Chapter 7. Vision: From Eye to Brain
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Madhusree Mukerjee By displaying images on an iPad, researchers tested patients' ability to detect contrast after their vision was restored by cataract surgery. In a study of congenitally blind children who underwent surgery to restore vision, researchers have found that the brain can still learn to use the newly acquired sense much later in life than previously thought. Healthy infants start learning to discern objects, typically by their form and colour, from the moment they open their eyes. By the time a baby is a year old vision development is more or less complete, although refinements continue through childhood. But as the brain grows older, it becomes less adaptable, neuroscientists generally believe. "The dogma is that after a certain age the brain is unable to process visual inputs it has never received before," explains cognitive scientist Amy Kalia of the Massachusetts Institute of Technology (MIT) in Cambridge. Consequently, eye surgeons in India often refuse to treat children blinded by cataracts since infancy if they are over the age of seven. Such children are not usually found in wealthier countries such as the United States — where cataracts are treated as early as possible — but are tragically plentiful in India. In the study, which was published last week in Proceedings of the National Academy of Sciences1, Kalia and her collaborators followed 11 children enrolled in Project Prakash2, a humanitarian and scientific effort in India that provides corrective surgery to children with treatable cataracts and subsequently studies their visual abilities. ('Prakash' is Sanskrit for light.) © 2014 Nature Publishing Group
Mantis shrimp's super colour vision debunked Jessica Morrison Mantis shrimp don’t see colour like we do. Although the crustaceans have many more types of light-detecting cell than humans, their ability to discriminate between colours is limited, says a report published today in Science1. Researchers found that the mantis shrimp’s colour vision relies on a simple, efficient and previously unknown mechanism that operates at the level of individual photoreceptors. The results upend scientists' suspicions that the shrimp, with 12 different types of colour photoreceptors, could see hues that humans, with just 3, could not, says study co-author Justin Marshall, a marine neuroscientist at the University of Queensland in Brisbane, Australia. When the human eye sees a yellow leaf, photoreceptors send signals to the brain announcing relative levels of stimuli: receptors sensitive to red and green light report a lot of activity, whereas receptors sensitive to blue light report little. The brain compares the information from each type of receptor to come up with yellow. Using this system, the human eye can distinguish between millions of different colours. To test whether the mantis shrimp, with its 12 receptors, can distinguish many more, Marshall's team trained shrimp of the species Haptosquilla trispinosa to recognize one of ten specific colour wavelengths, ranging from 400 to 650 nanometres, by showing them two colours and giving them a frozen prawn or mussel when they picked the right one. In subsequent testing, the shrimp could discriminate between their trained wavelengths and another colour 50–100 nanometres up or down the spectrum. But when the difference between the trained and test wavelengths was reduced to 12–25 nanometres, the shrimp could no longer tell them apart. © 2014 Nature Publishing Group
Want to read someone’s mind? Look at their pupils. A person about to answer “yes” to a question, especially if they are more used to answering “no,” will have more enlarged pupils than someone about to answer “no,” according to a new study. Normally, pupils dilate when a person is in a darkened environment to let more light into the eye and allow better vision. But pupil size can also be altered by levels of signaling chemicals naturally produced by the brain. In the study, published online this week in the Proceedings of the National Academy of Sciences, scientists observed the pupils of 29 people as they pressed a “yes” or “no” button to indicate whether they’d seen a difficult-to-detect visual cue on a screen in front of them. When a person was deciding how to answer—in the seconds before pressing a button—their pupils grew larger. And if a person was normally biased toward answering “no” when they weren’t sure on the visual cue, then the pupil change was even more profound in the decision-making seconds before a “yes” answer. The finding could lead to new ways to detect people’s intrinsic biases and how confident they are in an answer given, important variables in many sociological and psychological studies. © 2014 American Association for the Advancement of Science.
|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