Project Background

Why is Noise-Induced Hearing Loss Important?

Noise is a very common environmental sound exposure around the world. The most well-understood health impact of noise – noise-induced hearing loss (NIHL) – is also one of the most common illnesses globally [1-3]. Individuals afflicted with NIHL suffer from a wide variety of adverse social, health, and occupational impacts [4-6]. These can include communication and relationship difficulties; social withdrawal and isolation; reduced quality of life; depression and mental health issues; and potentially loss of employment [7,8]. Additionally, children and young adults suffering from NIHL have substantial lifelong educational-related impacts [9]. While often considered more of a nuisance than a disease, NIHL is in fact a debilitating – but entirely preventable – condition.

What guidelines are available for preventing noise-induced hearing loss among members of the public?

In 1999, the World Health Organization (WHO) published guidelines to reduce the risk of NIHL among adults and children [10]. In these guidelines, the recommended exposure limit, intended to eliminate the risk of any NIHL in virtually all exposed people, was a 24-hour average sound pressure level of 70 decibels measured using A-weighting, which mimics the sensitivity of the human ear. This limit is referred to as a 24-hour average LEQ, or 70 dBA LEQ24h. The 1999 WHO guideline has recently been supplemented by an initiative (Make Listening Safe campaign), to reduce the risk of NIHL among children and adolescents who listen to music through personal listening devices. As part of this campaign, the WHO and the University of Michigan oversaw the development of 2018 guidelines focused specifically on music exposure. The music-specific guidelines from WHO suggest that an LEQ24h exposure of 75 dBA, which is equal to an 8-hour average exposure (LEQ8h) of 80 dBA, is sufficiently protective against NIHL for adults, children, and adolescents. This level is more protective than the exposure limit of 85 dBA LEQ8h used to protect workers’ hearing in virtually every country in the world [12].

Why are the University of Michigan and Apple Inc conducting this study?

NIHL affects tens of millions of people around the world [3]. This disease has traditionally affected adult workers with high exposures to occupational noise [13]. However, recreational noise exposures (for example, listening to music, attending concerts and sporting events, riding motorcycles or public transit, etc.) appear to be increasing in the US and around the world [14-17]. In fact, research suggests that roughly 90% of urban and suburban residents in the US and other countries exceed the WHO’s recommended limit of 70 dBA LEQ24h from recreational activities alone [18-20].

The potential risk of NIHL from amplified music and music experienced through personal listening devices (for example, MP3 players and smartphones) has received great attention in recent years. Research suggests that music may be the primary source of noise exposure among urban residents [18,21-23]. It is unclear whether risk of NIHL among children and young adults is increasing or decreasing over time [24-29], but there is some evidence that they may be listening to music for longer periods, and at higher levels [30].

How is noise-induced hearing loss measured?

NIHL can be assessed in several ways. Our study will utilize two different tests, pure tone audiometry and speech-in-noise. Pure tone audiometry measures how much sound it takes a person to hear at different frequencies. Participants are presented with a pure tone stimulus at a range of different frequencies (typically between 125 Hz and 8000 Hz), and their hearing ability at each frequency is measured in decibels of hearing level (dB HL). The speech-in-noise test measures how well a person hears words in the presence of background noise. This test provides a measure of functional word recognition in background noise, and is summarized as a speech recognition threshold (SRT).

How are the University of Michigan and Apple Inc. conducting this study?

The impacts of NIHL are extensive and widespread. However, we have little information about music exposure levels and listening patterns in the US, or on the associated risk of hearing loss. The introduction of new technology into the iPhone and Apple Watch platforms, along with enhancements to iOS, have created an opportunity for us to evaluate exposures to music, as well as exposures to environmental sound, and to assess hearing ability using conventional tests. Our study will take advantage of these opportunities to evaluate the levels of sound at which participating Americans listen to music, as well as their listening patterns for both music and non-music media delivered via iPhones. Additionally, we will measure hearing ability among study participants using pure tone audiometry and a speech-in-noise test. Having this data will allow us to assess the relationship between listening intensity and duration and hearing health outcomes [31,32]. With enhancements to the Apple Watch that allow us to measure environmental sound levels and heart rates, we will, for the first time ever, be able to assess the associations between sound exposure and hearing and heart health. Finally, we will explore the impacts of two different user interfaces within the app on participants’ listening behavior.

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