How We Hear

While the visual regions of the brain have been intensively mapped, many important regions for auditory processing remain "uncharted territory." Now, researchers at the Hebrew University of Jerusalem and elsewhere have identified a region responsible for a key auditory process-perceiving "sound space," the location of sounds, even when the listener is not concentrating on those sounds. The findings settle a controversy in earlier studies that failed to establish the auditory region, called the planum temporale, as responsible for perception of auditory space by default. Full Story

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How Your Brain Focuses on Certain Sounds

September 2007

On September 19, a research report by Helsinki University of Technology, Laboratory of Computational Engineering scientists appeared in the online, open-access journal PLoS ONE (Public Library of Science), showing that selective attention increases both gain and feature selectivity of the human auditory cortex. The ability to select task-relevant sounds for awareness, while ignoring irrelevant ones, constitutes one of the most fundamental of human faculties, but the underlying neural mechanisms have remained elusive. While most of the literature explains the neural basis of selective attention by means of an increase in neural gain, a number of papers propose enhancement in neural selectivity as an alternative or a complementary mechanism. Full Story

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The acute effects of alcohol on auditory thresholds

October 2007

There is very little knowledge about alcohol-induced hearing loss. Alcohol consumption and tolerance to loud noise is a well observed phenomenon as seen in the Western world where parties get noisier by the hour as the evening matures. This leads to increase in the referrals to the "hearing aid clinic" and the diagnosis of "cocktail party deafness" which may not necessarily be only due to presbyacusis or noise-induced hearing loss. Full Story

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Good Hearing Dooms Young Loiterers

October 2007

The mosquito is no longer just a blood-sucking pest -- it is also the name of an ultra-sonic teenage deterrent system that is being introduced to the Regina market. Using a high-frequency tone, the device annoys youths and deters them from loitering and being in its general vicinity within minutes of activation. It has been used in the United Kingdom since 2005 and is now being implemented in Canadian markets, such as Vancouver, and it might make its debut in Saskatchewan very soon. "It is currently being used at convenience stores, schools, pubs, and malls," Michael Gibson of Moving Sound Technologies said Friday from Vancouver. "Store owners are using the devices to get kids that are hanging out in front of stores and (hurting business) to leave the storefront." Gibson said his company has installed these devices in four locations of a large convenience store chain in Vancouver and Victoria that had unwanted traffic. He said store patrons simply weren't going into the store because they didn't want to encounter unwanted people hanging around outside. Full Story

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Non-nerve cells key for development of hearing

November 2007

New research indicates that non-nerve cells play a critical role in stimulating auditory nerve firing in the absence of sound, in preparation for the development of hearing. "It was known that this 'spontaneous' activity helps auditory nerves make proper connections with other nerve cells in the brain, which enables the accurate encoding of sound; however, the trigger that initiates this activity was not known," senior author Dr. Dwight E. Bergles told Reuters Health. "We discovered that non-nerve cells in the developing inner ear stimulate electrical activity in nerves that carry sound information from the ear to the brain." Dr. Bergles, from the Johns Hopkins School of Medicine in Baltimore, said the discovery that non-nerve cells were involved in the initial stimulatory activity was particularly surprising since it had been thought that these cells were merely bystanders. Full Story

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Hearing Chemicals More Complicated Than Scientists Thought

December 2007

While neurotrophins have historically been prized for the survival value they impart to nerve cells, the researchers found that in the cochlea they do a great deal more. Their presence in relative proportions transforms the spiral ganglion neurons into either fast-firing transmitters to carry high-pitched sound messages to the brain, or slow-firing carriers for the transmission of lower pitched signals. The neurotrophins accomplish this at the molecular level by tightly regulating a newly defined and complex series of signaling proteins. Davis explained that one end of the cochlea is home to the slower-firing neurons characterized by a preponderance of NT-3, while the other cochlear end is rich in BDNF, making those neurons faster-firing. Both neurotrophins are present in gradients throughout the range, but at any specific locale their amounts vary relative to each other - lots of BDNF and a little NT-3 in the high frequency transmitters, for example, and the reverse as you move toward the other end. Full Story

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The Cocktail Party Effect

September 2008

Researchers study animal behavior to help humans better cut through the chatter.

The next time you attend a cocktail party, notice how quickly everyone instinctively raises their voice as the room begins to fill with many speakers, each focused on different conversational partners. Thanks to the so-called "cocktail party effect," most of us are able to filter out the background chatter and pick out that particular voice of greatest interest. This ability to selectively respond even as infants to auditory stimuli embedded in noise is not unique to humans. Many animals, such as penguins, fish and frogs, share with us this remarkable skill. Full Story

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Listener's Brain Predicts Speaker's Words

September 2008

Scientists at the University of Rochester in New York have shown for the first time that our brains automatically consider many possible words and their meanings before we've even heard the final sound of the word. Previous theories have proposed that listeners can only keep pace with the rapid rate of spoken language - up to five syllables per second - by anticipating a small subset of all words known by the listener, much like Google search anticipates words and phrases as you type. This subset consists of all words that begin with the same sounds, such as "candle," "candy," and "cantaloupe," and makes the task of understanding the specific word more efficient than waiting until all the sounds of the word have been presented. But until now, researchers had no way to know if the brain also considers the meanings of these possible words. The new findings are the first time that scientists, using an MRI scanner, have been able to actually see this split-second brain activity. The study was a team effort among former Rochester graduate student Kathleen Pirog Revill, now a postdoctoral researcher at Georgia Tech, and three faculty members in the Department of Brain and Cognitive Sciences at the University of Rochester. Full Story

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Prosthetic Ears Improve Hearing and Speech Recognition

October 2008

Prosthetic ears appear to improve hearing and speech recognition in noisy environments, according to a report in the September/October issue of Archives of Facial Plastic Surgery, one of the JAMA/Archives journals. Some patients require prosthetic ears because their pinna (outer ear) was removed during surgery for cancer or damaged by trauma, according to background information in the article. "Their external auditory canal is usually intact, and the remainder of their auditory system should function normally," the authors write. "In these patients, the physician must strive not only to correct the aesthetic defect caused by the missing pinna but also to correct the hearing loss caused by its absence." William E. Walsh, MD, CMI, of Northwestern University Feinberg School of Medicine, Chicago, and colleagues analyzed eight different silicone rubber prostheses in a two-part study. In the first part, the researchers used a life-sized plastic foam head with a 12-millimeter hole drilled through at the location of the external auditory canal. A microphone was placed at the entrance of the ear canal to measure sound pressure levels both with and without the prosthesis while the head was rotated 360° in 30° increments. Full Story

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Hard to hear at holiday parties? Blame your brain

January 2009

It's almost New Year's Eve, a time for plunging into boisterous crowds bathed in loud music. And for some of us, that means turning to an old friend and hearing things like this: "Did you know (BOOM-da-da-BOOM) went over (Bob! You look wonder-) so she said (clink-clink) and then I (Here, have another one) what would you do?" Huh? Too noisy to hear! But wait - how come these younger people understood what she said? What's wrong with your ears? Actually, part of the problem may be your brain. In fact, it may lie in your brain's dimmer switch for controlling the input from your ears. That bit of brain circuitry appears to falter with age, and scientists are getting some clues about why. Full Story

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Cochlear Dead Zones: What are they and what do you do about them?

March 2009

I've heard a lot about "cochlear dead regions," but I'd like to hear exactly how you define them?

Sure, here goes. They are regions in the cochlea where the inner hair cells and/or the neurons are effectively not functioning at all. As you probably know, the inner hair cells are laid out in a row along the length of the basilar membrane. Each inner hair cell normally responds to the vibration of the basilar membrane in the region where it is located. Each region or place is tuned and responds most strongly to one specific frequency, which is called the characteristic frequency (CF). The CF is low toward the apex of the cochlea and high toward the base. This is sometimes called tonotopic organization, or frequency-to-place mapping. When the inner hair cells and/or neurons are not functioning at a given place along the basilar membrane, then no information about the basilar membrane at that place is transmitted to the brain. It is as if there is an infinite hearing loss at that place. This is what I call a dead region. Often, when the inner hair cells are badly damaged or nonfunctioning, the neurons connecting to them degenerate. Full Story

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Hearing Through Your Bones

May 2009

"The Air Force is interested in reducing hearing loss, by building better hearing protection devices for people that work in very noisy environments, which means under airplanes," Wismer said. "The Air Force wants to know all the pathways by which sound can reach the ear and cause damage to hearing, because even if you block the air pathways, noise can still reach the eardrum through these bones." The fact that sound travels through the skull has been recognized for ages. Beethoven, for example, found a way to hear music through his jaw after he became deaf, by biting a rod attached to his piano. Bone-conducted hearing also explains why we sound strange to ourselves on a recording: we're used to hearing our voice through bone-conducted sound-waves; when it comes exclusively through our ear canal, our voice seems distorted. Despite extensive study, however, the phenomenon is not well understood. Full Story

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Humans Hear Better Than Some Animals

May 2009

In the savage world of nature, the ability to hear - and hear well - is a survival trait. Many animals rely on their keen sense of hearing to detect danger lurking in the savannah brush. Some animals have hearing mechanisms like humans. Others hear with their entire bodies. And although many animals have very sophisticated acute hearing for survival reasons, a recent study demonstrated humans actually can distinguish between pitch better than other animals. Full Story

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When an Ear Witness Decides the Case

June 2009

Spoken clearly, the sounds "dah" and "bah" are easy to distinguish. Yet if you play a film clip in which the soundtrack says "dah" while the image on the screen shows a mouth saying "bah," people will swear they heard "bah." If you ask people to count the number of times that a light flashes, and you flash the light seven times together with a sequence of eight beeping tones, people will say the light flashed eight times. When confronted with conflicting pieces of information, the brain decides which sense to trust. In the first scenario, those clearly percussing lips could never be articulating a "d," and so vision claimed the upper hand. But on matters that demand a temporal analysis, and making sense of similar sounds in a sequence, the brain reflexively counts on hearing. Click click click. You can listen to a series of clicks at 20 beats per second and know they are separate clicks rather than a single continuous tone. Run a series of images together at 20 frames per second and - welcome to the movies. Full Story

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Studies Demonstrate Human Preference For Listening With Right Ear

July 2009

In a series of three studies looking at ear preference in communication between humans, Dr. Luca Tommasi and Daniele Marzoli from the University "Gabriele d'Annunzio" have shown that a natural side bias, depending on hemispheric asymmetry in the brain, manifests itself in everyday human behavior. Their findings were just published online in the Springer Science journal Naturwissenschaften. One of the best known asymmetries in humans is the right ear dominance for listening to verbal stimuli, which is believed to reflect the brain's left hemisphere superiority for processing verbal information. However, until now, the majority of studies looking at ear preference in human communication have been controlled laboratory studies and there is very little published observational evidence of spontaneous ear dominance in everyday human behavior. Tommasi and Marzoli's three studies specifically observed ear preference during social interactions in noisy nightclub environments. Full Story

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Where's that sound coming from?

July 2009

Where's that sound coming from? Thanks to stereophonic hearing and fast-operating brain circuitry, most people with properly functioning ears can detect almost instantaneously where sounds originate. But how? Gaining an understanding of how the brain accomplishes this task is the aim of Michael Burger, Ph.D., assistant professor of neuroscience at Lehigh University in Bethlehem, Penn. Full Story

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Hearing Loss and the Perception of Speech

November 2009

A general strategy underlying hearing aid design is the selective amplification of portions of the input sound spectrum to compensate for a loss of hearing sensitivity. Major advances in engineering and fitting procedures have resulted in more successful hearing aid use in recent years (Kochkin, 2005). Nevertheless, the effortless understanding of speech enjoyed by people with normal hearing is not realized by many individuals with sensorineural hearing loss-even with amplification-because the effects of the loss are not limited to a reduction in sensitivity. Full Story