Links for Keyword: Vision
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Davide Castelvecchi People can detect flashes of light as feeble as a single photon, an experiment has demonstrated — a finding that seems to conclude a 70-year quest to test the limits of human vision. The study, published in Nature Communications on 19 July1, “finally answers a long-standing question about whether humans can see single photons — they can!” says Paul Kwiat, a quantum optics researcher at the University of Illinois at Urbana–Champaign. The techniques used in the study also open up ways of testing how quantum properties — such as the ability of photons to be in two places at the same time — affect biology, he adds. “The most amazing thing is that it’s not like seeing light. It’s almost a feeling, at the threshold of imagination,” says Alipasha Vaziri, a physicist at the Rockefeller University in New York City, who led the work and tried out the experience himself. Experiments on cells from frogs have shown that sensitive light-detecting cells in vertebrate eyes, called rod cells, do fire in response to single photons2. But, in part because the retina processes its information to reduce ‘noise’ from false alarms, researchers hadn’t been able to confirm whether the firing of one rod cell would trigger a signal that would be transmitted all the way to the brain. Nor was it clear whether people would be able to consciously sense such a signal if it did reach the brain. Experiments to test the limits of human vision have also had to wait for the arrival of quantum-optics technologies that can reliably produce one photon of light at a time. © 2016 Macmillan Publishers Limited
Jon Hamilton Letting mice watch Orson Welles movies may help scientists explain human consciousness. At least that's one premise of the Allen Brain Observatory, which launched Wednesday and lets anyone with an Internet connection study a mouse brain as it responds to visual information. "Think of it as a telescope, but a telescope that is looking at the brain," says Christof Koch, chief scientific officer of the Allen Institute for Brain Science, which created the observatory. The hope is that thousands of scientists and would-be scientists will look through that telescope and help solve one of the great mysteries of human consciousness, Koch says. "You look out at the world and there's a picture in your head," he says. "You see faces, you see your wife, you see something on TV." But how does the brain create those images from the chaotic stream of visual information it receives? "That's the mystery," Koch says. There's no easy way to study a person's brain as it makes sense of visual information. So the observatory has been gathering huge amounts of data on mice, which have a visual system that is very similar to the one found in people. The data come from mice that run on a wheel as still images and movies appear on a screen in front of them. For the mice, it's a lot like watching TV on a treadmill at the gym. But these mice have been genetically altered in a way that allows a computer to monitor the activity of about 18,000 neurons as they respond to different images. "We can look at those neurons and from that decode literally what goes through the mind of the mouse," Koch says. Those neurons were pretty active when the mice watched the first few minutes of Orson Welles' film noir classic Touch of Evil. The film is good for mouse experiments because "It's black and white and it has nice contrasts and it has a long shot without having many interruptions," Koch says. © 2016 npr
Related chapters from BP7e: Chapter 18: Attention and Higher Cognition; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 14: Attention and Consciousness; Chapter 7: Vision: From Eye to Brain
Link ID: 22438 - Posted: 07.14.2016
By Karen Weintraub Researchers at Stanford University have coaxed brain cells involved in vision to regrow and make functional connections—helping to upend the conventional dogma that mammalian brain cells, once damaged, can never be restored. The work was carried out in visually impaired mice but suggests that human maladies including glaucoma, Alzheimer’s disease and spinal cord injuries might be more repairable than has long been believed. Frogs, fish and chickens are known to regrow brain cells, and previous research has offered clues that it might be possible in mammals. The Stanford scientists say their new study confirms this and shows that, although fewer than 5 percent of the damaged retinal ganglion cells grew back, it was still enough to make a difference in the mice’s vision. “The brain is very good at coping with deprived inputs,” says Andrew Huberman, the Stanford neurobiologist who led the work. “The study also supports the idea that we may not need to regenerate every neuron in a system to get meaningful recovery.” Other researchers praised the study, published Monday in Nature Neuroscience. “I think it’s a significant step forward toward getting to the point where we really can regenerate optic nerves,” says Don Zack, a professor of ophthalmology at Johns Hopkins University who was not involved in the research. He calls it “one more indication that it may be possible to bring that ability back in humans.” © 2016 Scientific American
By Shayla Love In 2005, astronaut John Phillips took a break from his work on the International Space Station and looked out the window at Earth. He was about halfway through a mission that had begun in April and would end in October. When he gazed down at the planet, the Earth was blurry. He couldn’t focus on it clearly. That was strange — his vision had always been 20/20. He wondered: Was his eyesight getting worse? “I’m not sure if I reported that to the ground,” he said. “I think I didn’t. I thought it would be something that would just go away, and fix itself when I got to Earth.” It didn’t go away. During Phillips’ post-flight physical, NASA found that his vision had gone from 20/20 to 20/100 in six months. John Phillips began experiencing sight issues during his time on the International Space Station in 2005, but was reluctant to say anything while in space. (NASA) Rigorous testing followed. Phillips got MRIs, retinal scans, neurological tests and a spinal tap. The tests showed that not only had his vision changed, but his eyes had changed as well. The backs of his eyes had gotten flatter, pushing his retinas forward. He had choroidal folds, which are like stretch marks. His optic nerves were inflamed. Phillips case became the first widely recognized one of a mysterious syndrome that affects 80 percent of astronauts on long-duration missions in space. The syndrome could interfere with plans for future crewed space missions, including any trips to Mars.
By Patrick Monahan Animals like cuttlefish and octopuses can rapidly change color to blend into the background and dazzle prospective mates. But there’s only one problem: As far as we know, they can’t see in color. Unlike our eyes, the eyes of cephalopods—cuttlefish, octopuses, and their relatives—contain just one kind of color-sensitive protein, apparently restricting them to a black and white view of the world. But a new study shows how they might make do. By rapidly focusing their eyes at different depths, cephalopods could be taking advantage of a lensing property called “chromatic blur.” Each color of light has a different wavelength—and because lenses bend some wavelengths more than others, one color of light shining through a lens can be in focus while another is still blurry. So with the right kind of eye, a quick sweep of focus would let the viewer figure out the actual color of an object based on when it blurs. The off-center pupils of many cephalopods—including the w-shaped pupils of cuttlefish (above)—make this blurring effect more extreme, according to a study published this week in the Proceedings of the National Academy of Sciences. In that study, scientists built a computer model of an octopus eye and showed that—for an object at least one body length away—it could determine the object’s color just by changing focus. Because this is all still theoretical, the next step is testing whether live cephalopods actually see color this way—and whether any other “colorblind” animals might, too. © 2016 American Association for the Advancement of Science.
By Jessica Hamzelou Imagine if each of the words in this article had their own taste, or the music you’re listening to played out as visual scene in your mind. For synaesthetes – a small proportion of people whose senses intertwine – this is the stuff of the every day. “Most people describe it as a gift,” says Jamie Ward, a neuroscientist at the University of Sussex in the UK. Now, he and his colleagues have found a new form of synaesthesia – one that moves beyond written language to sign language. It is the first time the phenomenon has been observed. “People with synaesthesia experience the ordinary world in extraordinary ways,” says Ward. In theory, any two senses can overlap. Some synaesthetes connect textures with words, while others can taste them. More commonly, written letters seem to have corresponding colours. An individual synaesthete may always associate the letter A with the colour pink, for instance. This type of synaesthesia has been found across many written languages, prompting Ward’s team to wonder if it can also apply to sign language. They recruited 50 volunteers with the type of synaesthesia that means they experience colours with letters, around half of whom were fluent in sign language too. All the participants watched a video of sign language and were asked if it triggered any colours. © Copyright Reed Business Information Ltd.
Related chapters from BP7e: Chapter 8: General Principles of Sensory Processing, Touch, and Pain; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 5: The Sensorimotor System; Chapter 7: Vision: From Eye to Brain
Link ID: 22390 - Posted: 07.02.2016
When you walk into a room, your eyes process your surroundings immediately: refrigerator, sink, table, chairs. "This is the kitchen," you realize. Your brain has taken data and come to a clear conclusion about the world around you, in an instant. But how does this actually happen? Elissa Aminoff, a research scientist in the Department of Psychology and the Center for the Neural Basis of Cognition at Carnegie Mellon University, shares her insights on what computer modeling can tell us about human vision and memory. What do you do? What interests me is how the brain and the mind understand our visual environment. The visual world is really rich with information, and it’s extremely complex. So we have to find ways to break visual data down. What specific parts of our [visual] world is the brain using to give us what we see? In order to answer that question, we’re collaborating with computer scientists and using computer vision algorithms. The goal is to compare these digital methods with the brain. Perhaps they can help us find out what types of data the brain is working with. Does that mean that our brains function like a computer? That’s something you hear a lot about these days. No, I wouldn’t say that. It’s that computers are giving us the closest thing that we have right now to an analogous mechanism. The brain is really, really complex. It deals with massive amounts of data. We need help in organizing these data and computers can do that. Right now, there are algorithms that can identify an object as a phone or as a mug, just like the brain. But are they doing the same thing? Probably not. © 2016 Scientific American,
By Aviva Rutkin Machine minds are often described as black boxes, their decision-making processes all but inscrutable. But in the case of machine intelligence, researchers are cracking that black box open and peering inside. What they find is that humans and machines don’t pay attention to the same things when they look at pictures – not at all. Researchers at Facebook and Virginia Tech in Blacksburg got humans and machines to look at pictures and answer simple questions – a task that neural-network-based artificial intelligence can handle. But the researchers weren’t interested in the answers. They wanted to map human and AI attention, in order to shed a little light on the differences between us and them. “These attention maps are something we can measure in both humans and machines, which is pretty rare,” says Lawrence Zitnick at Facebook AI Research. Comparing the two could provide insight “into whether computers are looking in the right place”. First, Zitnick and his colleagues asked human workers on Amazon Mechanical Turk to answer simple questions about a set of pictures, such as “What is the man doing?” or “What number of cats are lying on the bed?” Each picture was blurred, and the worker would have to click around to sharpen it. A map of those clicks served as a guide to what part of the picture they were paying attention to. © Copyright Reed Business Information Ltd.
Worldwide voting for the BEST ILLUSION OF THE YEAR will take place online from 4pm EST on June 29th to 4pm EST on June 30th. The winning illusions will receive a $3,000 award for 1st place, a $2,000 award for 2nd place, and a $1,000 award for 3rd place. Anybody with an internet connection (that means YOU!) can vote to pick the Top 3 Winners from the current Top 10 List! The Best illusion of the Year Contest is a celebration of the ingenuity and creativity of the world’s premier illusion research community. Contestants from all around the world submitted novel illusions (unpublished, or published no earlier than 2015), and an international panel of judges rated them and narrowed them to the TOP TEN.
By Vinicius Donisete Goulart The “new world” monkeys of South and Central America range from large muriquis to tiny pygmy marmosets. Some are cute and furry, others bald and bright red, and one even has an extraordinary moustache. Yet, with the exception of owl and howler monkeys, the 130 or so remaining species have one thing in common: A good chunk of the females, and all of the males, are colorblind. This is quite different from “old world” primates, including us Homo sapiens, who are routinely able to see the world in what we humans imagine as full color. In evolutionary terms, colorblindness sounds like a disadvantage, one which should really have been eliminated by natural selection long ago. So how can we explain a continent of the colorblind monkeys? I have long wondered what makes primates in the region colorblind and visually diverse, and how evolutionary forces are acting to maintain this variation. We don’t yet know exactly what kept these seemingly disadvantaged monkeys alive and flourishing—but what is becoming clear is that colorblindness is an adaptation not a defect. The first thing to understand is that what we humans consider “color” is only a small portion of the spectrum. Our “trichromatic” vision is superior to most mammals, who typically share the “dichromatic” vision of new world monkeys and colorblind humans, yet fish, amphibians, reptiles, birds, and even insects are able to see a wider range, even into the UV spectrum. There is a whole world of color out there that humans and our primate cousins are unaware of. What is becoming clear is that color blindness is an adaptation not a defect.
Related chapters from BP7e: Chapter 10: Vision: From Eye to Brain; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 7: Vision: From Eye to Brain
Link ID: 22345 - Posted: 06.22.2016
By Sarah Kaplan Some 250 million years ago, when dinosaurs roamed the Earth and early mammals were little more than tiny, fuzzy creatures that scurried around attempting to evade notice, our ancestors evolved a nifty trick. They started to become active at night. They developed sensitive whiskers and an acute sense of hearing. Their circadian rhythms shifted to let them sleep during the day. Most importantly, the composition of their eyes changed — instead of color-sensing cone photoreceptor cells, they gained thousands of light-sensitive rod cells, which allowed them to navigate a landscape lit only by the moon and stars. Mammals may no longer have to hide from the dinosaurs, but we bear the indelible marks of our scrappy, nocturnal past. Unlike every other vertebrate on land and sea, we still have rod-dominated eyes — human retinas, for example, are 95 percent rods, even though we're no longer active at night. "How did that happen? What is the mechanism that made mammals become so different?" asked Anand Swaroop, chief of the Neurobiology Neurodegeneration and Repair Laboratory at the National Eye Institute. He provides some answers to those questions in a study published in the journal Developmental Cell Monday. The findings are interesting from an evolutionary standpoint, he said, but they're also the keys to a medical mystery. If Swaroop and his colleagues can understand how our eyes evolved, perhaps they can fix some of the problems that evolved with them.
Related chapters from BP7e: Chapter 10: Vision: From Eye to Brain; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 7: Vision: From Eye to Brain
Link ID: 22342 - Posted: 06.21.2016
By Stephen L. Macknik Every few decades there’s a major new neuroscience discovery that changes everything. I’m not talking about your garden variety discovery. Those happen frequently (this is the golden age of neuroscience after all). But no, what I’m talking about are the holy-moly, scales-falling-from-your-eyes, time-to-rewrite-the-textbooks, game-changing discoveries. Well one was reported in this last month—simultaneously by two separate labs—and it redefines the primary organizational principle of the visual system in the cortex of the brain. This may sound technical, but it concerns how we see light and dark, and the perception of contrast. Since all sensation functions at the pleasure of contrast, these new discoveries impact neuroscience and psychology as a whole. I’ll explain below. The old way of thinking about how the wiring of the visual cortex was organized orbited around the concept of visual-edge orientation. David Hubel (my old mentor) and Torsten Wiesel (my current fellow Brooklynite)—who shared the Nobel Prize in Physiology or Medicine in 1981—arguably made the first major breakthrough concerning how information was organized in the cortex versus earlier stages of visual processing. Before their discovery, the retina (and the whole visual system) was thought to be a kind of neural camera that communicated its image into the brain. The optic nerves connect the eyes’ retinas to the thalamus at the center of the brain—and then the thalamus connects to the visual cortex at the back of the brain through a neural information superhighway called the optic radiations. Scientists knew, even way back then, that neurons at a given point of the visual scene lie physically next to the neuron that sees the neighboring piece of the visual scene. The discovery of this so called retinotopic map in the primary visual cortex (by Talbot and Marshall) was of course important, but because it matched the retinotopic mapping of the retina and thalamus, it didn’t constitute a new way of thinking. It wasn’t a game-changing discovery. © 2016 Scientific American
By Jordana Cepelewicz Colors exist on a seamless spectrum, yet we assign hues to discrete categories such as “red” and “orange.” Past studies have found that a person's native language can influence the way colors are categorized and even perceived. In Russian, for example, light blue and dark blue are named as different colors, and studies find that Russian speakers can more readily distinguish between the shades. Yet scientists have wondered about the extent of such verbal influence. Are color categories purely a construct of language, or is there a physiological basis for the distinction between green and blue? A new study in infants suggests that even before acquiring language, our brain already sorts colors into the familiar groups. A team of researchers in Japan tracked neural activity in 12 prelinguistic infants as they looked at a series of geometric figures. When the shapes' color switched between green and blue, activity increased in the occipitotemporal region of the brain, an area known to process visual stimuli. When the color changed within a category, such as between two shades of green, brain activity remained steady. The team found the same pattern in six adult participants. The infants used both brain hemispheres to process color changes. Language areas are usually in the left hemisphere, so the finding provides further evidence that color categorization is not entirely dependent on language. At some point as a child grows, language must start playing a role—just ask a Russian whether a cloudless sky is the same color as the deep sea. The researchers hope to study that developmental process next. “Our results imply that the categorical color distinctions arise before the development of linguistic abilities,” says Jiale Yang, a psychologist at Chuo University and lead author of the study, published in February in PNAS. “But maybe they are later shaped by language learning.” © 2016 Scientific American
Related chapters from BP7e: Chapter 10: Vision: From Eye to Brain; Chapter 7: Life-Span Development of the Brain and Behavior
Related chapters from MM:Chapter 7: Vision: From Eye to Brain; Chapter 13: Memory, Learning, and Development
Link ID: 22291 - Posted: 06.07.2016
By Jane E. Brody Joanne Reitano is a professor of history at LaGuardia Community College in Long Island City, Queens. She writes wonderful books about the history of the city and state, and has recently been spending many hours — sometimes all day — at her computer to revise her first book, “The Restless City.” But while sitting in front of the screen, she told me, “I developed burning in my eyes that made it very difficult to work.” After resting her eyes for a while, the discomfort abates, but it quickly returns when she goes back to the computer. “If I was playing computer games, I’d turn off the computer, but I need it to work,” the frustrated professor said. Dr. Reitano has a condition called computer vision syndrome. She is hardly alone. It can affect anyone who spends three or more hours a day in front of computer monitors, and the population at risk is potentially huge. Worldwide, up to 70 million workers are at risk for computer vision syndrome, and those numbers are only likely to grow. In a report about the condition written by eye care specialists in Nigeria and Botswana and published in Medical Practice and Reviews, the authors detail an expanding list of professionals at risk — accountants, architects, bankers, engineers, flight controllers, graphic artists, journalists, academicians, secretaries and students — all of whom “cannot work without the help of computer.” And that’s not counting the millions of children and adolescents who spend many hours a day playing computer games. Studies have indicated 70 percent to 90 percent of people who use computers extensively, whether for work or play, have one or more symptoms of computer vision syndrome. The effects of prolonged computer use are not just vision-related. Complaints include neurological symptoms like chronic headaches and musculoskeletal problems like neck and back pain. © 2016 The New York Times Company
Sara Reardon Every time something poked its foot, the mouse jumped in pain. Researchers at Circuit Therapeutics, a start-up company in Menlo Park, California, had made the animal hypersensitive to touch by tying off a nerve in its leg. But when they shone a yellow light on its foot while poking it, the mouse did not react. The treatment is one of several nearing clinical use that draw on optogenetics — a technique in which light is used to control genes and neuron firing. In March, RetroSense Therapeutics of Ann Arbor, Michigan, began the first clinical-safety trial of an optogenetic therapy to treat the vision disorder retinitis pigmentosa. Many scientists are waiting to see how the trial turns out before they decide how to move forward with their own research on a number of different applications. “I think it will embolden people if there’s good news,” says Robert Gereau, a pain researcher at Washington University in St Louis, Missouri. “It opens up a whole new range of possiblilities for how to treat neurological diseases.” Retinitis pigmentosa destroys photoreceptors in the eye. RetroSense’s treatment seeks to compensate for this loss by conferring light sensitivity to retinal ganglion cells, which normally help to pass visual signals from photoreceptors to the brain. The therapy involves injecting patients who are blind or mostly blind with viruses carrying genes that encode light-sensitive proteins called opsins. The cells fire when stimulated with blue light, passing the visual information to the brain. Chief executive Sean Ainsworth says that the company has injected several individuals in the United States with the treatment, and plans to enroll a total of 15 blind patients in its trial. RetroSense will follow them for two years, but may release some preliminary data later this year. © 2016 Nature Publishing Group
Related chapters from BP7e: Chapter 10: Vision: From Eye to Brain; Chapter 3: Neurophysiology: The Generation, Transmission, and Integration of Neural Signals
Related chapters from MM:Chapter 7: Vision: From Eye to Brain; Chapter 3: Neurophysiology: The Generation, Transmission, and Integration of Neural Signals
Link ID: 22235 - Posted: 05.21.2016
By Roni Caryn Rabin Here’s another reason to eat your fruits and veggies: You may reduce your risk of vision loss from cataracts. Cataracts that cloud the lenses of the eye develop naturally with age, but a new study is one of the first to suggest that diet may play a greater role than genetics in their progression. Researchers had about 1,000 pairs of female twins in Britain fill out detailed food questionnaires that tracked their nutrient intake. Their mean age was just over 60. The study participants underwent digital imaging of the eye to measure the progression of cataracts. The researchers found that women who consumed diets rich in vitamin C and who ate about two servings of fruit and two servings of vegetables a day had a 20 percent lower risk of cataracts than those who ate a less nutrient-rich diet. Ten years later, the scientists followed up with 324 of the twin pairs, and found that those who had reported consuming more vitamin C in their diet — at least twice the recommended dietary allowance of 75 milligrams a day for women (the R.D.A. for adult men is 90 milligrams) — had a 33 percent lower risk of their cataracts progressing than those who get less vitamin C. The researchers concluded that genetic factors account for about 35 percent of the difference in cataract progression, while environmental factors like diet account for 65 percent. “We found no beneficial effect from supplements, only from the vitamin C in the diet,” said Dr. Christopher Hammond, a professor of ophthalmology at King’s College London and an author of the study,published in Ophthalmology. Foods high in vitamin C include oranges, cantaloupe, kiwi, broccoli and dark leafy greens. © 2016 The New York Times Company
Monya Baker A surgical technique to treat cataracts in children spurs stem cells to generate a new, clear lens. Discs made of multiple types of eye tissue have been grown from human stem cells — and that tissue has been used to restore sight in rabbits. The work, reported today in Nature1, suggests that induced pluripotent stem (iPS) cells — stem cells generated from adult cells — could one day be harnessed to provide replacement corneal or lens tissue for human eyes. The discs also could be used to study how eye tissue and congenital eye diseases develop. “The potential of this technique is mind-boggling,” says Mark Daniell, head of corneal research at the Centre for Eye Research Australia in Melbourne, who was not involved in the research. “It’s almost like an eye in a dish.” A second, unrelated paper in Nature2 describes a surgical procedure that activates the body’s own stem cells to regenerate a clear, functioning lens in the eyes of babies born with cataracts. The two studies are “amazing, almost like science fiction”, Daniell says. In the first study, a team led by Kohji Nishida, an ophthalmologist at Osaka University Graduate School of Medicine in Japan, cultivated human iPS cells to produce discs that contained several types of eye tissue. © 2016 Nature Publishing Group
By Virginia Morell Butterflies may not have a human’s sharp vision, but their eyes beat us in other ways. Their visual fields are larger, they’re better at perceiving fast-moving objects, and they can distinguish ultraviolet and polarized light. Now, it turns out that one species of swallowtail butterfly from Australasia, the common bluebottle (Graphium sarpedon, pictured), known for its conspicuous blue-green markings, is even better equipped for such visual tasks. Each of their eyes, scientists report in Frontiers in Ecology and Evolution, contains at least 15 different types of photoreceptors, the light-detecting cells required for color vision. These are comparable to the rods and cones found in our eyes. To understand how the spectrally complex retinas of butterflies evolved, the researchers used physiological, anatomical, and molecular experiments to examine the eyes of 200 male bluebottles collected in Japan. (Only males were used because the scientists failed to catch a sufficient number of females.) They found that different colors stimulate each class of receptor. For instance, UV light stimulates one, while slightly different blue lights set off three others; and green lights trigger four more. Most insect species have only three classes of photoreceptors. Even humans have only three cones, yet we still see millions of colors. Butterflies need only four receptor classes for color vision, including spectra in the UV region. So why did this species evolve 11 more? The scientists suspect that some of the receptors must be tuned to perceive specific things of great ecological importance to these iridescent butterflies—such as sex. For instance, with eyes alert to the slightest variation in the blue-green spectrum, male bluebottles can spot and chase their rivals, even when they’re flying against a blue sky. © 2016 American Association for the Advancement of Science
Our eyes constantly send bits of information about the world around us to our brains where the information is assembled into objects we recognize. Along the way, a series of neurons in the eye uses electrical and chemical signals to relay the information. In a study of mice, National Institutes of Health scientists showed how one type of neuron may do this to distinguish moving objects. The study suggests that the NMDA receptor, a protein normally associated with learning and memory, may help neurons in the eye and the brain relay that information. “The eye is a window onto the outside world and the inner workings of the brain,” said Jeffrey S. Diamond, Ph.D., senior scientist at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS), and the senior author of the study published in Neuron. “Our results show how neurons in the eye and the brain may use NMDA receptors to help them detect motion in a complex visual world.” Vision begins when light enters the eye and hits the retina, which lines the back of the eyeball. Neurons in the retina convert light into nerve signals which are then sent to the brain. Using retinas isolated from mice, Dr. Alon Poleg-Polsky, Ph.D. a postdoctoral fellow in Dr. Diamond’s lab, studied neurons called directionally selective retinal ganglion cells (DSGCs), which are known to fire and send signals to the brain in response to objects moving in specific directions across the eye. Electrical recordings showed that some of these cells fired when a bar of light passed across the retina from left to right, whereas others responded to light crossing in the opposite direction. Previous studies suggested these unique responses are controlled by incoming signals sent from neighboring cells at chemical communication points called synapses. In this study, Dr. Poleg-Polsky discovered that the activity of NMDA receptors at one set of synapses may regulate whether DSGCs sent direction-sensitive information to the brain.
By C. CLAIBORNE RAY Q. What’s the No. 1 cause of blindness in seniors in the United States? A. “It sounds like a simple question, but there’s no perfect answer,” said Dr. Susan Vitale, a research epidemiologist at the National Eye Institute of the National Institutes of Health. “It depends on age, how blindness is measured and how statistics are collected.” For example, some studies have relied on the self-reported answer to the vague question: “Do you have vision problems?” The best available estimates, she said, come from a 2004 paper aggregating many other studies, some in the United States and some in other countries, updated by applying later census data. This paper and others have found striking differences by age and by racial and socioeconomic groups, Dr. Vitale said. In white people, she said, the major cause of blindness at older ages is usually age-related macular degeneration, progressive damage to the central portion of the retina. In older black people, the major causes are likely to be glaucoma or cataracts. In older people of working age, from their 40s to their 60s, the major cause, regardless of race, is diabetic retinopathy, damage to the retina as a result of diabetes. Many studies have shown that white people are more likely to have age-related macular degeneration, Dr. Vitale said, but as for cataracts, for which blindness is preventable by surgery, there are questions about access to health care and whether those affected can get the needed surgery. It is not known why black people are at higher risk of glaucoma. There are also some gender differences, she said, with white women more likely than white men to become blind. Studies have not found the same difference by gender in black and Hispanic people. Because many of the causes of blindness at all ages are preventable, Dr. Vitale said, it is essential to have regular eye checkups, even if there are no obvious symptoms. © 2016 The New York Times Company