Noise

[00:00:00] Listen, Listen, Listen, Listen, Listen, Listen, Listen, Listen, Listen, Listen, Listen, Listen, Listen. Welcome to Listen Here, a podcast about the soundscape surround us and the stories they tell us about the places where we find ourselves. I'm your host Kristen Page.

[00:00:24] Have you thought much about how sounds make you feel? There are so many kinds of sounds around us that maybe you don't think much about them until they're annoying or interrupting your sleep. There are sounds that I really love.

[00:01:02] I love waking to the birdsong of the dawn chorus. I also love owls, and when I hear them it makes me feel in awe. And I really love a thunderstorm. There are also sounds that I dislike. Mostly I struggle with noises made by people when they're eating.

[00:02:27] In my job as a college professor one of my favorite things to do is to visit with children in elementary or middle schools. Not too long ago I visited with several middle school science classes and we talked about sounds and how they make us feel.

[00:02:42] I was there to talk about my career as a disease ecologist, but I couldn't resist telling them about my new explorations of soundscape ecology. We talked quite a bit about sounds and how they make us feel, and I found the list of sounds that they mentioned intriguing.

[00:03:00] There were a few natural sounds listed like birdsong, which seems to make a lot of us feel good. Others mentioned thunder, and there were mixed responses. Some said that they felt anxious when at thunders, and others said that they really like to listen to thunderstorms.

[00:03:33] However most of the sounds that they mentioned were not natural sounds. They mentioned white noise and how it helped them sleep and it made them feel good. And several of them mentioned tornado sirens, and we all agreed they make us feel bad.

[00:04:23] Acoustic noise is defined by the Oxford English Dictionary as unwanted sound. In his book The Soundscape, Our Sonic Environment and the Tuning of the World, pioneering acoustic ecologist R. Murray Schaefer expanded the idea of noise

[00:04:40] to include unmusical sound, any loud sound, or disturbance of any signaling system like static. Noise has been understood as unwanted sound for a long time, at least since the earliest reference in the Oxford English Dictionary in the 1200s.

[00:05:14] Well if noise is unwanted sound, then it seems to me that what I consider noise could be quite different to someone else. The idea of unwanted sound doesn't necessarily imply that the sound is disliked, but when I asked the classroom of young scientists what sounds they disliked,

[00:05:34] they almost entirely included sounds that would fall into Schaefer's loud sounds category. They mentioned sirens, and screaming, and fireworks. And most of what we would consider to be noise today would be sounds that exceed a certain level measured in decibels.

[00:06:14] The World Health Organization recommends that to protect our hearing, we should not be exposed to sounds exceeding 70 decibels for more than 24 hours, or 85 decibels for an hour.

[00:06:27] There are certainly natural sounds like thunder or a rock slide that can exceed these levels, but most noise is comprised of anthrophony. Bernie Kraus in his book The Great Animal Orchestra Finding the Origins of Music in the World's Wildest Places explains that there are four types of anthrophony,

[00:06:56] electromechanical, physiological, controlled, and incidental. Electromechanical sources of anthrophony are what I immediately think of when I think of noise. This category includes noises of transportation, for example planes, or trains, or highways, or tools of construction, and technology like telephones and radios.

[00:08:13] Kraus' second category is physiological, sounds made by our bodies, coughing, sneezing, breathing, talking, snoring. These sounds are more localized, and you might not consider them noise unless they're happening in your classroom or while you're trying to sleep.

[00:08:46] Controlled sound is referring to sounds that are managed, for example live music. But if we're mindful this category might not be considered noise unless the live music is from a garage band that's rehearsing late at night when you're trying to sleep.

[00:09:16] The final category of anthrophony is incidental noise, like footsteps or wrestling clothes or scratching. Scientific literature suggests noise in our environment, like air traffic or trains, can have negative impacts on our health and our learning.

[00:09:52] But the group of middle school scientists that I was with when asked said that these kinds of sounds didn't bother them at all. They hardly noticed. Whether or not we're conscious of certain sounds that dominate our home soundscapes, they can have an impact on our hearing and beyond.

[00:10:14] The 2019 Global Burden of Disease study reported that 5% of the world's population experiences hearing loss. Globally, occupational noise exposure is the cause for 16% of adults with hearing loss. However, occupational noise exposure does not explain all hearing loss.

[00:10:33] For example, in the United States 25% of adults between 20 and 60 have some hearing loss, but occupational noise exposure is not linked to most of these cases.

[00:10:44] While chronic exposure to noise impacts our ability to hear, it has many other impacts on our health and well-being range from increased annoyance to physiological stress responses to slower recoveries from illness. I live less than 30 miles from two different international airports and a smaller regional airport.

[00:11:13] Now that I'm always thinking about soundscapes, I notice more often the air traffic over my house. One morning, during a holiday weekend, I went outside looking for some quiet. But this day, I counted a rate of four passenger jets flying over the house every 10 minutes.

[00:11:32] How do noises that I'm not really paying attention to impact me? The literature would suggest that the level of noise pollution in our environment could have a very significant impact on us, on our well-being and even our health.

[00:11:48] I've been reading a lot about how noise can impact our health. Most of the studies that I've read are looking at the impact of noises like airplanes and trains and highway noise or the impact of a noisy work environment on the health of people.

[00:12:15] There seems to be consensus that people that work in noisy environments or environments over 85 decibels experience higher blood pressure and pulse and other negative consequences that are attributed to the noise.

[00:12:31] There's also consensus that chronic exposure to noises like highway noise and train noise can have health effects, although the mechanism for these health effects aren't always agreed upon.

[00:12:45] For example, some studies show that noises like air traffic and trains just impact sleep and that lack of sleep is what causes the health effects. But other studies have found that we actually become habituated to noise in our environment and we actually sleep through these noises.

[00:13:05] So after reading all of this literature, I've become convinced that whether we're habituated or not the implications of noise, even noises that we don't notice are important. Many of the health impacts linked to noise result from the way that chronic noise impacts the production of stress hormones.

[00:13:23] Loud noises can signal danger, so when we experience them the fighter flight response kicks in. This is a problem because we now live in places that have continuous loud noises which can alter the way that stress hormones are produced.

[00:13:43] The research is prolific and compelling. In fact, the research goes beyond people. Many species have been studied. Measure changes in stress hormones, especially cortisol, have been documented in species ranging from seahorses to dogs to owls.

[00:14:01] These changes in stress hormones are linked to increased blood pressure and other cardiovascular problems as well as, and maybe most surprisingly, our immune response. Studies with animal models have revealed that noise exposure, even for short periods, impacts the immune system in many ways, including by decreasing T cells.

[00:14:25] Those are the white blood cells that are our front line of defense. Beyond changes in stress hormones, chronic noise exposure can impact the development of children and their experiences regarding learning and cognition. It's been shown surprisingly enough that chronic noise exposure can impact fetal development.

[00:14:53] While the scientific literature does not have complete consensus regarding risks, the CDC does recommend that pregnant women avoid exposure to sounds greater than 115 decibels because noises this loud could increase the risk of hearing damage to a fetus.

[00:15:11] There are other articles that I found that are suggesting correlations between chronic noise exposure and increases in preeclampsia as well as the increase in smaller birth weight babies.

[00:15:25] While it seems like more research is needed about the impact of noise on fetal development, there is compelling evidence that children experiencing chronic noise exposure are at great risk of cognitive and learning impairments.

[00:15:38] Many studies support the finding that chronic exposure to noise can have negative and long lasting impacts on memory and reading comprehension. One study that was conducted by Bronzecraft and McCarthy in the 1970s was quite compelling.

[00:15:55] In this study, the reading scores of children attending a public school in New York City were compared for students in classrooms on the quiet side of the school to those of students in classrooms on the side of the school that was just 200 feet from the elevated train track.

[00:16:12] In the classrooms adjacent to the train tracks, teaching was interrupted by approximately 80 trains each day between 9am and 3pm. The noise level in those classrooms increased from 59 decibels to 89 decibels every time a train went by.

[00:16:35] And just so you know, the World Health Organization recommends learning environments should not exceed 35 decibels, so the starting level of noise was quite high compared to what is recommended.

[00:16:47] The authors of this study reported that the children on the noisy side of the building had lower test scores than their peers on the quiet side, and that this difference lasted months to even a year.

[00:17:01] Other more recent studies suggest that noise from aircraft is associated with reading delays, and this type of noise also seems to have a lasting impact.

[00:17:12] There are many studies that demonstrate the negative learning outcomes for children who experience chronic noise exposure, but animal models allow us to understand some of the underlying mechanisms.

[00:17:31] In one compelling study by Jaffari and others, a mouse model was used to understand how chronic noise exposure impacted brain structure and development in young mice. In this study, young mice were randomly assigned to traffic noise in the day versus night or to a control with no noise.

[00:17:51] Mice exposed to chronic traffic noise had measurably different brain structures as well as altered behaviors. They exhibited changes in anxiety-like behaviors, they had impaired memory, poor balance and poor motor coordination.

[00:18:07] These changes occurred in all noise-exposed mice regardless of the time of day that they experienced the noise. This further supports the idea that noise exposure has consequences regardless of our awareness.

[00:18:21] Not surprisingly, the increased stress response due to chronic noise, even noise we aren't noticing, impacts more than our physiology. It has impacts on our behavior. People living in noisy environments like those near airports and also those near wind turbines report increased feelings of annoyance.

[00:18:46] Sleep-deprived people report decreases in well-being. Healthcare workers report that noises associated with hospital environments are contributing to burnout and decreased work performance. Additionally, patients, especially neonates and the elderly, are vulnerable to the stress-related impacts of chronic noise.

[00:19:15] Finally, one very compelling study by Hayner found that violent crime is even associated with chronic noise. In this study, the noise associated with flight patterns at a large international airport could explain increases in violent crimes in areas with as little as 1 decibel increase in noise.

[00:19:36] Chronic noise has wider implications than that of human health and well-being. Many species are impacted by noise, and there is increasing evidence that the differing responses of species to noise can have ecosystem level effects.

[00:19:52] It turns out that many other species are impacted by noise. And I want to be clear here when I'm talking about noise, I'm talking about anthropogenic sound.

[00:20:02] Species that depend on acoustic signaling to fulfill their ecological roles, like birds that maintain territories and attract mates with songs and calls, can be profoundly impacted by noise.

[00:20:14] Sound is important to pollinators like bees and hummingbirds, and changes in pollinator behavior can be both positively and negatively impacted by noise.

[00:20:36] I read about black-chinned hummingbirds and how they preferentially nest in noisy habitats. In their research, Francis and others found that pollination by this species was actually higher in locations with more noise. Many predators use acoustic signals to locate their prey, so noisy habitats can impact the predator-prey dynamics.

[00:20:58] Ultimately, changes in predator-prey dynamics can lead to changes in community composition. There are several papers that link road noise to decreases in predation, especially among bats.

[00:21:13] And other research implicates noise and community composition change. For example, one important study by McClure and others found that bird abundance decreased more than 25% in areas close to road noise. Impacts of noise pollution on ecosystems seems to go beyond the direct impacts of acoustic signaling.

[00:21:39] There are studies that report indirect changes to community structure and ecosystem function as a result of increased noise. There are several different kinds of mechanisms that have been described, but in reality most of the literature seems to be unclear on what is causing this community level change.

[00:21:59] It's possible that changes in foraging strategies are driving community level change. I read several papers across taxa, across ecosystems, and found lots of different types of responses to noise with regard to foraging that could explain community level change.

[00:22:17] For example, humpback whales and harbor porpoises change their foraging strategies in waters where there's increased noise from ships. Bats also seem to change their foraging strategies in multiple ways, but in one study the Asian-particolored bat actually increased their foraging when they were exposed to chronic automobile traffic noise.

[00:22:38] Other species like song sparrows forage less in noisy environments, but beyond changes in foraging strategy seed dispersal can also be impacted by noise. Western scrub jays avoid noisy environments and this avoidance can lead to changes in plant communities because scrub jays are so important in seed dispersal.

[00:22:59] If they aren't visiting noisy places then seeds do not disperse to these habitats. Fisher and others were able to demonstrate that pinion pine seedling recruitment was lower in noisy habitats.

[00:23:12] And there was another study by Phillips and others in which noise associated with natural gas wells was enough to decrease the survival and recruitment of juniper and pine seedlings.

[00:23:23] Most alarming to me is that once the noise was mitigated, the vegetation did not recover to the same community composition. The research is quite compelling. Human dominated soundscapes have significant impacts on ecosystem health.

[00:23:39] And as a disease ecologist I might remind you that ecosystem health and human health are tightly linked. Consider this. What might happen if increased noise in a soundscape impacted the immunity of a reservoir host for a new virus? A virus that could make people sick.

[00:24:03] What if these soundscapes that were dominated by human sounds impacted that reservoir host in such a way that the host shed a lot more virus than it would otherwise?

[00:24:15] And what if the soundscape also impacted the behavior of that host so that it began increasing its foraging and using habitats in a way that it brought it closer to humans? Well this is the stuff of zoonotic spillovers and nightmares.

[00:24:32] And it might sound familiar because one recent literature review by he and others makes a strong case that this is a real possible explanation for the spillover of SARS-CoV-2. All the more reason to care a lot about the ways we impact soundscapes.

[00:24:50] Until next time, keep your ear to the ground and listen here wherever you go. Listen.