When an archer fish gets peckish and goes hunting for a juicy insect meal, it cruises toward the water’s surface with its ammunition packed in its mouth: As soon as it spots an insect above the surface, it fires out a jet of spit. This remarkable marksman has been known to bring down insects hanging from tree limbs as high as 3 feet above the water’s surface. And according to a study just published in the Proceedings of the National Academy of Sciences, it uses a visual processing technique that was previously thought to exist only in mammals.
The study found that fish pay attention to something called orientation saliency, which means that fish can more easily spot an object that is oriented differently from its background. The researchers first trained some archer fish to spit at the image of an insect projected on a LCD screen above their tanks, then presented images of objects that were either aligned with or perpendicular to a patterned background. They found that the fish spit far more accurately at objects that were not lined up with the background. (See video of a spitting fish in the lab below.)
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From Ed Yong:
Right from its entrance, Disneyland is designed to cast an illusion upon its visitors. The first area – Main Street – seems to stretch for miles towards the towering castle in the distance. All of this relies on visual trickery. The castle’s upper bricks and the upper levels of Main Street’s buildings are much smaller than their ground-level counterparts, making everything seem taller. The buildings are also angled towards the castle, which makes Main Street seem longer, building the anticipation of guests.
These techniques are examples of forced perspective, a trick of the eye that makes objects seem bigger or smaller, further or closer than they actually are. These illusions were used by classical architects to make their buildings seem grander, by filmmakers to make humans look like hobbits, and by photographers to create amusing shots. But humans aren’t the only animals to use forced perspective. In the forests of Australia, the male great bowerbird uses the same illusions to woo his mate.
Read the rest of this post at Not Exactly Rocket Science.
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Six patients’ eyes have connected with “biosynthetic” replacement corneas, growing nerves and cells into the fakes as if they were real human tissue. With more trials and improvements in implant technique, researchers say the biosynthetic corneas might replace the expensive, rejection-prone, and scarce cadaver corneas that are currently used in transplants. This is good news for people who have lost vision due to inflamed or scarred corneas, and who are hoping to bring the world back into focus.
The findings appeared yesterday in Science Translational Medicine. The corneas allowed six out of a total of ten trial patients with advanced keratoconus, a condition which causes corneal scarring, to see just as well as if they had a traditional cadaver cornea replacement. Natural corneas, which refract light coming into the eye and help it to focus, consist of parallel strands of collagen; the biosynthetic corneas used collagen made in a lab by the biotech company Fibrogen.
“This study … is the first to show that an artificially fabricated cornea can integrate with the human eye and stimulate regeneration,” said May Griffith of the Ottawa Hospital Research Institute, who led the study. “With further research, this approach could help restore sight to millions of people who are waiting for a donated human cornea for transplantation.” [Reuters]
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When a person’s cornea is burned it’s not necessarily the splashed chemicals or hot liquids that causes blindness, but the eye’s recovery. Scar tissue, formed from cells in the white part of the eye, can cover the cornea in a cloudy haze. But researchers have found that cells drawn from another part of the body can correct the problem.
A paper published yesterday in the New England Journal of Medicine brings news of a regenerative stem cell treatment that has had striking success: It restored sight to 82 of 117 eyes with burnt corneas, and worked partially on 14 others. The treatment also seems to have a long-lasting impact; in one patient, the beneficial effect has lasted for ten years and counting.
The treatment offers hope to those who received little benefit from existing therapies–such as artificial cornea replacements, which can also be overpowered and clouded by white-colored cells, or stem cell or cornea transplants from cadavers, which patients can reject.
“[The patients] were incredibly happy. Some said it was a miracle,” said one of the study leaders, Graziella Pellegrini of the University of Modena’s Center for Regenerative Medicine in Italy. “It was not a miracle. It was simply a technique.” [AP]
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The weird phenomenon of blindsight—in which people take in visual information about objects without actually “seeing” them—has long intrigued scientists, and with good reason. They’ve watched people navigate obstacle courses and identify colors while being technically blind. This week, in a study in Nature, neuroscientists point to a part of the brain called the lateral geniculate nucleus (LGN) as the neural key that might make blindsight possible.
They used macaques in which the primary visual cortex had been destroyed. The monkeys’ eye-focusing movements revealed that they were “seeing” images shown at the periphery of their visual field, but only if their LGN was intact [New Scientist].
The authors refer to the LGN as the “main relay” between the retina and main visual cortex.
Other work had shown that the LGN also has projections to a number of secondary visual areas, suggesting that it may serve as a major hub in the visual system. To test this suggestion, the authors injected the LGN with a chemical that activates the receptor for a major inhibitory signaling molecule…. When the chemical is present, nerve cells receive a signal telling them to stop signaling, so this this injection has the effect of shutting the LGN down entirely [Ars Technica].
When the scientists shut down the LGN, the primates in the study didn’t experience any blindsight, as it appears no information was reaching any of their brains’ visual centers.
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We know that there’s a whole spectrum of different wavelengths of light beyond the puny band of visible light we humans can see. And we knew that some animals, like certain species of fish and birds, have vision that extended beyond ours into wavelengths like ultraviolet. But a new study in Current Biology demonstrates that not only can damselfish see in UV, but that they can discern specific patterns in UV light, which is much more than we ever gave them credit for.
The findings are the first to show an animal “that is able to discriminate between fine-scale UV patterns using only their short-wavelength receptors (UV cones),” the researchers wrote in their study. These fish seem to use the UV cues to distinguish their own from other similar-looking species [Scientific American]. Prior to this, many researchers thought the fish’s UV vision just allowed them to detect the presence of UV light, and wasn’t refined enough to detect any kind of patterns.
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A new study comparing Americans’ vision today to what it was like nearly 40 years ago says that our nation’s eyesight is getting worse as myopia, or nearsightedness, continues to become more prevalent. The study, led by Susan Vitale, appears in the Archives of Ophthalmology.
Vitale and colleagues used data from the National Health and Nutrition Examination Survey (NHANES) to compare the percentage of black and white Americans aged 12 to 54 with myopia in 1971-1972 and 1999-2004 [Reuters]. In the early 1970s only a quarter of people were nearsighted, but by the study’s 1999 to 2004 window that number had shot up to 42 percent.
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Sharks and humans seem more and more alike with each new scientific find. Not only do some sharks have hunting patterns that resemble those of serial killers, but now scientists have discovered that the hammerhead shark’s distinctive head shape allows it to see like a human.
Binocular vision occurs when the fields of two eyes overlap, allowing the accurate perception of depth and distance. It is especially important for predators which need to judge the distance to their prey [BBC News]. Researcher Stephen Kajiura, a sensory biologist, suggests that the stereo vision helps the sharks hunt prey like squid that dart around in three dimensions. The wide set eyes also allow the sharks to see through 360 degrees of vision, according to the researchers, who published their findings in The Journal of Experimental Biology.
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Contact lenses provide a number of convenience advantages over glasses, but one they come up short in one area—you can’t get contacts that automatically adjust to the sun’s UV light and darken, like the photochromic lenses many bespectacled people enjoy. But that could soon change: Researchers in Singapore led by Jackie Ying have now created a contact lens that responds to UV light.
Transition lenses for glasses are coated with a dye that is transparent when out of the sun, but responds to UV light by changing shape and darkening. Few previous attempts have been made to design transition contact lenses, largely because it’s difficult to apply dye coatings uniformly to the delicate, soft surface of a contact lens. Ying and her colleagues got around this by developing a contact lens that embeds dyes uniformly throughout the material [Technology Review].
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Some migratory birds that have to navigate across continents have an extremely useful tool at their disposal–an internal compass that points unerringly towards magnetic north. Researchers already knew that some birds possess these biological compasses, but their mechanism has been unclear. “This is basically the sixth sense of biology, but no one knows how it works…. The magnetic sense is by far the least understood sense in the natural world,” [Science News], says study coauthor Henrik Mouritsen.
Now, researchers have determined that light-sensing cells in the eye convey the crucial message to a special visual center of a robin’s brain, called cluster N. Special proteins called cryptochromes in the birds’ eyes may mediate this light-dependent magnetic sensing, Mouritsen says. Light hitting the proteins produces a pair of free radicals, highly reactive molecules with unpaired electrons. These electrons have a property called spin which may be sensitive to Earth’s magnetic field. Signals from the free radicals may then move to nerve cells in cluster N, ultimately telling the birds where north is [Science News].
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A new discovery about how mantis shrimp process light could give rise to new and more powerful consumer electronics, according to a new study. Mantis shrimp possess the animal kingdom’s most complicated eyes, capable of distinguishing between 100,000 colors — 10 times as many as humans — and seeing circular polarized light, or CPL, which can’t be detected by any other creature [Wired.com]. Circular polarized light is one of two forms of polarized light, or light waves that travel in a specific plane.
The specialized CPL detecting cells in shrimp eye are similar to the optical detectors found in DVD players; each can convert polarized light into other forms so it can be stored or processed. However, shrimp eyes can do this with all colors of circular polarized light across the spectrum, according to the study in Nature Photonics. The detectors in DVD and CD players can only recognize circular polarized light in a few colors. The research team thinks that in the future, optics devices might be beefed up by chemically engineered crystals that could mimic the light polarizing cells of the mantis shrimp eye.
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Looking for an easy, cheap way to spy on your neighbors? Researchers are working on a device that may be just the thing, which uses a simple wireless network to “see” through a wall and detect people moving around in the room beyond. But paranoid apartment-dwellers will be glad to know that the system still has plenty of limitations. At the moment the system can only track movement within a three-foot range, and it can only sense motion–it can’t put together a picture of what or who’s moving.
The system relies on the variations of radio signals in a wireless network. The signal strength at any point in a network is the sum of all the paths the radio waves can take to get to the receiver. Any change in the volume of space through which the signals pass, for example caused by the movement of a person, makes the signal strength vary. So by “interrogating” this volume of space with many signals, picked up by multiple receivers, it is possible to build up a picture of the movement within it [Technology Review]. The paper describing the technology has been posted on the arXiv pre-print server, and has not yet been peer-reviewed.
The device could be more than a boon for voyeurs or robbers. The researchers argue that the technology could be used in search and rescue operations, with emergency teams using the same radio technology used by Wi-Fi networks to build a web of sensors around a disaster site, revealing the location of victims and survivors [Telegraph].
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For two squirrel monkeys nicknamed Dalton and Sam, life has gotten a lot more colorful. Researchers used gene therapy to correct the color blindness of the two adult monkeys, giving them the ability to distinguish between red and green for the first time. The fascinating accomplishment suggests that scientists may someday be able to cure other kinds of blindness in humans. And because the treated monkeys were “middle aged”, it challenges the assumption that gene therapies cannot work in adults because their brain connections are too set in their ways to change beneficially [New Scientist].
The field of gene therapy, in which a malfunctioning gene in a patient’s body is replaced with a functional one, fell into disarray one decade ago following the death of an 18-year-old in a clinical trial. But since then scientists have regrouped, using animal studies to probe the technique’s safety. Last year, researchers progressed to the point of safety trials in humans for the treatment of one rare eye condition called Leber congenital amaurosis, and were able to dramatically improve the patients’ sight. Those results were stunning, but they were also achieved in children, whose still-growing brains can rewire themselves on the fly in response to new sources of visual stimuli [Wired.com].
In the new study, published in Nature, the researchers used a type of squirrel monkey in which the males lack a visual pigment called L-opsin. Its absence renders the monkeys color-blind, unable to distinguish reds and green. Most of the females, on the other hand, see in full color. So the scientists got to wondering: what would happen if they gave a boy squirrel monkey the same opsin that girls have [Scientific American]. They used a harmless virus to ferry in the gene that makes opsin, injecting the virus behind the monkeys’ retinas.
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A person can witness an event in real life, see a doctored video of the same event, and then convince themselves that what they saw on the video is what actually happened, according to a recent study that casts doubt on the reliability of eyewitness testimony.
Psychologists set up an experiment where they filmed two people sitting side by side–one experimental subject and one researcher pretending to be a participant–playing a gambling game where they bet phony money on whether or not they could answer multiple choice questions correctly. They were told that the person with the most money at the end would win a prize.
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It’s a movie cliche: the moment when the lost traveler intersects a set of footprints, only to realize that the prints where made by his very own boot soles. The hero then realizes, with plunging heart, that he’s been walking in circles while trying to walk a straight course through the featureless expanse. Now a small study has shown that the cliche is true. Without the sun, a compass or a landmark, people trying to follow a straight course through a forest or a desert ended up back where they started [HealthDay News].
In the first experiment, six participants tried to follow a straight course through a forest in Germany, in an area where the land is flat and the trees quickly begin to look alike. The two subjects who walked on a sunny day stayed on a fairly straight course (as tracked by a GPS device), except for the first 15 minutes when the sun was behind the clouds. But the four who walked on an overcast day repeatedly traveled in circles, sometimes crossing their own paths after only 10 minutes. Says lead researcher Jan Souman: “They didn’t really believe when we showed them afterwards…. I think that’s certainly a point to take away, people may feel very confident about the direction where they’re going but it’s not certain” [ABC News].
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