Chapter 10. Vision: From Eye to Brain
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By Jessica Hamzelou People who experience migraines that are made worse by light might be better off seeing the world in green. While white, blue, red and amber light all increase migraine pain, low-intensity green light seems to reduce it. The team behind the finding hope that specially developed sunglasses that screen out all wavelengths of light except green could help migraineurs. Many people experience sensitivity to light during a migraine. Photophobia, as it is known, can leave migraineurs resorting to sunglasses in well-lit rooms, or seeking the comfort of darkness. The reaction is thought to be due to the brain’s wiring. In a brain region called the thalamus, neurons that transmit sensory information from our retinas cross over with other neurons that signal pain. As a result, during migraine, light can worsen pain and pain can cause visual disturbance, says Rami Burstein at Harvard University. But not all colours of light have the same effect. Six years ago, Burstein and his colleagues studied migraine in sufferers who are blind, either due to the loss of an eye or retina, or because of retinal damage. They found that people who had some remaining retinal cells had worse migraines when they were in brightly lit environments, and that blue light seemed to have the strongest impact. The finding caused a flurry of excitement, and the promotion of sunglasses that filter out blue light. © Copyright Reed Business Information Ltd.
Sara Reardon Every time something poked its foot, the mouse jumped in pain. Researchers at Circuit Therapeutics, a start-up company in Menlo Park, California, had made the animal hypersensitive to touch by tying off a nerve in its leg. But when they shone a yellow light on its foot while poking it, the mouse did not react. The treatment is one of several nearing clinical use that draw on optogenetics — a technique in which light is used to control genes and neuron firing. In March, RetroSense Therapeutics of Ann Arbor, Michigan, began the first clinical-safety trial of an optogenetic therapy to treat the vision disorder retinitis pigmentosa. Many scientists are waiting to see how the trial turns out before they decide how to move forward with their own research on a number of different applications. “I think it will embolden people if there’s good news,” says Robert Gereau, a pain researcher at Washington University in St Louis, Missouri. “It opens up a whole new range of possiblilities for how to treat neurological diseases.” Retinitis pigmentosa destroys photoreceptors in the eye. RetroSense’s treatment seeks to compensate for this loss by conferring light sensitivity to retinal ganglion cells, which normally help to pass visual signals from photoreceptors to the brain. The therapy involves injecting patients who are blind or mostly blind with viruses carrying genes that encode light-sensitive proteins called opsins. The cells fire when stimulated with blue light, passing the visual information to the brain. Chief executive Sean Ainsworth says that the company has injected several individuals in the United States with the treatment, and plans to enroll a total of 15 blind patients in its trial. RetroSense will follow them for two years, but may release some preliminary data later this year. © 2016 Nature Publishing Group
Link ID: 22235 - Posted: 05.21.2016
By Daniel Barron No matter where we call home, where we were raised, or what we ate for breakfast, our brains process information pretty much the same as anyone else in the world. Which makes sense—our genomes are 99.6-99.9% identical, which makes our brains nearly so. Look at a landscape or cityscape and comparable computations occur in your brain as in someone from another background or country. Zhangjiajie National Forest Park, China. Credit: Chensiyuan, via Wikimedia Commons under GFDL Consider my recent walk through China’s Zhangjiajie National Forest Park, an inspiration for James Cameron’s Avatar. Some of our first steps into the park involved a 1,070 foot ascent in the Bailong elevator, the world’s tallest outdoor elevator. Crammed within the carriage were travelers from Japan, India, China, the U.S.A., and Korea. No matter our origin, the Wulingyuan landscape didn’t disappoint: the towering red and green rock formations stretched towards the sky as they defied gravity. Gasps and awes were our linguistic currency while our visual cortices gleefully fired away. The approximately 3000 quartzite sandstone pillars, with their unusual red and green contrasts, mesmerized our visual centers, demanding our attention. One of the brain’s earliest visual processing centers, V1, lies at the middle of the back of our head. V1 identifies simple forms like vertical, horizontal, and diagonal edges of contrasting intensities, or lines. Look at a vertical line, and neurons that are sensitive to vertical lines will fire more quickly; look at a horizontal line, and our horizontal neurons buzz away. © 2016 Scientific American
By Stephen L. Macknik, Susana Martinez-Conde The renowned Slydini holds up an empty box for all to see. It is not really a box—just four connected cloth-covered cardboard walls, forming a floppy parallelogram with no bottom or top. Yet when the magician sets it down on a table, it looks like an ordinary container. Now he begins to roll large yellow sheets of tissue paper into balls. He claps his hands—SMACK!—as he crumples each new ball in a fist and then straightens his arm, wordlessly compelling the audience to gaze after his closed hand. He opens it, and ... the ball is still there. Nothing happened. Huh. Slydini's hand closes once more around the tissue, and it starts snaking around, slowly and gracefully, like a belly dancer's. The performance is mesmerizing. With his free hand, he grabs an imaginary pinch of pixie dust from the box to sprinkle on top of the other hand. This time he opens his hand to reveal that the tissue is gone! Four balls disappear in this fashion. Then, for the finale, Slydini tips the box forward and shows the impossible: all four balls have mysteriously reappeared inside. Slydini famously performed this act on The Dick Cavett Show in 1978. It was one of his iconic tricks. Despite the prestidigitator's incredible showmanship, though, the sleight only works because your brain cannot multitask. © 2016 Scientific American,
Link ID: 22114 - Posted: 04.19.2016
By Roni Caryn Rabin Here’s another reason to eat your fruits and veggies: You may reduce your risk of vision loss from cataracts. Cataracts that cloud the lenses of the eye develop naturally with age, but a new study is one of the first to suggest that diet may play a greater role than genetics in their progression. Researchers had about 1,000 pairs of female twins in Britain fill out detailed food questionnaires that tracked their nutrient intake. Their mean age was just over 60. The study participants underwent digital imaging of the eye to measure the progression of cataracts. The researchers found that women who consumed diets rich in vitamin C and who ate about two servings of fruit and two servings of vegetables a day had a 20 percent lower risk of cataracts than those who ate a less nutrient-rich diet. Ten years later, the scientists followed up with 324 of the twin pairs, and found that those who had reported consuming more vitamin C in their diet — at least twice the recommended dietary allowance of 75 milligrams a day for women (the R.D.A. for adult men is 90 milligrams) — had a 33 percent lower risk of their cataracts progressing than those who get less vitamin C. The researchers concluded that genetic factors account for about 35 percent of the difference in cataract progression, while environmental factors like diet account for 65 percent. “We found no beneficial effect from supplements, only from the vitamin C in the diet,” said Dr. Christopher Hammond, a professor of ophthalmology at King’s College London and an author of the study,published in Ophthalmology. Foods high in vitamin C include oranges, cantaloupe, kiwi, broccoli and dark leafy greens. © 2016 The New York Times Company
Link ID: 22044 - Posted: 03.29.2016
By C. CLAIBORNE RAY Current treatments for the so-called wet form of macular degeneration, involving injections inside the eye, are already “very effective” compared with laser treatments, which were used before intravitreal injections, said Dr. Ronald C. Gentile, the surgeon director at the New York Eye and Ear Infirmary of Mount Sinai. But several ways to improve their results are in the works, he said. The shots deliver drugs that fight a substance called vascular endothelial growth factor, and thus shrink the growth of what amounts to an abnormal blood vessel harming the retina. A major hurdle now involves the frequency and cost of the needed treatments. Once the drug is inside the eye, the effects wear off and a new injection is needed, Dr. Gentile said. The shots are also less effective in some patients. Even when they work well, some people need a shot as often as every four weeks, while some can wait two or three months. If both eyes are affected and the period of effectiveness is short, doctor visits can be very frequent, so drugs that last longer in the eyeball are being pursued. Researchers are working on slow-release medications as well as a delivery system that acts like a tiny pump in the eye, with a tank that can be refilled every six months. There is also a new drug target: a substance called platelet-derived growth factor that causes abnormal vessel growth as well. Combination drug treatments may be more effective against macular degeneration, Dr. Gentile said. The so-called dry form of macular degeneration, which often underlies the wet form, is harder to fight, he said, and although advances are being made, current antioxidant treatments with vitamins and minerals do not to improve vision; they just prevent it from worsening. © 2016 The New York Times Company
Link ID: 22004 - Posted: 03.19.2016
BRAINS get data about the world through senses – sight, hearing, taste, smell and touch. In a lab in North Carolina, a group of rats is getting an extra one. Thanks to implants in their brains, they have learned to sense and react to infrared light. The rats show the brain’s ability to process unfamiliar data– an early step towards augmenting the human brain. Miguel Nicolelis of Duke University School of Medicine is leading the experiment. His team implanted four clusters of electrodes in the rats’ barrel cortex – the part of the brain that handles whisker sensation (doi.org/bdb6). Each cluster is connected to a sensor that converts infrared light into an electrical signal. Feeding stations placed at the four corners of the rats’ cage take turns emitting infrared signals that guide the rats to them, releasing a reward only when the rats press a button on the feeding station that is emiting the infrared signal. In an older, single sensor version of the experiment, it took the rats one month to adapt. With four sensors, it took them just three days. “This is a truly remarkable demonstration of the plasticity of the mammalian brain,” says Christopher James of the University of Warwick, UK. All the extra data that goes into making the rats’ new sense doesn’t appear to diminish their original senses. “The results show that nature has apparently designed the adult mammalian brain with the possibility of upgrades, and Nicolelis’ team is leading the way showing how to do it,” says Andrea Stocco of the University of Washington in Seattle. © Copyright Reed Business Information Ltd.
By BARBARA K. LIPSKA AS the director of the human brain bank at the National Institute of Mental Health, I am surrounded by brains, some floating in jars of formalin and others icebound in freezers. As part of my work, I cut these brains into tiny pieces and study their molecular and genetic structure. My specialty is schizophrenia, a devastating disease that often makes it difficult for the patient to discern what is real and what is not. I examine the brains of people with schizophrenia whose suffering was so acute that they committed suicide. I had always done my work with great passion, but I don’t think I really understood what was at stake until my own brain stopped working. In the first days of 2015, I was sitting at my desk when something freakish happened. I extended my arm to turn on the computer, and to my astonishment realized that my right hand disappeared when I moved it to the right lower quadrant of the keyboard. I tried again, and the same thing happened: The hand disappeared completely as if it were cut off at the wrist. It felt like a magic trick — mesmerizing, and totally inexplicable. Stricken with fear, I kept trying to find my right hand, but it was gone. I had battled breast cancer in 2009 and melanoma in 2012, but I had never considered the possibility of a brain tumor. I knew immediately that this was the most logical explanation for my symptoms, and yet I quickly dismissed the thought. Instead I headed to a conference room. My colleagues and I had a meeting scheduled to review our new data on the molecular composition of schizophrenia patients’ frontal cortex, a brain region that shapes who we are — our thoughts, emotions, memories. But I couldn’t focus on the meeting because the other scientists’ faces kept vanishing. Thoughts about a brain tumor crept quietly into my consciousness again, then screamed for attention. © 2016 The New York Times Company
Monya Baker A surgical technique to treat cataracts in children spurs stem cells to generate a new, clear lens. Discs made of multiple types of eye tissue have been grown from human stem cells — and that tissue has been used to restore sight in rabbits. The work, reported today in Nature1, suggests that induced pluripotent stem (iPS) cells — stem cells generated from adult cells — could one day be harnessed to provide replacement corneal or lens tissue for human eyes. The discs also could be used to study how eye tissue and congenital eye diseases develop. “The potential of this technique is mind-boggling,” says Mark Daniell, head of corneal research at the Centre for Eye Research Australia in Melbourne, who was not involved in the research. “It’s almost like an eye in a dish.” A second, unrelated paper in Nature2 describes a surgical procedure that activates the body’s own stem cells to regenerate a clear, functioning lens in the eyes of babies born with cataracts. The two studies are “amazing, almost like science fiction”, Daniell says. In the first study, a team led by Kohji Nishida, an ophthalmologist at Osaka University Graduate School of Medicine in Japan, cultivated human iPS cells to produce discs that contained several types of eye tissue. © 2016 Nature Publishing Group
Link ID: 21971 - Posted: 03.10.2016
By Virginia Morell Butterflies may not have a human’s sharp vision, but their eyes beat us in other ways. Their visual fields are larger, they’re better at perceiving fast-moving objects, and they can distinguish ultraviolet and polarized light. Now, it turns out that one species of swallowtail butterfly from Australasia, the common bluebottle (Graphium sarpedon, pictured), known for its conspicuous blue-green markings, is even better equipped for such visual tasks. Each of their eyes, scientists report in Frontiers in Ecology and Evolution, contains at least 15 different types of photoreceptors, the light-detecting cells required for color vision. These are comparable to the rods and cones found in our eyes. To understand how the spectrally complex retinas of butterflies evolved, the researchers used physiological, anatomical, and molecular experiments to examine the eyes of 200 male bluebottles collected in Japan. (Only males were used because the scientists failed to catch a sufficient number of females.) They found that different colors stimulate each class of receptor. For instance, UV light stimulates one, while slightly different blue lights set off three others; and green lights trigger four more. Most insect species have only three classes of photoreceptors. Even humans have only three cones, yet we still see millions of colors. Butterflies need only four receptor classes for color vision, including spectra in the UV region. So why did this species evolve 11 more? The scientists suspect that some of the receptors must be tuned to perceive specific things of great ecological importance to these iridescent butterflies—such as sex. For instance, with eyes alert to the slightest variation in the blue-green spectrum, male bluebottles can spot and chase their rivals, even when they’re flying against a blue sky. © 2016 American Association for the Advancement of Science
Link ID: 21968 - Posted: 03.09.2016
Our eyes constantly send bits of information about the world around us to our brains where the information is assembled into objects we recognize. Along the way, a series of neurons in the eye uses electrical and chemical signals to relay the information. In a study of mice, National Institutes of Health scientists showed how one type of neuron may do this to distinguish moving objects. The study suggests that the NMDA receptor, a protein normally associated with learning and memory, may help neurons in the eye and the brain relay that information. “The eye is a window onto the outside world and the inner workings of the brain,” said Jeffrey S. Diamond, Ph.D., senior scientist at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS), and the senior author of the study published in Neuron. “Our results show how neurons in the eye and the brain may use NMDA receptors to help them detect motion in a complex visual world.” Vision begins when light enters the eye and hits the retina, which lines the back of the eyeball. Neurons in the retina convert light into nerve signals which are then sent to the brain. Using retinas isolated from mice, Dr. Alon Poleg-Polsky, Ph.D. a postdoctoral fellow in Dr. Diamond’s lab, studied neurons called directionally selective retinal ganglion cells (DSGCs), which are known to fire and send signals to the brain in response to objects moving in specific directions across the eye. Electrical recordings showed that some of these cells fired when a bar of light passed across the retina from left to right, whereas others responded to light crossing in the opposite direction. Previous studies suggested these unique responses are controlled by incoming signals sent from neighboring cells at chemical communication points called synapses. In this study, Dr. Poleg-Polsky discovered that the activity of NMDA receptors at one set of synapses may regulate whether DSGCs sent direction-sensitive information to the brain.
Link ID: 21966 - Posted: 03.08.2016
By C. CLAIBORNE RAY Q. What’s the No. 1 cause of blindness in seniors in the United States? A. “It sounds like a simple question, but there’s no perfect answer,” said Dr. Susan Vitale, a research epidemiologist at the National Eye Institute of the National Institutes of Health. “It depends on age, how blindness is measured and how statistics are collected.” For example, some studies have relied on the self-reported answer to the vague question: “Do you have vision problems?” The best available estimates, she said, come from a 2004 paper aggregating many other studies, some in the United States and some in other countries, updated by applying later census data. This paper and others have found striking differences by age and by racial and socioeconomic groups, Dr. Vitale said. In white people, she said, the major cause of blindness at older ages is usually age-related macular degeneration, progressive damage to the central portion of the retina. In older black people, the major causes are likely to be glaucoma or cataracts. In older people of working age, from their 40s to their 60s, the major cause, regardless of race, is diabetic retinopathy, damage to the retina as a result of diabetes. Many studies have shown that white people are more likely to have age-related macular degeneration, Dr. Vitale said, but as for cataracts, for which blindness is preventable by surgery, there are questions about access to health care and whether those affected can get the needed surgery. It is not known why black people are at higher risk of glaucoma. There are also some gender differences, she said, with white women more likely than white men to become blind. Studies have not found the same difference by gender in black and Hispanic people. Because many of the causes of blindness at all ages are preventable, Dr. Vitale said, it is essential to have regular eye checkups, even if there are no obvious symptoms. © 2016 The New York Times Company
Link ID: 21958 - Posted: 03.07.2016
By Susana Martinez-Conde, Stephen L. Macknik In the forests of Australia and New Guinea lives a pigeon-sized creature that is not only a master builder but a clever illusionist, too. The great bowerbird (Chlamydera nuchalis)—a cousin of crows and jays—has an elaborate mating ritual that relies on the male's ability to conjure forced perspective. Throughout the year he painstakingly builds and maintains his bower: a 60-centimeter-long corridor made of twigs, leading to a courtyard decorated with gray and white pebbles, shells and bones. Some species also add flowers, fruits, feathers, bottle caps, acorns, abandoned toys—whatever colorful knickknacks they can find. The male takes great care to arrange the objects according to size so that the smallest pieces are closest to the bower's entrance and the largest items are farthest away. The elaborate structure is not a nest. Its sole purpose is to attract a female for mating. Once construction is complete, the male performs in the courtyard for a visiting female, who—poised like a critical American Idol judge—evaluates the routine from the middle of the corridor. He sings, dances and prances, tossing around a few select trinkets to impress his potential mate. Her viewpoint is very narrow, and so she perceives objects paving the courtyard as being uniform in size. This forced perspective makes the choice offerings appear grander and therefore all the more enticing. The offerings, and the male himself, appear larger than life because of an effect that visual scientists call the Ebbinghaus illusion, which causes an object to look bigger if it is surrounded by smaller objects. © 2016 Scientific American
Floaters, those small dots or cobweb-shaped patches that move or “float” through the field of vision, can be alarming. Though many are harmless, if you develop a new floater, “you need to be seen pretty quickly” by an eye doctor in order to rule out a retinal tear or detachment, said Dr. Rebecca Taylor, a spokeswoman for the American Academy of Ophthalmology. Floaters are caused by clumping of the vitreous humor, the gel-like fluid that fills the inside of the eye. Normally, the vitreous gel is anchored to the back of the eye. But as you age, it tends to thin out and may shrink and pull away from the inside surface of the eye, causing clumps or strands of connective tissue to become lodged in the jelly, much as “strands of thread fray when a button comes off on your coat,” Dr. Taylor said. The strands or clumps cast shadows on the retina, appearing as specks, dots, clouds or spider webs in your field of vision. Such changes may occur at younger ages, too, particularly if you are nearsighted or have had a head injury or eye surgery. There is no treatment for floaters, though they usually fade with time. But it’s still important to see a doctor if new floaters arise because the detaching vitreous gel can pull on the retina, causing it to tear, which can lead to retinal detachment, a serious condition. The pulling or tugging on the retina may be perceived as lightning-like flashes, “like a strobe light off to the side of your vision,” Dr. Taylor said. See an eye doctor within 24 to 48 hours if you have a new floater, experience a sudden “storm” of floaters, see a gray curtain or shadow move across your field of vision, or have a sudden decrease in vision. © 2016 The New York Times Company
Link ID: 21868 - Posted: 02.08.2016
By Susana Martinez-Conde Take a look at the red chips on the two Rubik cubes below. They are actually orange on the left and purple on the right, if you look at them in isolation. They only appear more or less equally red across the images because your brain is interpreting them as red chips lit by either yellow or blue light. This kind of misperception is an example of perceptual constancy, the mechanism that allows you to recognize an object as being the same in different environments, and under very diverse lighting conditions. Constancy illusions are adaptive: consider what would have happened if your ancestors thought a friend became a foe whenever a cloud hid the sun, or if they lost track of their belongings–and even their own children—every time they stepped out of the cave and into the sunlight. Why, they might have even eaten their own kids! You are here because the perceptual systems of your predecessors were resistant to annoying changes in the physical reality–as is your own (adult) perception. There are many indications that constancy effects must have helped us survive (and continue to do so). One such clue is that we are not born with perceptual constancy, but develop it many months after birth. So at first we see all differences, and then we learn to ignore certain types of differences so that we can recognize the same object as unchanging in many varied scenarios. When perceptual constancy arises, we lose the ability to detect multiple contradictions that are nevertheless highly noticeable to young babies. © 2016 Scientific American
by Laura Sanders Young babies get a bad rap. They’re helpless, fickle and noisy. And even though they allegedly sleep for 16 hours a day, those hours come in 20-minute increments. Yet hidden in the chaos of a young infant’s life are some truly magnificent skills — perceptual feats that put adults to shame. So next time your baby loses it because she can’t get her thumb into her mouth, keep in mind that her strengths lie elsewhere. Six-month-old babies can spot subtle differences between two monkey faces easy as pie. But 9-month-olds — and adults — are blind to the differences. In a 2002 study of facial recognition, scientists pitted 30 6-month-old babies against 30 9-month-olds and 11 adults. First, the groups got familiar with a series of monkey and human faces that flashed on a screen. Then new faces showed up, interspersed with already familiar faces. The idea is that the babies would spend more time looking at new faces than ones they had already seen. When viewing human faces, all of the observers, babies and adults alike, did indeed spend more time looking at the new people, showing that they could easily pick out familiar human faces. But when it came to recognizing monkey faces, the youngsters blew the competition out of the water. Six-month-old babies recognized familiar monkey faces and stared at the newcomers longer. But both adults and 9-month-old babies were flummoxed, and looked at the new and familiar monkey faces for about the same amount of time. © Society for Science & the Public 2000 - 2015
By Ana Swanson Earlier this year, the famous blue-and-black (or white-and-gold) dress captivated the Internet, serving as a reminder that color is truly in the eye of the beholder. The dress was also a lesson in the power of social media, the science of shifting colors, and the fun of optical illusions. Here we present a visual story from February 27 that rounded up some of the best-known optical illusions on the Web. The Internet erupted in an energetic debate yesterday about whether an ugly dress was blue and black or white and gold, with celebrities from Anna Kendrick (white) to Taylor Swift (black) weighing in. (For the record, I’m with Taylor – never a bad camp to be in.) It sounds inane, but the dress question was actually tricky: Some declared themselves firmly in the blue and black camp, only to have the dress appear white and gold when they looked back a few hours later. Wired had the best explanation of the science behind the dress’s shifting colors. When your brain tries to figure out what color something is, it essentially subtracts the lighting and background colors around it, or as the neuroscientist interviewed by Wired says, tries to “discount the chromatic bias of the daylight axis.” This is why you can identify an apple as red whether you see it at noon or at dusk. The dress is on some kind of perceptual boundary, with a pretty even mix of blue, red and green. (Frankly, it’s just a terrible, washed out photo.) So for those who see it as white, your eyes may be subtracting the wrong background and lighting.
Link ID: 21742 - Posted: 01.02.2016
by Laura Sanders There’s only so much brainpower to go around, and when the eyes hog it all, the ears suffer. When challenged with a tough visual task, people are less likely to perceive a tone, scientists report in the Dec. 9 Journal of Neuroscience. The results help explain what parents of screen-obsessed teenagers already know. For the study, people heard a tone while searching for a letter on a computer screen. When the letter was easy to find, participants were pretty good at identifying a tone. But when the search got harder, people were less likely to report hearing the sound, a phenomenon called inattentional deafness. Neural responses to the tone were blunted when people worked on a hard visual task, but not when the visual task was easy, researchers found. By showing that a demanding visual job can siphon resources away from hearing, the results suggest that perceptual overload can jump between senses. © Society for Science & the Public 2000 - 2015
By John Bohannon It may sound like a bird-brained idea, but scientists have trained pigeons to spot cancer in images of biopsied tissue. Individually, the avian analysts can't quite match the accuracy of professional pathologists. But as a flock, they did as well as trained humans, according to a new study appearing this week in PLOS ONE. Cancer diagnosis often begins as a visual challenge: Does this lumpy spot in a mammogram image justify a biopsy? And do cells in biopsy slides look malignant or benign? Training doctors and medical technicians to tell the difference is expensive and time-consuming, and computers aren't yet up to the task. To see whether a different type of trainee could do better, a team led by Richard Levenson, a pathologist and technologist at the University of California, Davis, and Edward Wasserman, a psychologist at the University of Iowa, in Iowa City, turned to pigeons. In spite of their limited intellect, the bobble-headed birds have certain advantages. They have excellent visual systems, similar to, if not better than, a human's. They sense five different colors as opposed to our three, and they don’t “fill in” the gaps like we do when expected shapes are missing. However, training animals to do a sophisticated task is tricky. Animals can pick up on unintentional cues from their trainers and other humans that may help them correctly solve problems. For example, a famous 20th century horse named Clever Hans was purportedly able to do simple arithmetic, but was later shown to be observing the reactions of his human audience. And although animals can perform extremely well on tasks that are confined to limited circumstances, overtraining on one set of materials can lead to total inaccuracy when the same information is conveyed slightly differently. © 2015 American Association for the Advancement of Science
Susan Milius Certain species of the crawling lumps of mollusk called chitons polka-dot their armor-plated backs with hundreds of tiny black eyes. But mixing protection and vision can come at a price. The lenses are rocky nuggets formed mostly of aragonite, the same mineral that pearls and abalone shells are made of. New analyses of these eyes support previous evidence that they form rough images instead of just sensing overall lightness or darkness, says materials scientist Ling Li of Harvard University. Adding eyes to armor does introduce weak spots in the shell. Yet the positioning of the eyes and their growth habits show how chitons compensate for that, Li and his colleagues report in the November 20 Science. Li and coauthor Christine Ortiz of MIT have been studying such trade-offs in biological materials that serve multiple functions. Human designers often need substances that multitask, and the researchers have turned to evolution’s solutions in chitons and other organisms for inspiration. Biologists had known that dozens of chiton species sprinkle their armored plates with simple-seeming eye spots. (The armor has other sensory organs: pores even tinier than the eyes.) But in 2011, a research team showed that the eyes of the West Indian fuzzy chiton (Acanthopleura granulata) were much more remarkable than anyone had realized. Their unusual aragonite lens can detect the difference between a looming black circle and a generally gray field of vision. Researchers could tell because chitons clamped their shells defensively to the bottom when a scary circle appeared but not when an artificial sky turned overall shadowy. © Society for Science & the Public 2000 - 2015