When my mother's mother was in her early twenties, a century ago, a suitor took her duck hunting in a rowboat on a lake near Austin, Texas, where she grew up. He steadied his shotgun by resting the barrel on her right shoulder—she was sitting in the bow—and when he fired he not only missed the duck but also permanently damaged her hearing, especially on that side. The loss became more severe as she got older, and by the time I was in college she was having serious trouble with telephones. ("I'm glad it's not raining! " I'd shout, for the third or fourth time, while my roommates snickered.) Her deafness probably contributed to one of her many eccentricities: ending phone conversations by suddenly hanging up.
I'm a grandparent myself now, and lots of people I know have hearing problems. A guy I played golf with last year came close to making a hole in one, then complained that no one in our foursome had complimented him on his shot—even though, a moment before, all three of us had complimented him on his shot. (We were walking behind him.) The man who cuts my wife's hair began wearing two hearing aids recently, to compensate for damage that he attributes to years of exposure to professional-quality blow-dryers. My sister has hearing aids, too. She traces her problem to repeatedly listening at maximum volume to Anne's Angry and Bitter Breakup Song Playlist, which she created while going through a divorce.
My ears ring all the time—a condition called tinnitus. I blame China, because the ringing started, a decade ago, while I was recovering from a monthlong cold that I'd contracted while breathing the filthy air in Beijing, and whose symptoms were made worse by changes in cabin pressure during the long flight home. Tinnitus is almost always accompanied by hearing loss. My internist ordered an MRI, to make sure I didn't have a brain tumor, and held up a vibrating tuning fork and asked me to tell him when I could no longer hear it. After a while, he leaned forward to make sure the tuning fork was still humming, since he himself could no longer hear it. (We're about the same age.) There's no cure for tinnitus. The ringing in my ears is constant, high-pitched, and fairly loud—it reminds me of the cicadas I listened to on sweltering summer nights when I was a kid—but I'm usually able to ignore it, unless I'm lying awake in bed or, as I discovered recently, writing about tinnitus.
Unlike taste buds and olfactory receptors, which the body replenishes continuously, the most delicate elements of the human auditory system don't regenerate. The National Center for Health Statistics has estimated that thirty-seven million American adults have lost some hearing, and, according to the National Academy of Sciences, hearing loss is, worldwide, the "fifth leading cause of years lived with disability." Hearing problems can lead to social isolation and cognitive decline, both of which make getting older—itself a cause of hearing loss—seem worse than it does already.
In recent years, scientists searching for ways to restore hearing have made a number of promising discoveries. There are also increasingly effective methods of preventing damage in the first place, and of compensating for it once it's occurred. The natural human tendency, though, is to do nothing and hope for the best, usually while pretending that nothing is wrong. (People who notice they're having hearing problems typically wait more than ten years before doing anything about them.) I recently heard a joke about a man who was worried his wife was going deaf. He told his doctor, who suggested a simple test. When the man got home, he stood at the door of the kitchen, where his wife was at the stove, and asked, "Honey, what's for dinner?" She didn't respond, so he moved closer and asked again. She still didn't respond, so he stood directly behind her and asked one more time. She turned around and snapped, "For the third time, chicken!"
Two years ago, in Dallas, I went out to eat with a large group in a noisy restaurant. I was seated near one end of the table and couldn't hear what anyone at the other end was saying. I assumed that that was because I was the oldest person there, but then a young guy sitting across from me asked the young guy sitting next to him whether he could hear anything. "No," he said. "I'm just nodding and smiling." A little later, one of the young guys cupped his hands around his ears, like an ear trumpet, and the other asked whether doing that helped. He said that it helped a lot, so we all tried it—and, indeed, I found that I could even home in on particular speakers.
The part of the ear that sticks out—the auricle, or pinna—functions like a smaller version of a cupped hand: it funnels sound waves into the external auditory canal, which is the thing you're not supposed to stick a Q-tip into. At the other end of the canal, roughly an inch inside your head, those waves strike the tympanic membrane, also known as the eardrum, and the resulting vibrations pass through three small bones and into the cochlea, a fluid-filled organ shaped like a snail. There the vibrations are transmitted to orderly arrays of "hair cells," which are tuned to specific frequencies. Each hair cell is topped with a neat bundle of bristle-like stereocilia, arranged in curving rows of different heights. As the stereocilia are nudged back and forth, they generate electrical signals. These produce nerve impulses, which travel to the parts of the brain that interpret sounds.
A hair-cell stereocilium is almost impossible to glimpse with an optical microscope, because it's only as wide as the smallest wavelength of visible light. I saw some recently, though, in the lab of David Corey, a neurobiology professor at Harvard Medical School. The image was an electron micrograph of a mouse hair cell, which measures about one-five-thousandth of an inch across and is structurally similar to a human one. Hair cells are exquisitely sensitive. "Humans can detect a sound that vibrates our cilia by about the diameter of an atom, or a few atoms," Corey said. "We can also hear sounds ten million times as loud. Yet a cilium's entire operating range of motion is only about half of its diameter."
Damage to hair cells or to the nerve synapses they're attached to is the most common source of hearing loss. Aging and noise are the leading causes; among the others are the chemotherapy drug cisplatin, the aminoglycoside family of antibiotics, and various autoimmune diseases, including the one that deafened (but didn't silence) Rush Limbaugh. Corey showed me another electron micrograph, from the ear of a mouse that had been exposed for two hours to sound as intense as that experienced by someone using a chainsaw. The cilia looked like tree trunks thrown around by a tornado.
Hair cells can recover if a noise isn't too loud and doesn't last too long, but permanent injuries accumulate. A widely cited damage threshold for sustained exposure is eighty-five or ninety decibels. (The human hearing range is so wide that it has to be described logarithmically to keep the numbers from becoming unmanageable: every ten-decibel increase represents a tenfold increase in sound energy.) An unsettling number of everyday activities lie at or above the danger line, including lawn-mowing, motorcycle-riding, rock-concert-going, Shop-Vac-ing, milkshake-making, subway-riding, and power-tool-using. "Most carpenters have lost a lot of hearing by the time they're fifty," Corey said. "I'm sometimes around construction sites, and I often pass out ear protection."
At louder volumes, a single instance can cause permanent damage, as it did with my grandmother. A gunshot a metre away can measure more than a hundred and forty decibels. A professor at the University of Texas at San Antonio told me that a major unrecognized cause of hearing loss is recreational shooting. Hunters often say they can't wear ear protection because they need to be able to hear things like deer walking through dry leaves—although, of course, people who gradually deafen themselves can't hear those things, either.
Members of the military face greater risks. Combat soldiers experience periods of intense gunfire, and also far louder explosive blasts, from bombs, rocket-propelled grenades, and improvised explosive devices. And military hearing threats aren't limited to battle zones. James Henry, a research scientist at a U.S. Department of Veterans Affairs facility in Portland, Oregon, told me, "Aircraft carriers are a real problem—especially on deck, but really everywhere. Even when you're sleeping on an aircraft carrier the noise can be above a damaging level." Soldiers have access to effective sound-protection gear, but, like hunters, they're often reluctant to use it. A fifth of all hearing aids sold in the United States are purchased by the V.A.
Hearing problems were part of Henry's life before he began working with veterans. In the nineteen-seventies, he was the lead guitarist for Eli, a rock band that (after he quit) performed as a warmup act for Kiss. "I remember going home at night and having this roaring in my ears," he said. "I didn't realize that the roaring would eventually become a permanent condition." That's not what led him to his profession, though. Henry and his wife have a daughter who was born with virtually no hearing (because of genetic bad luck, not Eli concerts experienced in utero). In the early eighties, they moved to Portland so that she could attend the Tucker Maxon School, which specializes in teaching speech and listening skills to deaf children. That experience prompted Henry to earn a master's degree in audiology, and after he went to work at the V.A. he got a Ph.D. in behavioral neuroscience.
Henry's daughter is now thirty-eight. When she was twenty, she received a cochlear implant—a surgically placed electronic device that transmits sound impulses from a microphone near the ear to electrodes in the cochlea, bypassing the eardrum and directly stimulating the hair cells and the auditory nerve fibres. The Food and Drug Administration initially approved cochlear implants only for adults, but research has shown that they're vastly more effective if they're put in before the parts of the brain that process speech have developed fully. Henry's daughter has a daughter, now five years old, also born deaf, who was fitted with cochlear implants in infancy. "The difference between my daughter and my granddaughter is that my daughter had great difficulty learning speech skills," Henry said. "But my granddaughter can hear things and repeat them back without looking at the person who's speaking."
At the V.A., Henry's specialty is tinnitus, which is both his own principal auditory problem and the leading cause of service-connected disability claims made by veterans. (Hearing loss is second.) Tinnitus is believed to be similar to the phantom-limb pain suffered by some amputees: as fewer impulses reach the cochlear nerve, the brain's auditory circuitry compensates by becoming overactive, creating an illusion of sound. Soldiers who have both tinnitus and hearing loss often find the tinnitus more bothersome, since it's an unceasing reminder of whatever horrifying incident caused it; in severe cases, sufferers sometimes require psychotherapy. Tinnitus treatment also often includes hearing aids, which can disguise the problem by bringing up the volume of everything else. For milder cases, air-conditioners, fans, and other masking devices can be helpful, especially at night. I sometimes pretend that the ringing in my ears is a sound I play on purpose to mask the ringing in my ears—a Zen-like switcheroo that works better than you might think.
A few weeks ago, David Corey, at Harvard, and his colleague Bence György showed me a sequence of videos in which three mice were dropped into a tank of water. The mouse in the first video paddled back and forth, trying to escape. "This is a normal mouse, and that's the way a normal mouse swims," Corey said. "He knows which way is up, and he always keeps his head above the water." The second mouse had been bred with a specific genetic mutation, as a consequence of which it could hear nothing and had no sense of balance. (Balance is governed by a separate but connected part of the inner ear, and also depends on hair cells—a reason that hearing loss and balance problems sometimes occur together.) The second mouse thrashed wildly underwater, as though caught in a turbulent current. "He doesn't know which way is up, and he just tumbles, and we have to rescue him," Corey said. The third mouse had the same mutation, but had been given a functioning version of the faulty gene, delivered to its cochlea by a harmless virus. "He's not quite as good a swimmer as the control mouse," Corey said, "but he has enough of a balance system now to keep his head above the water." The treated mouse was also able to hear, as it demonstrated by responding to a loud handclap. György and Corey said that although genetic mutations cause only a small percentage of hearing-loss cases, the viral delivery mechanism holds promise as a treatment for other types of hearing loss as well.
The inaugural breakthrough in the field of hearing restoration occurred in the late nineteen-eighties, when two researchers discovered, independently, that the ears of young chickens do something that human ears don't: they rapidly regrow dead hair cells, restoring lost hearing within weeks. No mammal is known to share that enviable capability, but self-healing hair cells look enough like non-self-healing hair cells that scientists have been tantalized ever since by the possibility that human ears might be induced to repair themselves, too. In 2011, the Hearing Health Foundation, based in New York, created the Hearing Restoration Project, a consortium of fourteen scientists who agreed to work together toward that goal, partly with funding from the foundation. One of the originators of the project, Edwin Rubel, who was a co-discoverer of hair-cell regrowth in chickens, told me, "It's potentially the best thing that ever happened, because it really does bring together a lot of different kinds of expertise."
Four years ago, Albert Edge—a member of the consortium and a researcher at the Eaton-Peabody Laboratories, part of Massachusetts Eye and Ear—led a group of scientists who showed that young mice with noise-damaged ears could regenerate hair cells and recover some hearing if a drug was delivered into their inner ears shortly after they were deafened. It was the first time that mammals had proved able to regenerate hair cells. The drug, which had been developed for treating Alzheimer's but turned out to be unsuitable for that, suppresses the activity of a protein that prevents hair cells from being created by so-called supporting cells—cells in the cochlea that function something like stem cells. "What that shows, beautifully, is that there is something there that can support regeneration," Rubel said. "We just have to figure out how to goose it along."
I visited Edge's lab not long ago. A postdoctoral fellow there told me that she and her colleagues were currently able to improve the hearing of a deafened mouse by about fifteen decibels. "Which is good," she said, "but we'd like to improve it further." She took me up a flight of stairs to a small room containing a piece of equipment about the size of a washing machine. "This is the chamber we use to deliver high levels of noise, to kill off hair cells," she said. On a black-and-white video monitor, I could see that the chamber contained a small cage with several mice inside. The mice appeared to be running around normally, but they were being subjected to two hours of steady noise at above a hundred decibels—enough to ruin their hearing, like being in a front-row seat at a Metallica concert.
Recently, Edge and several other researchers succeeded in causing supporting cells they'd extracted from normal mice to divide and differentiate into large clusters of hair cells. At the lab, Danielle Lenz, a co-author of the paper describing that experiment, put on latex gloves, washed her hands with alcohol, and removed two plastic trays from a shelf in an incubator, then placed them under a microscope. "In the second tray," she said, "you can clearly see the organoids that have been formed from the single cells in the first tray, and you can see that they are multicellular." The benefit right now is in the laboratory—having access to a big supply of living hair cells in dishes makes screening potential remedies easier—but there are hopes for bigger things. Edge told me, "The ear is maybe a little bit behind the eye, in terms of treatment, but there has been a lot of progress, and between the soldiers and the baby boomers there's a lot of interest."
Eaton-Peabody's director is Charles Liberman, whose office is down the hall from the mouse-deafening chamber. In a major study a decade ago, he and his colleague Sharon Kujawa solved a mystery that had puzzled some audiologists for years: the fact that two people with identical results on a standard hearing test, called an audiogram, could have markedly different abilities to understand speech, especially against a background of noise. The reason, they discovered, has to do with nerve connections. Scientists had known for a long time that most hearing impairment involves damage to the synapses and nerve fibres to which hair cells are attached, but they had assumed that the nerve damage followed hair-cell loss, and was a consequence of it. "What we discovered is that it's actually the connections between the sensory cells and the nerve fibres that go first," Liberman told me. "They are much more vulnerable than the sensory cells." The hearing of a person who has trouble understanding speech can appear normal or nearly normal on an audiogram, because a standard hearing test measures only the ability to detect pure tones along a scale of frequencies. It requires only functioning hair cells, Liberman said, and is unaffected by nerve damage until more than eighty per cent of the synapses are gone. For that reason, the phenomenon he and Kujawa explained is now usually referred to as "hidden hearing loss."
A disturbing implication of their finding is that hearing can be damaged at decibel levels and exposure times that have traditionally been considered safe. Nonetheless, among researchers, the discovery has been a cause for optimism, because reconnecting nerve synapses is almost certain to be easier than regenerating functioning hair cells inside human ears. "This is the simplest sensory circuit that you could possibly have," Liberman said. "It's one sensory cell type and one neuronal cell type, and it's possible to do local delivery through the eardrum." He and others have successfully restored some damaged connections in lab animals, and he believes that far greater advances are to come. "In the past five years, there's been an explosion of biotech companies getting serious about the inner ear for the first time," he continued. "I think most people in the field would say it's no longer a question of if we will be able to unlock enough of the secrets but merely a question of when."
If I could relive my adolescence, I wouldn't listen to Steppenwolf with loudspeakers leaning against my head, and I wouldn't have cherry-bomb fights with my friends unless I was wearing ear protection. On the recommendation of James Henry, at the V.A., I now own several sets of so-called musician's earplugs, which reduce the over-all level of sound but maintain the full sonic spectrum—unlike regular foam earplugs, which disproportionately mute high frequencies. I wear them even while vacuuming (or will the next time I vacuum anything), and if I were a hunter I would buy a pair of microprocessor-controlled earmuffs, which amplify quiet sounds but turn gunshots into muffled pops.
Luckily for those of us who have been careless with our ears, there are hearing aids. Most of them are made by six major manufacturers, only one of which is based in the United States: Starkey Hearing Technologies, whose headquarters are in Eden Prairie, Minnesota. Starkey's greatest marketing triumph occurred in 1983, when President Ronald Reagan revealed that he was wearing one of its products. (The main source of Reagan's hearing problem was a gun that someone fired near his right ear on a movie set in the early thirties.)
I visited Starkey in February, and when I arrived at the company's testing department the receptionist greeted me in a voice that she seemed to have turned up a couple of notches—an occupational necessity, I assumed. Another employee told me, as I waited to be examined by an audiologist, that I had been preceded recently by two members of a well-known rock band that's been around since the early seventies. The rockers, she said, looked "very old and very weathered," and had hearing problems they'd apparently ignored for decades. "Oh, my gosh, they've lived hard," she said. But they have hearing aids at last.
Before my ears were tested, a technician used a digital otoscope and a curette—a long, wirelike tool with a tiny scoop at the end—to remove wax from my external auditory canals, while I watched on a video monitor that magnified everything forty times. The wax pieces look like boulders made of amber. The technician pointed out several bumps, which he said were exostoses, benign bone growths that form in response to repeated exposure to cold water and are common among surfers (who refer to the condition as "surfer's ear"). Large exostoses can cause hearing loss, by blocking the auditory canal. "But yours are too small to worry about," the technician said.
Then I sat in an insulated booth and pressed a button every time I heard a tone. An audiologist outside the booth plotted the results on an audiogram, and showed me that, while most of my hearing falls within the lower half of the normal range, I have a mild loss in both ears above four thousand hertz, which is about the frequency of the highest C on a piano—a typical result for a non-rocker in his early sixties. As sounds at those frequencies fade, speech becomes harder to understand, because consonants are pitched higher than vowels and when they disappear sentences turn to mush. Struggling to make out what other people are saying leaves less brain power for anything else. A Starkey research scientist told me that, as people lose hearing, they rely more on unconscious lipreading, which even in people with good hearing accounts for as much as twenty per cent of comprehension. To demonstrate, he covered his mouth. "If you can't get those visual clues," he said, "listening becomes more challenging and more effortful, even for something like this."
Based on my audiogram, I was fitted for a pair of Starkey's Muse hearing aids. Each unit sits behind an ear, as my grandmother's hearing aid did, but is so small that it's all but invisible. A coated wire leads to a receiver—red for right, blue for left. Each receiver is about half an inch long and the diameter of a kitchen match, and it goes right into the ear canal. A button on the part behind the ear allows me to choose among settings programmed by the audiologist. Two of them add a subtle tone that's meant to mask my tinnitus, which during my hearing test she pinpointed at about six thousand hertz. My main reaction when I first put the hearing aids on was mild annoyance at the sound of my voice. I also became more aware of turning pages, creaking doors, and the surprisingly varied noises made by my pants. The audiologist said that people with new hearing aids get used to all that within about a month, as the brain adjusts.
With my hearing aids on, I was given a tour of the premises. Hearing aids that fit snugly into the ear canal, as many do, are custom-made from silicone impressions that audiologists create by injecting goop into patients' ears. The cured impressions look like miniature Henry Moore sculptures. Laser scanners turn them into three-dimensional digital files, and the images are trimmed, shaped, and manipulated by technicians using an in-house computer program that's essentially Photoshop for ear canals. I saw test hearing aids being subjected to stresses that were meant to replicate the surprisingly hostile microenvironment of an external auditory canal: baking in an oven suffused with "salt fog"; lengthy exposure to blowing clouds of dustlike talc; submersion for days at the bottom of a metre-tall column of water.
The Starkey line with the most features is Halo, the first version of which was introduced in 2014. Halo wearers can stream music, phone calls, recorded books, television shows, and other audio content via Bluetooth directly into their hearing aids from all current Apple devices. The hearing aids adjust automatically to different environments. They eliminate wind noise and reduce background sounds between spoken syllables during conversations in crowded places, and they can be used with a smartphone app that enables them to do things like switch to a customized automobile mode as soon as the phone's accelerometer detects that the wearer is moving faster than ten miles an hour. Chris McCormick, who is Starkey's chief marketing officer, told me, "If you regularly visit a Starbucks, you can fine-tune a setting for that particular environment—the barista grinding coffee beans, other customers talking—and then geotag it, so that when you pull into the parking lot your hearing aids will switch to that mode."
Successfully linking hearing aids and iPhones required a long collaboration between Starkey and Apple. One challenge was that hearing aids, because of their size, have to operate on minuscule voltages, much lower than the ones that smartphones use. Another was that the human body acts like a sponge for many radio frequencies, blocking communication between the device in your left ear and the phone in your right pocket. In Starkey's main research building, I stepped into a chamber that from the outside looked like a walk-in freezer. Mounted on a pedestal and surrounded by a ring of sensors was a plastic head, with ears. "It contains a gel that mimics the frequency-absorption characteristics of a human head," a scientist said. A technician outside the chamber had been bombarding it with radio waves and studying the results on four large color monitors.
Starkey's newest hearing aid, the SoundLens Synergy, is even smaller than Halo and Muse—too small for Bluetooth. Each unit looks scarcely larger than the aspirin-size battery it runs on, and is designed to be inserted deep into an ear canal. Chris McCormick pushed one into his own ear, and turned his head to the side; I could see no part of it, even from close up. He retrieved it by pulling on a snippet of nylon filament.
In 2013, Charlie Rose devoted a program to hearing loss, and during the broadcast two of the participants—Eric Kandel, a scientist who won a Nobel Prize in 2000, and Rose himself—were wearing hearing aids. (David Corey, the Harvard Medical School professor I met with, appeared on the program as well, and got a good look.) Yet neither man mentioned that fact, even though the program lasted nearly an hour and hearing aids were a major topic of discussion. The wearing of hearing aids has long been stigmatized in a way that the wearing of eyeglasses has not, and, as a consequence, hearing-aid manufacturers have invested heavily in inconspicuousness—one of several reasons that hearing aids like Halo and SoundLens sell for more than three thousand dollars each.
Attitudes about visibility may be changing, though, now that people of all ages walk around with electronic gadgets sticking out of their ears. Hearing-aid companies increasingly compete with manufacturers of over-the-counter devices known as "personal sound-amplification products." The cheapest PSAPs, some of which sell for less than fifty dollars, are notoriously junky and may even exacerbate hearing loss by indiscriminately amplifying harmful sounds. But some companies make user-adjustable Bluetooth devices that have received favorable reviews from technology critics and people with mild hearing problems.
A couple of weeks ago, I had lunch with Kevin Franck, an audiologist at Bose, the sound-equipment company. Snow had fallen overnight, and the restaurant I'd picked, near my home, in Connecticut, wasn't as crowded and loud as it usually is. "That's too bad," Franck said, as we were seated. He was on his way to New York, and had made a detour to show me a new Bose product, still in limited release, called Hearphones—high-fidelity headphones designed, in part, to help people cope with conversations in places like noisy restaurants.
In comparison with SoundLens hearing aids, Hearphones look like a technological throwback: a pair of acorn-size earpieces connected by wires to a choker-like yoke (which can be concealed under a shirt collar). But because Hearphones aren't meant to be invisible they have room for a long antenna, a big rechargeable battery, high-quality microphones and speakers, and far more power-hungry sound-processing and noise-cancelling technology than could be concealed inside an ear canal.
I put them on. "One of the things you get really good at when demonstrating this device is talking without saying much," Franck said, then chatted away. I used a smartphone app to raise and lower background sound levels. I could also focus specifically on Franck's voice or widen the range to include, first, the tables on either side of ours, then some chefs and waiters moving around in the kitchen, behind me. If my cell phone had rung, directional microphones inside the earpieces would have aimed themselves toward my mouth when I answered it. Once I'd found a sound level I liked, I used a slider in the app to fine-tune the pitch. I was able to play music in the background as we conversed—with far better fidelity than is possible with even the most expensive hearing aids—and I could raise and lower its volume independently from everything else.
You wouldn't wear Hearphones on a first date, probably. But, if I'd had a pair at that noisy restaurant I went to in Dallas, I'd have been able to hear everyone at the table without cupping my ears, and, during the boring bits, to tune out the entire room and listen in peace to my audiobook of "A Game of Thrones." ♦