This note presents the overall hypothesis framework of the Quiet Cities Project. Please refer to individual notes for details on each hypothesis.
Background
While traffic noise is recognized as a daily environmental stressor in urban areas, its impact is often overlooked as something people "get used to." For individuals with sensory sensitivity, traffic noise can become a serious barrier that prevents them from going outdoors.
The World Health Organization (WHO) recommends in its environmental noise guidelines that annual average exposure levels to road traffic noise be kept below 53dB(A), but many locations along major roads in Japan exceed 70dB.
However, the problem is not solely in the absolute dB values. What actually causes stress in humans is "suddenness," "contrast ratio (gap with silence)," "frequency of repetition," and "semantic meaning of sounds (modified motorcycle sounds, loudspeakers, etc.)," none of which can be captured by current time-averaged indicators.
Furthermore, no research exists worldwide that addresses the outdoor mobility experiences of individuals with sensory sensitivity and misophonia. While misophonia tendencies are reported in 12-20% of the general population (Jager et al., 2020; Naylor et al., 2021), it is a distinct concept from sensory sensitivity in ASD and other conditions, though there is overlap. This project treats these as separate concepts.
Four Research Hypotheses
H1: Sensory-Sensitive Individuals × Outdoor Mobility Routes × Physiological Data
People with sensory sensitivity and misophonia tendencies show significantly higher physiological stress responses during urban outdoor mobility compared to the general public, which constrains their frequency of outings and route selection. First research in this field worldwide.
→ Details: How Much Do Sensory-Sensitive Individuals Suffer Outdoors
H2: Zoning Regulations × Noise Disparity (Environmental Justice Hypothesis)
Low-income groups and people with disabilities tend to concentrate in affordable housing along major roads, and the severity of noise damage is inversely proportional to income. A Japanese version of "environmental noise injustice" exists. First empirical study in Japan.
→ Details: People Living Along Major Roads Experience Greater Noise Damage
H3: Existence of Complaint Void Zones
Many "complaint void residents" exist who suffer from noise damage but have not filed complaints with authorities, distorting administrative priorities for noise countermeasures.
→ Details: The Phenomenon of Complaint Voids
H4: Context-Dependent Noise Stress
Even with the same dB level of noise, stress responses vary significantly depending on the type of sound and the context in which it occurs. Current dB averaging indicators are insufficient as proxy indicators for sensory stress.
→ Details: What dB Alone Cannot Measure
Research Gap Certainty Ranking
| Gap | Certainty | Evidence |
|---|---|---|
| Sensory-sensitive individuals × outdoor mobility routes × physiological data | ◎ World first | Complete non-intersection of wearable urban research and sensory sensitivity research |
| Zoning regulations × noise disparity (Japanese version) | ◎ Japan first | International theory exists, Ministry of the Environment recognition exists, zero empirical studies |
| Direct identification of complaint void zones | ○ Not implemented in Japan | Methods exist in the US but no application examples in Japan |
| Context-dependent noise stress (sensory sensitivity focused) | ○ Sensory sensitivity gap | Research for general public exists |
What Should Be Done / What Doesn't Need to Be Done
What Should Be Done
- Real-time physiological and subjective data collection during outdoor mobility of sensory-sensitive individuals
- Japan's first empirical study on zoning × noise disparity
- Mapping complaint void zones and categorizing "reasons for not reporting"
- Development of context-dependent sensory stress indicators
- Creation of policy recommendation reports integrating the above
What Doesn't Need to Be Done
- Indoor acoustic measurements (sufficient accumulation by Sakuma, Matsui, and others)
- Re-proving that "noise is bad for health" (already confirmed by WHO)
- Creating noise maps using only dB (Ministry of Environment's national noise map exists)
- General theory of noise × real estate value (already established by Poznan research, etc.)
- Fieldwork
- Stakeholder interviews
- Complaint void survey
- Sensor network
- Citizen-participatory collection
- Zoning measurement
- Real-time map
- Policy proposal report
- Academic papers
- Light sensitivity added
- Multi-city expansion
- Index standardization
- Fieldwork
- Stakeholder interviews
- Complaint void survey
- Sensor network
- Citizen-participatory collection
- Zoning measurement
- Real-time map
- Policy proposal report
- Academic papers
- Light sensitivity added
- Multi-city expansion
- Index standardization
References
Environmental Noise Guidelines for the European Region
World Health Organization (WHO). WHO Regional Office for Europe
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Auditory and non-auditory effects of noise on health
Basner, M. et al.. The Lancet, 383(9925), 1325-1332
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騒音に係る環境基準について（告示）
環境省. 環境省
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Architecture for Autism: Concepts and Built Environment
Mostafa, M.. Archnet-IJAR, 8(1), 143-158
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聴覚過敏と暮らしの音環境
佐久間哲哉. 日本音響学会誌, 77(5), 296-301
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発達障害に伴う聴覚過敏と音環境に関する実態調査
松井温子・佐久間哲哉. 日本建築学会技術報告集, 26(62), 169-172
Read source
Prevalence and Profile of Misophonia: A Large-Scale Population Study
Jager, I. et al.. PLOS ONE, 15(2), e0227118
Read source