Chapter 6. Hearing, Balance, Taste, and Smell
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By Geoffrey Giller The experience of seeing a lightning bolt before hearing its associated thunder some seconds later provides a fairly obvious example of the differential speeds of light and sound. But most intervals between linked visual and auditory stimuli are so brief as to be imperceptible. A new study has found that we can glean distance information from these minimally discrepant arrival times nonetheless. In a pair of experiments at the University of Rochester, 12 subjects were shown projected clusters of dots. When a sound was played about 40 or 60 milliseconds after the dots appeared (too short to be detected consciously), participants judged the clusters to be farther away than clusters with simultaneous or preceding sounds. Philip Jaekl, the lead author of the study and a postdoctoral fellow in cognitive neuroscience, says it makes sense that the brain would use all available sensory information for calculating distance. “Distance is something that's very difficult to compute,” he explains. The study was recently published in the journal PLOS ONE. Aaron Seitz, a professor of psychology and neuroscience at the University of California, Riverside, who was not involved in the work, says the results may be useful clinically, such as by helping people with amblyopia (lazy eye) improve their performance when training to see with both eyes. And there might be other practical applications, including making virtual-reality environments more realistic. “Adding in a delay,” says Nick Whiting, a VR engineer for Epic Games, “can be another technique in our repertoire in creating believable experiences.” © 2016 Scientific American,
Link ID: 21807 - Posted: 01.21.2016
Bret Stetka In June of 2001 musician Peter Gabriel flew to Atlanta to make music with two apes. The jam went surprisingly well. At each session Gabriel, a known dabbler in experimental music and a founding member of the band Genesis, would riff with a small group of musicians. The bonobos – one named Panbanisha, the other Kanzi — were trained to play in response on keyboards and showed a surprising, if rudimentary, awareness of melody and rhythm. Since then Gabriel has been working with scientists to help better understand animal cognition, including musical perception. Plenty of related research has explored whether or not animals other than humans can recognize what we consider to be music – whether they can they find coherence in a series of sounds that could otherwise transmit as noise. Many do, to a degree. And it's not just apes that respond to song. Parrots reportedly demonstrate some degree of "entrainment," or the syncing up of brainwave patterns with an external rhythm; dolphins may — and I stress may — respond to Radiohead; and certain styles of music reportedly influence dog behavior (Wagner supposedly honed his operas based on the response of his Cavalier King Charles Spaniel). But most researchers agree that fully appreciating what we create and recognize as music is a primarily human phenomenon. Recent research hints at how the human brain is uniquely able to recognize and enjoy music — how we render simple ripples of vibrating air into visceral, emotional experiences. It turns out, the answer has a lot to do with timing. The work also reveals why your musician friends are sometimes more tolerant of really boring music. © 2015 npr
By C. CLAIBORNE RAY Q. We know that aquatic mammals communicate with one another, but what about fish? A. Fish have long been known to communicate by several silent mechanisms, but more recently researchers have found evidence that some species also use sound. It is well known that fish communicate by gesture and motion, as in the highly regimented synchronized swimming of schools of fish. Some species use electrical pulses as signals, and some use bioluminescence, like that of the firefly. Some kinds of fish also release chemicals that can be sensed by smell or taste. In 2011, a scientist in New Zealand suggested that what might be called fish vocalization has a role, at least in some ocean fish. In the widely publicized work, done for his doctoral thesis at the University of Auckland, Shahriman Ghazali recorded reef fish in the wild and in captivity, and found two dominant vocalizations, the croak and the purr, in choruses that lasted up to three hours, as well as a previously undescribed popping sound. The sounds of one species recorded in captivity — the bigeye, or Pempheris adspersa — carried 100 feet or more, and the researcher suggested it could be used to keep a group of fish together during nocturnal foraging. Another species, the bluefin gurnard, or Chelidonichthys kumu, was also very noisy, he found. “Vocalization” is a bit of a misnomer, as the sounds these fish make are produced by contracting and vibrating the swim bladder, not by using the mouth. © 2015 The New York Times Company
By Christopher Intagliata Back in ancient times, philosophers like Aristotle were already speculating about the origins of taste, and how the tongue sensed elemental tastes like sweet, bitter, salty and sour. "What we discovered just a few years ago is that there are regions of the brain—regions of the cortex—where particular fields of neurons represent these different tastes again, so there's a sweet field, a bitter field, a salty field, etcetera." Nick Ryba [pron. Reba], a sensory neuroscientist at the National Institutes of Health. Ryba and his colleagues found that you can actually taste without a tongue at all, simply by stimulating the "taste" part of the brain—the insular cortex. They ran the experiment in mice with a special sort of brain implant—a fiber-optic cable that turns neurons on with a pulse of laser light. And by switching on the "bitter" sensing part of the brain, they were able to make mice pucker up, as if they were tasting something bitter—even though absolutely nothing bitter was touching the tongues of the mice. In another experiment, the researchers fed the mice a bitter flavoring on their tongues—but then made it more palatable by switching on the "sweet" zone of the brain. "What we were doing here was adding the sweetness, but only adding it in the brain, not in what we were giving to the mouse." Think adding sugar to your coffee—but doing it only in your mind. The findings appear in the journal Nature. © 2015 Scientific American
Keyword: Chemical Senses (Smell & Taste)
Link ID: 21648 - Posted: 11.20.2015
Rachel England Brussels sprouts, Marmite, stinky cheese … these are all foods guaranteed to create divisions around the dinner table –and sometimes extreme reactions. A friend once ordered a baked camembert at dinner and I had to physically remove myself from the vicinity, such was its overpowering stench. Yet foods that once turned my stomach – mushrooms and prawns, in particular – now make a regular appearance on my plate. How is it that my opinion of a juicy grilled mushroom has gone from yuk to yum after 30 years of steadfast objection? And why is it that certain foods leave some diners gagging theatrically while others tuck in with vigour? Taste is a complicated business. In evolutionary terms we’re programmed to prefer sweeter flavours to bitter tastes: sweet ripe fruits provide a good source of nutrients and energy, for example, while bitter flavours can be found in dangerous plant toxins, which we’re better off avoiding. We’re also more likely to go for fatty foods with a high calorie count which would provide the energy needed for hunting our next meal. But now we live in a world where bitter vegetables such as kale reign supreme, kids salivate over eye-wateringly sour sweets and hunting dinner is as strenuous as picking up the phone. There are some environmental factors at play. When you eat something, molecules in the food hit your taste cells in such a way as to send a message to your brain causing one of five sensations: sweetness, saltiness, bitterness, sourness or umami (a loanword from Japanese meaning ‘pleasant savoury taste’). Mix up these taste cells and messages with external influences and the results can be dramatic. © 2015 Guardian News and Media Limited
Keyword: Chemical Senses (Smell & Taste)
Link ID: 21628 - Posted: 11.12.2015
Your sense of smell might be more important than you think. It could indicate how well your immune system is functioning, a study in mice suggests. Evidence of a connection between the immune system and the olfactory system – used for sense of smell – has been building for some time. For instance, women seem to prefer the scent of men with different immune system genes to their own. Meanwhile, other studies have hinted that the robustness of your immune system may influence how extraverted you are. To investigate further, Fulvio D’Acquisto at Queen Mary University of London and his colleagues studied mice missing a recombinant activating gene (RAG), which controls the development of immune cells. Without it, mice lack a working immune system and some genes are expressed differently, including those involved in the olfactory system. “That rang bells, because people with immune deficiencies often lose their sense of smell,” says D’Acquisto. Systemic lupus erythematosus, an autoimmune disease in which the immune system mistakenly attacks tissues in the skin, joints, kidneys, brain, and other organs, is one such example. His team measured how long it took mice to find chocolate chip cookies buried in their cages. Those missing RAG took five times as long as normal mice. They also failed to respond to the scent of almond or banana, which mice usually find very appealing – although they did still react to the scent of other mice. Further study uncovered abnormalities in the lining of their noses; physical evidence that their sense of smell might be disrupted. © Copyright Reed Business Information Ltd.
Nicole Fisher , We know that the brain is neuroplastic — adapts to changes in behavior, environment, thinking and emotions — and may even rewire itself in certain ways. Life experience also teaches us that the tongue is a learning tool that shapes our brain. During early development, babies test everything by placing it in their mouths. As children age they stick out their tongues when concentrating on tasks such as drawing. Even as adults we let our tongue tell us about the world around us through eating, drinking and kissing. During basketball games, some players stick out their tongues while shooting. Now, knowing that there is such a rich nerve connection to the brain, scientists and doctors are turning to the tongue as a way to possibly stimulate the brain for neural retraining and rehabilitation after traumatic injuries or disease. The team at Helius Medical Technologies believe combining physical therapy with stimulation of the tongue may improve impairment of brain function and associated symptoms of injury. “We have already seen that stimulation of various nerves can improve symptoms of a range of neurological diseases. However, we believe the tongue is a much more elegant and direct pathway for stimulating brain structures and inducing neuroplasticity. We are focused on investigating the tongue as a gateway to the brain to hopefully ease the disease of brain injury,” said Dr. Jonathan Sackier, CMO at Helius. It has been argued by some that the era of small molecule is gone. Instead, recognition that the entire body is a closed electrical circuit, is leading to new therapeutic modalities that are known in certain circles as “electroceuticals.”
By Diana Kwon Six years before her husband was diagnosed with Parkinson’s disease, a progressive neurodegenerative disorder marked by tremors and movement difficulties, Joy Milne detected a change in his scent. She later linked the subtle, musky odor to the disease when she joined the charity Parkinson’s UK and met others with the same, distinct smell. Being one of the most common age-related disorders, Parkinson’s affects an estimated seven million to 10 million people worldwide. Although there is currently no definitive diagnostic test, researchers hope that this newly found olfactory signature will lead help create one. Milne, a super-smeller from Perth, Scotland, wanted to share her ability with researchers. So when Tilo Kunath, a neuroscientist at the University of Edinburgh, gave a talk during a Parkinson’s UK event in 2012, she raised her hand during the Q&A session and claimed she was able to smell the disease. “I didn’t take her seriously at first,” Kunath says. “I said, ‘No, I never heard of that, next question please.’” But months later Kunath shared this anecdote with a colleague and received a surprising response. “She told me that that lady wasn’t wrong and that I should find her,” Kunath says. Once the researchers found Milne, they tested her claim by having her sniff 12 T-shirts: six that belonged to people with Parkinson’s and six from healthy individuals. Milne correctly identified 11 out of 12, but miscategorized one of the non-Parkinson’s T-shirts in the disease category. It turned out, however, she was not wrong at all—that person would be diagnosed with Parkinson’s less than a year later. © 2015 Scientific American
When we hear speech, electrical waves in our brain synchronise to the rhythm of the syllables, helping us to understand what’s being said. This happens when we listen to music too, and now we know some brains are better at syncing to the beat than others. Keith Doelling at New York University and his team recorded the brain waves of musicians and non-musicians while listening to music, and found that both groups synchronised two types of low-frequency brain waves, known as delta and theta, to the rhythm of the music. Synchronising our brain waves to music helps us decode it, says Doelling. The electrical waves collect the information from continuous music and break it into smaller chunks that we can process. But for particularly slow music, the non-musicians were less able to synchronise, with some volunteers saying they couldn’t keep track of these slower rhythms. Rather than natural talent, Doelling thinks musicians are more comfortable with slower tempos because of their musical training. As part of his own musical education, he remembers being taught to break down tempo into smaller subdivisions. He suggests that grouping shorter beats together in this way is what helps musicians to process slow music better. One theory is that musicians have heard and played much more music, allowing them to acquire “meta-knowledge”, such as a better understanding of how composers structure pieces. This could help them detect a broader range of tempos, says Usha Goswami of the University of Cambridge. © Copyright Reed Business Information Ltd.
By JAMES GORMAN No offense to tenors, but outside of opera, a high male voice is seldom, if ever, considered seductive. Scientific research has shown that women find deep male voices attractive, and the same is true in other species, like howler monkeys. Stories from Our Advertisers But evolution is often stingy in its gifts, and researchers investigating male competition to reproduce have discovered an intriguing trade-off in some species of howler monkeys: the deeper the call, the smaller the testicles. Jacob Dunn of Cambridge University, one of the leaders of the research, said that species evolved either to make lower-frequency sounds, or have larger testicles, but none had both a very low sound and very large testicles. “It’s a great study,” said Stuart Semple, an evolutionary anthropologist at the University of Roehampton in London who was not involved in the research. “It shows this really clear trade-off.” Dr. Dunn and other researchers, including W. Tecumseh Fitch, of the University of Vienna, and Leslie A. Knapp, of the University of Utah, studied the size of a bone in the vocal apparatus, which is directly related to how deep the calls are, and the size of testicles, to come up for averages in nine species of howlers. They had been intrigued by great variations in both the size of the howlers’ hyoid bones in museum collections and in the size of the monkeys’ testicles as seen in the field. Dr. Knapp said that some of them are large enough that they are quite obvious “when you look up into the trees.” They used the museum samples of the bone and living monkeys in zoos for testicle measurements, and reported their findings Thursday in the journal Current Biology. © 2015 The New York Times Company
By WILLIAM GRIMES The first show at the Museum of Food and Drink’s new space in Brooklyn is “Flavor: Making It and Faking It,” and it wastes no time in getting to the point. “What makes your favorite food so delicious?” the text on a large free-standing panel near the entrance asks. The one-word answer: “Chemicals.” The word is deflating. It’s a little like being told that the human soul has a specific atomic weight. Chemicals? Yuck. But maybe not. Flavors come in two varieties, natural and artificial, but what do the words really mean? This is the looming question in an exhibition about food and culture that opens next Wednesday, in a museum that until now has been a free-floating idea rather than a building with an address. The show follows the history of lab-created flavors from the middle of the 19th century, when German scientists created artificial vanilla, to the present day, when the culinary spin doctors known as flavorists tweak and blend the myriad tastes found in virtually every food product on supermarket shelves. Flavor is a complex, beguiling subject. At one of several “smell machines” throughout the exhibition, where specific aromas are emitted through silver hoses at the push of a button, visitors learn that coffee gets a little lift — the je ne sais quoi that makes it irresistible in the morning — from a sulfur compound also found in skunk spray. Tiny edible pellets distributed from gumball machines send the message in tactile form. This is an exhibition that is not just hands-on, but tongue-on and nostrils-on. © 2015 The New York Times Company
Keyword: Chemical Senses (Smell & Taste)
Link ID: 21536 - Posted: 10.21.2015
The invaders put on a disguise and infiltrate the nest with dark plans: to kill the queen and enslave the kingdom. Usually when ants take pupae from other colonies as future slaves all hell breaks loose in ensuing battles. The enslaved individuals sometimes even strike back against their overlords. It’s a relatively dramatic affair, usually resulting in the aggressive slave-makers carrying the pupae back to their own colony, says Terrence McGlynn at California State University. But a species of ant found in the eastern US, Temnothorax pilagens, does things differently. It is the first ant species known to waltz into a colony and enslave others without killing, and one of a few that take not only pupae but adult workers, too. “This was extremely surprising as ants are usually able to detect foreign species or even individuals from a different colony through their chemical profile and react aggressively towards them,” says Isabelle Kleeberg at Johannes Gutenberg-Universität Mainz, Germany, whose team has found how they get away with it. Kleeberg tracked the behaviour of T. pilagens and their preferred slave species, Temnothorax ambiguus, in 43 raiding experiments using colour-marked individuals. In each experiment the colonies of these two ant species, each housed in a plastic box, were placed 12 centimetres apart from each other. © Copyright Reed Business Information Ltd.
Using a sensitive new technology called single-cell RNA-seq on cells from mice, scientists have created the first high-resolution gene expression map of the newborn mouse inner ear. The findings provide new insight into how epithelial cells in the inner ear develop and differentiate into specialized cells that serve critical functions for hearing and maintaining balance. Understanding how these important cells form may provide a foundation for the potential development of cell-based therapies for treating hearing loss and balance disorders. The research was conducted by scientists at the National Institute on Deafness and Other Communication Disorders (NIDCD), part of the National Institutes of Health. In a companion study led by NIDCD-supported scientists at the University of Maryland School of Medicine and scientists at the Sackler School of Medicine at Tel Aviv University, researchers used a similar technique to identify a family of proteins critical for the development of inner ear cells. Both studies were published online on October 15 in the journal Nature Communications. “Age-related hearing loss occurs gradually in most of us as we grow older. It is one of the most common conditions among older adults, affecting half of people over age 75,” said James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. “These new findings may lead to new regenerative treatments for this critical public health issue.” Specialized sensory epithelial cells in the inner ear include hair cells and supporting cells, which provide the hair cells with crucial structural and functional support. Hair cells and supporting cells located in the cochlea — the snail-shaped structure in the inner ear — work together to detect sound, thus enabling us to hear. In contrast, hair cells and supporting cells in the utricle, a fluid-filled pouch near the cochlea, play a critical role in helping us maintain our balance.
By Nancy Szokan Sensory deprivation is Sushma Subramanian’s topic in the October issue of Women’s Health magazine, and she offers a couple of extreme examples. Julie Malloy, 33, from York, Pa., describes living without the sense of touch: “I was born with a rare sensory illness that leaves me unable to feel pain, temperature, deep pressure, or vibrations in my arms, legs, and the majority of my chest and back. I use vision to compensate as much as I can. . . . “I always wash my face with cold water; I once burned myself without realizing it. . . . When I drive, I can’t really tell how hard I’m pushing on the pedals. I watch others really enjoy it when someone kisses their arm or get tingly when someone hugs them, but I can’t even feel anything during sex.” Erin Napoleone, 31, from Havre de Grace, Md., describes losing her sense of smell: “As a teen, I was in a car accident. A few days later, I watched my father make homemade tomato sauce — but I didn’t smell a thing. Then I couldn’t detect my mom’s familiar perfume. A head CT scan confirmed my sense of smell was gone for good.” The magazine points out that some senses naturally deteriorate with age and that taking care of your skin — say, by keeping it moisturized and protecting it from damage — can help preserve the sense of touch. But olfactory nerves facing “prolonged exposure to rank odors (think freeway fumes or curbside trash)” can be permanently damaged.
Music can be a transformative experience, especially for your brain. Musicians’ brains respond more symmetrically to the music they listen to. And the size of the effect depends on which instrument they play. People who learn to play musical instruments can expect their brains to change in structure and function. When people are taught to play a piece of piano music, for example, the part of their brains that represents their finger movements gets bigger. Musicians are also better at identifying pitch and speech sounds – brain imaging studies suggest that this is because their brains respond more quickly and strongly to sound. Other research has found that the corpus callosum – the strip of tissue that connects the left and right hemisphere of the brain – is also larger in musicians. Might this mean that the two halves of a musician’s brain are better at communicating with each other compared with non-musicians? To find out, Iballa Burunat at the University of Jyväskylä in Finland and her colleagues used an fMRI scanner to look at the brains of 18 musicians and 18 people who have never played professionally. The professional musicians – all of whom had a degree in music – included cellists, violinists, keyboardists and bassoon and trombone players. While they were in the scanner, all of the participants were played three different pieces of music – prog rock, an Argentinian tango and some Stravinsky. Burunat recorded how their brains responded to the music, and used software to compare the activity of the left and right hemispheres of each person’s brain. © Copyright Reed Business Information Ltd.
Now hear this. Anthropologists have estimated the hearing abilities of early hominins – reconstructing a human ancestor’s sensory perception. Rolf Quam from Binghamton University in New York and his colleagues studied skulls and ear bones from Australopithecus africanus and Paranthropus robustus, two species that lived between 1 million and 3 million years ago, as well as modern humans and chimpanzees. Using CT scans of the bones, they built 3D reconstructions of the ear of each species. Then they fed a series of anatomical measurements into a computer model to predict their hearing abilities. The results for humans and chimpanzees fitted well with laboratory data, suggesting the model aligned well with real performance. For each species, they then estimated the frequency range they can hear best. Modern humans and chimpanzees perform similarly below 3 kilohertz, but humans have better hearing than chimps in the 3-5 kHz range. The early hominins had a similar sensitive range to chimpanzees, but shifted slightly towards that of modern humans, so they have better hearing than chimps do for 3-4 kHz sounds. Australopithecus and Paranthropus are not believed to have been capable of language, but they almost certainly communicated vocally as other primates do, says Quam. Quam thinks this shift in hearing sensitivity would have helped them communicate in open environments, such as African savannahs, where human ancestors are thought to have evolved bipedalism. © Copyright Reed Business Information Ltd.
Bill McQuay and Christopher Joyce Acoustic biologists who have learned to tune their ears to the sounds of life know there's a lot more to animal communication than just, "Hey, here I am!" or "I need a mate." From insects to elephants to people, we animals all use sound to function and converse in social groups — especially when the environment is dark, or underwater or heavily forested. "We think that we really know what's going on out there," says Dartmouth College biologist Laurel Symes, who studies crickets. But there's a cacophony all around us, she says, that's full of information still to be deciphered. "We're getting this tiny slice of all of the sound in the world." Recently scientists have pushed the field of bioacoustics even further, to record whole environments, not just the animals that live there. Some call this "acoustic ecology" — listening to the rain, streams, wind through the trees. A deciduous forest sounds different from a pine forest, for example, and that soundscape changes seasonally. Neuroscientist Seth Horowitz, author of the book The Universal Sense: How Hearing Shapes the Mind, is especially interested in the ways all these sounds, which are essentially vibrations, have shaped the evolution of the human brain. "Vibration sensitivity is found in even the most primitive life forms," Horowitz says — even bacteria. "It's so critical to your environment, knowing that something else is moving near you, whether it's a predator or it's food. Everywhere you go there is vibration and it tells you something." © 2015 NPR
Christopher Joyce Ornithologist Arthur Allen of the Cornell Lab or Ornithology was a pioneer, hauling balky recording gear into the wilderness in the 1940s, and actually cutting acetate records of bird song on-site. Let's fast forward 45 years, and talk to Ted Parker, who inherited Allen's gift for recording birds and but added a twist. "Up here in the canopy, these are the hardest birds to detect," he told an NPR Radio Expeditions team in 1991 in the Bolivian rain forest. Parker was an ornithologist with Conservation International who spent months at a time in the tropics, lugging around a portable tape recorder. His skill in using his ears to investigate the world was legendary. "My parents bought me records of bird recordings that were made by people at Cornell," Parker tells the NPR team in 1991. "I spent hours moving the needle back and forth, and back and forth, and my mother would say, 'You are going to destroy the record player.' " Some called Parker the Mozart of ornithology. He'd memorized the sounds of more than 4,000 bird species. He used this knowledge and his tape recorder to quickly take an extensive and detailed census of birds in the tropics. "These birds spend all their time in that foliage that's 130 to 140 feet above the ground," Parker explains on the tape. "And if you don't know their voices, there's no way you could come to a place like this and come up with a good list of canopy species." © 2015 NPR
They are rather diminutive to be kings of the jungle, but two species of mirid bug make sounds similar to the roars of big cats. These calls have never before been heard in insects, and we’re not sure why, or how, the insects produce the eerie calls. The roars are too weak to be heard by humans without a bit of help. But Valerio Mazzoni of the Edmund Mach Foundation in Italy and his team made them audible by amplifying them using a device called a laser vibrometer. The device detects the minute vibrations that the bugs produce on the leaves on which they live. “When you listen to these sounds through headphones you’d think you were next to a tiger or lion,” Mazzoni. The team found that when two males were introduced on the same leaf, they seemed to compete in roaring duets. When one insect heard a roar, it always sounded its own, apparently in response. This suggests that, as in big cats, the roars might serve to establish dominance or attract females. Female mirids don’t seem to roar. But unlike the roars of big cats, the sounds produced by bugs are transmitted through the solid material beneath their feet, usually a leaf, rather than by the vibration of air molecules. Thousands of insect species communicate through such vibration, but these roars are unlike any other known insect noise. © Copyright Reed Business Information Ltd.
Nell Greenfieldboyce Picking a mate can be one of life's most important decisions. But sometimes people make a choice that seems to make no sense at all. And humans aren't the only ones — scientists have now seen apparently irrational romantic decisions in frogs. Little tungara frogs live in Central America, and they're found everywhere from forests to ditches to parking lot puddles. These frogs are only about 2 centimeters long, but they are loud. The males make calls to woo the females. Amanda Lea, a biologist in the laboratory of Mike Ryan at the University of Texas, Austin, says past studies have given scientists a pretty good idea of what the females find appealing. "They tend to like longer calls. They also like lower-frequency calls," says Lea. "Then, the other thing that's a really big one for these gals is the 'call rate.' They love faster call rates. The faster a male can call, the better." But in real life, love is complicated. Female frogs face countless suitors. So Lea and Ryan wondered: Would a female really always pick the male that scored highest on the froggy love-call meter? To find out, they put female frogs in a room with some loudspeakers. From one speaker the scientists played a recording of frog call that had a really fast rate. But other features in this voice were less attractive. Then the researchers played a second, different call for the female frogs. This voice was more attractive, but it was slower. The ladies had to make a choice. "They have two traits to evaluate," Lea explains. "They have the call rate and they have the attractiveness of the call." © 2015 NPR