Tuesday, August 20, 2019

Skeletal shapes key to rapid recognition of objects

"You can think of it like a child's stick drawing of a person," says Emory psychologist Stella Lourenco, explaining the skeletal geometry that aids the vision system in object recognition. (Getty Images)

By Carol Clark

In the blink of an eye, the human visual system can process an object, determining whether it’s a cup or a sock within milliseconds, and with seemingly little effort. It’s well-established that an object’s shape is a critical visual cue to help the eyes and brain perform this trick. A new study, however, finds that while the outer shape of an object is important for rapid recognition, the object’s inner “skeleton” may play an even more important role.

Scientific Reports published the research by psychologists at Emory University, showing that a key visual tool for object recognition is the medial axis of an object, or its skeletal geometry.

“When we think of an object’s shape, we typically imagine the outer contours,” explains Vladislav Ayzenberg, first author of the paper and an Emory PhD candidate in psychology. “But there is also a deeper, more abstract property of shape that’s described by skeletal geometry. Our research suggests that this inner, invisible mechanism may be crucial to recognizing an object so quickly.”

“You can think of it like a child’s stick drawing of a person,” adds Stella Lourenco, senior author of the study and an associate professor of psychology at Emory. “Using a stick figure to represent a person gives you the basic visual information you need to immediately perceive the figure’s meaning.”

The Lourenco lab researches human visual perception, cognition and development. Visual perception of an object begins when light hits our eyes and the object is projected as a two-dimensional image onto the photoreceptor cells of the retina.

“A lot of internal machinery is whirring between the eyes and brain to facilitate perception and recognition within 70 milliseconds,” Ayzenberg says. “I’m fascinated by the neural computations that go into that process.”

Although most people take it for granted, object recognition is a remarkable feat. “You can teach a two-year-old what a dog is by pointing out a real dog or showing the child a picture in a book,” Lourenco says. “After seeing such examples a child can rapidly and with ease recognize other dogs as dogs, despite variations in their individual appearances.”



The human ability at object recognition is robust despite changes in a class of objects such as outer contours, sizes, textures and colors. For the current paper, the researchers developed a series of experiments to test the role of skeletal geometry in the process.

In one experiment, participants were presented with paired images of 150 abstract 3D objects on a computer. The objects had 30 different skeletal structures. Each object was rendered with five different surface forms, to change the visible shape of the object, without altering the underlying skeleton. The participants were asked to judge whether each pair of images showed the same or different objects. The results found that skeletal similarity was a significant predictor for a correct response.

A second experiment, based on adaptations of three of the objects, tested the effects of proportional changes to the shape skeleton. Participants were able to accurately predict object similarity at a rate significantly above chance at every level of skeletal change.

A third experiment tested whether an object’s skeleton was a better predictor of object similarity than its surface form. Participants successfully matched objects by their skeletal structure or surface forms when each cue was presented in isolation. They showed a preference, however, to match objects by their skeletons, as opposed to their surface forms, when these cues conflicted with one another.

The results suggest that the visual system is not only highly sensitive to the skeletal structure of objects, but that this sensitivity may play an even bigger role in shape perception than object contours.

“Skeletal geometry appears to be more important than previously realized, but it is certainly not the only tool used in object recognition,” Lourenco says. “It may be that the visual system starts with the skeletal structure, instead of the outline of an object, and then maps other properties, such as textures and colors, onto it.”

In addition to adding to fundamental knowledge of the human vision system, the study may give insights into improving capabilities for artificial intelligence (AI). Rapid and accurate object recognition, for example, is vital for AI systems on self-driving cars.

“The best model for a machine-learning system is likely a human-learning system,” Ayzenberg says. “The human vision system has solved the problem of object recognition through evolution and adapted quite well.”

Related:
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Thursday, August 1, 2019

Protection from mosquitoes key to avoid West Nile virus

"In Georgia, West Nile virus is primarily spread by the southern house mosquito Culex quinquefasciatus," says Gonzalo Vazquez-Prokopec, associate professor in Emory's Department of Environmental Sciences. (CDC/James Gathany)

August to September is the peak of the West Nile virus (WNV) season and Atlanta area health officials have reported finding mosquitoes testing positive for the pathogen, including from 11 locations across DeKalb County. No human cases, however, have been reported.

WNV is most commonly spread to people by the bite of an infected mosquito. Most people who become infected do not feel sick, but about one in five develop a fever and other symptoms. And about one out of 150 people infected develop a serious, sometimes fatal, illness, according to the CDC.

Gonzalo Vazquez-Prokopec, associate professor in Emory University's Department of Environmental Sciences, is an expert in mosquito-borne diseases. His lab has studied the urban ecology of metro Atlanta and the Culex mosquito — a vector for WNV and other human pathogens.

Vazquez-Prokopec is currently in the field in Brazil, but we caught up with him via email for a brief Q and A.

What should people know about the particular type of mosquito that spreads WNV?

In Georgia, West Nile virus is primarily spread by the southern house mosquito Culex quinquefasciatus. This light-brown colored species bites at dusk and dawn, and is found in high numbers in and around houses and in open areas, such as parks.

Is it normal to detect WNV in so many Atlanta-area mosquitoes this time of year? 

Yes, the infection rates in mosquitoes, gathered from different mosquito traps, are following trends that we’ve seen in previous years. What we do not see is human cases — so far this year none have been reported for Georgia.

Is Atlanta normally at higher or average risk for human cases of WNV? 

Human infection with WNV is low in Georgia compared to some states in the Northeast or Midwest. This is remarkably different from what we see in mosquitoes and birds which, in Atlanta, have equally high WNV levels compared to the Northeast and Midwest. What seems to be different is the rate of spillover of the virus, or transfer from the wildlife cycle to humans, which definitely appears to be suppressed in the Southeastern United States.

How can people best protect themselves? 

Reducing human exposure to Culex mosquitoes is key to maintaining the low rates of human infection. It’s best to follow the recommendations on the CDC web site to use insect repellent and wear long-sleeved shirts and long pants when outside to protect yourself from mosquito bites, and to remove any standing water around your home. Dekalb County has a great checklist on its web site to help locate potential mosquito breeding sites around your yard.

Related:
Cardinals may reduce West Nile virus spillover in Atlanta
Sewage raises West Nile virus risk

Wednesday, July 31, 2019

Chemists teach old drug new tricks to target deadly staph bacteria

Emory chemist Bill Wuest, far right, with some of his graduate students, from left: Erika Csatary, Madeleine Dekarske and Ingrid Wilt. Photo by Ann Watson.

"Saying superbugs, one antibiotic at a time,” is the motto of Bill Wuest’s chemistry lab at Emory University. Wuest (it rhymes with “beast”) leads a team of students fighting drug-resistant bacteria — some of the scariest, most dangerous bugs on the planet.

Most recently, they created new molecules for a study published in PNAS. Their work helped verify how bithionol — a drug used to treat parasitic infections — can weaken the cell membranes of “persister” cells of methicillin-resistant Staphylococcus aureus (MRSA), a deadly staph bacterium. They also synthesized new compounds, to learn more about how bithionol works and enhance its potential for clinical use.

“Just before I entered graduate school, my mother was diagnosed with a severe staph infection,” says Ingrid Wilt, a PhD candidate, explaining what drives her passion to tackle MRSA.

“She was in a hospital in the ICU for about two weeks,” Wilt adds. “Luckily, a last-resort antibiotic worked for her and she’s okay now.”

Click here to read the full story.

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Monday, July 22, 2019

Cheerleader study highlights need for real-time energy balance

"It's not just how much you eat and what you eat but when you eat it that matters," says Dan Benardot, senior author of the study and a professor of practice at Emory's Center for the Study of Human Health.

It’s well-known that many athletes, especially women athletes and those participating in sports with an aesthetic component, can be chronically energy deficient. A new study suggests that professional cheerleaders also struggle to maintain an optimal balance between energy consumed and energy burned during exercise.

The Journal of Science in Sport and Exercise published the finding, led by researchers at Emory University’s Center for the Study of Human Health and Rollins School of Public Health. The results showed that some study participants had hourly energy balance deficits that were significantly below their estimated energy needs during a typical training day.

“An offensive lineman doesn’t have to worry about what he looks like but appearance matters for professional cheerleaders, and that may affect their food choices,” says Moriah Bellissimo, first author of the study and a graduate student at Rollins. “Some of our study participants reported really low caloric intakes for the amount of physical training they do. Those with the lowest caloric intakes were not eating enough to maintain an optimal body composition of lean mass compared to fat for high-performance athletics.”

“It is not just how much you eat and what you eat but when you eat it that matters,” adds senior author Dan Benardot, professor of practice at Emory’s Center for the Study of Human Health.

Benardot, who is also an emeritus professor of nutrition at Georgia State University, is an expert in the interrelationship between energy intake, body composition and within-day energy balance, and has worked as a team nutritionist for Olympians and professional athletes.

“The body works in real time,” Benardot says. “If you’re not eating enough and not often enough to avoid low blood sugar and high cortisol, your body adapts to this negative energy balance. Your brain will direct the body to find more energy by breaking down muscle mass to satisfy the need for energy. It sets you up for a downward spiral where you continually have to eat less and less to keep from gaining weight.”

The problem is particularly acute for athletes, especially female athletes and those in aesthetic sports, who deplete lean muscle mass at a faster rate than less active people because of the exercise-associated severe energy balance deficit they achieve. The researchers wanted to investigate whether professional cheerleaders, who may train four hours a day practicing dance routines, faced a similar challenge for real-time energy balance as some other female athletes in aesthetic sports.

“I have a vested interest in human performance and nutrition from a personal standpoint,” says Bellissimo, who was a collegiate athlete for five years before entering the Rollins PhD program for Nutrition and Health Science. “I know that how you are eating makes a difference in how you perform.”

Bellissimo says it was challenging to maintain a proper nutritional balance when she was an undergraduate and master’s student, while also competing in Division I volleyball tournaments. She notes that professional cheerleaders often work full-time jobs on top of training and performing and may find it especially challenging to carefully strategize all of their nutritional needs.

For the current study, the researchers conducted 24-hour dietary and activity surveys with professional cheerleaders during an active training period — including an hour-by-hour assessment of what and how much they ate, and hourly energy expenditures throughout the day. They inputted the data into a software tool called NutriTiming®, developed by Benardot, to calculate each participants’ hourly energy balance — and whether they were exercising at a calorie surplus or deficit.

For female athletes, previous research has shown that sustaining an energy balance of plus or minus 300 calories throughout the day is beneficial to avoid the lean tissue breakdown associated with larger energy deficits.

The body mass and body composition of the study participants was also measured, using a bioelectrical impedance analyzer — which painlessly assesses the density of biological tissue.

The results showed that those participants who spent fewer hours in a negative energy balance had a lower, more optimal, percentage of body fat and those who spent more time within the plus-or-minus zone of 300 calories also had a lower percentage of body fat.

The cheerleader study was small and of short duration, but the finding is consistent with other research on female athletes and other populations, Benardot says.

“Athletes expend energy rapidly,” he adds. “They need to eat frequently, just not too much at a time, so their bodies have enough fuel to burn as they need it.”

It is important to study the nutritional needs of people involved in competitive sports and other intensive exercise, both to help them perform at their maximum level and to maintain their health, Bellissimo says. “Research has shown that chronic energy balance deficits in athletes can lead to hormonal imbalances, and that can have long-term health implications,” she says.

Additional authors of the study include Ashley Licata, from the University of Alabama at Birmingham, and Anita Nucci and Walt Thompson, from Georgia State University.

Related:
'Nutrition for the Performing Arts' course focuses on science behind peak performance

Friday, July 5, 2019

Emory mathematician to present a proof of the Sensitivity Conjecture

Emory mathematician Hao Huang says that the algebraic tool that he developed to tackle the problem "might also have some potential to be applied to other combinatorial and complexity problems important to computer science.”

The Sensitivity Conjecture has stood as one of the most important, and baffling, open problems in theoretical computer science for nearly three decades. It appears to have finally met its match through work by Hao Huang, an assistant professor of mathematics at Emory University.

Huang will present a proof of the Sensitivity Conjecture during the International Conference on Random Structures and Algorithms, set for Zurich, Switzerland, July 15 to 19.

“I’ve been attacking this problem off and on since 2012,” Huang says, “but the key idea emerged for me just about a week ago. I finally identified the right tool to solve it.”

Huang posted the proof on his home page and it soon generated buzz among mathematicians and computer scientists on social media, who have praised its remarkable conciseness and simplicity.

The Sensitivity Conjecture relates to boolean data, which maps information into a true-false, or 1-0 binary. Boolean functions play an important role in complexity theory, as well in the design of circuits and chips for digital computers.

“In mathematics, a boolean function is one of the most basic discrete subjects — just like numbers, graphs or geometric shapes,” Huang explains.

There are many complexity measures of a boolean function, and almost all of them — including the decision-tree complexity, the certificate complexity, the randomized query complexity and many others — are known to be polynomially related. However, there is one unknown case, the so-called sensitivity of a boolean function, which measures how sensitive the function is when changing one input at a time.

In 1994, mathematicians Noam Nisan and Mario Szegedy proposed the Sensitivity Conjecture concerning this unknown case.

“Their conjecture says the sensitivity of a boolean function is also polynomially related to the other measures,” Huang says. “If true, then it would cease to be an outlier and it would join the rest of them.”

Huang developed an algebraic method for proving the conjecture. “I hope this method might also have some potential to be applied to other combinatorial and complexity problems important to computer science,” he says.

The research was supported in part by the Simons Foundation.