On numerous visits to Manhattan, I have found myself poking around the city trying to find a moment of quiet and once located a hint of it in Central Park during a windless, late-night snowfall. There I stood absolutely still in the lemon glow of the city, a sky full of snow. The city still roared from all sides, a thousand noises compressed down to just one. I counted that distant, mild roar as quiet, a welcome relief from the more pressing noises of the daytime city.
During the day, though, heavy traffic tends to run around 85 decibels, a level that takes just eight continuous hours to permanently kink the hairs transmitting sound through your inner ear. The average subway ride comes to around 112 dB, somewhere between a shouted conversation and a power saw going off near your head.
An audiology researcher in Berkeley, Calif., informally tested the sound of his local transit system and found sustained peaks at the level of a rock concert (around 120 decibels). On top of that, he noted, many passengers were wearing ear buds, listening to music loud enough to mask the external noise, far exceeding limits on volume and time-exposure that lead to permanent damage and hearing loss.
Hearing is something that, once lost, people cannot get back. Each ear contains about 17,000 "hair" cells that turn vibrations into neural impulses. Chronic noise causes permanent degradation in these hairs. Recent research with human embryo stem cells at University of Sheffield in the U.K. suggests these cells may be artificially replicable, and last year an Italian team managed to reverse inner-ear damage in mice by using stem cells from human umbilical cords. We can hope that at least one line of research will lead to success in humans, but that is the future. For now, the damage is irreversible.
Because of the loud world Americans live in, hearing loss has become epidemic in the United States. A study released in March by Johns Hopkins University found that 1 in 3 adults has trouble hearing. The increase in hearing problems comes not only from an aging population but from an upsurge in younger people listening to loud music and being exposed to loud work and living environments. Hearing loss is reported in 8.5 percent of people in their 20s and 17 percent of those in their 30s.
But when it comes to health problems caused by sound, hearing loss is only the tip of an aural iceberg. It should come as no surprise that rats exposed to a buzzer sounding for six out of every 30 seconds, seven hours a day for 35 days suffer from high blood pressure. There is some sign of habituation over time, but these buzzer-rats are still darting back and forth across their cages by day 35, while rats in quieter cages have markedly lower blood pressure and tend not to pace so nervously.
For humans, six hours of exposure to 90-decibel sound significantly elevates the heart rate and leaves it there up to an hour after the noise is gone. Nearly every significant study looking for a link between exposure to noise and risk of heart attack has found one. In 2005, research in Berlin hospitals looking at more than 4,000 cases (half of them heart attacks) revealed that people subjected to loud environments are at a 50 percent greater risk of having a heart attack.
Among school kids, the effect of noise shows up in the form of learning disabilities. A 2005 study out of the University of London tested 2,800 children in 89 schools and concluded that reading skills are markedly delayed in children exposed to high levels of aircraft noise. A mere 5-decibel increase is enough to delay learning by up to two months. Lorraine Maxwell, a leading sound researcher at Cornell University, says, "When children are in schools or housing situations where airplanes take off every 30 seconds or truck traffic is going by, those kids are constantly subjected to noise (that) neither they nor their teacher nor their parents can control. For them, long-term memory is interrupted. They stop paying attention. It requires too much energy. We call it cognitive fatigue."
Maxwell has been looking at classroom performance for decades, finding that learning problems and physical ailments are tied directly to noise. "We see children's blood pressure rising over time," Maxwell says. "When they are removed from that environment, or if the airport changes its flight pattern, then they recover. But they don't habituate if they stay in that situation. They may say noise doesn't bother them because they've gotten used to it, but blood pressure still stays borderline high, and they still exhibit learning problems."
Maxwell's research mostly focuses on loud, inner-urban areas with freeways and major airports. But she has found the same results in smaller towns. One preschool she looked at was loud not because of outside noise, but because of the way the building was designed. "The architect did not take into account at all that these are preschool children who make lots of noise," Maxwell says. "Classroom walls did not go all the way to the ceiling, which made a very nice open design, except it was a disaster for the kids and the teachers. The kids would walk around holding their ears or would hide in their cubbies. We put in sound baffles, which helped absorb some of the sound, then ran our study again. Kids' attention levels had gone up and teachers noticed kids weren't walking around with their hands over their ears."
Theodore Wachs, a psychology professor at Purdue University studying environmental influences on childhood development, coined the term "stimulus shelter." Wachs and his colleagues found that noise and chaos at home delay cognitive growth and language skills. He suggests not only turning down the general volume, but establishing a quiet place in the house where children can retreat to — a stimulus shelter. "Even if it's a closet, at least they have some space to themselves," Wachs says.
It is no wonder some of us linger in tranquil places, in parks and along bridges. If quiet is restorative enough to help kids grow, one might assume it is good for adults, too. It can certainly feel that way.
Looking for my own stimulus shelter in Manhattan one autumn midnight, I popped a hatch on a fourth-floor Greenwich Village roof. I sat on tarpaper listening to an erratic tangle of jet noise punctuated by motorcycles and groaning diesels, sirens wailing suddenly over the shout of someone in the street. Though traffic was way down from the day, this was not the sensory closet I was looking for; there was simply too much noise.
Noise, of course, is not an objective state; it's a subjective combination of decibels, tonality, pitch and annoyance. It ranges from the piercing warning of heavy machinery to a mouse pattering through the wall behind your head when you are trying to sleep. Noise is simply what you do not want to hear.
Though defined as the presence of little or no noise, quiet is equally subjective. I was in New York, looking for what, to me, constituted the perfect quiet: no clanking or roaring. I finally honed in on a rainy Sunday morning on Wall Street, figuring the financial district would be dead asleep, no traffic, no noise. Just getting there, though, I had to hop on a Brooklyn-bound 4 train, which is like sticking your head inside a bullhorn. The ride took 20 minutes, 10 minutes shy of 110-dB Occupational Safety and Health Administration limits that warn, YOU'RE GOING DEAF!
I got off at an empty station. It was about 5 in the morning; there was not a soul to be seen. The train rumbled away, its mechanical cacophony replaced by a buzz of electricity, a sound that would cock a dog's head. It emanated from paths of fluorescent lights and from conduits in the ceiling.
If sound had a flavor, I would name the Wall Street station Electric Yellow Piss. Curious, but distasteful. I could take it for about 10 minutes. When clicks and squeals began swarming down the tracks from the next train, I pushed my way out through the turnstiles and took the stairs into an early morning rain. There were no cars, no people, just the buildings standing tall and gray. The only sound was a steady fizz of rain on the street. The average rainfall comes in at 50 dB, a volume you could listen to forever without damage or distraction. Relieved by the sound, I snapped open my umbrella and walked into the thin, wet light of dawn.
We often think hearing plays second fiddle to sight. We may believe we are reading and watching more than anything else, but, in fact, we are hearing just as much if not more. We just don't always know it.
"Why do we need hearing when we've got vision?" asks Bill Yost, a leading psychoacoustic researcher at Arizona State University. "If you talk to people who are congenitally blind and deaf — never heard or never saw in their lives — and ask them if they could have a sense they would like restored, they usually say hearing. They understand the connection between hearing, speech and communication, and how important that communication is. In vision, because it's spatial, you can give an idea what seeing is like by saying it is a way of finding where something is. If you try to tell them what sound is, what music is, what a voice is, there is no analogy. They are in complete mystery as to what this thing is they are missing."
What they are missing is an auditory scene the brain is constantly paying attention to. By hearing alone, you can tell how far away a garbage truck is or how close you are to someone who's speaking. Picking up on sound reflections, you can actually listen to shapes and sizes, and whether a space is open or closed.
The ear turns a wash of incoming sound into a neural code, which the brain analyzes to picture an auditory environment. Pitch, frequency, tone and timbre are magnified through the convolutions of the outer ear, setting off the miniature tuning forks of the inner-ear bones. Sound then flows across "hair" cells in the inner ear like wind through tall grass, and the brain reads this wind. In essence, you see the air with your ears. The human ear can distinguish between 1,500 different pitches, detecting changes in the air up to one-billionth of an atmospheric pressure (that is, 14.7 pounds per square inch divided by 1,000,000,000). The cells moving auditory information into the brain are the fastest in the body, making hearing the most real-time sense we have.
Yost says, "The auditory system is always computing information because what I said just a second ago is gone, so the brain has got to keep track of that over time."
Throw this kind of sensitivity and attentiveness into a loud, modern environment, and it is maddening. You might think you are tuning out most noise, but the simple fact is that you are not. "There's the cocktail party effect," Yost says. "You want to attend to one voice, but it's difficult because of all the other sounds being generated. You can do better at solving the problem if the various sound sources are spatially separated, are in different locations, because we can use our ears to calculate where sound is in space. But all those other sounds are getting in there. At the cocktail party, you're trying hard not to hear them, but your nervous system is processing them.
"Listening is not the same as hearing. We get lots of information traveling through the auditory nervous system, but whether we are paying attention to it, listening to it — there's a whole other issue."
Yost defines listening as being consciously aware of sounds; hearing is the neural processing of everything that enters the ear. As researchers working with school kids point out, even students in loud environments who do not complain about noise still have trouble learning.
What does all this extra sound do to a person? Evidence points to physical and mental depletion. Those with hearing loss strain to listen, while those without hearing loss are overloaded. (A hearing-aid researcher once commented that he gets many complaints from new hearing-aid users who say they liked it better when they could not hear every damn thing.)
A study published in March by the American Physiological Society found that if participants performed a mentally fatiguing task prior to a difficult physical exercise, they reached exhaustion more quickly than when they did the same exercise while mentally rested. Add to that a 2003 study in Europe by the Danish Institute for Social Research, which found that those with hearing loss were 20 percent more likely to complain of physical fatigue, and the connection seems clear. As a population, we are losing our hearing at increasing rates, draining our energy and dropping our performance levels. For those in the Danish study, the unemployment rate was 7.5 percent for people with hearing loss, as compared to a general unemployment rate of 4.8 percent. Again, noise might be only one factor. But it is a loud one.
I searched for quiet places from city to city; an elevator in Minneapolis (ominous motor sound) and echo-tubes of dry sewage tunnels under Tucson (street sounds muffled through manhole covers). It seemed no matter where I went, quiet always came with a caveat: quiet but for jet-noise, quiet but for a refrigerator-hum, quiet but for a distant motor.
Wondering if I would ever find such a thing as silence — not just a lack of noise, but a complete absence of sound — I eventually arrived at an anechoic chamber in the basement of a building at the University of California, Berkeley. This soundless chamber sits on the bottom floor of the Hafter Hearing Center, overseen by retired audiologist Erv Hafter, who took me inside. Hafter carefully explained that an anechoic chamber is not an infinitely silent place. As far as he knows no such thing exists on Earth. He said there are movements in the ground, vibrations, jackhammers, even distant earthquakes.
As we stood in the master bedroom-sized chamber, I asked if I should be able to hear anything, and he said no.
"Sound may enter your ears, but you're not hearing it," Hafter said.
"It's not reaching the brain?" I asked.
"Yes, it reaches the brain, but the brain is a filter," he answered. "One of perception's most important functions is to forget."
In other words, silence, like noise, is what your brain allows you to consciously experience. The rest you decode and dismiss.
Covered top to bottom and side to side with foam-core filters, the space absorbed all noise but what was aimed directly at me, in this case Hafter's voice. I could not stop staring at his mouth as he talked. It was as if he were speaking down a tube. I could hear his spit. Between words came a brief and eerie deadness, the room absorbing every sound. There was not a single detectable reverberation.
Hafter went to the large airlock door. "I'll just shut you in. Take as much time as you need." He drew closed the door, and I stood in silence, listening for earthquakes in China.
Used for sound experiments, the chamber is lined with speakers and trunks of electrical cables. The floor is a springy net of wire suspended over geometric baffles. The wires strained, sounding like violin strings under my feet as I slowly paced the room's perimeter. I could not hear where I was, my ears fighting with my other senses. My eyes said I was in a closed space, but my ears said I was floating in an infinite void. Usually a person hears an entire auditory environment by detecting waves bouncing this way and that. In the chamber there was no context; it's a sensory black hole.
An audiologist doing sound research with babies once told me anechoic chambers always made them cry. He said, "You have a perfectly quiet, normal 10-month-old, happy as a lark, maybe even half asleep; you bring them into an anechoic chamber, and they go berserk."
I pulled the chains on four light bulbs, plunging the room into total darkness. It felt like my senses were suddenly cut off, a sensation that would have driven a 10-month-old stark raving mad.
With vision removed from the equation, I focused on what I could hear, which at first was nothing. Muscle tension eased off my tympanic membrane, and the tiny bones in my ears relaxed, their tendons letting the hammer down. I began to hear the soft thrum of my heart. Then came a fainter noise, a hiss. It was not as sharp as the ringing in the ears known as tinnitus (the result of damaged hearing where auditory neurons fire off randomly because they are not being stimulated). I thought it was an air duct, but no air comes or goes from an anechoic chamber. I tilted my head one way and the other, trying to fix on the sound's singular location, and realized it was in my head. It was, I believe, the sound of blood flow echoing through my skull, like sand pouring across velvet.
I lasted 45 minutes, then pulled the chain on each light, popped open the heavy door and emerged. I took an elevator up, pushed through the outside doors and stepped onto campus as if coming up for air. It was like getting my senses back, the relief of jet-noise and thousands of bustling students.
It takes technology to make the quiet of an anechoic chamber. I've been down in the lightless pit of a cave and never heard such vacuousness. It is the kind of silence that noise-canceling headphones are aiming for. Walk through an airport, and you will notice more and more of these devices, people finding their own slice of silence, like portable anechoic chambers. The headphones work by sampling ambient noise and emitting sound waves back, the collision forming an audio firewall. The headphones essentially put a dome around your head so you don't have to turn up your music so loud it leaves your ears ringing.
But is auditory oblivion — the masking of all external sound - really the answer to our noisy world? Brent Edwards, head of research for Starkey Laboratories, the largest hearing-aid company in the U.S., says no. "Your ears are a constant monitoring system for everything around you," Edwards says. "There's a field called auditory scene analysis where we create a scene of the world from auditory cues. When there are a lot of sources making sounds that overlap in time and frequency, we can still identify the sources. If you looked at a spectrogram of that sound, it would just be a mess. But our brains make sense of it."
Even working with top technology, Edwards says, he cannot create an instrument that segregates sounds into their components and locations as well as the human ear.
"I like the fact I can hear so much going on," he says. "Our cognitive system has built up an alert mechanism from when mankind had to worry about tigers sneaking up on them in the forest. When there is constant sound around you, that kind of indicates that it is not a threat, nothing you need to pay attention to, and you tend to ignore it. You tend not to even know it's there. When it changes, that is when you are alerted."
In artificial silence, nothing changes. The ear is left grasping at an unnatural zero. Designing hearing aids, Edwards works with noise reduction and de-reverberation algorithms, trying to clear out audio clutter and focus on what people want to hear. But he is not sure that is the best answer. "A fundamental question for me is, 'Do you want to get rid of all the echoes and reverberation?' I think they help us. Certainly for people who are blind, sound reflections are critical in understanding the world around them. We all use the information to a certain extent; we just don't realize it. When the acoustics of your environment don't match what you know of your environment, like in an anechoic chamber, the disconnect can be alarming."
What does quiet do to the brain? Although Wachs' stimulus shelter has proven helpful for childhood development, there is little data to support occasional silence as an antidote to general noisiness. Brent Edwards says, "I'm sure that there is a psychological impact of being able to relax in a quiet environment after a long day of exposure to constant loud sounds, although I don't know if there is any physiological rehabilitative benefit."
ASU's Bill Yost weighs in on the subject with a similar shrug, saying, "I do not know of many data that indicate a positive effect on hearing from being in quiet."
Cornell's Lorraine Maxwell reports, "We know that a period of restoration - a place away from noise — helps to combat cognitive fatigue in adults and children, and both seem to be able to concentrate better after a period in a place providing restoration."
So it can be proven that noise contributes to heart attack risk, but the opposite remains uncertain. Even in science, quiet seems hard to get ahold of.
Still, I wanted it. I wanted the anechoic chamber but without the chamber. No walls, no ceiling, no airplanes rumbling by at 30,000 feet, no far-off highway noise, no sound.
Ron Minson, a sound therapist from Denver, describes this kind of natural quiet as a roar, like the sound of the ocean, but with no ocean. An avid mountain climber, Minson says, "I've hiked with people from the city, and when we camp out, sometimes they can't sleep because it is too quiet. They can't stand the silence. They say it's too loud. They are so used to air conditioning or street noise it takes a couple of nights for them to adjust."
Minson, a former hospital surgeon and former chief of psychiatry at Denver's Presbyterian Medical Center, treats psychological disorders with sound. He filters Mozart violin concerti into high frequencies and feeds the results into people's heads. Basically, he is using high and melodic pitches to tickle the shriveled hairs of the cochlea, giving the brain a highly directed sensory perk. "The fundamental principle is that the ear is a battery to the brain," Minson explains. "By using sound to stimulate the ear in specific ways, we can enhance the function of the brain."
Would he seek refuge from a hyper-stimulating world in an anechoic chamber? He says he prefers the mountains. "In many places in nature, particularly high mountains where the air is thinner, I certainly do enjoy the silence," Minson says. "There is something clean, pristine, cleansing, purifying about the quiet I experience up there."
Minson sees quiet as not merely a sensory absence. Rather, it is a state of sound. "It seems to be a tonality that maybe even your ears are emitting," he says. "I'm wondering if in places of silence we aren't also experiencing something tactile on our skin that supports or resonates with what we perceive as audible."
In the Gran Desierto of Sonora, Mexico, I searched for this next level of quiet. The region is a sandy black-rock desert dotted with dormant volcanoes and abandoned, burned-out rancherias. Along the west side, dunes stretch across the horizon, the tallest rising 800 feet, like liquid mountains.
At first, it seemed all I could find in these dunes was a bone-scraping wind. It hardly paused, swirling and scribbling across the sand, a never-ending orchestration of sound. After several straight days it became a tad maddening, my mouth salted with blowing sand.
Then one night the wind stopped. It was as if the world suddenly held its breath. I left my camp and climbed to a slender dune crest, listening to the last breezes snaking away. I was nearly in the center of 4,000 square miles of sand. A gibbous moon settled low in the south, illuminating the ivory dune field. I clapped my hands, listened for an echo. The sand absorbed most of the sound, reflecting just enough so I could hear the clap riding away. I hooted loud, listened to my voice fleeing across the dunes.
And then I was still. I listened. A lever was pushing up my senses. It was like listening to the sky itself. Not a stifling silence like the anechoic chamber with blood hissing through my head, this was an audible hugeness.
The sound that came to me out there was thankfully much softer than Minson's roar. It had the timbre of a gentle rain. As Minson says, real silence is not merely an absence. It employs all the senses, a full-body recognition of a vast stillness. Unlike the total void of artificial silence, which masks all incoming sound waves, here I was receiving information. I was an antenna planted in the sand.
Perhaps the susurrant whisper I heard came from wrinkles in the air. In his work, Minson has seen patients with such heightened sensitivity, they claim to hear floating dust motes. He believes the arrhythmic white noise they describe comes from a phenomenon known as Brownian motion, molecular collisions moving tiny particles in the air. Considering the ear's sensitivity to pressure, it is not out of the question. At the same time, I could have been listening to the sound of my own auditory neurons twiddling their thumbs inside my head. Whatever it was, it was real, and it sounded perfect enough to finally call it a night.
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