the skin conductance level showed the largest decrease when the participants heard agricultural sounds and the smallest decrease when they heard conversations.

#### 3.1.3. Effects on Respiratory Rate Changes

Differences were observed in the subjects' respiratory rates for different types of soundscapes in the system pilot area (Table 3). Compared with the silent environment, their respiratory rates increased by 0.87 resp, 0.97 resp, 1.37 resp, 1.36 resp, 0.84 resp, 1.25 resp, and 1.03 resp when they heard sounds of insects, birds, water, mixed natural sounds, conversations, agricultural sounds, mixed natural, and unnatural sounds, respectively. Overall, the respiratory rate showed the most significant increases when the participants listened to water sounds and the smallest increase when they listened to conversations.

#### *3.2. Effects of Different Soundscapes on Human Psychology*

A single-factor analysis of variance was performed on the subjects' psychological response data for the seven different types of soundscapes (Table 4). The results showed significant differences in comfort, excitement, and distinctiveness for the seven soundscapes (*p* < 0.001). Comfort (3.92), excitement (3.32), and distinctiveness in response to insect sounds (2.91) had the highest scores (psychological cognitive score), and comfort (1.92), excitement (2.14), and distinctiveness (1.88) in response to conversation sounds had the lowest scores. The overall scores in terms of the comfort of natural sounds such as insects, birds, mixed natural sounds, and water sounds were higher than those of agricultural sounds, conversation sounds, natural, and unnatural sounds. Similar trends were observed for the index of excitement. However, there were differences in the distinctiveness of the seven soundscapes. Bird sounds were more likely to cause subjects to experience the distinctiveness of this sound. Overall, natural sound received higher scores than unnatural and mixed sounds in the matrix of comfort, excitement, and distinctiveness.


**Table 4.** The effects of different soundscapes on human psychology.

Note: \*\* represents the significant difference at the level of 0.01. Data = mean ± SD (standard deviation). Data with different letters in the same column are significantly different.

#### *3.3. Correlation between Physiological Variation and Psychological Response*

The test results showed a significant correlation between heart rate and skin conductance level (*p* = 0.018), and between heart rate and respiratory rate (*p* = 0.001). The correlation coefficient between heart rate and skin conductance was −0.839, and the significant level was above 0.05. The correlation coefficient between heart rate and respiratory rate was 0.948, and the significant level was above 0.01. In addition, there was a significant correlation between comfort and excitement (*p* = 0.001), and between comfort and distinctiveness (*p* < 0.001). Their correlation coefficients were 0.956 and 0.968, respectively. Both passed the significance test at 1%. Moreover, excitement was significantly correlated with distinctiveness (*p* < 0.001), and the correlation coefficient was 0.977, which passed the significance test at 1%. No significant correlation was observed between the physiological indices and psychological indices. Hence, heart rate has a significant negative correlation with the skin conductance level. The correlations between all of the other indices were strongly positive (Table 5).

**Table 5.** The correlation between the physiological changes and psychological indices.


Note: \*\* indicates the significance level of 1%, \* indicates the significance level of 5%.

#### **4. Discussion**

#### *4.1. Effects of Soundscapes in System Pilot Area on Physiology*

This study found significant changes in the heart rate (*p* < 0.05) of subjects when they listened to different types of soundscapes in the system pilot areas of national parks in China. However, the changes in the respiratory rates and skin conductance levels were not significantly different. The subjects had increased heart rates and respiratory rates as well as decreased skin conductance levels when they were exposed to various sounds.

The increase in the heart rate indicates that the sympathetic nerve activity increased, resulting in the excitation or happiness of the subjects. Hume and Ahtamad recorded the heart rate of 80 participants who listened to different sounds and found that after listening to pleasant sounds, the participants' heart rates increased [17]. Natural soundscapes play

a positive role in changes in heart rates. Water sounds had the most profound influence on the heart rate, and conversation sounds the least influence. The system pilot area is an important area under water source protection and contains the source of the Qiantang River, Zhejiang Province's "Mother River" and "water tower", which has nurtured the budding Chinese civilization in the Qiantang River Basin. The region is rich in water resources, and known for the numerous rivers, lakes, and waterfalls. This directly affects the relationship between water sounds and the human heart rate. Buxton et al. surveyed the natural soundscapes in the 221 locations of 68 U.S. national parks. They arrived at the conclusion that water sounds were the most effective at increasing positive emotions and maintaining health [38]. Their conclusions were consistent with that of Barton and Pretty: the natural environment, especially the water environment, provides important health benefits for the public [39]. This means that not only national parks but also soundscapes have ecological functions in humans. The results in this study confirm the conclusions of Buxton, Barton, and Pret-ty et al. on the natural soundscape, but they are also incomplete to some extent. The main reason is that although the study area is a national park, there are a certain number of inhabitants in it, and the places they live in are relatively concentrated. Therefore, artificial soundscapes such as conversation sound and agricultural sound has also been the focus of research. This study confirms that the impact of conversation sounds on heart rate variation is minimal, but this has not been fully confirmed as it is affected by the positioning of national parks in different countries (there are no or few inhabitants in most national parks).

Skin conductance activity is an electrical phenomenon that occurs due to functional changes in the skin sweat glands. It reflects the activity of the sympathetic nerves and is an index of emotional and cognitive load [40]. The changes in the skin conductance level of the subjects for different types of soundscapes indicate that agricultural sound had the most significant impact and conversation sound had the least impact on the skin conductance response. The pilot area has a population of 9744 and covers many reservoirs such as Bijiahe Reservoir and Qixi Reservoir. Most local villagers make a living through agricultural and forestry production. Agricultural sound is related to water conservancy projects and vehicles as well as other agricultural and livestock activities. These sounds are loud, disruptive, and last for extended periods of time, affecting the skin conductance response of the subjects. Li et al. conducted a tourist survey on the soundscape of Meiling National Forest Park. They found that loud noise irritated people and a very quiet soundscape made people uneasy and nervous [41]. Zhu et al. reported significant differences in the skin conductance levels of subjects in different forest environments, and unnatural sounds (e.g., footsteps) had a significant impact on the skin conductance level [33]. Although the research results of Li and Zhu et al. on artificial soundscapes could not fully support the conclusions of this study, they were sufficient to confirm that soundscapes with various artificial elements exerted a more typical impact on human skin conductance activity. Therefore, policy makers should ensure relaxing and pleasant experiences for visitors through soundscape improvement, in order to plan forest trails and tourist routes of national parks.

The analysis of the effect of different types of soundscapes indicated that a mixture of water and natural sounds had the largest influence on the subjects' respiratory rates and conversation sounds had the least influence. Cui et al. established a soundscape comfort model for the Zhongshan Scenic Area. They reported that a soundscape with a moderate sound level was comfortable for people, and an overly noisy soundscape made people irritable [42]. Bradley et al. found happy people and unhappy people had stark differences in their respiratory rate [43]. The research results of Gomez and Danuser showed that the respiratory rate increased when people listened to music after listening to noises [44]. They also found that compared with a silent environment, natural sounds evoke more pleasant feelings and increase the respiratory rates. This study concluded that it is not comprehensive to explore the effects of a national park soundscape on respiratory rate changes from the perspective of various types of soundscapes. According to the research

results, although the change in respiratory frequency caused by water sound was the largest while that caused by conversation sound was the smallest, it does not mean that natural sounds are more likely to cause changes in respiratory frequency than artificial sounds. This is mainly because the impact of natural soundscapes such as insect songs and bird chirps on the change in respiratory frequency is also small as a whole. Therefore, referring to the research conclusions of Bradley, Gomez, and Danus-er et al., this study believes that the impact of soundscapes on respiratory frequency may be related to the volume of soundscape and emotional elements, which needs to be further demonstrated in future studies.

#### *4.2. Effects of Soundscapes in System Pilot Area on Psychology*

Significant differences in the three psychological indices (comfort, excitement, and distinctiveness) (*p* < 0.001) were observed among the different types of soundscapes. In general, the sounds of insects, birds, water, mixed natural sounds, and other natural sounds of the forest soundscapes had a positive impact on human psychology. The sound of insects evoked feelings of comfort and excitement, while the sound of birdsong was more likely to intrigue subjects. Our research results are consistent with those of previous studies [45]. Forest sounds that include insect sounds as the main component have a relatively high sound frequency, and those with bird sounds as the main component have a high variability and melodiousness. The pilot area is known as a "Mysterious Primitive Forest and Paradise of Wild Bird". According to local biodiversity statistics (data provided by the National Park Service), it is home to 238 species of wild birds in 17 orders and 63 families in the pilot area. For instance, Syrmaticus ellioti, a national I-level key protected species, is abundant here. In addition, bird species such as Lophura nycthemera, Streptopelia orientalis, and Carrulax canorus are common. Wang et al. analyzed the psychological indices of college students in urban areas, woodlands, flower fields, and near water bodies and found that the values of the psychological indices were greatly varied in woodlands and water landscapes and less variable in urban areas [46]. This finding indicates that the blue–green natural space has a positive impact on human psychology. The sound of water has therapeutic effects [47]; it masks noises while increasing the sense of tranquility and calms emotions in people [48].

This study preliminarily proved that the soundscapes of national parks dominated by natural sounds can lift people's mood and deliver a more pleasant experience, and invoke a more pleasant feeling. This study attempts to reveal the different psychological responses to sounds when external interference is excluded. For future research, it is necessary to use controllable simulations and more advanced technologies to achieve a more comprehensive evaluation.

#### *4.3. Effects of Different Types of Soundscapes in National Parks on Human Body*

Physiological and psychological data show that the soundscapes of national parks may be related to the people's physical state. The soundscapes of national parks can change people's physiological and psychological states and have an impact on people's physical health to a certain extent. Compared with a silent environment, soundscapes increase heart rates, reduce the skin conductance level, and increase respiratory rates. In addition, we found significant differences in psychological indices such as excitement and distinctiveness between the different types of soundscapes. This result indicates that the participants' sympathetic nervous system excitement level increased, and the excitability of the parasympathetic nervous system decreased, resulting in a relatively pleasant and excited mental state. This conclusion is consistent with Hao et al.'s findings that the heart rates increased and the skin conductance levels decreased when people heard pleasant sounds [31]. Annerstedt et al. explored the physiological recovery status of subjects in different soundscape environments by collecting their cardiovascular data and saliva cortisol. The results showed that the subjects' parasympathetic nerve excitability significantly changed in a natural acoustic environment, indicating that this environment is conducive to people's physiological recovery and a potential connection exists between the natural soundscape and stress recovery [45]. This study confirms, from a physiological perspective, that sound stimulation related to the forest environment has better health benefits than a silent environment or visual stimulation [49].

On the other hand, there were differences in the health benefits of different types of soundscapes. The sound of water and mixed natural sounds had the largest impact on the health benefits, which may be related to the landscape features of the pilot area. The pilot area is rich in water resources, and most of the roads are surrounded by rivers and waterfalls; thus, the sound of the water is heard in most areas. In recent years, water landscapes have played an increasingly important role in natural therapy. Tedja et al. reported that listening to the sound of running water helped people to meditate and facilitated the relaxation of the body and mind [50]. This shows that waterscapes (water sound) require attention in the future planning and management of the soundscape of national parks. In addition, the system pilot area sets to leverage its water resources and sounds to develop a forest-centered therapy center. Mixed natural sounds generally contain more than two types of sounds such as the rhythmic sounds of birds, insects, water, and wind. Therefore, a soundscape characterized by loudness, a strong rhythm, and high variability inspires excitement. Buxton et al. argue that the sound of running water helps to regulate emotions and maintain health, and bird sounds reduce stress and annoyance [38], which is consistent with the results of this study. From the aspect of psychological response, insects and bird sounds are more abundant than other sounds; therefore, they have a larger influence on the health benefits than quiet soundscapes and monotonous, noisy, and unnatural sounds. Ratcliffe et al. conducted semi-structured interviews with 20 subjects and found that birdsong was the most suitable natural sound type for releasing stress and restoring attention, which was of significant potential for stress recovery [51]. Our study also verified the decompression theory of Ulrich et al. [52], who observed that a positive environment substantially relaxed people, reduced the sense of pressure, and provided a positive physiological response.

#### *4.4. Research Prospects and Deficiencies*

Few systematic studies have been conducted on the improvement in human physiology and psychology by soundscapes in national parks. In this study, the health effects of various forest soundscapes were clarified by investigating the psychological and physiological changes caused by different forest soundscapes in the system pilot area. This experiment only used a soundscape evaluation, and not a visual evaluation, to reveal the different reactions of the subjects after they heard forest sounds without external interference. However, this approach has some limitations. For instance, Ratcliffe et al. found that the soundscape of green spaces had higher health benefits, which might be related to the high vegetation coverage [51]. Watts et al. found that the higher health benefits of blue spaces were related to the restorative benefits of water sounds as well as visual landscape features [53]. In addition, due to the limitations of the existing physiological and psychological indicators, the existing research results cannot fully cover the impact of soundscapes on the human body. Subsequent research will incorporate more typical physiological indicators such as the heart rate variability to assess the effects of soundscape more comprehensively.

Limitations exist in this study as it was restricted by the existing objective experiments. Although ecological validity of the subjects' response to sample stimulation was ensured in the research on soundscape perception in a simulated indoor environment, the complex acoustic environment was inevitably driven by other factors, which exerted a certain impact on the results. Therefore, although our conclusions enjoyed statistical significance, whether it has universal significance needs further verification. In later research, more advanced technical means will be used to create a controllable simulated natural environment to produce a more comprehensive evaluation. The researchers of this study are aware of the necessity for further research and advanced technology to create a more realistic environment for simulation. Some researchers believe that the results of indoor experiments differ

from those obtained in a natural environment. For example, Ishiyama analyzed the adverse effects of traffic noise on subjects, and observed that the irritability of the subjects caused by noise was related to the number of sound samples. This study selected college students as subjects, which also have a demographic bias. In the future, the authors will invite a wider scope of stakeholders such as residents of national park communities or foreign tourists to participate in this soundscape research. In addition, high-frequency sounds were more likely to cause the subjects to feel irritable [54]. In the future, our group plans to explore the use of virtual reality to investigate audiovisual forest landscapes in national parks. In addition, the authors will collaborate with ornithologists and entomologists as well as scientists of other fields to analyze the effects of different bird and insect sounds on physiology and psychology.

## **5. Conclusions**

This study took the Qianjiangyuan National Park System Pilot Area as the object, analyzed the impact of soundscape stimulation on human physiological changes and psychological responses, and discussed the relationship between physiology and psychology based on soundscape stimulation. The following conclusions were drawn. (1) Significant changes in the heart rate (*p* = 0.003) of subjects exposed to different types of soundscapes. However, the changes in the respiratory rate and skin conductance level were not significantly different. The soundscape influenced the physiological responses of the subjects to varying degrees. The heart rate and the respiratory rate increased, and the skin conductance level decreased. The sound of water had the most significant influence on the heart rate and respiratory rate. Agricultural sound substantially affected the skin conductance level, and the sound of conversation had the least overall impact on the subjects' physiology. (2) The soundscape caused changes in the subjects' psychology to different degrees. Different types of soundscapes caused significant differences in comfort, excitement, distinctiveness, and other psychological indices. The sound of insects made people feel comfortable and excited, and the sounds of birds made them feel curious. Unnatural sounds resulted in the lowest scores. (3) No significant correlation was observed between the physiological indices and psychological indices. Except for a significant negative correlation between the change in heart rate and the change in the skin conductance level, all other indicators presented a positive correlation.

This study clarified the influence of different types of soundscapes in national parks on human physiological and psychological changes, and revealed the interrelationship between physiological changes and psychological responses, thus promoting the inclusion of the effects of soundscapes on the human body in national park management. Based on the research results, the following two suggestions are put forward: (1) Make full use of the existing terrain, optimize the hearing experience of national parks through the occlusion function of the terrain, and create an attractive soundscape; and (2) birdsong and underwater sounds have certain therapeutic functions. We suggest planning tree species in key areas that can attract birds and bees, optimizing plant configuration, and creating a natural soundscape through biological means. By exploring the impact of different types of soundscapes on the psychological and physiological changes, this study proves that the soundscapes of national parks have an impact on people's health. In future research, we will continue to explore the impact of mixed sounds (e.g., the mixed sounds of birds, those of insects, and those of other creatures) on people's health and investigate the audio–visual interaction in national parks, paying attention to both audio signals and visual behavior.

**Author Contributions:** Conceptualization, P.W. and J.C.; Methodology, P.W.; Software, W.Y.; Validation, N.L.; Formal analysis, Y.H.; Investigation, W.Y.; Resources, N.L.; Data curation, W.Y.; Writing original draft preparation, P.W. and J.C.; Writing—review and editing, P.W. and J.C.; Visualization, N.L.; Supervision, J.C.; Project administration, N.L.; Funding acquisition, P.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China (52008389) and the Fundamental Research Funds of ICBR (Grant No. 1632021030).

**Data Availability Statement:** Not applicable.

**Acknowledgments:** All authors are very grateful to the Qianjiangyuan National Park Administration in China who provided the data. We also thank three classmates (Le Li, Haodong Liu, and Zhiqiang Gao) for their help on the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**

