Chapter 10. Vision: From Eye to Brain

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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,

Keyword: Vision
Link ID: 22379 - Posted: 06.30.2016

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.

Keyword: Vision
Link ID: 22378 - Posted: 06.30.2016

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.

Keyword: Vision
Link ID: 22375 - Posted: 06.29.2016

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.

Keyword: Vision; Evolution
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.

Keyword: Vision; Evolution
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

Keyword: Vision
Link ID: 22301 - Posted: 06.09.2016

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

Keyword: Vision; Development of the Brain
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

Keyword: Vision
Link ID: 22262 - Posted: 05.30.2016

Bradley George All sorts of health information is now a few taps away on your smartphone, from how many steps you take — to how well you sleep at night. But what if you could use your phone and a computer to test your vision? A company is doing just that — and eye care professionals are upset. Some states have even banned it. A Chicago-based company called Opternative offers the test. The site asks some questions about your eyes and overall health; it also wants to know your shoe size to make sure you're the right distance from your computer monitor. You keep your smartphone in your hand and use the Web browser to answer questions about what you see on the computer screen. Like a traditional eye test, there are shapes, lines and letters. It takes about 30 minutes. "We're trying to identify how bad your vision is, so we're kind of testing your vision to failure, is the way I would describe it," says Aaron Dallek, CEO of Opternative. Dallek co-founded the company with an optometrist, who was searching for ways to offer eye exams online. "Me being a lifetime glasses and contact wearer, I was like 'Where do we start?' So, that was about 3 1/2 years ago, and we've been working on it ever since," Dallek says. © 2016 npr

Keyword: ADHD
Link ID: 22250 - Posted: 05.26.2016

By Jessica Hamzelou People who experience migraines that are made worse by light might be better off seeing the world in green. While white, blue, red and amber light all increase migraine pain, low-intensity green light seems to reduce it. The team behind the finding hope that specially developed sunglasses that screen out all wavelengths of light except green could help migraineurs. Many people experience sensitivity to light during a migraine. Photophobia, as it is known, can leave migraineurs resorting to sunglasses in well-lit rooms, or seeking the comfort of darkness. The reaction is thought to be due to the brain’s wiring. In a brain region called the thalamus, neurons that transmit sensory information from our retinas cross over with other neurons that signal pain. As a result, during migraine, light can worsen pain and pain can cause visual disturbance, says Rami Burstein at Harvard University. But not all colours of light have the same effect. Six years ago, Burstein and his colleagues studied migraine in sufferers who are blind, either due to the loss of an eye or retina, or because of retinal damage. They found that people who had some remaining retinal cells had worse migraines when they were in brightly lit environments, and that blue light seemed to have the strongest impact. The finding caused a flurry of excitement, and the promotion of sunglasses that filter out blue light. © Copyright Reed Business Information Ltd.

Keyword: Pain & Touch; Vision
Link ID: 22237 - Posted: 05.23.2016

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

Keyword: Vision
Link ID: 22235 - Posted: 05.21.2016

By Daniel Barron No matter where we call home, where we were raised, or what we ate for breakfast, our brains process information pretty much the same as anyone else in the world. Which makes sense—our genomes are 99.6-99.9% identical, which makes our brains nearly so. Look at a landscape or cityscape and comparable computations occur in your brain as in someone from another background or country. Zhangjiajie National Forest Park, China. Credit: Chensiyuan, via Wikimedia Commons under GFDL Consider my recent walk through China’s Zhangjiajie National Forest Park, an inspiration for James Cameron’s Avatar. Some of our first steps into the park involved a 1,070 foot ascent in the Bailong elevator, the world’s tallest outdoor elevator. Crammed within the carriage were travelers from Japan, India, China, the U.S.A., and Korea. No matter our origin, the Wulingyuan landscape didn’t disappoint: the towering red and green rock formations stretched towards the sky as they defied gravity. Gasps and awes were our linguistic currency while our visual cortices gleefully fired away. The approximately 3000 quartzite sandstone pillars, with their unusual red and green contrasts, mesmerized our visual centers, demanding our attention. One of the brain’s earliest visual processing centers, V1, lies at the middle of the back of our head. V1 identifies simple forms like vertical, horizontal, and diagonal edges of contrasting intensities, or lines. Look at a vertical line, and neurons that are sensitive to vertical lines will fire more quickly; look at a horizontal line, and our horizontal neurons buzz away. © 2016 Scientific American

Keyword: Attention; Vision
Link ID: 22204 - Posted: 05.11.2016

By Stephen L. Macknik, Susana Martinez-Conde The renowned Slydini holds up an empty box for all to see. It is not really a box—just four connected cloth-covered cardboard walls, forming a floppy parallelogram with no bottom or top. Yet when the magician sets it down on a table, it looks like an ordinary container. Now he begins to roll large yellow sheets of tissue paper into balls. He claps his hands—SMACK!—as he crumples each new ball in a fist and then straightens his arm, wordlessly compelling the audience to gaze after his closed hand. He opens it, and ... the ball is still there. Nothing happened. Huh. Slydini's hand closes once more around the tissue, and it starts snaking around, slowly and gracefully, like a belly dancer's. The performance is mesmerizing. With his free hand, he grabs an imaginary pinch of pixie dust from the box to sprinkle on top of the other hand. This time he opens his hand to reveal that the tissue is gone! Four balls disappear in this fashion. Then, for the finale, Slydini tips the box forward and shows the impossible: all four balls have mysteriously reappeared inside. Slydini famously performed this act on The Dick Cavett Show in 1978. It was one of his iconic tricks. Despite the prestidigitator's incredible showmanship, though, the sleight only works because your brain cannot multitask. © 2016 Scientific American,

Keyword: Attention
Link ID: 22114 - Posted: 04.19.2016

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

Keyword: Vision
Link ID: 22044 - Posted: 03.29.2016

By C. CLAIBORNE RAY Current treatments for the so-called wet form of macular degeneration, involving injections inside the eye, are already “very effective” compared with laser treatments, which were used before intravitreal injections, said Dr. Ronald C. Gentile, the surgeon director at the New York Eye and Ear Infirmary of Mount Sinai. But several ways to improve their results are in the works, he said. The shots deliver drugs that fight a substance called vascular endothelial growth factor, and thus shrink the growth of what amounts to an abnormal blood vessel harming the retina. A major hurdle now involves the frequency and cost of the needed treatments. Once the drug is inside the eye, the effects wear off and a new injection is needed, Dr. Gentile said. The shots are also less effective in some patients. Even when they work well, some people need a shot as often as every four weeks, while some can wait two or three months. If both eyes are affected and the period of effectiveness is short, doctor visits can be very frequent, so drugs that last longer in the eyeball are being pursued. Researchers are working on slow-release medications as well as a delivery system that acts like a tiny pump in the eye, with a tank that can be refilled every six months. There is also a new drug target: a substance called platelet-derived growth factor that causes abnormal vessel growth as well. Combination drug treatments may be more effective against macular degeneration, Dr. Gentile said. The so-called dry form of macular degeneration, which often underlies the wet form, is harder to fight, he said, and although advances are being made, current antioxidant treatments with vitamins and minerals do not to improve vision; they just prevent it from worsening. © 2016 The New York Times Company

Keyword: ADHD
Link ID: 22004 - Posted: 03.19.2016

BRAINS get data about the world through senses – sight, hearing, taste, smell and touch. In a lab in North Carolina, a group of rats is getting an extra one. Thanks to implants in their brains, they have learned to sense and react to infrared light. The rats show the brain’s ability to process unfamiliar data– an early step towards augmenting the human brain. Miguel Nicolelis of Duke University School of Medicine is leading the experiment. His team implanted four clusters of electrodes in the rats’ barrel cortex – the part of the brain that handles whisker sensation (doi.org/bdb6). Each cluster is connected to a sensor that converts infrared light into an electrical signal. Feeding stations placed at the four corners of the rats’ cage take turns emitting infrared signals that guide the rats to them, releasing a reward only when the rats press a button on the feeding station that is emiting the infrared signal. In an older, single sensor version of the experiment, it took the rats one month to adapt. With four sensors, it took them just three days. “This is a truly remarkable demonstration of the plasticity of the mammalian brain,” says Christopher James of the University of Warwick, UK. All the extra data that goes into making the rats’ new sense doesn’t appear to diminish their original senses. “The results show that nature has apparently designed the adult mammalian brain with the possibility of upgrades, and Nicolelis’ team is leading the way showing how to do it,” says Andrea Stocco of the University of Washington in Seattle. © Copyright Reed Business Information Ltd.

Keyword: Robotics; Vision
Link ID: 21999 - Posted: 03.17.2016

By BARBARA K. LIPSKA AS the director of the human brain bank at the National Institute of Mental Health, I am surrounded by brains, some floating in jars of formalin and others icebound in freezers. As part of my work, I cut these brains into tiny pieces and study their molecular and genetic structure. My specialty is schizophrenia, a devastating disease that often makes it difficult for the patient to discern what is real and what is not. I examine the brains of people with schizophrenia whose suffering was so acute that they committed suicide. I had always done my work with great passion, but I don’t think I really understood what was at stake until my own brain stopped working. In the first days of 2015, I was sitting at my desk when something freakish happened. I extended my arm to turn on the computer, and to my astonishment realized that my right hand disappeared when I moved it to the right lower quadrant of the keyboard. I tried again, and the same thing happened: The hand disappeared completely as if it were cut off at the wrist. It felt like a magic trick — mesmerizing, and totally inexplicable. Stricken with fear, I kept trying to find my right hand, but it was gone. I had battled breast cancer in 2009 and melanoma in 2012, but I had never considered the possibility of a brain tumor. I knew immediately that this was the most logical explanation for my symptoms, and yet I quickly dismissed the thought. Instead I headed to a conference room. My colleagues and I had a meeting scheduled to review our new data on the molecular composition of schizophrenia patients’ frontal cortex, a brain region that shapes who we are — our thoughts, emotions, memories. But I couldn’t focus on the meeting because the other scientists’ faces kept vanishing. Thoughts about a brain tumor crept quietly into my consciousness again, then screamed for attention. © 2016 The New York Times Company

Keyword: Consciousness; Vision
Link ID: 21984 - Posted: 03.14.2016

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

Keyword: Vision
Link ID: 21971 - Posted: 03.10.2016

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

Keyword: Vision
Link ID: 21968 - Posted: 03.09.2016

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.

Keyword: Vision
Link ID: 21966 - Posted: 03.08.2016