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 Stephanie Pappas The justices of the Supreme Court may be among the best legal minds in the country, but they have no eye for distances — and new research may help explain why. During oral arguments Wednesday (Jan. 15) in a case about the constitutionality of laws prohibiting protestors from gathering close to abortion clinic entrances, the justices were stumped at the size of the 35-foot-long (10.6 meters) buffer zone in question. "It's pretty much this courtroom, kind of," ABC News quoted Associate Justice Elena Kagan as saying. In fact, the courtroom is more than 90 feet (30 m) long. After a back-and-forth discussion, the deputy solicitor arguing the case clarified that the no-go zone is the size of the 3-point zone on an NBA basketball court. But judging distances and depth may be trickier than it seems. A recent study, published Oct. 23 in the Journal of Neuroscience, finds that people's depth perception depends on their perception of their arm's length. Trick someone into thinking their arm is shorter or longer, and you can influence how they perceive distances between two objects. Depth perception, the ability to judge the distances of objects from one another, is an important ability; without it, one would have no way of knowing that a marble in their hand and a basketball 6 feet away were actually two different sizes. © 2014 Scientific American
Link ID: 19165 - Posted: 01.25.2014
Ian Sample, science correspondent Two men with progressive blindness have regained some of their vision after taking part in the first clinical trial of a gene therapy for the condition. The men were among six patients to have experimental treatment for a rare, inherited, disorder called choroideremia, which steadily destroys eyesight and leaves people blind in middle age. After therapy to correct a faulty gene, the men could read two to four more lines on an optician's sight chart, a dramatic improvement that has held since the doctors treated them. One man was treated more than two years ago. The other four patients, who had less advanced disease and good eyesight before the trial, had better night vision after the therapy. Poor sight in dim light is one of the first signs of the condition. Writing in The Lancet , doctors describe the progress of the patients six months after the therapy. If further trials are as effective, the team could apply for approval for the therapy in the next five years. Some other forms of blindness could be treated in a similar way. Toby Stroh, 56, a solicitor from London, was in his early 20s when a consultant told him he would be blind by the age of 50. "I said 'what do you mean?' and he said, 'you won't be able to see me'. It was a long way away, but still a bit of a shock." Stroh was told later that his vision had deteriorated so much he would have to stop driving. Then, when he joined a solicitors' firm he told a partner his eyesight was not expected to last. The response was: "We'll be sorry to see you go." © 2014 Guardian News and Media Limited
Link ID: 19143 - Posted: 01.16.2014
by Anil Ananthaswamy Next time you happen to be snorkelling near a coral reef, keep an eye out for mantis shrimp. In all likelihood, these crustaceans, which resemble small lobsters, will have spotted you: they scan their surroundings with rapid eye movements just like those of primates. Justin Marshall of the University of Queensland in Brisbane, Australia, and colleagues have been studying mantis shrimp for years, and it is how they use their eyes that interests Marshall. Their eyes are on stalks and can dart around. Humans use similar rapid eye movements, called saccades, to "acquire" or lock on to new objects, and to track them as they move. "It was not clear whether the shrimp eye movements were anything to do with acquiring objects, or just repositioning the eyes," Marshall says. To find out, the team placed mantis shrimp in a perspex tube inside an aquarium, and suddenly introduced a small coloured disc into their line of sight. A camera outside the aquarium filmed their eyes. The team found that the mantis shrimp's fovea – the part of the eye with the highest resolution – was using saccades to home in on the coloured disc. This sort of behaviour is normally found in animals like primates, says Marshall. The saccadic eye movements are extremely rapid. Human saccades can sweep through a field of view at a rate of 200-300 degrees per second. "[Mantis shrimp] are actually going up to twice that amount," says Marshall. © Copyright Reed Business Information Ltd.
Link ID: 19113 - Posted: 01.09.2014
By Susana Martinez-Conde If you’re a bit lax with your post-holiday brushing, this little-known illusion may give you the incentive you need to keep those candy canes in check, or at least brush and floss afterwards. Vision scientist Robert O’Shea and his colleagues published a recent study in PLoS One showing that dentists can fall prey to a visual illusion of size and make larger holes in teeth than needed. The illusion fooling the dentists is a variant of a classical perceptual phenomenon known as the Delboeuf illusion, named after its creator, the Belgian natural philosopher, experimentalist, mathematician and hypnotist Joseph Remi Leopold Delboeuf. The scientists supplied 8 specialist dentists and endodontists, who served as experimental subjects, with a large pool of extracted teeth. The teeth contained holes, and the task of the dentists was to cut cavities in preparation for filling. Unknown to the dentists, each tooth presented a more or less powerful version of the Delboeuf illusion, making the holes appear smaller than their actual size. The results showed that the smaller the holes looked, the larger the cavities that the dentists made for later filling. The researchers recommend that dentists and other health practitioners receive training in “illusion awareness” (my words, not theirs), so that they may counteract these and related perceptual effects. © 2013 Scientific American,
Link ID: 19073 - Posted: 12.28.2013
By Michelle Roberts Health editor, BBC News online Scientists say they have been able to successfully print new eye cells that could be used to treat sight loss. The proof-of-principle work in the journal Biofabrication was carried out using animal cells. The Cambridge University team says it paves the way for grow-your-own therapies for people with damage to the light-sensitive layer of tissue at back of the eye - the retina. More tests are needed before human trials can begin. At the moment the results are preliminary and show that an inkjet printer can be used to print two types of cells from the retina of adult rats―ganglion cells and glial cells. These are the cells that transmit information from the eye to certain parts of the brain, and provide support and protection for neurons. The printed cells remained healthy and retained their ability to survive and grow in culture. Co-authors of the study Prof Keith Martin and Dr Barbara Lorber, from the John van Geest Centre for Brain Repair at the University of Cambridge, said: "The loss of nerve cells in the retina is a feature of many blinding eye diseases. The retina is an exquisitely organised structure where the precise arrangement of cells in relation to one another is critical for effective visual function. Human eye The retina sits at the back of the eye BBC © 2013
By Phil Plait Our brains are massively complex machines, constantly processing huge amounts of data from our senses. Our eyes provide most of that input; they send a huge amount of information to the brain, and it’s actually rather astonishing we can figure anything out from it. Given that, our ability to detect motion is pretty amazing. Despite all that noise, if something moves, something changes, our brain targets right on it. To see motion, you need at least two objects, so that one can move relative to the other. Sometimes, one of those objects is you. If you turn your head, the room you’re sitting in looks like it’s turning the other way. But our brain compensates for that; it “knows” it’s moving, so you perceive the room as motionless. But this works the other way, too: You can make the brain think something is moving even when it’s not. That’s the principle behind this wonderful optical illusion video created by brusspup: Isn’t that great? Your brain will swear those drawings are moving, even when you can see they are not. Even the cat was fooled! This video looks fantastically complicated, but the way it works is actually pretty simple. Basically, it’s fooling your brain into ignoring the thing that is moving, and making it look like the motionless thing is what’s doing the moving. © 2013 The Slate Group, LLC.
Link ID: 19040 - Posted: 12.17.2013
By Melissa Hogenboom Science reporter, BBC News Changes to specific cells in the retina could help diagnose and track the progression of Alzheimer's disease, scientists say. A team found genetically engineered mice with Alzheimer's lost thickness in this layer of eye cells. As the retina is a direct extension of the brain, they say the loss of retinal neurons could be related to the loss of brain cells in Alzheimer's. The findings were revealed at the US Society for Neuroscience conference. The team believes this work could one day lead to opticians being able to detect Alzheimer's in a regular eye check, if they had the right tools. Alterations in the same retinal cells could also help detect glaucoma - which causes blindness - and is now also viewed as a neurodegenerative disease similar to Alzheimer's, the researchers report. Scott Turner, director of the memory disorders programme at Georgetown University Medical Center, said: "The retina is an extension of the brain so it makes sense to see if the same pathologic processes found in an Alzheimer's brain are also found in the eye." Dr Turner and colleagues looked at the thickness of the retina in an area that had not previously been investigated. This included the inner nuclear layer and the retinal ganglion cell layer. They found that a loss of thickness occurred only in mice with Alzheimer's. The retinal ganglion cell layer had almost halved in size and the inner nuclear layer had decreased by more than a third. BBC © 2013
SAN DIEGO, CALIFORNIA—The nine-banded armadillo (Dasypus novemcinctus) has many hidden skills—it can sniff out insects buried 20 cm underground, for example, and jump more than a meter into the air when startled. Seeing, however, is not one of its natural talents. Because its eyes lack light-detecting cells called cones, it has fuzzy, colorless vision. The light-receptive cells that an armadillo does have, called rods, are so sensitive that daylight renders the nocturnal animals practically blind. But the deficit may have a silver lining for humans. To study diseases that cause blindness in people, scientists typically genetically “knock out” cone-related genes in animals like mice. Such studies are limited, because they examine only one gene at a time, when a number of different genes contribute to cone dysfunction, researchers say. By comparing the armadillo gene to other closely related mammals, a team of scientists has now identified several cone-related genes in the armadillo genome that became nonfunctional millions of years ago, they report today at the Society for Neuroscience conference in San Diego, California. This makes the animals "excellent candidates" for gene therapy experiments that could restore color vision and point the way to potential human treatments, they say. © 2013 American Association for the Advancement of Science.
SAN DIEGO, CALIFORNIA—How do we recognize emotions in the facial expressions of others? A small, almond-shaped structure called the amygdala, located deep within the brain (yellow in image above), plays a key role, but exactly what it responds to is unclear. To learn more, neuroscientists implanted electrodes into the amygdalae of seven epileptic patients who were about to undergo brain surgery for their condition. They recorded the activity of 200 single amygdala neurons and determined how they responded while the patients viewed photographs of happy and fearful faces. The team found a subset of cells that distinguish between what the patients thought to be happy and fearful faces, even when they perceived ambiguous facial expressions incorrectly. (The team carefully manipulated some of the photos of fearful faces, so that some of the subjects perceived them as being neutral.) The findings, presented here yesterday at the 43rd annual meeting of the Society for Neuroscience, suggest that amygdala neurons respond to the subjective judgement of emotions in facial expressions, rather than the visual characteristics of faces that convey emotions. The scientists also found that the cellular responses persisted long after each of the photographs disappeared, further suggesting that the amygdala cooperates with other brain regions to create awareness of the emotional content of faces. Thus, when it comes to recognizing the facial expressions of others, what we think we see seems to be more important than what we actually see. © 2013 American Association for the Advancement of Science.
Ewen Callaway Children with autism make less eye contact than others of the same age, an indicator that is used to diagnose the developmental disorder after the age of two years. But a paper published today in Nature1 reports that infants as young as two months can display signs of this condition, the earliest detection of autism symptoms yet. If the small study can be replicated in a larger population, it might provide a way of diagnosing autism in infants so that therapies can begin early, says Warren Jones, research director at the Marcus Autism Center in Atlanta, Georgia. Jones and colleague Ami Klin studied 110 infants from birth — 59 of whom had an increased risk of being diagnosed with autism because they had a sibling with the disorder, and 51 of whom were at lower risk. One in every 88 children has an autism spectrum disorder (ASD), according to the most recent survey by the US Centers for Disease Control and Prevention in Atlanta. At ten regular intervals over the course of two years, the researchers in the new study showed infants video images of their carers and used eye-tracking equipment and software to track where the babies gazed. “Babies come into the world with a lot of predispositions towards making eye contact,” says Jones. “Young babies look more at the eyes than at any part of the face, and they look more at the face than at any part of the body.” Twelve children from the high-risk group were diagnosed with an ASD — all but two of them boys — and one male from the low-risk group was similarly diagnosed. Between two and six months of age, these children tended to look at eyes less and less over time. However, when the study began, these infants tended to gaze at eyes just as often as children who would not later develop autism. © 2013 Nature Publishing Group
by Flora Graham These specs do more than bring blurry things into focus. This prototype pair of smart glasses translates visual information into images that blind people can see. Many people who are registered as blind can perceive some light and motion. The glasses, developed by Stephen Hicks of the University of Oxford, are an attempt to make that residual vision as useful as possible. They use two cameras, or a camera and an infrared projector that can detect the distance to nearby objects. They also have a gyroscope, a compass and GPS to help orient the wearer. The collected information can be translated into a variety of images on the transparent OLED displays, depending on what is most useful to the person sporting the shades. For example, objects can be made clearer against the background, or the distance to obstacles can be indicated by the varying brightness of an image. Hicks has won the Royal Society's Brian Mercer Award for Innovation for his work on the smart glasses. He plans to use the £50,000 prize money to add object and text recognition to the glasses' abilities. © Copyright Reed Business Information Ltd.
By Cheryl G. Murphy Is it possible that our vision can affect our taste perception? Let’s review some examples of studies that claim to have demonstrated that sometimes what we see can override what we think we taste. From wine to cheese to soft drinks and more it seems that by playing with the color palette of food one can trick our palates into thinking we taste things that aren’t necessarily there. © 2013 Scientific American
Reindeer may have a unique way of coping with the perpetual darkness of Arctic winters: During that season, their eyes become far more sensitive to light. Like many vertebrates and most mammals, especially those that are nocturnal, reindeer (Rangifer tarandus) have a light-reflecting layer of collagen-containing tissue behind the retinas of their eyes. This structure, called the tapetum lucidum (Latin for “bright tapestry”), gives the eye’s light-sensitive neurons a second chance to detect scarce photons in low-light conditions. (The layer also produces the “eyeshine” that can make animal eyes appear to glow in the dark.) During sunny months, reindeer have yellow eyeshine. But in the wintertime, light reflected from the tapetum lucidum takes on a decidedly bluish sheen—a seasonal shift that hasn’t been noted in other mammals, the researchers say. To study this unusual color change, the researchers brought some disembodied reindeer eyeballs into the lab and placed small weights on them. When under pressure, the eyeballs changed the color of eyeshine almost immediately. That fits with what happens in the wild over the course of seasons, the researchers say. In winter, reindeer pupils are constantly dilated, which increases fluid pressure. That, in turn, decreases the spacing of collagen fibers in the tapetum lucidum, further increasing the scattering of light within the eye and shifting the reflected light toward the lower wavelengths of light which are predominant at dusk. These changes make the reindeer’s eyes between 100 and 1000 times more light-sensitive, the researchers report today in the Proceedings of the Royal Society B. Although this decreases the creature’s sharpness of vision, it’s a tradeoff that, on the whole, probably boosts reindeer survival by helping them better detect predators in the dark, the researchers contend. © 2013 American Association for the Advancement of Science
Link ID: 18852 - Posted: 10.30.2013
Think fast. The deadly threat of snakes may have driven humans to develop a complex and specialized visual system. The sinuous shape triggers a primal jolt of recognition: snake! A new study of the monkey brain suggests that primates are uniquely adapted to recognize the features of this slithering threat and react in a flash. The results lend support to a controversial hypothesis: that primates as we know them would never have evolved without snakes. A tussle with a snake meant almost certain death for our preprimate ancestors. The reptiles slithered through the forests of the supercontinent Gondwana roughly 100 million years ago, squeezing the life out of the tiny rodent-sized mammalian ancestors of modern primates. About 40 million years later, likely after primates had emerged, some snakes began injecting poison, which made them an even deadlier and more immediate threat. Snakes were “the first and most persistent predators” of early mammals, says Lynne Isbell, a behavioral ecologist the University of California, Davis. They were such a critical threat, she has long argued, that they shaped the emergence and evolution of primates. By selecting for traits that helped animals avoid them, snakes ultimately endowed us with forward-facing eyes, for example, and enlarged visual centers deep in our brains that are specialized for picking out specific features in the world around us, such as the general shape of a snake’s body camouflaged among leaves. Isbell published her “Snake Detection Theory” in 2006. To support it, she showed that the rare primates that have not encountered venomous snakes in the course of their evolution, such as lemurs in Madagascar, have poorer vision than those that evolved alongside snakes. © 2013 American Association for the Advancement of Science
By Daisy Yuhas For more than a century researchers have been trying and failing to link perception and intelligence—for instance, do intelligent people see more detail in a scene? Now scientists at the University of Rochester and at Vanderbilt University have demonstrated that high IQ may be best predicted by combining what we perceive and what we cannot. In two studies in the journal Current Biology, researchers asked 67 people to take IQ tests. They then viewed milli-second-long video clips in which black-and-white stripes moved left or right. The split-second films challenged viewers: the stripes moved within a circular frame that could differ in size, varying from the width of a thumb to a fist held at arm's length. After each clip, the viewers guessed whether the bars moved toward the left or right. The investigators discovered that performance on this test was more correlated with IQ than any other sensory-intelligence link ever explored—but the high-IQ participants were not simply scoring better overall. Individuals with high IQ indeed detected movement accurately within the smallest frame—a finding that suggests, perhaps unsurprisingly, that the ability to rapidly process information contributes to intelligence. More intriguing was the fact that subjects who had higher IQ struggled more than other subjects to detect motion in the largest frame. The authors suggest that the brain may perceive large objects as background and subsequently may try to ignore their movements. “Suppressing information is a really important thing that the brain does,” explains University of Rochester neuroscientist Duje Tadin. He explains that the findings underscore how intelligence requires that we think fast but focus selectively, ignoring distractions. © 2013 Scientific American
Kerri Smith Jack Gallant perches on the edge of a swivel chair in his lab at the University of California, Berkeley, fixated on the screen of a computer that is trying to decode someone's thoughts. On the left-hand side of the screen is a reel of film clips that Gallant showed to a study participant during a brain scan. And on the right side of the screen, the computer program uses only the details of that scan to guess what the participant was watching at the time. Anne Hathaway's face appears in a clip from the film Bride Wars, engaged in heated conversation with Kate Hudson. The algorithm confidently labels them with the words 'woman' and 'talk', in large type. Another clip appears — an underwater scene from a wildlife documentary. The program struggles, and eventually offers 'whale' and 'swim' in a small, tentative font. “This is a manatee, but it doesn't know what that is,” says Gallant, talking about the program as one might a recalcitrant student. They had trained the program, he explains, by showing it patterns of brain activity elicited by a range of images and film clips. His program had encountered large aquatic mammals before, but never a manatee. Groups around the world are using techniques like these to try to decode brain scans and decipher what people are seeing, hearing and feeling, as well as what they remember or even dream about. © 2013 Nature Publishing Group
By Phil Plait Thanks to my evil twin Richard Wiseman (a UK psychologist who specializes in studying the ways we perceive things around us, and how easily we can be fooled), I saw this masterful illusion video that will keep you guessing on what’s real and what isn’t. It’s only two minutes long, so give it a gander: Cool, eh? The reason you got fooled, at least twice, is that we get confused when our three-dimensional world is translated into two dimensions. We perceive distance for nearby objects using binocular vision, which depends on the angles between our eyes and the objects. If you create a picture of an object that is carefully distorted to match those changing angles, you can fool the brain into thinking it’s seeing a real object when in fact it’s a flat representation. We’re actually very good at taking subtle cues and turning them into three-dimensional interpretations. However, because of that very sensitivity, it’s easy to throw a monkey in the wrench, messing up our perception. Still don’t believe me? Then watch this, and if it doesn’t melt your brain, I can no longer help you. Our brains are very, very easy to fool. I’ll note that the way we see color is very easy to trick, too. I wrote an article about a fantastic, astonishing color illusion back in 2009, and it spurred a lot of arguments in the comments, even when I showed clearly how it works. Amazing. © 2013 The Slate Group, LLC
Link ID: 18825 - Posted: 10.23.2013
by Susan Milius Your calamari, it turns out, may have come from a temporary transvestite with rainbows in its armpits. Well, not armpits, but spots just below where the fins flare out. “Finpits,” cell biologist Daniel DeMartini nicknamed them. He and his colleagues have documented unusual color-change displays in female California market squid, popular in restaurants. Squids, octopuses and cuttlefishes are nature’s iPads, changing their living pixels at will. DeMartini, of the University of California, Santa Barbara, saw so many sunset shimmers, blink-of-an-eye blackouts and other marvels in California’s Doryteuthis opalescens that it took him a while to notice that only females shimmered the finpit stripe. It shows up now and then during life, and reliably for about 24 hours after decapitation, DeMartini found. The squid are color-blind, and what prompts their display is known only to them. But the researchers have figured out how it works. The squid make rainbows when color-change cells called iridocytes lose water. Other kinds of color-change cells work their magic via pigments, but not iridocytes. “If you take a bunch of iridocyte cells in red, blue, green or yellow and you grind them up, then you wouldn’t see any color,” DeMartini says. Instead, little stacks of protein plates inside the cells turn colorful only when water rushes out of the stack. How closely the plates snug together determines whether the stack looks blue, scarlet or anything in between. © Society for Science & the Public 2000 - 2013
By Brian Palmer Myopia isn’t an infectious disease, but it has reached nearly epidemic proportions in parts of Asia. In Taiwan, for example, the percentage of 7-year-old children suffering from nearsightedness increased from 5.8 percent in 1983 to 21 percent in 2000. An incredible 81 percent of Taiwanese 15-year-olds are myopic. If you think that the consequences of myopia are limited to a lifetime of wearing spectacles—and, let’s be honest, small children look adorable in eyeglasses—you are mistaken. The prevalence of high myopia, an extreme form of the disorder, in Asia has more than doubled since the 1980s, and children who suffer myopia early in life are more likely to progress to high myopia. High myopia is a risk factor for such serious problems as retinal detachment, glaucoma, early-onset cataracts, and blindness. The explosion of myopia is a serious public health concern, and doctors have struggled to identify the source of the problem. Nearsightedness has a strong element of heritability, but the surge in cases shows that a child’s environment plays a significant role. A variety of risk factors has been linked to the disorder: frequent reading, participation in sports, television watching, protein intake, and depression. When each risk factor was isolated, however, its overall effect on myopia rates seemed to be fairly minimal. Researchers believe they are now closing in on a primary culprit: too much time indoors. In 2008 orthoptics professor Kathryn Rose found that only 3.3 percent of 6- and 7-year-olds of Chinese descent living in Sydney, Australia, suffered myopia, compared with 29.1 percent of those living in Singapore. The usual suspects, reading and time in front of an electronic screen, couldn’t account for the discrepancy. The Australian cohort read a few more books and spent slightly more time in front of the computer, but the Singaporean children watched a little more television. On the whole, the differences were small and probably canceled each other out. The most glaring difference between the groups was that the Australian kids spent 13.75 hours per week outdoors compared with a rather sad 3.05 hours for the children in Singapore. © 2013 The Slate Group, LLC.
Monya Baker When Cris Niell said that he wanted to study how mice see, it did not go over well with more-senior neuroscientists. Mice are nocturnal and navigate largely using their noses and whiskers, so many researchers believed that the nursery rhyme — Three Blind Mice — was true enough to make many vision experiments pointless. The obvious alternative model was monkeys, which have large, forward-looking eyes and keen vision. What's more, scientists could rely on decades of established techniques using primates, and it is relatively straightforward to apply the results to the human visual system. “People were saying, 'studying vision in mice, that's crazy,'” Niell recalls. But he was convinced that the rodents offered unique opportunities. Since the 1960s, researchers have used cats and monkeys to uncover important clues about how the brain turns information from the eyes into images recognized by the mind. But to investigate that process at the cellular level, researchers must be able to manipulate and monitor neurons precisely — difficult in cats and monkeys, much easier in mice. If mice and primates turned out to process visual stimuli similarly, Niell thought, that discovery could unleash a torrent of data about how information is extracted from stimuli — and even, more generally, about how the brain works. He found a rare supporter in Michael Stryker at the University of California, San Francisco, who had already seen his share of crazy experiments in mouse vision. Stryker offered Niell a postdoctoral position in his lab, and the pair began setting up experiments in 2005. Nearly a decade later, the two researchers are in better company. At last year's annual meeting of the Society for Neuroscience, Niell attended packed sessions on mouse vision. © 2013 Nature Publishing Group
Link ID: 18782 - Posted: 10.12.2013