Chapter 6. Hearing, Balance, Taste, and Smell
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By Christopher Intagliata Two decades ago, Swiss researchers had women smell the tee shirts that various men had slept in for two nights. Turned out that if women liked the aroma of a particular shirt, the guy who’d worn it was likely to have genetically coded immunity that was unlike the woman’s. Well the effect isn't just limited to sweaty shirts. Turns out we all smell things a little differently—you pick up a note of cloves, say, where I smell something more soapy—and that too gives clues to our degree of genetic similarity. Researchers tried that test with 89 people—having them sniff a couple dozen samples, and label each one using terms like lemony, coconut, fishy and floral. And each volunteer classified the scents differently enough that the researchers could single them out in subsequent tests, based on what they called each subject’s "olfactory fingerprint." Researchers then repeated that sniff test on another 130 subjects. But this time they did a blood test, too, to figure out each person's HLA type—an immune factor that determines whether you'll reject someone's organ, for example. They found that people who perceived smells similarly also had similar HLA types. Study author Lavi Secundo, a neuroscientist at the Weizmann Institute of Science in Israel, says the smell test could have real-world applications. "For organ donation you can think of this method as a quick, maybe a quick and dirty, method to sift between the best and the rest." He and his colleagues say it might even eliminate the need for 30 percent of the HLA tests done today. The work appears in the Proceedings of the National Academy of Sciences. [Lavi Secundo et al, Individual olfactory perception reveals meaningful nonolfactory genetic information] © 2015 Scientific American
By Sarah Lewin Evolutionary biologists have long wondered why the eardrum—the membrane that relays sound waves to the inner ear—looks in humans and other mammals remarkably like the one in reptiles and birds. Did the membrane and therefore the ability to hear in these groups evolve from a common ancestor? Or did the auditory systems evolve independently to perform the same function, a phenomenon called convergent evolution? A recent set of experiments performed at the University of Tokyo and the RIKEN Evolutionary Morphology Laboratory in Japan resolves the issue. When the scientists genetically inhibited lower jaw development in both fetal mice and chickens, the mice formed neither eardrums nor ear canals. In contrast, the birds grew two upper jaws, from which two sets of eardrums and ear canals sprouted. The results, published in Nature Communications, confirm that the middle ear grows out of the lower jaw in mammals but emerges from the upper jaw in birds—all supporting the hypothesis that the similar anatomy evolved independently in mammals and in reptiles and birds. (Scientific American is part of Springer Nature.) Fossils of auditory bones had supported this conclusion as well, but eardrums do not fossilize and so could not be examined directly. © 2015 Scientific American
Sarah Schwartz A person’s sense of smell may reveal a lot about his or her identity. A new test can distinguish individuals based upon their perception of odors, possibly reflecting a person’s genetic makeup, scientists report online June 22 in Proceedings of the National Academy of Sciences. Most humans perceive a given odor similarly. But the genes for the molecular machinery that humans use to detect scents are about 30 percent different in any two people, says neuroscientist Noam Sobel of the Weizmann Institute of Science in Rehovot, Israel. This variation means that nearly every person’s sense of smell is subtly different. Nobody had ever developed a way to test this sensory uniqueness, Sobel says. Sobel and his colleagues designed a sensitive scent test they call the “olfactory fingerprint.” In an experiment, test subjects rated how strongly 28 odors such as clove or compost matched 54 adjectives such as “nutty” or “pleasant.” An olfactory fingerprint describes individuals’ perceptions of odors’ similarities, not potentially subjective scent descriptions. All 89 subjects in the study had distinct olfactory fingerprints. The researchers calculated that just seven odors and 11 descriptors could have identified each individual in the group. With 34 odors, 35 descriptors, and around five hours of testing per person, the scientists estimate they could individually identify about 7 billion different people, roughly the entire human population. © Society for Science & the Public 2000 - 2015.
By Rachel Feltman Here's why you hate the sound of your own voice(1:07) If you've ever listened to your voice recorded, chances are you probably didn't like what you heard. So, why do most people hate the sound of their own voice? The answer: It's all in how sound travel to your ears. (Pamela Kirkland/The Washington Post) Whether you've heard yourself talking on the radio or just gabbing in a friend's Instagram video, you probably know the sound of your own voice -- and chances are pretty good that you hate it. As the video above explains, your voice as you hear it when you speak out loud is very different from the voice the rest of the world perceives. That's because it comes to you via a different channel than everyone else. When sound waves from the outside world -- someone else's voice, for example -- hit the outer ear, they're siphoned straight through the ear canal to hit the ear drum, creating vibrations that the brain will translate into sound. When we talk, our ear drums and inner ears vibrate from the sound waves we're putting out into the air. But they also have a another source of vibration -- the movements caused by the production of the sound. Our vocal cords and airways are trembling, too, and those vibrations make their way over to auditory processing as well. Your body is better at carrying low, rich tones than the air is. So when those two sources of sound get combined into one perception of your own voice, it sounds lower and richer. That's why hearing the way your voice sounds without all the body vibes can be off-putting -- it's unfamiliar -- or even unpleasant, because of the relative tinniness.
Link ID: 21062 - Posted: 06.17.2015
By Brian Handwerk When it comes to mating, female mice must follow their noses. For the first time, scientists have shown that hormones in mice hijack smell receptors in the nose to drive behavior, while leaving the brain completely out of the loop. According to the study, appearing this week in Cell, female mice can smell attractant male pheromones during their reproductive periods. But during periods of diestrus, when the animals are unable to reproduce, the hormone progesterone prompts nasal sensory cells to block male pheromone signals so that they don't reach a female's brain. During this time, female mice display indifference or even hostility toward males. The same sensors functioned normally with regard to other smells, like cat urine, showing they are selective for male pheromones. When ovulation begins, progesterone levels drop, enabling the females to once more smell male pheromones. In short, the system "blinds" female mice to potential mates when the animals are not in estrus. The finding that the olfactory system usurped the brain's role shocked the research team, says lead author Lisa Stowers of the Scripps Research Institute. “The sensory systems are just supposed to sort of suck up everything they can in the environment and pass it all on to the brain. The result just seems wacky to us,” Stowers says. “Imagine this occurring in your visual system," she adds. "If you just ate a big hamburger and then saw a buffet, you might see things like the table and some people and maybe some fruit—but you simply wouldn't see the hamburgers anymore. That's kind of what happens here. Based on this female's internal-state change, she's missing an entire subset of the cues being passed on to her brain.”
How echolocation really works By Dwayne Godwin and Jorge Cham © 2015 Scientific American
Link ID: 21017 - Posted: 06.06.2015
By Emily DeMarco For owners of picky cats, that disdainful sniff—signaling the refusal of yet another Friskies flavor—can be soul-crushing. Some cats are notoriously finicky eaters, but the reasons behind such fussy behavior remain fuzzy. Previous research has shown that cats can’t taste sweet flavors, but little is known about how they perceive bitter tastes. Now, researchers in the pet food industry have identified two bitter taste receptors in domestic cats, which could help explain why some felines are so choosy when it comes to their chow. In the study, published today in BMC Neuroscience, the scientists used cell-based experiments to see how the two cat taste receptors, known as Tas2r38 and Tas2r43, responded to bitter compounds such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP)—which have molecular structures similar to ones in Brussels sprouts and broccoli—as well as aloin (from the aloe plant) and denatonium (used to prevent inadvertent ingestion of some chemicals). When compared with the human versions of these receptors, the researchers found that the cat bitter receptor Tas2r38 was less sensitive to PTC and did not respond to PROP, whereas Tas2r43 was less sensitive to aloin but more sensitive to denatonium, leading the researchers to conclude that cats taste different, and perhaps more narrow, ranges of bitter flavors than humans. The research could help pharmaceutical and pet food manufacturers create compounds that block or inhibit these bitter taste receptors, the team says, potentially leading to more appetizing medicines (if such a thing exists) and foods for our feline companions. © 2015 American Association for the Advancement of Science
Lauren Silverman Jiya Bavishi was born deaf. For five years, she couldn't hear and she couldn't speak at all. But when I first meet her, all she wants to do is say hello. The 6-year-old is bouncing around the room at her speech therapy session in Dallas. She's wearing a bright pink top; her tiny gold earrings flash as she waves her arms. "Hi," she says, and then uses sign language to ask who I am and talk about the ice cream her father bought for her. Jiya is taking part in a clinical trial testing a new hearing technology. At 12 months, she was given a cochlear implant. These surgically implanted devices send signals directly to the nerves used to hear. But cochlear implants don't work for everyone, and they didn't work for Jiya. A schoolboy with a cochlear implant listens to his teacher during lessons at a school for the hearing impaired in Germany. The implants have dramatically changed the way deaf children learn and transition out of schools for the deaf and into classrooms with non-disabled students. "The physician was able to get all of the electrodes into her cochlea," says Linda Daniel, a certified auditory-verbal therapist and rehabilitative audiologist with HEAR, a rehabilitation clinic in Dallas. Daniel has been working with Jiya since she was a baby. "However, you have to have a sufficient or healthy auditory nerve to connect the cochlea and the electrodes up to the brainstem." But Jiya's connection between the cochlea and the brainstem was too thin. There was no way for sounds to make that final leg of the journey and reach her brain. © 2015 NPR
By Meeri Kim The dangers of concussions, caused by traumatic stretching and damage to nerve cells in the brain that lead to dizziness, nausea and headache, has been well documented. But ear damage that is sometimes caused by a head injury has symptoms so similar to the signs of a concussion that doctors may misdiagnose it and administer the wrong treatment. A perilymph fistula is a tear or defect in the small, thin membranes that normally separate the air-filled middle ear from the inner ear, which is filled with a fluid called perilymph. When a fistula forms, tiny amounts of this fluid leak out of the inner ear, an organ crucial not only for hearing but also for balance. Losing even a few small drops of perilymph leaves people disoriented, nauseous and often with a splitting headache, vertigo and memory loss. While most people with a concussion recover within a few days, a perilymph fistula can leave a person disabled for months. There is some controversy around perilymph fistula due to its difficulty of diagnosis — the leak is not directly observable, but rather identified by its symptoms. However, it is generally accepted as a real condition by otolaryngologists and sports physicians, and typically known to follow a traumatic event. But concussions — as well as post-concussion syndrome, which is marked by dizziness, headache and other symptoms that can last even a year after the initial blow — also occur as the result of such an injury.
By SINDYA N. BHANOO Male Java sparrows are songbirds — and, scientists reported on Wednesday, natural percussionists. The sparrows click their bills against a hard surface while singing. That clicking is done in coordination with the song, much as a percussion instrument accompanies a melody. Researchers at Hokkaido University in Japan observed the birds producing clicks frequently toward the beginning of their songs and around specific notes. Birds that were related produced similar percussive patterns, but whether this behavior is learned or innate is unclear. Next the scientists, who described their findings on Wednesday in the journal PLOS One, would like to know whether male sparrows use bill clicks during courtship communication. © 2015 The New York Times Company
Jon Hamilton When Sam Swiller used hearing aids, his musical tastes ran to AC/DC and Nirvana – loud bands with lots of drums and bass. But after Swiller got a cochlear implant in 2005, he found that sort of music less appealing. "I was getting pushed away from sounds I used to love," he says, "but also being more attracted to sounds that I never appreciated before." So he began listening to folk and alternative music, including the Icelandic singer Bjork. There are lots of stories like this among people who get cochlear implants. And there's a good reason. A cochlear implant isn't just a fancy hearing aid. When his cochlear implant was first switched on, the world sounded different. "A hearing aid is really just an amplifier," says Jessica Phillips-Silver, a neuroscience researcher at Georgetown University. "The cochlear implant is actually bypassing the damaged part of the ear and delivering electrical impulses directly to the auditory nerve." As a result, the experience of listening to music or any other sound through the ear, with or without a hearing aid, can be completely unlike the experience of listening through a cochlear implant. "You're basically remapping the audio world," Swiller says. Swiller is 39 years old and lives in Washington, D.C. He was born with an inherited disorder that caused him to lose much of his hearing by his first birthday. That was in the 1970s, and cochlear implants were still considered experimental devices. So Swiller got hearing aids. They helped, but Swiller still wasn't hearing what other people were. © 2015 NPR
By Virginia Morell Like humans, dolphins, and a few other animals, North Atlantic right whales (Eubalaena glacialis) have distinctive voices. The usually docile cetaceans utter about half a dozen different calls, but the way in which each one does so is unique. To find out just how unique, researchers from Syracuse University in New York analyzed the “upcalls” of 13 whales whose vocalizations had been collected from suction cup sensors attached to their backs. An upcall is a contact vocalization that lasts about 1 to 2 seconds and rises in frequency, sounding somewhat like a deep-throated cow’s moo. Researchers think the whales use the calls to announce themselves and to “touch base” with others of their kind, they explained in a poster presented today at the Meeting of the Acoustical Society of America in Pittsburgh, Pennsylvania. After analyzing the duration and harmonic frequency of these upcalls, as well as the rate at which the frequencies changed, the scientists found that they could distinguish the voices of each of the 13 whales. They think their discovery will provide a new tool for tracking and monitoring the critically endangered whales, which number about 450 and range primarily from Florida to Newfoundland. © 2015 American Association for the Advancement of Science.
By Chris Cesare For bats, too many echoes can be like blurry vision. That’s because the nocturnal creatures navigate by bouncing ultrasonic sound off of their surroundings, a technique known as echolocation. In cramped spots, these sounds can reverberate, creating a noisy background that clouds the mammals’ sonic sight. Now, new research published online before print in the Proceedings of the National Academy of Sciences has discovered one way that bats might overcome this auditory ambush. Scientists found that the animals modify the width of their navigation pulses on the fly by adjusting the size of their mouth gape. The researchers used an array of cameras, flashes, and ultrasonic recorders to take snapshots of bats while they swooped down to take a sip at a desert pond in Israel. As the bats descended toward the confined banks of the pond, they opened their mouths wider to more tightly focus their sound pulses. As the bats left, they narrowed their mouths, projecting an ultrasonic beam up to four times wider than on the descending leg. These counterintuitive effects were due to diffraction, which causes sound waves traveling through a smaller hole to spread out more. The researchers repeated the experiment with captive bats and found the same effect, controlling for the possibility that they had observed a behavior tied to drinking. The team writes that these changes in gape allow the animals to “zoom in” on their view of an area, potentially reducing the amount of distracting echoes in a tight space. © 2015 American Association for the Advancement of Science
Link ID: 20901 - Posted: 05.09.2015
by Clare Wilson WHAT is it like to be a bat? It's a question philosophers interested in consciousness like to ponder. Yet a few people already have something of a bat's world view. Brian Borowski, a 59-year-old Canadian who was born blind, began teaching himself to echolocate aged 3. He clicks with his tongue or snaps his fingers as he moves about, unconsciously decoding the echoes. Although many blind people get information from sounds around them, few turn this into a supersense by making sounds to help themselves get around. "When I'm walking down a sidewalk and I pass trees, I can hear the tree: the vertical trunk of the tree and maybe the branches above me," says Borowski. "I can hear a person in front of me and go around them." Borowski, who works as a programmer at Western University in London, Ontario, suspects he experiences "images" in a similar way to people who can see, just with less detail. "I store maps of information in my head and I compare what I have in my memory with what I'm hearing around me," he says. "I am matching images of some sort." This probably isn't too far from the truth – we know from brain scans of Borowski and another echolocator that the strategy co-opts the same parts of the brain that usually deal with visual information. For his latest scientific collaboration, he helped a team of researchers to explore how well echolocators can determine the relative sizes and distances of objects. © Copyright Reed Business Information Ltd
Link ID: 20898 - Posted: 05.08.2015
By Paca Thomas Wasabi and Sriracha each activate different receptors on the tongue, both of which warn your brain of the atomic reaction to come. These key flavor receptors, TRPA1 and TRPV1, have been the subject of recent research—but why all the scientific study of hot and spicy condiments? One word: pain. The video above explains how our tongues react to heat in our food, and how that often triggers the body’s own bespoke painkiller.
Keyword: Chemical Senses (Smell & Taste)
Link ID: 20879 - Posted: 05.04.2015
Nala Rogers People who are ill often complain of changes in their sense of taste. Now, researchers report that this sensory shift may be caused by a protein that triggers inflammation. Mice that cannot produce the protein, called tumour necrosis factor-α (TNF-α), are less sensitive to bitter flavours than normal mice, according to a study published on 21 April in Brain, Behavior, and Immunity1. People with infections, autoimmune disease or other inflammatory conditions have higher levels of TNF-α than healthy people, and the protein has been shown to reduce food intake2. To investigate the influence of TNF-α on taste, researchers at the Monell Chemical Senses Center in Philadelphia, Pennsylvania, used engineered mice that could not produce the protein. The researchers offered the engineered mice and normal mice water that contained different types and concentrations of flavours. The mice that could not produce TNF-α had normal reactions to sweet, sour, salty and umami flavours, but were less sensitive to bitter ones. “Normal mice will pick up [that taste] at a much lower concentration. They will know this is bitter; they will not like it,” says Hong Wang, a molecular biologist at Monell and an author of the study. “But if the TNF-α gene is not there, then the mice will only start to avoid the bitter solution at higher concentrations.” © 2015 Nature Publishing Group
By Rachel E. Gross “By being a guy’s best first move … Axe is designed to keep guys a step ahead in the dating game,” boasts Unilever, the company that sells Axe products. Of course, if you don’t happen to be a gullible 13-year-old boy, you probably don’t believe that body spray or deodorant is a magic elixir with the power to turn nice girls naughty. But what if it were possible to change a person’s mood with just a scent? The idea may not be that far-fetched, according to a new study in the journal Psychological Science—reporting work that was funded by Unilever. The study found that it might be possible to subconsciously trigger a state of happiness using the scent of—deep breath now—human sweat. People send all kinds of secret messages through their secretions. When smelling chemicals in male sweat, women become more alert, and they can even tell whether that sweat was made by a guy who was particularly turned on. (Cautions the New York Times: “No man should imagine that based on these conclusions he can improve his sex life by refraining from bathing.”) But until now, most sweat studies have focused on sexual arousal or negative emotions like fear. For obvious reasons, these emotions are crucial to survival and evolutionary success. If your friend spots a puma, it may be helpful for you to be able to sniff out instant cues to be on the alert or flee for cover. Being able to transmit positive emotions may also have a profound social impact, says Gün Semin, a psychologist at Utrecht University in the Netherlands and lead researcher on the study. After all, “the pursuit of happiness is not an individual enterprise,” as he and his fellow researchers write rather eloquently in the new study. So Semin’s team decided to test whether people could communicate happiness via sweat.
By Emily DeMarco Mice and rats communicate in the ultrasonic frequency range, and it’s thought that cats evolved the ability to hear those high-pitched squeaks to better hunt their prey. Now, a new study suggests that sensitivity to higher pitched sounds may cause seizures in some older cats. After receiving reports of the problem, nicknamed the “Tom and Jerry syndrome” because of how the cartoon cat is often startled by sounds, researchers surveyed cat owners and examined their pets’ medical records, looking for insight into the types and durations of seizures and the sounds that provoked them. In 96 cats, they found evidence of the syndrome they call feline audiogenic reflex seizures. The most common types of seizure-eliciting sounds included crinkling tinfoil, clanking a metal spoon on a ceramic feeding bowl, and clinking glass. The severity of the seizure ranged from brief muscle jerks to more serious episodes where the cat lost consciousness and stiffened and jerked for several minutes, the researchers report online today in the Journal of Feline Medicine and Surgery. Both pedigree and nonpedigree cats were susceptible, although one breed was common: Thirty of the 96 cats were Birmans (pictured). Because the seizures coincided with old age—the average age of onset was 15 years—veterinarians could miss the disorder while dealing with the felines’ other health issues, the researchers say. Minimizing exposure to the problematic sounds and preliminary, therapeutic trials with levetiracetam—an anticonvulsant medication used to control epilepsy—among a small sample of the cats seemed to help limit the occurrence of seizures. © 2015 American Association for the Advancement of Science.
by Helen Thomson Tinnitus is the debilitating sensation of a high-pitched noise without any apparent source. It can be permanent or fleeting, and affects at least 25 million people in the US alone. To understand more about the condition, William Sedley at the University of Newcastle, UK, and his colleagues took advantage of a rare opportunity to study brain activity in a man with tinnitus who was undergoing surgery for epilepsy. Surgeons placed recording electrodes in several areas of his brain to identify the source of his seizures. The man – who they knew as Bob (not his real name) – was awake during the procedure, which allowed Sedley's team to manipulate his tinnitus while recording from his brain. First they played him 30 seconds of white noise, which suppressed his tinnitus for about 10 seconds before it gradually returned. Bob was asked to rate the loudness of his tinnitus before the experiment started, as well as immediately after the white noise finished and 10 seconds later. This protocol was then repeated many times over two days. "Normally, studies compare brain activity of people with and without tinnitus using non-invasive techniques," says Sedley. "Not only are these measurements less precise, but the people with tinnitus might be concentrating on the sound, while the ones without tinnitus might be thinking about their lunch." This, he says, can make the results hard to interpret. © Copyright Reed Business Information Ltd
Link ID: 20847 - Posted: 04.25.2015
Hannah Devlin, science correspondent They may stop short of singing The Bells of Saint Mary’s, as demonstrated by the mouse organ in Monty Python, but scientists have discovered that male mice woo females with ultrasonic songs. The study shows for the first time that mouse song varies depending on the context and that male mice have a specific style of vocalisation reserved for when they smell a female in the vicinity. In turn, females appear to be more interested in this specific style of serenade than other types of squeak that male mice produce. “It was surprising to me how much change occurs to these songs in different social contexts, when the songs are thought to be innate,” said Erich Jarvis, who led the work at Duke University in North Carolina. “It is clear that the mouse’s ability to vocalise is a lot more limited than a songbird’s or human’s, and yet it’s remarkable that we can find these differences in song complexity.” The findings place mice in an elite group of animal vocalisers, that was once thought to be limited to birds, whales, and some primates. Mouse song is too high-pitched for the human ear to detect, but when listened to at a lower frequency, it sounds somewhere between birdsong and the noise of clean glass being scrubbed. The Duke University team recorded the male mice when they were roaming around their cages, when they were exposed to the smell of female urine and when they were placed in the presence of a female mouse. They found that males sing louder and more complex songs when they smell a female but don’t see her. By comparison, the songs were longer and simpler when they were directly addressing their potential mate, according to the findings published in Frontiers of Behavioural Neuroscience. © 2015 Guardian News and Media Limited