Chapter 7. Vision: From Eye to Brain
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
By Phil Plait From the twisted mind of brusspup comes another brain-hurting illusion. This one is really, really convincing, so tell me: When you look at this video, you’re seeing a circle of eight dots rotating as it spins around inside a bigger circle, right? No, you’re not. As brusspup shows, each individual white dot is moving in a straight line! The trick here is two-fold: One is that the dots aren’t moving at constant velocity (you can see that in the video at the 0:44 mark), and that combined their motion mimics what we’d see if a smaller circle is rolling around inside a big one. Try as I may, when I look at this video I can’t make my brain see the dots moving linearly; it looks like a circle rolling. If I focus on one of the dots I can see it moving back and forth along a line, but the others still look like the rim of a circle rolling around. For most illusions there’s a moment when your brain can see what’s going on and the illusion shatters, but not with this one. It’s maddening. When I was a kid, Spirograph was a very popular “game.” It wasn’t really a game, but a set of clear plastic disks with gear teeth around them (or rings with teeth on the inside). They had holes in them; you’d pin a ring down on a piece of paper, then take another disk, place it inside the ring, put your pencil tip in a hole, and roll the inner disk around inside the outer ring. The results were really lovely and graceful interlocking and overlapping curves. If you’re a lot younger than me and missed this craze, here’s a video that’ll help you picture it: © 2014 The Slate Group LLC.
Link ID: 19874 - Posted: 07.24.2014
By Sid Perkins Forget the phrase “blind as a bat.” New experiments suggest that members of one species of these furry flyers—Myotis myotis, the greater mouse-eared bat—can do something no other mammal is known to do: They detect and use polarized light to calibrate their long-distance navigation. Previous research hinted that these bats reset their magnetic compass each night based on cues visible at sunset, but the particular cue or cues hadn’t been identified. In the new study, researchers placed bats in boxes in which the polarization of light could be controlled and shifted. After letting the bats experience sundown at a site near their typical roost, the team waited until after midnight (when polarized light was no longer visible in the sky), transported the animals to two sites between 20 and 25 kilometers from the roost, strapped radio tracking devices to them, and then released them. In general, bats whose polarization wasn’t shifted took off for home in the proper direction. But those that had seen polarization shifted 90° at sunset headed off in directions that, on average, pointed 90° away from the true bearing of home, the researchers report online today in Nature Communications. It’s not clear how the bats discern the polarized light, but it may be related to the type or alignment of light-detecting pigments in their retinas, the team suggests. The bats may have evolved to reset their navigation system using polarized light because that cue persists long after sunset and is available even when skies are cloudy. Besides these bats (and it’s not known whether other species of bat can do this, too), researchers have found that certain insects, birds, reptiles, and amphibians can navigate using polarized light. © 2014 American Association for the Advancement of Science
Associated Press Scientists at the Massachusetts Institute of Technology are developing an audio reading device to be worn on the index finger of people whose vision is impaired, giving them affordable and immediate access to printed words. The so-called FingerReader, a prototype produced by a 3-D printer, fits like a ring on the user's finger, equipped with a small camera that scans text. A synthesized voice reads words aloud, quickly translating books, restaurant menus and other needed materials for daily living, especially away from home or office. Reading is as easy as pointing the finger at text. Special software tracks the finger movement, identifies words and processes the information. The device has vibration motors that alert readers when they stray from the script, said Roy Shilkrot, who is developing the device at the MIT Media Lab. For Jerry Berrier, 62, who was born blind, the promise of the FingerReader is its portability and offer of real-time functionality at school, a doctor's office and restaurants. "When I go to the doctor's office, there may be forms that I want to read before I sign them," Berrier said. He said there are other optical character recognition devices on the market for those with vision impairments, but none that he knows of that will read in real time. Berrier manages training and evaluation for a federal program that distributes technology to low-income people in Massachusetts and Rhode Island who have lost their sight and hearing. He works from the Perkins School for the Blind in Watertown, Mass. Developing the gizmo has taken three years of software coding, experimenting with various designs and working on feedback from a test group of visually impaired people. Much work remains before it is ready for the market, Shilkrot said, including making it work on cell phones. © 2014 Hearst Communications, Inc.
By NICHOLAS BAKALAR Can too much studying ruin your eyesight? Maybe. A German study has found that the more education a person has, the greater the likelihood that he will be nearsighted. The researchers did ophthalmological and physical examinations on 4,685 people ages 35 to 74. About 38 percent were nearsighted. But of those who graduated after 13 years in the three-tiered German secondary school system, about 60.3 percent were nearsighted, compared with 41.6 percent of those who graduated after 10 years, 27.2 percent of those who graduated after nine years and 26.9 percent of those who never graduated. The percentage of myopic people was also higher among university graduates than among graduates of vocational schools or those who had no professional training at all. The study was published online in Ophthalmology. The association remained after adjusting for age, gender and many known myopia-associated variations in DNA sequences. “The effect on myopia of the genetic variations is much less than the effect of education,” said the lead author, Dr. Alireza Mirshahi, an ophthalmologist at the University Medical Center in Mainz. “We used to think that myopia was predetermined by genetics. This is one proof that environmental factors have a much higher effect than we thought.” © 2014 The New York Times Company
Link ID: 19805 - Posted: 07.09.2014
Check out the winner of the 2014 Best Illusion of the Year Contest. Created by psychologists at the University of Nevada, Reno, this optical illusion starts with an image of a circle surrounded by other circles. As the video begins and the exterior circles grow and shrink, it looks like the center circle is changing size, too—but it isn’t. Dubbed “The Dynamic Ebbinghaus,” the trick is a spinoff of the original Ebbinghaus mirage created in the 1800s.
Link ID: 19800 - Posted: 07.08.2014
Hassan DuRant The colorful little guy pictured above puts the eyes of every other animal to shame. Whereas humans receive color information via three color receptors in our eyes, mantis shrimp (Neogonodactylus oerstedii) have 12. Six of these differentiate five discrete wavelengths of ultraviolet light, researchers report online today in Current Biology. The mantis shrimp’s vision is possible by making use of specially tuned, UV-specific optical filters in its color-detecting cone cells. The optical filters are made of mycosporine-like amino acids (MAAs), a substance commonly found in the skin or exoskeleton of marine organisms. Often referred to as nature’s sunscreens, MAAs are usually employed to protect an organism from DNA-damaging UV rays; however, the mantis shrimp has incorporated them into powerful spectral tuning filters. Though the reason for the mantis shrimp’s complex visual perception is poorly understood, one possibility is that the UV detection could help visualize otherwise difficult-to-see prey on coral reefs. Many organisms absorb UV light—these organisms would be easy to spot as black objects in a bright world. © 2014 American Association for the Advancement of Science
Link ID: 19789 - Posted: 07.04.2014
Simon Makin Running helps mice to recover from a type of blindness caused by sensory deprivation early in life, researchers report. The study, published on 26 June in eLife1, also illuminates processes underlying the brain’s ability to rewire itself in response to experience — a phenomenon known as plasticity, which neuroscientists believe is the basis of learning. More than 50 years ago, neurophysiologists David Hubel and Torsten Wiesel cracked the 'code' used to send information from the eyes to the brain. They also showed that the visual cortex develops properly only if it receives input from both eyes early in life. If one eye is deprived of sight during this ‘critical period’, the result is amblyopia, or ‘lazy eye’, a state of near blindness. This can happen to someone born with a droopy eyelid, cataract or other defect not corrected in time. If the eye is opened in adulthood, recovery can be slow and incomplete. In 2010, neuroscientists Christopher Niell and Michael Stryker, both at the University of California, San Francisco (UCSF), showed that running more than doubled the response of mice's visual cortex neurons to visual stimulation2 (see 'Neuroscience: Through the eyes of a mouse'). Stryker says that it is probably more important, and taxing, to keep track of the environment when navigating it at speed, and that lower responsiveness at rest may have evolved to conserve energy in less-demanding situations. “It makes sense to put the visual system in a high-gain state when you’re moving through the environment, because vision tells you about far away things, whereas touch only tells you about things that are close,” he says. © 2014 Nature Publishing Group
by Sarah Zielinski Would you recognize a stop sign if it was a different shape, though still red and white? Probably, though there might be a bit of a delay. After all, your brain has long been trained to expect a red-and-white octagon to mean “stop.” The animal and plant world also uses colorful signals. And it would make sense if a species always used the same pattern to signal the same thing — like how we can identify western black widows by the distinctive red hourglass found on the adult spiders’ back. But that doesn’t always happen. Even with really important signals, such as the ones that tell a predator, “Don’t eat me — I’m poisonous.” Consider the dyeing dart frog (Dendrobates tinctorius), which is found in lowland forests of the Guianas and Brazil. The backs of the 5-centimeter-long frogs are covered with a yellow-and-black pattern, which warns of its poisonous nature. But that pattern isn’t the same from frog to frog. Some are decorated with an elongated pattern; others have more complex, sometimes interrupted patterns. The difference in patterns should make it harder for predators to recognize the warning signal. So why is there such variety? Because the patterns aren’t always viewed on a static frog, and the different ways that the frogs move affects how predators see the amphibians, according to a study published June 18 in Biology Letters. Bibiana Rojas of Deakin University in Geelong, Australia, and colleagues studied the frogs in a nature reserve in French Guiana from February to July 2011. They found 25 female and 14 male frogs, following each for two hours from about 2.5 meters away, where the frog wouldn’t notice a scientist. As a frog moved, a researcher would follow, recording how far it went and in what direction. Each frog was then photographed. © Society for Science & the Public 2000 - 2013.
By HELENE STAPINSKI A few months ago, my 10-year-old daughter, Paulina, was suffering from a bad headache right before bedtime. She went to lie down and I sat beside her, stroking her head. After a few minutes, she looked up at me and said, “Everything in the room looks really small.” And I suddenly remembered: When I was young, I too would “see things far away,” as I once described it to my mother — as if everything in the room were at the wrong end of a telescope. The episodes could last anywhere from a few minutes to an hour, but they eventually faded as I grew older. I asked Paulina if this was the first time she had experienced such a thing. She shook her head and said it happened every now and then. When I was a little girl, I told her, it would happen to me when I had a fever or was nervous. I told her not to worry and that it would go away on its own. Soon she fell asleep, and I ran straight to my computer. Within minutes, I discovered that there was an actual name for what turns out to be a very rare affliction — Alice in Wonderland Syndrome. Episodes usually include micropsia (objects appear small) or macropsia (objects appear large). Some sufferers perceive their own body parts to be larger or smaller. For me, and Paulina, furniture a few feet away seemed small enough to fit inside a dollhouse. Dr. John Todd, a British psychiatrist, gave the disorder its name in a 1955 paper, noting that the misperceptions resemble Lewis Carroll’s descriptions of what happened to Alice. It’s also known as Todd’s Syndrome. Alice in Wonderland Syndrome is not an optical problem or a hallucination. Instead, it is most likely caused by a change in a portion of the brain, likely the parietal lobe, that processes perceptions of the environment. Some specialists consider it a type of aura, a sensory warning preceding a migraine. And the doctors confirmed that it usually goes away by adulthood. © 2014 The New York Times Company
By Gary Stix James DiCarlo: We all have this intuitive feel for what object recognition is. It’s the ability to discriminate your face from other faces, a car from other cars, a dog from a camel, that ability we all intuitively feel. But making progress in understanding how our brains are able to accomplish that is a very challenging problem and part of the reason is that it’s challenging to define what it isn’t and is. We take this problem for granted because it seems effortless to us. However, a computer vision person would tell you is that this is an extremely challenging problem because each object presents an essentially infinite number of images to your retina so you essentially never see the same image of each object twice. SA: It seems like object recognition is actually one of the big problems both in neuroscience and in the computational science of machine learning? DiCarlo: That’s right., not only machine learning but also in psychology or cognitive science because the objects that we see are the sources in the world of what we use to build higher cognition, things like memory and decision-making. Should I reach for this, should I avoid it? Our brains can’t do what you would call higher cognition without these foundational elements that we often take for granted. SA: Maybe you can talk about what’s actually happening in the brain during this process. DiCarlo: It’s been known for several decades that there’s a portion of the brain, the temporal lobe down the sides of our head, that, when lost or damaged in humans and non-human primates, leads to deficits of recognition. So we had clues that that’s where these algorithms for object recognition are living. But just saying that part of your brain solves the problem is not really specific. It’s still a very large piece of tissue. Anatomy tells us that there’s a whole network of areas that exist there, and now the tools of neurophysiology and still more advanced tools allow us to go in and look more closely at the neural activity, especially in non-human primates. We can then begin to decipher the actual computations to the level that an engineer might, for instance, in order to emulate what’s going on in our heads. © 2014 Scientific American
By Adam Brimelow Health Correspondent, BBC News Researchers from Oxford University say they've made a breakthrough in developing smart glasses for people with severe sight loss. The glasses enhance images of nearby people and objects on to the lenses, providing a much clearer sense of surroundings. They have allowed some people to see their guide dogs for the first time. The Royal National Institute of Blind People says they could be "incredibly important". Lyn Oliver has a progressive eye disease which means she has very limited vision. Now 70, she was diagnosed with retinitis pigmentosa in her early twenties. She can spot movement but describes her sight as "smudged and splattered". Her guide dog Jess helps her find her way around - avoiding most obstacles and hazards - but can't convey other information about her surroundings. Lyn is one of nearly two million people in the UK with a sight problem which seriously affects their daily lives. Most though have at least some residual sight. Researchers at Oxford University have developed a way to enhance this - using smart glasses. They are fitted with a specially adapted 3D camera. retinitis pigmentosa Dark spots across the retina (back of the eye) correspond with the extent of vision loss in retinitis pigmentosa The images are processed by computer and projected in real-time on to the lenses - so people and objects nearby become bright and clearly defined. 'More independent' Lyn Oliver has tried some of the early prototypes, but the latest model marks a key stage in the project, offering greater clarity and detail than ever before. Dr Stephen Hicks, from the University of Oxford, who has led the project, says they are now ready to be taken from the research setting to be used in the home. BBC © 2014
By EVAN FLEISCHER In two labs some 50 miles apart in Israel, computer scientists and engineers are refining devices that employ tiny cameras as translators of sorts. For both teams, the goal is to give blind people a form of sight — or at least an experience analogous to sight. At Bar-Ilan University near Tel Aviv, where Zeev Zalevsky is head of the electro-optics program, these efforts have taken shape in the form of a smart contact lens. The device begins with a camera mounted on a pair of glasses, and the contact lens, Dr. Zalevsky explained, is embedded with an electrode that will produce an image of what is before the camera directly on the cornea. The image would be experienced in one of two ways: If an apple is placed before the camera, it could be “seen” either as the contour of an apple or as a Braille-like shape that a trained user would recognize as a representation of an apple. Continue reading the main story Contact lens could open new vistas for the blind. Video by Reuters Yevgeny Beiderman, a graduate student who worked with Dr. Zalevsky in testing the prototype, said: “The first time, the usage of the glasses feels strange. It takes at least a few attempts to start using it.” The image captured by Dr. Zalevsky’s device is 110 by 110 pixels — hardly photograph-quality resolution, but Dr. Zalevsky said by email that the camera captures several images in time, and the compressed and encoded result “is enough to allow functionality to the blind person (for example: Braille contains only six points and is enough for reading.)” Dr. Zalevsky is awaiting permission from a hospital to test the electrode lens on people, so in the meantime he has conducted preliminary trials using lenses that apply air pressure to the cornea instead. He has also conducted tests in which participants identified various shapes based on electrical stimulation of the tongue, after the same sort of training that would let someone wearing his lens “see” an apple as a Braille-like pattern. © 2014 The New York Times Company
By C. CLAIBORNE RAY Q. Does the slit shape of a cat’s pupil confer any advantages over the more rounded pupils of other animals? A. “There are significant advantages,” said Dr. Richard E. Goldstein, chief medical officer of the Animal Medical Center in New York City. “A cat can quickly adjust to different lighting conditions, control the amount of light that reaches the eye and see in almost complete darkness,” he said. “Moreover, the slit shape protects the sensitive retina in daylight.” The slit-shaped pupil found in many nocturnal animals, including the domestic cat, presumably allows more effective control of how much light reaches the retina, in terms of both speed and completeness. “A cat has the capacity to alter the intensity of light falling on its retina 135-fold, compared to tenfold in a human, with a circular pupil,” Dr. Goldstein said. “A cat’s eye has a large cornea, which allows more light into the eye, and a slit pupil can dilate more than a round pupil, allowing more light to enter in dark conditions.” Cats have other visual advantages as well, Dr. Goldstein said. A third eyelid, between the regular eyelids and the cornea, protects the globe and also has a gland at the bottom that produces extra tears. The eyes’ location, facing forward in the front of the skull, gives cats a large area of binocular vision, providing depth perception and helping them to catch prey. © 2014 The New York Times Company
Link ID: 19706 - Posted: 06.07.2014
|By Christie Nicholson Conventional wisdom once had it that each brain region is responsible for a specific task. And so we have the motor cortex for handling movements, and the visual cortex, for processing sight. And scientists thought that such regions remained fixed for those tasks beyond the age of three. But within the past decade researchers have realized that some brain regions can pinch hit for other regions, for example, after a damaging stroke. And now new research finds that the visual cortex is constantly doing double duty—it has a role in processing not just sight, but sound. When we hear [siren sound], we see a siren. In the study, scientists scanned the brains of blindfolded participants as the subjects listened to three sounds: [audio of birds, audio of traffic, audio of a talking crowd.] And the scientists could tell what specific sounds the subjects were hearing just by analyzing the brain activity in the visual cortex. [Petra Vetter, Fraser W. Smith and Lars Muckli, Decoding Sound and Imagery Content in Early Visual Cortex, in Current Biology] The next step is to determine why the visual cortex is horning in on the audio action. The researchers think the additional role conferred an evolutionary advantage: having a visual system primed by sound to see the source of that sound could have given humans an extra step in the race for survival. © 2014 Scientific American
By Susana Martinez-Conde Expanding and contracting circles, mutating colors, and false image matches dominated the 2014 Best Illusion of the Year Contest, held on May 18th in the TradeWinds Island Grand in St. Petersburg, FL. One thousand perceptual scientists joined artists and the general public to determine the TOP THREE illusion masters from a pre-selected group of TOP TEN finalists, chosen by an international committee of judges. Each winner took home a trophy designed by the acclaimed Italian sculptor Guido Moretti: the trophies are visual illusions themselves. It was the 10th annual edition of the contest, which annually draws numerous accolades from attendees as well as international media coverage. Las Vegas magician Mac King was master of ceremonies for the event, hosted by the Neural Correlate Society, a non-profit organization whose mission is to promote public awareness of neuroscience research and discovery, and sponsored by Scientific American. Each of the 10 presenters displayed and described their creations for 5 minutes, to the sounds of music and confetti cannons, in an event unlike anything else in science. Afterwards, the audience voted on their favorite illusion while Mac King performed some of his signature magic tricks for the audience. The First Prize winner of the contest, an illusion by Christopher Blair, Gideon Caplovitz and Ryan Mruczek from University of Nevada Reno, took the classical Ebbinghaus illusion, where the perceived size of a central circle varies with the size of surrounding circles, and put it on steroids by making it into an ever-changing dynamic display. Blair rhymed his 5-minute presentation Dr. Seuss-style. Second Prize went to Mark Vergeer, Stuart Anstis and Rob van Lier from the University of Leuven, UC San Diego and Radboud University Nijmegen, for showing that a single colored image can produce several different color perceptions depending on the position of black outlines over the image. © 2014 Scientific American
Link ID: 19664 - Posted: 05.28.2014
By JAMES GORMAN H. Sebastian Seung is a prophet of the connectome, the wiring diagram of the brain. In a popular book, debates and public talks he has argued that in that wiring lies each person’s identity. By wiring, Dr. Seung means the connections from one brain cell to another, seen at the level of the electron microscope. For a human, that would be 85 billion brain cells, with up to 10,000 connections for each one. The amount of information in the three-dimensional representation of the whole connectome at that level of detail would equal a zettabyte, a term only recently invented when the amount of digital data accumulating in the world required new words. It equals about a trillion gigabytes, or as one calculation framed it, 75 billion 16-gigabyte iPads. He is also a realist. When he speaks publicly, he tells his audiences, “I am my connectome.” But he can be brutally frank about the limitations of neuroscience. “We’ve failed to answer simple questions,” he said. “People want to know, ‘What is consciousness?’ And they think that neuroscience is up to understanding that. They want us to figure out schizophrenia and we can’t even figure out why this neuron responds to one direction and not the other.” This mix of intoxicating ideas, and the profound difficulties of testing them, not only defines Dr. Seung’s career but the current state of neuroscience itself. He is one of the stars of the field, and yet his latest achievement, in a paper published this month, is not one that will set the world on fire. He and his M.I.T. colleagues have proposed an explanation of how a nerve cell in the mouse retina — the starburst amacrine cell — detects the direction of motion. If he’s right, this is significant work. But it may not be what the public expects, and what they have been led to expect, from the current push to study the brain. © 2014 The New York Times Company
By JAMES GORMAN Crowd-sourced science has exploded in recent years. Foldit enlists users to help solve scientific puzzles such as how proteins are put together. Zooniverse hosts dozens of projects, including searching for planets and identifying images of animals caught on automatic cameras. Eyewire, which came out of H. Sebastian Seung’s lab at the Massachusetts Institute of Technology about a year and a half ago, is neuroscience’s entry into the field. The EyeWirers, as the players are called, have scored their first scientific success, contributing to a paper in the May 4 issue of Nature by Dr. Seung and his M.I.T. colleagues that offers a solution to a longstanding problem in how motion is detected. Anyone can sign up online, learn to use the software and start working on what Amy Robinson, the creative director of Eyewire, calls a “3-D coloring book.” The task is something like tracing one piece of yarn through an extremely tangled ball. More than 130,000 players in 145 countries, at last count, work on a cube that represents a bit of retinal tissue 4.5 microns on a side. The many branches of neurons are densely packed within. A micron is .00004 inches or, in Eyewire’s calculus, about one-tenth the width of a human hair. Some of the players spend upward of 40 hours a week on Eyewire. These cubes are created by an automated process in which electron microscopes make images of ultrathin slices of brain tissue. Computers then analyze and compile the data to create a three-dimensional representation of a cube of tissue with every neuron and connection visible. © 2014 The New York Times Company
By KATE MURPHY The baseball hurtles toward the batter, and he must decide from its rotation whether it’s a fastball worth a swing or a slider about to drop out of the strike zone. Running full speed, the wide receiver tracks both the football flying through the air and the defensive back on his heels. Golfers must rapidly shift visual focus in order to drive the ball at their feet toward a green in the distance. Many athletes need excellent vision to perform well in their sports, and now many are adding something new to their practice regimens: vision training. The idea has been around for years, but only recently have studies hinted that it might really work — that it might be possible to train yourself to see better without resorting to glasses or surgery. “Vision training has been out there for a long time,” said Mark Blumenkranz, a professor of ophthalmology at Stanford University Medical School. “But it’s being made more respectable lately thanks to the attention it’s been getting from psychophysicists, vision scientists, neurologists and optometrists.” Vision training actually has little to do with improving eyesight. The techniques, a form of perceptual learning, are intended to improve the ability to process what is seen. The idea is that if visual sensory neurons are repeatedly activated, they increase their ability to send electrical signals from one cell to another across connecting synapses. If neurons are not used, over time these transmissions are weakened. “With sensory neurons, just like muscles, it’s use or lose it,” said Dr. Bernhard Sabel, a neuroscientist at Otto von Guericke University in Magdeburg, Germany, who studies plasticity in the brain. “This applies both to athletes and the partially blind.” Vision training may involve simple strategies — for instance, focusing sequentially on beads knotted at intervals on a length of string with one end held at the tip of the nose. This is said to improve convergence (inward turning of the eye to maintain binocular vision) and the ability to focus near and far. © 2014 The New York Times Company
|By Ariel Van Brummelen The presence of light may do more for us than merely allow for sight. A study by Gilles Vandewalle and his colleagues at the University of Montreal suggests that light affects important brain functions—even in the absence of vision. Previous studies have found that certain photoreceptor cells located in the retina can detect light even in people who do not have the ability to see. Yet most studies suggested that at least 30 minutes of light exposure is needed to significantly affect cognition via these nonvisual pathways. Vandewalle's study, which involved three completely blind participants, found that just a few seconds of light altered brain activity, as long as the brain was engaged in active processing rather than at rest. First the experimenters asked their blind subjects whether a blue light was on or off, and the subjects answered correctly at a rate significantly higher than random chance—even though they confirmed they had no conscious perception of the light. Using functional MRI, the researchers then determined that less than a minute of blue light exposure triggered changes in activity in regions of their brain associated with alertness and executive function. Finally, the scientists found that if the subjects received simultaneous auditory stimulation, a mere two seconds of blue light was enough to modify brain activity. The researchers think the noise engaged active sensory processing, which allowed the brain to respond to the light much more quickly than in previous studies when subjects rested while being exposed to light. The results confirm that the brain can detect light in the absence of working vision. They also suggest that light can quickly alter brain activity through pathways unrelated to sight. The researchers posit that this nonvisual light sensing may aid in regulating many aspects of human brain function, including sleep/wake cycles and threat detection. © 2014 Scientific American,
Mo Costandi A vast project to map neural connections in the mouse retina may have answered the long-standing question of how the eyes detect motion. With the help of volunteers who played an online brain-mapping game, researchers showed that pairs of neurons positioned along a given direction together cause a third neuron to fire in response to images moving in the same direction. It is sometimes said that we see with the brain rather than the eyes, but this is not entirely true. People can only make sense of visual information once it has been interpreted by the brain, but some of this information is processed partly by neurons in the retina. In particular, 50 years ago researchers discovered that the mammalian retina is sensitive to the direction and speed of moving images1. This showed that motion perception begins in the retina, but researchers struggled to explain how. When light enters the eye, it is captured by photoreceptor cells, which convert the information into electrical impulses and transmit them to deeper layers of the retina. Individual photoreceptors are not sensitive to the direction in which an object may be moving, so neuroscientist Jinseop Kim, of the Massachusetts Institute of Technology (MIT) in Cambridge, and his colleagues wanted to test whether the answer to the puzzle could lie in the way various types of cells in the retina are connected. Photoreceptors relay their signals via ‘bipolar neurons’, named this way because they have two stems that jut out of the cell's body in opposite directions. The signal then transits through ‘starburst amacrine cells’ — which have filaments, or dendrites, that extend in all directions similarly to light rays out of a star — before reaching the cells that form the optic nerve, which relays them into the brain. © 2014 Nature Publishing Group,
Link ID: 19576 - Posted: 05.05.2014