Chapter 6. Hearing, Balance, Taste, and Smell
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by Laura Sanders It truly pains me to bring you tired parents another round of “Is this bad for my baby?” But this week, a new study suggests that some white noise machines designed for babies can produce harmful amounts of sound. Before you despair about trashing your baby’s hearing, please keep in mind that like any study, the results are limited in what they can actually claim. And this one is no exception. I learned the power of white noise when Baby V and I ventured out to meet some new mamas for lunch. As I frantically tried to reverse the ensuing meltdown, another mom came over with her phone. “Try this,” she said as she held up her phone and blasted white noise. Lo and behold, her black magic worked. Instantly, Baby V snapped to attention, stopped screaming and stared wide-eyed at the dark wizardry that is the White Noise Lite app. Since then, I learned that when all else failed, the oscillating fan setting could occasionally jolt Baby V out of a screamfest. In general, I didn’t leave the noise on for long. It was annoying, and more importantly, it stopped working after the novelty wore off. But lots of parents do rely on white noise to soothe their babies and help them sleep through the night. These machines are recommended on top parenting websites by top pediatricians, parenting bloggers and, most convincingly, all of the other parents you know. Use liberally, the Internet experts recommend. To reap the benefits, white noise machines should be played all night long for at least the entire first year, many people think. And don’t be shy: The noise should be louder than you think. © Society for Science & the Public 2000 - 2013
Brian Owens The distinctive aroma of goats does more than just make barnyards extra fragrant. Male goats can use their heady scent to make female goats ovulate simply by being near them. Researchers had ascribed this 'male effect' to chemicals known as primer pheromones — a chemical signal that can cause long-lasting physiological responses in the recipient. Examples of primer pheromones are rare in mammals; the male effect in goats and sheep, and a similar effect in mice and rats, where the presence of males can speed up puberty in females, are the only known cases. But exactly what substances are at work and how has remained a mystery. Now, reproductive biologist Yukari Takeuchi from the University of Tokyo and her colleagues have identified a single molecule, known as 4-ethyloctanal, in the cocktail of male goat pheromones that activates the neural pathway that regulates reproduction in females1. ”It has long been thought that pheromones have pivotal roles in reproductive success in mammals, but the mechanisms are scarcely known,” says Takeuchi. The researchers found that male goat pheromones are generally synthesized in the animal's head skin, so they designed a hat containing a material that captured their odorous molecules and placed them on the goats for a week to collect the scent. Analysis of the gases collected identified a range of compounds, many of which were unknown and were not present in castrated males. When exposed to a cocktail of 18 of these chemicals, the brains of female goats showed a sudden increase in the activity of the gonadotropin-releasing hormone (GnRH) pulse generator — the neural regulator of reproduction. © 2014 Nature Publishing Group,
There is no biological cure for deafness—yet. We detect sound using sensory cells sporting microscopic hairlike projections, and when these so-called hair cells deep inside the inner ear are destroyed by illness or loud noise, they are gone forever. Or so scientists thought. A new study finds specific cells in the inner ear of newborn mice that regenerate these sensory cells—even after damage, potentially opening up a way to treat deafness in humans. Researchers knew that cells in the inner ear below hair cells—known as supporting cells—can become the sensory cells themselves when stimulated by a protein that blocks Notch signaling, which is an important mechanism for cell communication. Albert Edge, a stem cell biologist at Harvard Medical School in Boston, and his colleagues, attempted to identify the exact type of supporting cells that transform into sensory ones and fill in the gaps left by the damaged cells. The researchers removed the organ of Corti, which is housed within a seashell-shaped cavity called the cochlea and contains sensory hair cells, from newborn mice and kept the cells alive in culture plates. They damaged the hair cells using the antibiotic gentamicin, which destroys its sound-sensing projections. When they examined the organ of Corti under the microscope, they saw that small numbers of hair cells had regenerated on their own. But if they blocked Notch signaling, they saw even more regenerated hair cells, the team reports today in Stem Cell Reports. The number that developed varied, but in the base of cochlea, where the tissue received the most damage, hair cell numbers returned to about 40% of the original. “It’s interesting and encouraging that they are capable of regenerating,” Edge says. © 2014 American Association for the Advancement of Science.
By DEBORAH BLUM Toxicologists have long considered ethylene glycol, the active ingredient in many antifreeze and engine coolant formulas, to be a seductive and uniquely dangerous poison. For one thing, it’s sweet. “We actually had a mechanic who developed a taste for it,” recalled Dr. Marsha Ford, director of the Carolinas Poison Center in Charlotte, N.C. “He’d pour himself a little and sip it. And he kept doing that until he got sick.” And that’s the other danger: Ethylene glycol is a slow-acting poison. Even following a high dose, symptoms can take up to 48 hours to appear. The country’s poison control centers record more than 5,000 ethylene glycol ingestions annually; some 2,000 cases require medical treatment. Most are accidental, but ethylene glycol also figures in hundreds of suicide attempts every year — not to mention the occasional murder. Recently an Ohio woman was convicted of killing her fiancé by spiking raspberry iced tea with antifreeze. The situation for animals has been even more dangerous than for despised spouses. According to the Humane Society of the United States, as many as 90,000 pets and wild animals are poisoned annually by drinking spilled or carelessly stored products containing ethylene glycol. Now the manufacturers of those products have determined to do something about all the carnage. They are making antifreeze taste awful — so very bitter that it will be nigh impossible to drink by accident. © 2014 The New York Times Company
When you hear a friend’s voice, you immediately picture her, even if you can’t see her. And from the tone of her speech, you quickly gauge if she’s happy or sad. You can do all of this because your human brain has a “voice area.” Now, scientists using brain scanners and a crew of eager dogs have discovered that dog brains, too, have dedicated voice areas. The finding helps explain how canines can be so attuned to their owners’ feelings. “It’s absolutely brilliant, groundbreaking research,” says Pascal Belin, a neuroscientist at the University of Glasgow in the United Kingdom, who was part of the team that identified the voice areas in the human brain in 2000. “They’ve made the first comparative study using nonhuman primates of the cerebral processing of voices, and they’ve done it with a noninvasive technique by training dogs to lie in a scanner.” The scientists behind the discovery had previously shown that humans can readily distinguish between dogs’ happy and sad barks. “Dogs and humans share a similar social environment,” says Attila Andics, a neuroscientist in a research group at the Hungarian Academy of Sciences at Eötvös Loránd University in Budapest and the lead author of the new study. “So we wondered if dogs also get some social information from human voices.” To find out, Andics and his colleagues decided to scan the canine brain to see how it processes different types of sounds, including voices, barks, and natural noises. In humans, the voice area is activated when we hear others speak, helping us recognize a speaker’s identity and pick up on the emotional content in her voice. If dogs had voice areas, it could mean that these abilities aren’t limited to humans and other primates. © 2014 American Association for the Advancement of Science
Adrienne LaFrance For the better part of the past decade, Mark Kirby has been pouring drinks and booking gigs at the 55 Bar in New York City's Greenwich Village. The cozy dive bar is a neighborhood staple for live jazz that opened on the eve of Prohibition in 1919. It was the year Congress agreed to give American women the right to vote, and jazz was still in its infancy. Nearly a century later, the den-like bar is an anchor to the past in a city that's always changing. For Kirby, every night of work offers the chance to hear some of the liveliest jazz improvisation in Manhattan, an experience that's a bit like overhearing a great conversation. "There is overlapping, letting the other person say their piece, then you respond," Kirby told me. "Threads are picked up then dropped. There can be an overall mood and going off on tangents." Brain areas linked to meaning shut down during improvisational jazz interactions. In other words, this music is syntactic, not semantic. The idea that jazz can be a kind of conversation has long been an area of interest for Charles Limb, an otolaryngological surgeon at Johns Hopkins. So Limb, a musician himself, decided to map what was happening in the brains of musicians as they played. He and a team of researchers conducted a study that involved putting a musician in a functional MRI machine with a keyboard, and having him play a memorized piece of music and then a made-up piece of music as part of an improvisation with another musician in a control room. What researchers found: The brains of jazz musicians who are engaged with other musicians in spontaneous improvisation show robust activation in the same brain areas traditionally associated with spoken language and syntax. In other words, improvisational jazz conversations "take root in the brain as a language," Limb said. © 2014 by The Atlantic Monthly Group
By DOUGLAS QUENQUA The smell of a person’s earwax depends partly on his ethnic origin, a new study reports, suggesting that the substance could be an overlooked source of personal information. The earwax of Caucasian men contains more volatile organic compounds than that of East Asian men, researchers at the Monell Chemical Senses Center in Philadelphia found. Twelve such compounds are common to both groups, they said, but 11 of those are more plentiful in Caucasians. Monell researchers have previously found that underarm odor contains clues to a person’s age, health and sex. They suspected that earwax might contain similar markers, since a 2006 study found that a gene related to underarm odor, which also varies by ethnicity, helps determine a person’s type of earwax. (East Asians are more likely to have dry earwax, for example.) "We’re at the beginning of exploring a new and interesting biofluid secretion that has not been looked at in this manner before," said George Preti, an organic chemist at Monell and the senior author of the new study, which was published in The Journal of Chromatography B. Because of the fatty nature of earwax, or cerumen, Dr. Preti says it is a probable repository for odorants produced by diseases and the environment, and hence a potentially valuable diagnostic tool. A 2013 study showed that a whale’s earwax contains evidence of the animal’s exposure to pollutants and stress hormones, and earwax odor in humans is a known indicator of branched-chain ketoaciduria, also known as maple syrup urine disease. © 2014 The New York Times Company
Keyword: Chemical Senses (Smell & Taste)
Link ID: 19258 - Posted: 02.18.2014
by Bethany Brookshire CHIGAGO – From a cockatoo bopping to the Backstreet Boys to a sea lion doing the boogie, nothing goes viral like an animal swaying to the music. Now, research shows that not only can bonobos feel the beat, they can play along. Music “engages the brain in a way that no other stimulus can,” says cognitive psychologist Edward Large of the University of Connecticut in Storrs. He and Patricia Gray, a biomusic researcher at the University of North Carolina at Greensboro, wanted to see if bonobos, which share 98.7 percent of their DNA with humans, might respond similarly to musical rhythms. The researchers gave a group of bonobos access to a specially tailored drum, then showed them people drumming rhythmically. Eventually three animals picked up the beat and were able to match tempos with the scientists. Bonobos were also found to prefer a faster pace than most people. Large and Gray presented their findings February 15 at the American Association for the Advancement of Science annual meeting. Rhythm involves the coordination of many brain areas, such as auditory and motor regions. Further research could help scientists understand whether only a few species can keep the beat, or if moving to the groove is widespread in the animal kingdom. © Society for Science & the Public 2000 - 2013.
Carl Zimmer In 2011, a 66-year-old retired math teacher walked into a London neurological clinic hoping to get some answers. A few years earlier, she explained to the doctors, she had heard someone playing a piano outside her house. But then she realized there was no piano. The phantom piano played longer and longer melodies, like passages from Rachmaninov’s Piano Concerto number 2 in C minor, her doctors recount in a recent study in the journal Cortex. By the time the woman — to whom the doctors refer only by her first name, Sylvia — came to the clinic, the music had become her nearly constant companion. Sylvia hoped the doctors could explain to her what was going on. Sylvia was experiencing a mysterious condition known as musical hallucinations. These are not pop songs that get stuck in your head. A musical hallucination can convince people there is a marching band in the next room, or a full church choir. Nor are musical hallucinations the symptoms of psychosis. People with musical hallucinations usually are psychologically normal — except for the songs they are sure someone is playing. The doctors invited Sylvia to volunteer for a study to better understand the condition. She agreed, and the research turned out to be an important step forward in understanding musical hallucinations. The scientists were able to compare her brain activity when she was experiencing hallucinations that were both quiet and loud — something that had never been done before. By comparing the two states, they found important clues to how the brain generates these illusions. If a broader study supports the initial findings, it could do more than help scientists understand how the brain falls prey to these phantom tunes. It may also shed light on how our minds make sense of the world. © 2014 The New York Times Company
By SINDYA N. BHANOO Mosquito sperm have a sense of smell, researchers are reporting, in a finding that could suggest ways to help control the spread of disease-carrying insects. The sperm carries a set of chemical sensors identical to the olfactory receptors on the mosquitoes’ antennas, according to a study in Proceedings of the National Academy of Sciences. Mosquitoes mate just once in their lifetime, and the female stores the male’s sperm in an organ called a spermatheca. Before the eggs mature, the female seeks out blood using the receptors on her antennas. Soon after, chemical signals cause the sperm tails to beat rapidly and start the fertilization process. “The sperm may need a chemical signal to become ready for fertilization,” said Jason Pitts, a researcher at Vanderbilt University and an author of the study, which was supported by the Gates Foundation as part of its efforts to improve global health. Another author, Laurence Zwiebel, also a Vanderbilt researcher, called the dual use of the olfactory receptors a clear and clever example of convergent evolution: The mosquitoes, he said, “found something that works and use it in multiple ways.” The scientists think olfactory receptors may exist on the sperm of many other insects, and they are developing chemical compounds that can be applied to breeding grounds to block the receptors. “You can effectively confuse the sperm or make them inactive,” Dr. Zwiebel said. © 2014 The New York Times Company
by Bob Holmes Midnight fridge raids are part and parcel of a late-night marijuana smoking session. A study in mice has provided the most complete explanation yet for why a spliff triggers intense hunger pangs. The findings, which elucidate the role of smell, also suggest that we might eventually be able to treat common disorders such as obesity and loss of appetite with a simple nasal spray. We know that the active ingredient in cannabis, THC, binds to cannabinoid receptors in the brain called CB1s. This binding inhibits chemical signals that tell us not to eat, and so make us feel hungry. But this isn't the end of the story. Since smell plays such a central role in making us feel hungry, it must be part of the explanation - but no one knew exactly how it fit. To find out, Giovanni Marsicano of the French research agency INSERM in Bordeaux and his colleagues genetically modified mice to make it possible to turn on and off the CB1 receptor in particular nerve cells within the smell, or olfactory, system. The key proved to be a group of nerve cells that carry signals from the cerebral cortex down to the olfactory bulb, the primary smell centre of the brain. When the team switched off CB1 on these cells, they found that hungry mice no longer ate more than their well-fed counterparts. Conversely, activating CB1 in the same cells by injecting THC caused hungry mice to eat even more. THC-treated mice also responded to less-concentrated food smells than untreated mice, a sign that the chemical had enhanced their sense of smell. © Copyright Reed Business Information Ltd.
Dinsa Sachan Could being visually impaired have had a role in the musical genius of Stevie Wonder and Ray Charles? A study provides some clues by showing that adult mice kept in the dark quickly develop sharper hearing and become better at distinguishing pitch and frequency. The improvements were correlated with adaptations in the brain — such as strengthening of connections between neurons — that normally happen only early in life. For their study, published today in Neuron1, Hey-Kyoung Lee, a neuroscientist at Johns Hopkins University in Baltimore, Maryland, and her collaborators selected two sets of healthy adult mice. They kept the first group in a darkened environment for a week, while the other was exposed to natural light. The team used electrodes to measure activity in neurons in the animals' primary auditory cortex — the part of the brain that processes what a sound is, how loud it is and where it comes from. The researchers played sounds of different frequencies and intensities to the mice, and watched how their brain cells reacted. The results “showed that neurons in visually deprived animals can 'hear' much softer sounds” than in control animals, says Lee. “They also have much finer discrimination ability as far as identifying pitch goes.” Previous studies have found that changes in the auditory cortex take a long time, and that people who become blind early in life adapt better than those who lose their sight later. The team's findings, however, show that some modifications can occur rapidly in the adult brain, she says. “Moreover,” she adds, “the changes in the auditory cortex were achieved by changes in the strength of synaptic connections. These were believed to be unchangeable in adults.” © 2014 Nature Publishing Group
About two-thirds of people are left with ringing in their ears after a night out at a club, gig or pub, a poll suggests. Campaign group Action on Hearing Loss said the poll of 1,000 adults also showed a third would ignore the "safe level" on their music players. The group warns that people doing either increase the risk of tinnitus. DJ Paul Oakenfold urged people to wear ear defenders to gigs and to "turn down the volume". Half of those surveyed said they listened to music for between one and six hours a day - up to a third of their waking day - perhaps in the background at work or on their MP3 player on their way to and from work or studies. But one in five would not do anything differently to take any care of their hearing. Action on Hearing Loss warned that one in 10 people across the UK is affected by tinnitus every day, ranging from a "light buzzing" to a "constant roar" in the ears and head. It can affect everything from the ability to concentrate at work to getting to sleep at night. The poll also found that one in 10 people does not know what tinnitus is, with 3% thinking it was "big ears" and 4% a "repetitive strain injury". It has created an audio version of what tinnitus sounds like in order to raise awareness. Paul Breckell, chief executive of Action on Hearing Loss, said: "Listening to loud music for a long time can trigger tinnitus and is an indication of damaged hearing. BBC © 2014
Link ID: 19201 - Posted: 02.04.2014
|By Stephanie Pappas and LiveScience Even water tastes sweeter when you're in love, new research finds. But not every emotion heightens the senses. Jealousy fails to bring out bitter or sour tastes, despite metaphors that suggest it might, researchers report in the December 2013 issue of the journal Emotion. That love alters one's sensory perceptions and jealousy does not is important to psychologists who study what are called "embodied" metaphors, or linguistic flourishes people quite literally feel in their bones. For example, studies have shown that people induced to feel lonely rate the temperature of the room as colder than do their unprimed counterparts. And the idea that important things have heft plays out physically, too: When someone believes a book is important, it feels heavier. But "just because there is a metaphor does not necessarily imply that we will get these kind of sensations and perception effects," said study researcher Kai Qin Chan, a doctoral candidate at Radboud University Nijmegen in the Netherlands. After seeing previous research on emotional metaphors, like the studies linking loneliness to coldness and heaviness to importance, Chan and his colleagues wanted to expand the question. "We always say, 'love is sweet,' 'honey baby,' this kind of thing," Chan told LiveScience. "We thought, let's see whether this applies to love." © 2014 Scientific American
By TRICIA ROMANO Like many men of his generation, Larry Faust, 61, of Seattle, went to a lot of rock concerts in his youth. And like many men of his generation, his hearing isn’t what it used to be. “My wife has been bugging me for several years to do something about my hearing,” said Mr. Faust. “I spent part of the summer of 1969 at Woodstock. So that probably didn’t help.” Instead of going the traditional route — buying hearing aids through an audiologist or licensed hearing aid dispenser — Mr. Faust purchased a device that is classified as a personal sound amplifier product, or P.S.A.P., which is designed to amplify sounds in a recreational environment. Unlike hearing aids, P.S.A.P.’s are exempt from Food and Drug Administration oversight and can be sold as electronic devices directly to consumers, with no need to see a physician before buying one. They come with a range of features and vary widely in price. And while some hearing professionals have long cautioned against the devices, citing their unreliability and poor quality, many also say that a new generation of P.S.A.P.s that utilize the latest wireless technology are offering promising alternatives for some people with hearing loss. The device Mr. Faust bought, the CS10 from a Chicago-based company called Sound World Solutions, cost $299.99, thousands of dollars cheaper than most digital hearing aids. While it has many of the same features that high-end hearing aids have, including 16 channels to process sound, directional microphones, feedback insulation and noise reduction, it has one capability that hearing aids and other devices on the market currently don’t have. It comes with software that enables consumers to program it themselves, a feature made possible in part by the adoption of the widely available Bluetooth wireless technology, rather than the proprietary platforms used by most wireless hearing aids. © 2014 The New York Times Company
Link ID: 19144 - Posted: 01.16.2014
Ask a group of people to describe the color of a sheet of paper, a cloud, or a glass of milk, and chances are they’ll all say “white.” But ask the same group to describe the smell of cinnamon, and you’ll likely get a potpourri of answers, ranging from “spicy” to “smoky” to “sweet,” and sometimes all three. When it comes to naming smells, humans struggle to find concise, universal terms. Indeed, scientists have long thought the ability was out of our reach. But a new study indicates that the inhabitants of a remote peninsula in Southeast Asia can depict smells as easily as the rest of us pick colors. The study concerns the Jahai, nomadic hunter-gatherers who live in the mountain rainforests along the border between Malaysia and Thailand. Smell is very important to this society. Odors are often evoked in illness, or medicine, for example, and it is one of the few cultures to have words devoted exclusively to smells. “For example, the term pʔus (pronounced ‘pa-oos’) describes the smell of old huts, day-old food, and cabbage,” says Asifa Majid, a psychologist at the Centre for Language Studies at Radboud University Nijmegen in the Netherlands. This suggests, she says, that the Jahai can isolate basic smell properties, much like we can isolate the color white from milk. To find out if the Jahai are better at naming smells than the rest of us, Majid and colleagues asked native Jahai speakers and native English speakers to describe 12 different odors: cinnamon, turpentine, lemon, smoke, chocolate, rose, paint thinner, banana, pineapple, gasoline, soap, and onion. The Jahai easily and consistently named the odors, whereas English speakers struggled, the team reports in the February issue of Cognition. © 2014 American Association for the Advancement of Science
Keyword: Chemical Senses (Smell & Taste)
Link ID: 19129 - Posted: 01.14.2014
by Helen Thomson A drug for perfect pitch is just the start: mastering new skills could become easy if we can restore the brain's youthful ability to create new circuits WANNABE maestros, listen up. A mood-stabilising drug can help you achieve perfect pitch – the ability to identify any note you hear without inferring it from a reference note. Since this is a skill that is usually acquired only early in life, the discovery is the first evidence that it may be possible to revert the human brain to a childlike state, enabling us to treat disorders and unlock skills that are difficult, if not impossible, to acquire beyond a certain age. From bilingualism to sporting prowess, many abilities rely on neural circuits that are laid down by our early experiences. Until the age of 7 or so, the brain goes through several "critical periods" during which it can be radically changed by the environment. During these times, the brain is said to have increased plasticity. In order to take advantage of these critical periods, the brain needs to be stimulated appropriately so it lays down the neuronal circuitry needed for a particular ability. For example, young children with poor sight in one eye may develop lazy eye, or amblyopia. It can be treated by covering the better eye, forcing the child to use the lazy eye – but this strategy only works during the critical period. These windows of opportunity are fleeting, but now researchers are beginning to understand what closes them and how they might be reopened. © Copyright Reed Business Information Ltd.
Fifty million Americans experience chronic ringing in the ears, a condition known as tinnitus. But new research from the University of Michigan Medical School may soon provide solace to those suffering. The discovery helps to explain what is going on inside the brains of those with tinnitus and may provide a new approach to treat the nagging noise. The research team already has a patent pending and device in development. The findings, published in the Journal of Neuroscience, explain that a process called stimulus-timing dependent multisensory plasticity is altered in animals with tinnitus and the results have revealed the relationship between tinnitus, hearing loss and sensory input. Dr. Susan Shore, senior author of the paper notes that any treatment likely will have to be customized to each patient and delivered on a regular basis. Some patients may be more likely to benefit than others. © 1996-2013 MacNeil/Lehrer Productions
Link ID: 19050 - Posted: 12.18.2013
Bats can understand the emotional state of other bats from the intonations of their calls, a new study suggests. In the lab, researchers observed greater false vampire bats (Megaderma lyra, pictured) that had been trained to wait for food on a perch. In some tests, they played “aggression calls” over a speaker, typically made by a bat defending its place on a perch from an approaching bat. In other trials, the researchers played “appeasement calls” often made by a bat approaching one already ensconced on a perch and thus seeking to share its space. (Bats were tested individually, and the use of recorded calls ensured that the bats were responding to the content of the call and not visual cues from another bat.) In all tests, the scientists played a call once every 20 seconds until the bats began to ignore the call (by not turning toward the speaker), and then they played a slightly different version of the same call—one that was either more urgent (with shorter, more closely spaced syllables) or less urgent. The novel aggression calls always caused a bat to turn toward the speaker, but the novel appeasement calls only drew a response when they became more urgent, the researchers report online today in Frontiers of Zoology. The failure of a bat to react to weakening appeasement calls suggests that the bats can interpret the emotional content of the calls—a sign that such perception might exist more widely in mammals than previously thought. © 2013 American Association for the Advancement of Science.
Associated Press The U.S. Navy plans to increase sonar testing over the next five years, even as research it funded reveals worrying signs that the loud underwater noise could disturb whales and dolphins. Reported mass strandings of whale species have increased worldwide since the military started using sonar half a century ago. Scientists think the sounds scare animals into shallow waters where they can become disoriented and wash ashore, but technology capable of close monitoring has emerged only in the past decade. Aside from strandings, biologists are concerned marine mammals could suffer prolonged stress from changes in diving, feeding and communication. Two studies off the Southern California coast found certain endangered blue whales and beaked whales stopped feeding and fled from recordings of sounds similar to military sonar. Beaked whales are highly sensitive to sound and account for the majority of beachings near military exercises. Scientists, however, were surprised by the reaction of blue whales - the world's largest animal - long thought to be immune to the high-pitched sounds. It's unclear how the change in behavior would affect the overall population, estimated at between 5,000 and 12,000 animals. The studies involved only a small group of tagged whales, and noise levels were less intense than what's used by the Navy. Shy species - such as the Cuvier's beaked whale, which can dive 3,000 feet below the surface - have taken years to find and monitor. "This is a warning flag and deserves more research," said Stanford University biologist Jeremy Goldbogen, who led the blue whale study published this summer in the journal Proceedings of the Royal Society B. © 2013 Hearst Communications, Inc.