NEW ORLEANS (AP) — Two nonprofits named for children with the most common genetic cause of combined deafness and blindness have given $70,000 to continue research into Usher syndrome at the LSU Health Sciences Center New Orleans.
Following are a selection of interesting news items from our field. This section will be updated on a continuous basis so check back often in between issues, to see what is new.
David L. Chandler, MIT News Office
Even in a crowded room full of background noise, the human ear is remarkably adept at tuning in to a single voice — a feat that has proved remarkably difficult for computers to match. A new analysis of the underlying mechanisms, conducted by researchers at MIT, has provided insights that could ultimately lead to better machine hearing, and perhaps to better hearing aids as well.
Our ears’ selectivity, it turns out, arises from evolution’s precise tuning of a tiny membrane, inside the inner ear, called the tectorial membrane. The viscosity of this membrane — its firmness, or lack thereof — depends on the size and distribution of tiny pores, just a few tens of nanometers wide. This, in turn, provides mechanical filtering that helps to sort out specific sounds.
The new findings are reported in the Biophysical Journal by a team led by MIT graduate student Jonathan Sellon, and including research scientist Roozbeh Ghaffari, former graduate student Shirin Farrahi, and professor of electrical engineering Dennis Freeman. The team collaborated with biologist Guy Richardson of the University of Sussex.
In discriminating among competing sounds, the human ear is “extraordinary compared to conventional speech- and sound-recognition technologies,” Freeman says. The exact reasons have remained elusive — but the importance of the tectorial membrane, located inside the cochlea, or inner ear, has become clear in recent years, largely through the work of Freeman and his colleagues. Now it seems that a flawed assumption contributed to the longstanding difficulty in understanding the importance of this membrane.
Much of our ability to differentiate among sounds is frequency-based, Freeman says — so researchers had “assumed that the better we could resolve frequency, the better we could hear.” But this assumption turns out not always to be true.
In fact, Freeman and his co-authors previously found that tectorial membranes with a certain genetic defect are actually highly sensitive to variations in frequency — and the result is worse hearing, not better.
The MIT team found “a fundamental tradeoff between how well you can resolve different frequencies and how long it takes to do it,” Freeman explains. That makes the finer frequency discrimination too slow to be useful in real-world sound selectivity.
Too fast for neurons
Previous work by Freeman and colleagues has shown that the tectorial membrane plays a fundamental role in sound discrimination by carrying waves that stimulate a particular kind of sensory receptor. This process is essential in deciphering competing sounds, but it takes place too quickly for neural processes to keep pace. Nature, over the course of evolution, appears to have produced a very effective electromechanical system, Freeman says, that can keep up with the speed of these sound waves.
The new work explains how the membrane’s structure determines how well it filters sound. The team studied two genetic variants that cause nanopores within the tectorial membrane to be smaller or larger than normal. The pore size affects the viscosity of the membrane and its sensitivity to different frequencies.
The tectorial membrane is spongelike, riddled with tiny pores. By studying how its viscosity varies with pore size, the team was able to determine that the typical pore size observed in mice — about 40 nanometers across — represents an optimal size for combining frequency discrimination with overall sensitivity. Pores that are larger or smaller impair hearing.
“It really changes the way we think about this structure,” Ghaffari says. The new findings show that fluid viscosity and pores are actually essential to its performance. Changing the sizes of tectorial membrane nanopores, via biochemical manipulation or other means, can provide unique ways to alter hearing sensitivity and frequency discrimination.
William Brownell, a professor of otolaryngology at Baylor College of Medicine, says, “This is the first study to suggest that porosity may affect cochlear tuning.” This work, he adds, “could provide insight” into the development of specific hearing problems.
The research was supported by the National Institutes of Health; the National Science Foundation; and the Wellcome Trust.
Reprinted with permission of MIT News
Psychology Study Examines How Brains Process and Recall Sounds
Remember that sound bite you heard on the radio this morning? The grocery items your spouse asked you to pick up? Chances are, you won’t.
Researchers at the University of Iowa have found that when it comes to memory, we don’t remember things we hear nearly as well as things we see or touch.
“As it turns out, there is merit to the Chinese proverb ‘I hear, and I forget; I see, and I remember,” says lead author of the study and UI graduate student, James Bigelow.
“We tend to think that the parts of our brain wired for memory are integrated. But our findings indicate our brain may use separate pathways to process information. Even more, our study suggests the brain may process auditory information differently than visual and tactile information, and alternative strategies—such as increased mental repetition—may be needed when trying to improve memory,” says Amy Poremba, associate professor in the UI Department of Psychology and corresponding author on the paper, published this week in the journal PLoS One.
Bigelow and Poremba discovered that when more than 100 UI undergraduate students were exposed to a variety of sounds, visuals, and things that could be felt, the students were least apt to remember the sounds they had heard.
In an experiment testing short-term memory, participants were asked to listen to pure tones they heard through headphones, look at various shades of red squares, and feel low-intensity vibrations by gripping an aluminum bar. Each set of tones, squares and vibrations was separated by time delays ranging from one to 32 seconds.
Although students’ memory declined across the board when time delays grew longer, the decline was much greater for sounds, and began as early as four to eight seconds after being exposed to them.
While this seems like a short time span, it’s akin to forgetting a phone number that wasn’t written down, notes Poremba. “If someone gives you a number, and you dial it right away, you are usually fine. But do anything in between, and the odds are you will have forgotten it,” she says.
In a second experiment, Bigelow and Poremba tested participants’ memory using things they might encounter on an everyday basis. Students listened to audio recordings of dogs barking, watched silent videos of a basketball game, and touched and held common objects blocked from view, such as a coffee mug. The researchers found that between an hour and a week later, students were worse at remembering the sounds they had heard, but their memory for visual scenes and tactile objects was about the same.
Both experiments suggest that the way your mind processes and stores sound may be different from the way it process and stores other types of memories. And that could have big implications for educators, design engineers, and advertisers alike.
“As teachers, we want to assume students will remember everything we say. But if you really want something to be memorable you may need to include a visual or hands-on experience, in addition to auditory information,” says Poremba.
Previous research has suggested that humans may have superior visual memory, and that hearing words associated with sounds—rather than hearing the sounds alone—may aid memory. Bigelow and Poremba’s study builds upon those findings by confirming that, indeed, we remember less of what we hear, regardless of whether sounds are linked to words.
The study also is the first to show that our ability to remember what we touch is roughly equal to our ability to remember what we see. The finding is important, because experiments with nonhuman primates such as monkeys and chimpanzees have shown that they similarly excel at visual and tactile memory tasks, but struggle with auditory tasks. Based on these observations, the authors believe humans’ weakness for remembering sounds likely has its roots in the evolution of the primate brain.
The study was funded in part by the National Institutes of Health’s National Institute on Deafness and Other Communication Disorders (grant number DC0007156).
The paper is available online at http://dx.plos.org/10.1371/journal.pone.0089914.
Doctors at Great Ormond Street Hospital in London are Aiming to Reconstruct People’s Faces with Stem Cells Taken from Their Fat
The team has grown cartilage in the laboratory and believe it could be used to rebuild ears and noses.
They say the technique, published in the journal Nanomedicine, could revolutionise care.
Experts said there was some way to go, but it had the potential to be "transformative."
The team envisage an alternative - a tiny sample of fat would be taken from the child and stem cells would be extracted and grown from it.
An ear-shaped "scaffold" would be placed in the stem cell broth so the cells would take on the desired shape and structure. And chemicals would be used to persuade the stem cells to transform into cartilage cells.
Researchers at Karolinska Institutet in Sweden have identified a biological circadian clock in the hearing organ, the cochlea. This circadian clock controls how well hearing damage may heal and opens up a new way of treating people with hearing disabilities.
A research team from the University of Leicester investigating tinnitus has found new insights into the link between the exposure to loud sounds and hearing loss. Their study, published in the February 12 edition of Journal of Neuroscience helps to explain how damage to myelin— a protection sheet around cells — alters the transmission of auditory signals occurring during hearing loss.
Stonehenge has been the source of endless speculation since the strange formation of rocks was first discovered.
But a new theory may be the most interesting of all, with some now saying the rocks at Stonehenge were chosen because of their acoustic properties.
Some animals, like humans, can sense and respond to a musical beat, a finding that has implications for understanding how the skill evolved,
A study of bonobos, closely related to chimpanzees, shows they have an innate ability to match tempo and synchronize a beat with human experimenters.
Tinnitus Study Signals New Advance In Understanding Link Between Exposure To Loud Sounds And Hearing Loss
Research reveals why hearing loss is correlated with auditory signals failing to get transmitted along the auditory nerve.
A research team investigating tinnitus, from the University of Leicester, has revealed new insights into the link between the exposure to loud sounds and hearing loss.
Their study, published this week in J Neurosci, helps to understand how damage to myelin -- a protection sheet around cells -- alters the transmission of auditory signals occurring during hearing loss.
Having difficulty listening to conversations in noisy cafes and social gatherings could soon be a thing of the past for the hearing impaired, due to technology that cuts through background noise, according to a press release from the HEARing Cooperative Research Centre (HEARing CRC) at the University of Melbourne in Australia. The technology was developed by researchers at the HEARing CRC, the university, and the National Acoustic Laboratories (NAL) in Sydney, and initial testing has shown it can improve speech understanding in noisy environments by up to 50% for hearing aid users.