Proceedings of the Institute of Acoustics

 

 

Effects of aircraft noise on psychophysiological feedback in under route open spaces

 

Fei Qu¹, Shenzhen University, Shenzhen, China

Qi Xie², Shenzhen University, Shenzhen, China

 

ABSTRACT

 

Aircraft noise pollution is getting increasingly severe due to striding development of worldwide air transport. In high-density cities, a large number of residential areas are exposed to airport routes where flight-over noise poses a serious threat to public health. However, most existing research is limited to the thresholds for annoyance lacking in-depth exploration into the psychophysiological impacts that induce health responses. This study aims to examine the health effects of aircraft noise on both subjective evaluation and objective physiological indicators in a laboratory setting. Aircraft noise samples were collected in the under-route open spaces. The effects of aircraft noise on annoyance and physiological feedback, including Skin Conductance Response (EDA) and Heart Rate Variability (HRV), were examined using listening experiment and ErgoLab electrophysiological response monitoring. The study also analysed the effects of soundscape modulating and examined the relationship between psychophysiological responses and subjective annoyance. The results are expected to provide indicators to assess and improve the health of under-route communities.

 

1. INTRODUCTION

 

Aircraft noise is one of the most important environmental pollutions in cities. Studies have shown that the public opposition and psychological distress due to aircraft noise have been increasing[1]. Long-term exposure to aircraft noise can disrupt sleep and cognitive behaviour, induce cardiovascular disease, and reduce self-rated quality of life and psychological well-being[2]. In China, numerous airports are being integrated into cities, resulting in a large amount of noise radiation to the under route residential areas.

 

Research on aircraft noise has generally focused on the subjective assessment of annoyance, lacking in-depth exploration into the psychophysiological mechanisms that induce health responses. In the past decade, more research has been exploring the use of physiological indicators to objectively evaluate the effects of noise[3]. Physiological-psychological studies are based on the idea that humans will develop a stress response when exposed to external stimuli, which will be accompanied by changes in physiological signals and currents, and that these changes are closely related to psychological activities such as emotion and stress, which can infer feedback mechanisms in response to noise stimuli. Currently, few research has been conducted on the relationship between aircraft noise and physiological feedback.

 

Therefore, this study investigated the relationship between physiological feedback and subjective evaluations of aircraft noise using listening experiments based on ErgoLab electrophysiological monitoring. In addition, the aircraft noise samples were modulated with natural sounds to inform noise control strategies that incorporate overall soundscape perception.

 

2. METHODS

 

2.1. Noise Samples

 

Original aircraft noise sample

 

A 5-min recording of aircraft noise collected in the community setting was used as a sample for the listening experiment, the length of which allowed for a better recording of the pattern of changes in physiological indicators[4]. To achieve the effect of original field playback, the study conducted noise recording in community open spaces under the flight path that is heavily affected by aircraft noise. The recording was carried out using HEAD Acoustics' SQobold, which simulates the binaural configuration of the human body and the reflection of the shoulders, among other effects, to better record the spatial perception of sound during aircraft overflight. The microphones were placed at standing height facing the direction of the incoming aircraft for recording and each clip was imported into ArtemiS SUITE 12.0 software for filtering and interception. Figure 1 shows the measured sample (left ear channel), presenting the changes in sound pressure with time (FFT vs time) during three aircraft overflights.

 

 

Figure 1: Five minutes sound sample consisting of three flight events (Leq=68.8dBA).

 

Modulated aircraft noise sample

 

Studies on restorative soundscape have shown that natural sounds such as birdsong and water flow have a significantly positive effect on the restorative perception of the environment, especially for noises with acceptable sound intensity. The original 1min aircraft noise sample including a full flight event was overlaid with bird song and small waterfall recordings respectively to generate 2 new modulated samples, which were adjusted to 70 dBA(Leq) to control for the effect of sound pressure levels. Figure 2 illustrates the sound properties of the two modulated samples.

 

 

Figure 2: One minute modulated sound samples (Leq=70.0dBA).

 

2.2. Psychophysiological Evaluation

Physiological indicators collected include EDA (Electrodermal Activity), HR (Heart-Rate), IBI (Inter-Beat Interval), and HRV (Heart Rate Variability). These have been shown to be related to stress and emotions[5]. Increased HRV data are associated with decreased stress, while elevated EDA generally indicates that the stimulus has triggered emotions such as pleasure and arousal[6].

 

EDA represents autonomic changes in the electrical properties of the skin. The study used the Skin conductance level (SCL) to collect the tonic level of electrical conductivity of skin, which had been reported as the most appropriate index among the EDA indices in previous studies[7].

 

HRV reflects the changing pattern of Inter-Beat Interval (IBI) values, which is the time interval between two consecutive heartbeats. The metrics for HRV in this study include SDNN (Standard deviation of NN interval) and RMSSD (Root mean square of continuous variance of IBI), which have been widely used to evaluated the changes in heart rate over short term stimulation[8].

 

Physiological signals were measured with a smart wrist sensor, connected to the ErgoLAB3 software platform via Bluetooth. The sensor was connected to the skin at all times during the experiment, and two electrodes were attached to the middle and index finger of the non-dominant hand respectively[9].

 

2.3. Subjective Evaluation

 

Self-reported annoyance to each sound recording was examined using a numerical 0-10 scale (endpoints marked “not at all” and “extremely”), according to the standardised ISO Acoustics questions for assessing noise annoyance in surveys (ISO 15666-2003).

 

2.4. Experiment Procedure

 

The participants in the experiment were 60 university students from Shenzhen University, aged between 24-28. During the preparation of the experiment, the participant entered the lab and was asked to sit in front of the monitor screen. The researcher explained the entire process and asked for consent for the experiment. The participant put on the physiological bracelet and headphones, calibrating physiological signals in a calm state.

 

The physiological monitoring was automatically conducted for each segment using ErgoLAB3 software. The experiment procedure is illustrated in Figure 3. Firstly, the data from the resting state for 2 min was used as the baseline index, reflected the physiological relaxation state of the participants before noise stimulation. Then the sounds were presented in the following order: 5 min aircraft noise, 1min original aircraft sound clip, modulated samples adding birdsong and small waterfall sound respectively. The duration of each sound interval was set to 1 min, during which the participant filled in the corresponding questionnaire. The total time for the formal experiment was around 15 minutes.

 

 

Figure 3: Flow chart of the experiment procedure.

 

2.5. Statistical Analysis

 

Physiological datum in each segment was converted to the percentage of its difference from the baseline value of the resting. IBM SPSS 25.0 was used to create the database for physiological and subjective responses. Analyses of One-way ANOVAs were performed to compare the effects of different sound samples on physiological indicators. The relationship between subjective evaluation of annoyance and each physiological indicators were examined using Pearson’s coefficient.

 

3. RESULTS

 

3.1. Psychophysiological Response to Aircraft Noise Exposure

 

The physiological indicators of the participants changed in real time during the experiment. On the transient scale, there was no synergistic association between physiological signals and the level of aircraft exposure throughout the period of 5 min noise stimulation. Figure 4 shows the Leq and HRV (SDNN) in each 1s segment, changing with time. Bivariate correlation shows no significant association between sound pressure and HRV levels (Person’s r=.094, p=.103).

 

 

Figure 4: Changes in the sound pressure levels and HRV indicators in each 1s segment with time

 

3.2. Effects of Modulated Aircraft Noise

 

The modulated aircraft noise samples significantly affected participants’ physiological responses. Compared to the original acoustic samples, the experimental samples superimposed with birdsong increased skin conductance levels, as well as heart rate variability. However, the one-way ANOVAs indicated that the increase in both SDNN and RMSSD of the HRV indicators was not significant (Table 1).

 

The sample with the small waterfall sound further increased the HRV substantially with the mean SDNN-HRV value increased from 62 to 271. The differences in HRV indicators between waterfall modulated sound and original aircraft sound were statistically significant (p<.001, Table 2).

 

Table 1: ANOVAs of differences in physiological indicators responding to birdsong modulated sound and original aircraft sound.

 

 

Table 2: ANOVAs of differences in physiological indicators responding to waterfall modulated sound and original aircraft sound.

 

 

The findings demonstrated that both birdsong and water sound modulation significantly increased the SCL, which might indicate the emergence of emotions such as pleasure and arousal. The water sound modulation significantly increased HRV, which implied decreased stress.

 

3.3. The Relationship Between Physiological and Subjective Evaluations

 

The mean of annoyance to the original aircraft noise was 6.5 out of a scale of 0-10 (95% CI 5.6- 7.3), while the annoyance to the bird song modulation increased to 6.7 (95%CI 5.6-7.8), the level for the water sound modulation decreased to 5.2 (95%CI 4.1-6.3). One-way ANOVA test shows that only the decrease of annoyance in water sound modulation was significant at p<0.1 confidence level (F=3.322, p=.076).

 

No significant correlations was found between annoyance and physiological indicators.

 

4. CONCLUSIONS

 

The paper shows the effects of aircraft noise on physiological indicators and compares the effects of two soundscape modulation strategies. No synergistic association between physiological signals and the level of aircraft exposure was found on the transient scale. The modulated samples superimposed with birdsong and small waterfall sound significantly increased skin conductance levels (SCL), indicating the emergence of pleasure emotions. The soundscape masking with small waterfall sound can significantly increase the heart rate variability (HRV), demonstrating the possibility of decreased stress. The results of the study anticipate the potential to reduce the adverse health impacts of aircraft noise with the creation of community soundscape facilities of fountains and small waterfall features. This paper indicates no associations between subjectively reported annoyance and physiological indicators, which might be due to the fact that the sample was not sufficient and individual subjective differences were not fully controlled for. Nevertheless, the physiological based experiment that investigates the effects of soundscape modulation on aircraft noise evaluation can be developed in future study to achieve a higher generalisation of the current results.

 

5. ACKNOWLEDGEMENTS

 

The study is funded by Natural Science Foundation of Guangdong Province, 2021A1515010556.

 

6. REFERENCES

 

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4. Li Z, Kang J. Sensitivity analysis of changes in human physiological indicators observed in soundscapes. Landscape & Urban Planning, 190: 103593 (2019).

5. Kreibig S D. Autonomic nervous system activity in emotion: A review. Biological Psychology, 84(3): 394–421 (2010).

6. Suko Y, Saito K, Takayama N, et al. Effect of Faint Road Traffic Noise Mixed in Birdsong on the Perceived Restorativeness and Listeners’ Physiological Response: An Exploratory Study. International Journal of Environmental Research and Public Health, 16(24): 4985 (2019).

7. UMEZAWA A. Comparison of skin conductance and skin potential as an index in electrodermal biofeedback studies. Japanese Society of Biofeedback Research, 21: 29–36 (1994 ).

8. Li Z, Ba M, Kang J. Physiological indicators and subjective restorativeness with audio-visual interactions in urban soundscapes. Sustainable Cities and Society, 75: 103360 (2021).

9. Alvarsson J J, Wiens S, Nilsson M E. Stress Recovery during Exposure to Nature Sound and Environmental Noise. International Journal of Environmental Research and Public Health, 7(3): 1036–1046 (2010).

 

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¹ fqu@szu.edu.cn

² 2070325005@email.szu.edu.cn