Friday, December 4, 2009

AUDITORY ILLUSION: HOW OUR BRAINS CAN FILL IN THE GAPS TO CREATE CONTINUOUS SOUND

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It is relatively common for listeners to "hear" sounds that are not really there. In fact, it is the brain's ability to reconstruct fragmented sounds that allows us to successfully carry on a conversation in a noisy room. Now, a new study helps to explain what happens in the brain that allows us to perceive a physically interrupted sound as being continuous. The research, published by Cell Press in the November 25 issue of Neuron provides fascinating insight into the constructive nature of human hearing.

"In our day-to-day lives, sounds we wish to pay attention to may be distorted or masked by background noise, which means that some of the information gets lost. In spite of this, our brains manage to fill in the information gaps, giving us an overall 'image' of the sound," explains senior study author, Dr. Lars Riecke from the Department of Cognitive Neuroscience at Maastricht University in The Netherlands. Dr. Riecke and colleagues were interested in unraveling the neural mechanisms associated with this auditory continuity illusion, where a physically interrupted sound is heard as continuing through background noise.

The researchers investigated the timing of sensory-perceptual processes associated with the encoding of physically interrupted sounds and their auditory restoration, respectively, by combining behavioral measures where a participant rated the continuity of a tone, with simultaneous measures of electrical activity in the brain. Interestingly, slow brain waves called theta oscillations, which are involved in encoding boundaries of sounds, were suppressed during an interruption in a sound when that sound was illusorily restored. "It was as if a physically uninterrupted sound was encoded in the brain," says Dr. Riecke. This restoration-related suppression was most obvious in the right auditory cortex.

Taken together, the findings reveal a novel mechanism that enhances our understanding of the constructive nature of human hearing. "Our results revealed that spontaneous modulations in slow evoked auditory cortical oscillations may determine the perceived continuity of fragmented sounds in noise," concludes Dr. Riecke. Interestingly, the suppressive effect was present before an illusorily filled gap and reached maximum shortly after the gap's actual onset, suggesting that the mechanism may work rapidly or anticipatorily and thereby facilitate stable hearing of fragmented sounds in natural environments. The authors also suggest that their results might inspire future design of devices to assist people with hearing deficits.

Cell Press

THE CAUSE BEHIND THE CHARACTERISTIC SHAPE OF A LONG LEAF REVEALED

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Applied mathematicians dissected the morphology of the plantain lily (Hosta lancifolia), a characteristic long leaf with a saddle-like arc midsection and closely packed ripples along the edges. The simple cause of the lily's fan-like shape—elastic relaxation resulting from bending during differential growth—was revealed by using an equally simple technique, stretching foam ribbons.

Haiyi Liang, a postdoctoral student at Harvard's School of Engineering and Applied Sciences (SEAS), and L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics at SEAS and a core faculty member of the Wyss Institute for Biologically Inspired Engineering, were inspired to study the formation of laminae (thin leaf-like structures) because they are so commonplace in biology.

The work had its origins in conversations that Mahadevan had with experimental biologists Mimi Koehl at the University of California, Berkeley and Wendy Silk from the University of California, Davis, who showed him examples of such morphologies in long submarine algal blades.

"These blades have rippled edges when they grow in slowly moving water. When they are transplanted to environments that have rapidly moving water, they generate new blades which are much narrower," says Mahadevan. "This example of phenotypic plasticity, or the ability of the algae to change their shape in response to environmental forces, led to a paper co-authored with Koehl and Silk last year that focused primarily on the experimental findings."

Inspired by this, Mahadevan and Liang developed an analog model to understand how a long leaf is formed by pulling flat, foam ribbons, measuring approximately 4.3" x 1.5" (about the size of a large bookmark), beyond their elastic limit and then letting them go. These stretching strains were applied preferentially to the horizontal edges so that the foam ribbon naturally forms a saddle-like shape when it relaxes. In the same scenario, but with a four-fold increase of strain on the horizontal edges, ripples will form along the edges, producing a series of small undulating waves.

An equivalent growth-induced strain, highest along the edges and lessening toward the middle, occurs as a long leaf grows, leading to the elegant arc and serrated surface of the leaves in plants like the lily. This effect is widely seen, says Mahadevan, in a variety of common objects and activities.

"When knitting a scarf, as the number of stitches is increased as the knitter moves away from the center, the material forms a saddle shape. As the edge length becomes much larger ripples begin to appear. The same effect can be seen when thin potato slices are dropped into hot oil to make chips. You end up with a bulbous middle and wrinkled edges," he explains.

The researchers also dissected the leaves of the plantain lily to show that elastic strain resulting from differential growth led to the patterns seen in real leaves. From this simple experiment, the researchers then developed a mathematical model explaining the shape, using a combination of scaling concepts, stability analysis, and numerical simulations.

"While the phenomena has been studied previously, researchers did not consider the role of finite size of a leaf on the stability or the effect of boundaries. Further, our study characterizes, mathematically, the range of parameters that quantify the shape and diversity in leaf morphology," adds Mahadevan.

The resulting model has application in understanding a variety of artificial systems such as non-uniform thermal expansion, hydraulic swelling, and plasticity induced shape changes in thin laminae.

(Photo: Haiyi Liang and L. Mahadevan, Harvard School of Engineering and Applied Sciences)

Harvard University

A MECHANICAL MODEL OF VOCALIZATION

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When people speak, sing, or shout, they produce sound by pushing air over their vocal folds -- bits of muscle and tissue that manipulate the air flow and vibrate within it. When someone has polyps or some other problem with their vocal folds, the airflow can be altered, affecting the sound production.

"Voice disorders affect 30 percent of the general population and up to 60 percent of educators," says Plesniak. "The objective of our work is to develop a detailed understanding of the phonation process, which will enable the development of computational models."

Wanting to better characterize the physics of this process, George Washington University professor Michael Plesniak and his doctoral student Byron Erath teamed up with speech pathologists a few years ago, while Plesniak was at Purdue University, to investigate the velocity field and flow structures in the airflow that occur when a person speaks.

Plesniak and his students constructed a mechanical model of the vocal folds that had motorized, programmable components that can alter their shape and motion in various ways to mimic vocal folds. By placing this model in a wind tunnel, they examine normal vocalization and common pathologies like the formation of polyps and cysts.

An important feature of the model, says Plesniak, is that it is seven-and-a-half times larger than the actual physiology, which allows the dynamics to be studied in greater detail. The ultimate goal, he adds, is to create tools to help surgeons make preoperative assessments of how a vocal tract surgery will affect an individual's voice.

American Institute of Physics

MYSTERIOUSLY WARM TIMES IN ANTARCTICA

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A new study of Antarctica's past climate reveals that temperatures during the warm periods between ice ages (interglacials) may have been higher than previously thought. The latest analysis of ice core records suggests that Antarctic temperatures may have been up to 6°C warmer than the present day.

The findings, reported by scientists from the British Antarctic Survey (BAS), the Open University and University of Bristol in the journal Nature could help us understand more about rapid Antarctic climate changes.

Previous analysis of ice cores has shown that the climate consists of ice ages and warmer interglacial periods roughly every 100,000 years. This new investigation shows temperature 'spikes' within some of the interglacial periods over the last 340,000 years. This suggests Antarctic temperature shows a high level of sensitivity to greenhouse gases at levels similar to those found today.

Lead author Louise Sime of British Antarctic Survey said,

"We didn't expect to see such warm temperatures, and we don't yet know in detail what caused them. But they indicate that Antarctica's climate may have undergone rapid shifts during past periods of high CO2."

During the last warm period, about 125,000 years ago, sea level was around 5 metres higher than today.

Ice core scientist Eric Wolff of British Antarctic Survey is a world-leading expert on past climate. He said,

"If we can pin down how much warmer temperatures were in Antarctica and Greenland at this time, then we can test predictions of how melting of the large ice sheets may contribute to sea level rise."

The Natural Environment Research Council (NERC)
British Antarctic Survey (BAS)

PEOPLE WORK HARDER WHEN EXPECTING A FUTURE CHALLENGING TASK

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Consumers will work harder on a task if they're expecting to have to do something difficult at a later time, according to a new study in the Journal of Consumer Research.

In today's fast-paced world, consumers frequently undertake unrelated tasks in a sequence. An individual might make a grocery list, decide whether to take out a home improvement loan, search the Internet for a vacation spot, and choose a dinner location—all before preparing lunch. "It seems reasonable to expect that when consumers know that they will have to work hard on a future task, they will devote less effort to the current task, in order to save energy for the upcoming demanding task. This is not what we found," write authors Anick Bosmans, Rik Pieters (both Tilburg University, The Netherlands), and Hans Baumgartner (Pennsylvania State University).

In a series of five studies, the authors observed that the more difficult a future task was expected to be, the harder consumers worked on a current task. "For example, consumers consulted more information on a web page when they were asked to evaluate a new soft drink when they expected that they would later on have to work on a difficult and demanding task," write the authors. Other participants were better able to come up with weight loss ideas when they believed they would have to work hard on a future job.

The authors titled the phenomenon the "get ready mindset." "People seem to prepare themselves mentally for upcoming tasks, but in doing so, the resources that are freed up for the future task carry over to current tasks," the authors explain. "We found consistent evidence that if the mind gets ready to perform later, it is set to go now."

The authors found that the "get ready mindset" can be attenuated and even reversed when people are better at separating tasks, either because the situation helps then to do so or because they are habitually better at keeping tasks separate.

"These results imply that the amount of effort that consumers will invest in the decision-making process (such a searching for information, generating ideas, or evaluating alternatives) is dependent upon the anticipated difficulty level of future tasks," the authors conclude.

University of Chicago

IS 80-YEAR-OLD MISTAKE LEADING TO FIRST SPECIES TO BE FISHED TO EXTINCTION?

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A species of common skate is to become the first marine fish species to be driven to extinction by commercial fishing, due to an error of species classification 80 years ago, reveals research published in the journal Aquatic Conservation.

The European common skate, Dipturus batis, has been on the World Conservation Union's Red List of Threatened Species since 2006, with France currently being responsible for 60.2% of reported landings. These catches are predominantly registered under the name 'D.batis,' however researchers, led by Dr Samuel Iglésias, show that 'D. batis' is in fact two clearly distinct species which have been incorrectly categorised as one since the 1920s.

From the mid-19th century the common skate was described as two distinct species, the flapper skate, D. intermedia, and the blue skate, D. flossada. However, in an influential work in 1926 R.S Clark recognised only 'D. batis' as a valid species and this classification has largely gone unchallenged since.

This classification confusion has resulted in the depletion of the flapper skate, the more endangered species of the two, being masked in the catch record. This means the risk of extinction is far higher than previously assessed and without immediate and incisive action the species may be in an irreversible decline towards extinction.

When conducting sampling in fish markets during the start of this study Dr Iglésias observed noticeable morphological differences in the 'Dipturus batis' specimens he sampled. In order to understand these differences the researchers not only analysed the systematic molecular data but also reviewed the species' life history and analysed fishery statistics.

"As the species was listed as 'Critically endangered' I wanted to understand who's who? I estimated at the beginning that it would take some weeks to resolve this question, but in the end it took me about two years," said Iglésias. "Our research clearly shows that D. cf. flossada and D. cf. intermedia are distinct and should be resurrected as two valid species."

Common Skates, which were once abundant in British and European waters, have been in sharp decline for decades. In 2008 the International Council for the Exploration of the Sea (ICES) noted that the species is depleted in the Celtic and North Seas, the Skagerrak and the English Channel. The ICES advised no target fishing and that by-catch should be minimised.

"The threat of extinction for European Dipturus together with mislabelling in fishery statistics highlight the need for a huge reassessment of population for the different Dipturus species in European waters," concluded Iglésias. "Without revision and recognition of its distinct status the world's largest skate, D. cf. intermedia, could soon be rendered extinct."

Wiley

NEW HYDROGEN-STORAGE METHOD DISCOVERED

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Scientists at the Carnegie Institution have found for the first time that high pressure can be used to make a unique hydrogen-storage material. The discovery paves the way for an entirely new way to approach the hydrogen-storage problem. The researchers found that the normally unreactive, noble gas xenon combines with molecular hydrogen (H2) under pressure to form a previously unknown solid with unusual bonding chemistry.

The experiments are the first time these elements have been combined to form a stable compound. The discovery debuts a new family of materials, which could boost new hydrogen technologies. The paper is published in the November 22, 2009, advanced online publication of Nature Chemistry.

Xenon has some intriguing properties, including its use as an anesthesia, its ability to preserve biological tissues, and its employment in lighting. Xenon is a noble gas, which means that it does not typically react with other elements.

As lead author Maddury Somayazulu, research scientist at Carnegie's Geophysical Laboratory, explained: "Elements change their configuration when placed under pressure, sort of like passengers readjusting themselves as the elevator becomes full. We subjected a series of gas mixtures of xenon in combination with hydrogen to high pressures in a diamond anvil cell. At about 41,000 times the pressure at sea level (1 atmosphere), the atoms became arranged in a lattice structure dominated by hydrogen, but interspersed with layers of loosely bonded xenon pairs. When we increased pressure, like tuning a radio, the distances between the xenon pairs changed–the distances contracted to those observed in dense metallic xenon."

The researchers imaged the compound at varying pressures using X-ray diffraction, infrared and Raman spectroscopy. When they looked at the xenon part of the structure, they realized that the interaction of xenon with the surrounding hydrogen was responsible for the unusual stability and the continuous change in xenon-xenon distances as pressure was adjusted from 41,000 to 255,000 atmospheres.

Why was the compound so stable? "We were taken off guard by both the structure and stability of this material," said Przemek Dera, the lead crystallographer who looked at the changes in electron density at different pressures using single-crystal diffraction. As electron density from the xenon atoms spreads towards the surrounding hydrogen molecules, it seems to stabilize the compound and the xenon pairs.

"Xenon is too heavy and expensive to be practical for use in hydrogen-storage applications," remarked Somayazulu. "But by understanding how it works in this situation, researchers can come up with lighter substitutes."

"It's very exciting to come up with new hydrogen-rich compounds, not just for our interest in simple molecular systems, but because such discoveries can be the foundation for important new technologies," commented Russell Hemley, director of the Geophysical Laboratory and a co-author. "This hydrogen-rich solid represents a new pathway to forming novel hydrogen storage compounds and the new pressure-induced chemistry opens the possibility of synthesizing new energetic materials."

(Photo: Nature Chemistry)

Carnegie Institution

BIOENGINEERS SUCCEED IN PRODUCING PLASTIC WITHOUT THE USE OF FOSSIL FUELS

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A team of pioneering South Korean scientists have succeeded in producing the polymers used for everyday plastics through bioengineering, rather than through the use of fossil fuel based chemicals. This groundbreaking research, which may now allow for the production of environmentally conscious plastics, is published in two papers in the journal Biotechnology and Bioengineering to mark the journal's 50th anniversary.

Polymers are molecules found in everyday life in the form of plastics and rubbers. The team, from the prestigious KAIST University and the Korean chemical company LG Chem, led by Professor Sang Yup Lee focused their research on Polylactic Acid (PLA), a bio-based polymer which holds the key to producing plastics through natural and renewable resources.

"The polyesters and other polymers we use everyday are mostly derived from fossil oils made through the refinery or chemical process," said Lee. "The idea of producing polymers from renewable biomass has attracted much attention due to the increasing concerns of environmental problems and the limited nature of fossil resources. PLA is considered a good alternative to petroleum based plastics as it is both biodegradable and has a low toxicity to humans."

Until now PLA has been produced in a two-step fermentation and chemical process of polymerization, which is both complex and expensive. Now, through the use of a metabolically engineered strain of E.coli, the team, have developed a one-stage process which produces polylactic acid and its copolymers through direct fermentation. This makes the renewable production of PLA and lactate-containing copolymers cheaper and more commercially viable.

"By developing a strategy which combines metabolic engineering and enzyme engineering, we've developed an efficient bio-based one-step production process for PLA and its copolymers," said Lee. "This means that a developed E. coli strain is now capable of efficiently producing unnatural polymers, through a one-step fermentation process,"

This combined approach of systems-level metabolic engineering and enzyme engineering now allows for the production of polymer and polyester based products through direct microbial fermentation of renewable resources.

"Global warming and other environmental problems are urging us to develop sustainable processes based on renewable resources," concluded Lee. "This new strategy should be generally useful for developing other engineered organisms capable of producing various unnatural polymers by direct fermentation from renewable resources".

WILEY

GENERATING ELECTRICITY FROM AIR FLOW

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A group of researchers at the City College of New York is developing a new way to generate power for planes and automobiles based on materials known as piezoelectrics, which convert the kinetic energy of motion into electricity.

About a half-inch by one inch in size, these devices might be mounted on the roof or tail of a car or on an airplane fuselage where they would vibrate inside a flow, producing an output voltage. The power generated would not be enough to replace that supplied by the combustion engines, but it could run some system -- such as batteries that would be used to charge control panels and other small electronic devices such as mobile phones.

Led by CCNY professor Yiannis Andreopoulos, the researchers are currently attempting to optimize these devices by modeling the physical forces to which they are subjected in different air flows -- on the roof of a car, for instance, or on the back of a truck.

When the device is placed in the wake of a cylinder -- such as on the back of a truck -- the flow of air will cause the devices to vibrate in resonance, says Andreopoulos. On the roof of car, they will shake in a much more unsteady flow known as a turbulent boundary layer. In Minneapolis, Andreopoulos and his colleagues will present wind tunnel data showing how the devices work in both situations.

"These devices open the possibility to continuously scavenge otherwise wasted energy from the environment," says Andreopoulos.

The American Institute of Physics

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