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The invisible issue | what's hidden in plain sight
INVISIBLE
RAZZLE DAZZLE ‘EM T
O BE B BECOME M invisible, n first make ou lf conspicuous. s yourself It sounds ab abs d, especially ec absurd, once you learn that tthis con conceptt w was the brainchild of an eccentric ccent American m artist. Now, n a ccentury after it was put more than forward, tthe idea is finally being tested. The findings have revealed surprising insights into how camouflage fools – or fails to fool – the eye of the beholder. In 1909, the prevailing belief was that animals hid themselves by matching their surroundings. Then the painter and naturalist Abbott Handerson Thayer suggested a different mechanism was at work: highly conspicuous markings, such as the
To blend in, you’ve got to stand out
zebra’s stripes and the oystercatcher’s black-and-white plumage, are actually disguises. Predators, he reasoned, locate their prey by looking for their outlines, so animals with high-contrast markings that disrupt telltale edges and create false ones can evade detection. With this and other ideas about animal markings, Thayer earned himself the title “father of camouflage”. But although disruptive camouflage was cited in countless textbooks, it remained largely untested until 2005, when Innes Cuthill, Martin Stevens and their colleagues at the University of Bristol, UK, devised an experiment
using fake moths made from paper triangles. By pinning them to oak trees, the researchers found that “moths” with black markings on their edges were less likely to be attacked by birds than those with central markings or uniform colours. “It showed that disruption was indeed a very good way of being hidden,” says Stevens, now at the University of Exeter, UK. Using a similar approach, he and Cuthill later discovered that high-contrast markings become less effective once their contrast exceeds that in the creatures’ natural environment. One way to avoid this is for some parts of the body to blend in while others stand out.
TECHNICOLOUR DREAM CLOAK
The most cunning paint job may be no use as camouflage. It won’t do much to hide you from the prying eye of a thermal camera, or silence an inadvertent sneeze. Even something as subtle as a shadow can give your presence away. To win in the ultimate game of hide-and-seek, what you need is an invisibility cloak that goes way beyond simply not being visible. That might seem a tall order, yet researchers are racing to perfect the technology. So could their devices make you disappear completely? This is where the future of concealment begins to look hazy. First, consider what it would take to make you vanish. If you could wear something that bends light rays from
38 | NewScientist | 22 March 2014
the wall behind you smoothly around your body – like water flowing around a rock – then steer them towards someone looking in your direction, they would see nothing but the wall: no outline, no shadow. This trick is not too difficult to accomplish. Last year a team led by Hongsheng Chen from Zhejiang University in Hangzhou, China, used special optics to diffract light around a cat, making it vanish from view. Unfortunately, the effect only works at certain viewing angles. And the system isn’t portable – it uses a large and very heavy glass prism. Less cloak, more bunker. Rather more practical would be clothes made of synthetic metamaterials – assemblies of many small components that work together to warp light in unusual ways. The first metamaterial invisibility cloak was unveiled in 2006. Constructed from an array of
concentric metal rings, it successfully hid a small metal object – but only from a beam of microwave radiation. Now, researchers are devising cloaks that work with visible light. Last year a team from Stanford University in California designed a metamaterial made from an array of tiny metal rings shaped like crescent moons. Their calculations suggest
this high-tech “chain mail” could bend parts of the visible spectrum, hiding you completely in blue or green light, say. Don it in daylight and you would fade to a sort of ghostly, reddish hue. A material that bends light at all visible wavelengths is required if this monochrome spectre isn’t to betray you. But we have yet to find a
An invisible man needs to be more than just unseen PAUL REED/ASSOCIATED NEWSPAPERS/REX
How to stage the ultimate disappearing act
JIM RICHARDSON/NATIONAL GEOGRAPHIC CREATIVE
The best-hidden creatures wear high-vis outfits
metamaterial that curves all wavelengths the same amount. In theory, there’s no reason why it couldn’t work across the visual spectrum, says Tie Jun Cui, a metamaterials expert at Southeast University in Nanjing, China, but most researchers believe it can’t be done. Certainly you will have more luck stifling the noise of a cough or sneeze. Sound waves zip faster through a light, stiff material than through air and, according to Steven Cummer, an engineer at Duke University in Durham, North Carolina, that makes an acoustic cloak entirely feasible. Constructed from stacks of thin materials with the right compressibility and density, this wrap will effectively soundproof your presence. A similar idea will help keep your thermal signature to yourself. Sebastien Guenneau and colleagues at the Fresnel Institute in Marseille,
France, have used a two-dimensional metamaterial shield, made from a metal sheet patterned with rings, to divert heat around an object. If such a cloak can match the temperature of its outside edge to that of the surroundings, it should help keep even the hottest body out of sight. Lest you imagine that complete invisibility is within our grasp, think again. For now, there’s no way to combine technologies to simultaneously block visible light, heat and sound. The problem is that the materials to manipulate each of these waves work in different ways, and if you swathed yourself in a thick coat of cloaks stacked one on another, only the outer layer would perform as planned. For now, it might be better to stick with an old-fashioned cloak of paint. ■
Jeff Hecht is a consultant at New Scientist
Cuthill and Stevens revived interest in disruptive camouflage, but the first real insights into just how it works came only last year. Richard Webster at Carleton University in Ottawa, Canada, asked volunteers to search for virtual moths on a computer screen while an eye-tracker monitored their gaze. “We could almost get inside people’s eyes,” he says. He found that the more patches moths had on their edges, the more often volunteers failed to notice them, and they needed to fixate their gaze on them for longer to have any chance of spotting them. The eyetracking vindicated Thayer again: by breaking up an animal’s outline, disruptive camouflage does impair a predator’s ability to spot its prey. Although instructive, the experiment had an obvious shortcoming: humans do not prey on moths, let alone computer-generated ones. To test whether disruptive colouring fools its intended audience, Stevens has started field trials. In Zambia and South Africa, his team is studying groundnesting birds that rely on disruptive camouflage, including nightjars and plovers. His team measures the patterns on the birds’ feathers to quantify how well hidden they are in their environment. They also track the birds’ survival to determine how effectively they evade predators. Nightjars and plovers are difficult to spot in the first place, so the researchers have employed sharpsighted local guides to help find them. This raises the question of whether predators, like the guides, might be less easily fooled by disruptive markings as they become more familiar with them. Last year, Stevens and his team found that people do gradually get better at spotting virtual moths, especially if they see several at the same time. He suspects that the volunteers learn to stop the futile search for outlines, and instead start scanning for the highcontrast markings. Whether non-human predators adopt the same tactic is hard to say. They may not even see camouflage markings in the same way that we do. But if predators can learn to see through disruptive camouflage, it would suggest that this concealment strategy is more likely to evolve in > 22 March 2014 | NewScientist | 39
prey that face short-lived or generalist predators than long-lived or specialist ones. Another open question is whether one disruptive pattern might work in a variety of environments. Webster found that camouflage can fool humans even when the colours do not match the background, provided they are not too garish. “A jester’s costume is highly disruptive, but he’s always going to stand out,” he says. Perhaps that explains the British army’s recent decision to replace its long-standing woodland and desert camouflage patterns with a single “multi-terrain pattern” that includes green, brown
© ESTATE OF EDWARD WADSWORTH. ALL RIGHTS RESERVED, DACS 2013/BRIDGEMAN ART LIBRARY
INVISIBLE During both world wars, cubism was camouflage
and sandy yellow, following field trials indicating this print was better at concealing soldiers. “Cynics may say this is just a cost-cutting exercise,” says Webster. “But maybe they’ve worked out how to get the most out of disruptive colouration.” In fact, the military has a long history of using conspicuous patterns to fool observers. During both world wars, several US and British ships were painted with striking black-and-white geometric patterns. Some looked like floating checkerboards, others like Cubist zebras. Rather than hiding the vessels, these gaudy designs, known as “dazzle camouflage” in the UK and
ALL-SEEING EYES
Hypercolour Most of us don’t think of ourselves as colour-blind. But compared to the many animals blessed with superior colour vision, that’s exactly what we are. Strictly speaking, colours do not exist. Our brains generate the perception of colour by comparing the responses of colour-receptor cells in the eye tuned to different wavelengths. People with mutant receptors – which are surprisingly common – perceive light of a specific wavelength very differently. What’s more, the number of different colours we can distinguish depends on how many types of colour receptors we have. Early fish had four, which is why they and most of their descendants – including amphibians, reptiles and birds – have excellent colour vision. But during the many millions of years that early mammals spent hiding from the dinosaurs and coming out only at night, they lost two colour receptors.
40 | NewScientist | 22 March 2014
Most mammals therefore have poor colour vision. Our primate ancestors later re-evolved a third colour receptor, so humans can see hundreds of thousands of hues that are invisible to dogs or horses. But with a fourth receptor we would be able to see millions more – as a few people can. As many as 1 in 10 women have mutated receptors for red light in their eyes, as well as the normal one, effectively giving them four receptors in all. Neuroscientist Gabriele Jordan at Newcastle University in the UK has tested the perception of these women. Most have normal vision but one woman could see more colours than the rest of us. Jordan’s team has since identified others with this ability too. What it’s like for these people, of course, the rest of us can only imagine.
vision thanks to colour receptors optimised for detecting it, but at the cost of poorer vision at the red end of the spectrum. UV vision is used for different purposes by different species, from kestrels detecting the urine trails of prey to reindeer spotting polar bears. Reindeer were thought rare among mammals in having UV vision, but Ron Douglas of City University London reported this year that many mammals, including hedgehogs, cats, ferrets, seals, pigs and rabbits have lenses that let UV through. A few people can see into the near-UV spectrum. What do they have that the rest of us don’t? Well,
Sight beyond sight Our colour vision stretches from the longer wavelengths we see as red to the shorter wavelengths we see as violet. But ultraviolet vision is fairly common among insects, fish, reptiles and birds, especially those with smaller eyes that filter out less UV light. Bees have excellent UV
DOUG PERRINE/NATUREPL
Other animals perceive much that we can’t
actually, it’s what they don’t have. The receptors in our retinas can detect UV but wavelengths shorter than 400 nanometres are normally filtered out by the eye’s lens. People who develop cataracts and have their lens replaced with a UVtransparent one sometimes start seeing UV as a bluish or purplish glow. The painter Monet may have started seeing UV after a cataract operation at age 82, influencing his famous series of water lily pictures. The US defence department is working on several devices that people could wear to extend what they can see beyond the visible spectrum.
The colour of night Until recently, we thought nocturnal animals see at night the same way that we do – in shades of grey. But it turns out that several can see colours in the dark. Our colour vision depends on comparing the responses of three kinds of cone cells tuned to different wavelengths, but this works only when there is plenty of light. In dimmer conditions, we rely on rod cells that are far more sensitive to light but, because there is only one type of rod cell, they cannot help us to distinguish colour. Many nocturnal animals have the same two-part system as us, but max out on rods at the expense of cones, sacrificing colour perception in good light for better detail at night. Some animals do see colour in the dark, Almut Kelber of Lund University in Sweden discovered a few years ago. In the case of geckos, it happened by a kind of evolutionary accident. Their ancestors lost their rod cells altogether during millions of years as die-hard diurnal creatures, so maxing out on rods was not an option when they started to become nocturnal. Instead, their cone cells
“Bold make-up p and d bizarre iz hairstyles might gh thwart thwart art facial recognition” on The army is not alone in wanting to exploit Thayer’s insights. Governments’ efforts to keep an eye on their citizens are changing rapidly, and this year the Janus programme, run by the US intelligence community, will start collecting photographs from social media websites and public video feeds, to identify faces in the images by using algorithms that match them to
grew bigger to work better in low light – becoming 350 times as sensitive as human ones. This ability to distinguish far subtler shades of colour gave them the ability to see colour in the dark. The superpower comes with a trade-off, though. The bigger the cone cells, the less detail they can resolve, and so geckos have grainy vision in all light. Kelber and others have also found colour night-vision in a handful of insects, including hawkmoths and nocturnal carpenter bees, which use it to find flowers in the dark. There may be many more species that see colour at night, says Kelber, who is now studying frogs and toads. These discoveries have inspired those trying to develop better cameras. A team at Toyota’s R&D centre in Belgium is working on night-vision systems that use ordinary camera sensors to produce a much better image in low light by mimicking the way night-flying dung beetles process signals. Toyota wants to provide drivers with a better view of the road ahead at night, but this kind of technology might one day make colour night-vision systems widely available.
those on existing web profiles. Face recognition could also feature in drones, which are set to become a common feature outside war zones. Alarmed by the steady rise in surveillance, New York-based artist Adam Harvey aims to thwart facial recognition technologies by being conspicuous. The bold make-up and bizarre hairstyle showcased in his CV Dazzle project are certainly eccentric; whether they can foil an AI system is another matter. But it’s tempting to think that Thayer would have approved. ■ Ed Yong is a writer based in London
This is just a pigment of your imagination
BURKART/PLAINPICTURE
“razzle-dazzle” in the US, were supposed to make it harder for the enemy to judge a ship’s speed, size and bearing. There was scant evidence to support the idea, so Cuthill decided to test it. He found that people consistently underestimated the speed of on-screen dazzle patterns, such as checks and zigzags, by around 7 per cent – but only when the patterns moved quickly. Large warships are probably too slow to benefit from this “motion dazzle” illusion, he concludes, but it could allow a speeding Land Rover to evade enemy fire. Conspicuous markings might, likewise, help a fleeing zebra elude a pursuing lion.
Eyes in the back of our head Our forward-facing eyes move in unison, allowing us to judge distances accurately and see through solid objects. But with a little help from technology and our highly adaptable brains, we can swap these abilities for the 360-degree vision of a fly or the independently moving eyes of a chameleon. You can have a fly’s all-around vision using a head-mounted panoramic camera that beams a 360-degree view of the world onto a screen. According to its inventors at the ESIEA engineering school in Paris, France, “FlyVIZ” takes 15 minutes to get used to, doesn’t make you dizzy and enables wearers to dodge balls thrown from behind, grab objects they wouldn’t normally
see and walk backwards while navigating doorways with ease. The device is an unwieldy prototype at present but potential beneficiaries could include police, security guards and, perhaps, even teachers. Another group, led by Fumio Mizuno at the Tohoku Institute of Technology in Sendai, Japan, is working on a different kind of 360-degree vision based on chameleon eyes. Two cameras move independently to provide totally non-overlapping views. In experiments, 11 out of 12 volunteers could make sense of this strange view of the world even though it is so different from our own. ■
Caroline Williams is a freelance writer based in Godalming, UK
22 March 2014 | NewScientist | 41
RAZZLE DAZZLE ‘EM T
O BE B BECOME M invisible, n first make ou lf conspicuous. s yourself It sounds ab abs d, especially ec absurd, once you learn that tthis con conceptt w was the brainchild of an eccentric ccent American m artist. Now, n a ccentury after it was put more than forward, tthe idea is finally being tested. The findings have revealed surprising insights into how camouflage fools – or fails to fool – the eye of the beholder. In 1909, the prevailing belief was that animals hid themselves by matching their surroundings. Then the painter and naturalist Abbott Handerson Thayer suggested a different mechanism was at work: highly conspicuous markings, such as the
To blend in, you’ve got to stand out
zebra’s stripes and the oystercatcher’s black-and-white plumage, are actually disguises. Predators, he reasoned, locate their prey by looking for their outlines, so animals with high-contrast markings that disrupt telltale edges and create false ones can evade detection. With this and other ideas about animal markings, Thayer earned himself the title “father of camouflage”. But although disruptive camouflage was cited in countless textbooks, it remained largely untested until 2005, when Innes Cuthill, Martin Stevens and their colleagues at the University of Bristol, UK, devised an experiment
using fake moths made from paper triangles. By pinning them to oak trees, the researchers found that “moths” with black markings on their edges were less likely to be attacked by birds than those with central markings or uniform colours. “It showed that disruption was indeed a very good way of being hidden,” says Stevens, now at the University of Exeter, UK. Using a similar approach, he and Cuthill later discovered that high-contrast markings become less effective once their contrast exceeds that in the creatures’ natural environment. One way to avoid this is for some parts of the body to blend in while others stand out.
TECHNICOLOUR DREAM CLOAK
The most cunning paint job may be no use as camouflage. It won’t do much to hide you from the prying eye of a thermal camera, or silence an inadvertent sneeze. Even something as subtle as a shadow can give your presence away. To win in the ultimate game of hide-and-seek, what you need is an invisibility cloak that goes way beyond simply not being visible. That might seem a tall order, yet researchers are racing to perfect the technology. So could their devices make you disappear completely? This is where the future of concealment begins to look hazy. First, consider what it would take to make you vanish. If you could wear something that bends light rays from
38 | NewScientist | 22 March 2014
the wall behind you smoothly around your body – like water flowing around a rock – then steer them towards someone looking in your direction, they would see nothing but the wall: no outline, no shadow. This trick is not too difficult to accomplish. Last year a team led by Hongsheng Chen from Zhejiang University in Hangzhou, China, used special optics to diffract light around a cat, making it vanish from view. Unfortunately, the effect only works at certain viewing angles. And the system isn’t portable – it uses a large and very heavy glass prism. Less cloak, more bunker. Rather more practical would be clothes made of synthetic metamaterials – assemblies of many small components that work together to warp light in unusual ways. The first metamaterial invisibility cloak was unveiled in 2006. Constructed from an array of
concentric metal rings, it successfully hid a small metal object – but only from a beam of microwave radiation. Now, researchers are devising cloaks that work with visible light. Last year a team from Stanford University in California designed a metamaterial made from an array of tiny metal rings shaped like crescent moons. Their calculations suggest
this high-tech “chain mail” could bend parts of the visible spectrum, hiding you completely in blue or green light, say. Don it in daylight and you would fade to a sort of ghostly, reddish hue. A material that bends light at all visible wavelengths is required if this monochrome spectre isn’t to betray you. But we have yet to find a
An invisible man needs to be more than just unseen PAUL REED/ASSOCIATED NEWSPAPERS/REX
How to stage the ultimate disappearing act
JIM RICHARDSON/NATIONAL GEOGRAPHIC CREATIVE
The best-hidden creatures wear high-vis outfits
metamaterial that curves all wavelengths the same amount. In theory, there’s no reason why it couldn’t work across the visual spectrum, says Tie Jun Cui, a metamaterials expert at Southeast University in Nanjing, China, but most researchers believe it can’t be done. Certainly you will have more luck stifling the noise of a cough or sneeze. Sound waves zip faster through a light, stiff material than through air and, according to Steven Cummer, an engineer at Duke University in Durham, North Carolina, that makes an acoustic cloak entirely feasible. Constructed from stacks of thin materials with the right compressibility and density, this wrap will effectively soundproof your presence. A similar idea will help keep your thermal signature to yourself. Sebastien Guenneau and colleagues at the Fresnel Institute in Marseille,
France, have used a two-dimensional metamaterial shield, made from a metal sheet patterned with rings, to divert heat around an object. If such a cloak can match the temperature of its outside edge to that of the surroundings, it should help keep even the hottest body out of sight. Lest you imagine that complete invisibility is within our grasp, think again. For now, there’s no way to combine technologies to simultaneously block visible light, heat and sound. The problem is that the materials to manipulate each of these waves work in different ways, and if you swathed yourself in a thick coat of cloaks stacked one on another, only the outer layer would perform as planned. For now, it might be better to stick with an old-fashioned cloak of paint. ■
Jeff Hecht is a consultant at New Scientist
Cuthill and Stevens revived interest in disruptive camouflage, but the first real insights into just how it works came only last year. Richard Webster at Carleton University in Ottawa, Canada, asked volunteers to search for virtual moths on a computer screen while an eye-tracker monitored their gaze. “We could almost get inside people’s eyes,” he says. He found that the more patches moths had on their edges, the more often volunteers failed to notice them, and they needed to fixate their gaze on them for longer to have any chance of spotting them. The eyetracking vindicated Thayer again: by breaking up an animal’s outline, disruptive camouflage does impair a predator’s ability to spot its prey. Although instructive, the experiment had an obvious shortcoming: humans do not prey on moths, let alone computer-generated ones. To test whether disruptive colouring fools its intended audience, Stevens has started field trials. In Zambia and South Africa, his team is studying groundnesting birds that rely on disruptive camouflage, including nightjars and plovers. His team measures the patterns on the birds’ feathers to quantify how well hidden they are in their environment. They also track the birds’ survival to determine how effectively they evade predators. Nightjars and plovers are difficult to spot in the first place, so the researchers have employed sharpsighted local guides to help find them. This raises the question of whether predators, like the guides, might be less easily fooled by disruptive markings as they become more familiar with them. Last year, Stevens and his team found that people do gradually get better at spotting virtual moths, especially if they see several at the same time. He suspects that the volunteers learn to stop the futile search for outlines, and instead start scanning for the highcontrast markings. Whether non-human predators adopt the same tactic is hard to say. They may not even see camouflage markings in the same way that we do. But if predators can learn to see through disruptive camouflage, it would suggest that this concealment strategy is more likely to evolve in > 22 March 2014 | NewScientist | 39
prey that face short-lived or generalist predators than long-lived or specialist ones. Another open question is whether one disruptive pattern might work in a variety of environments. Webster found that camouflage can fool humans even when the colours do not match the background, provided they are not too garish. “A jester’s costume is highly disruptive, but he’s always going to stand out,” he says. Perhaps that explains the British army’s recent decision to replace its long-standing woodland and desert camouflage patterns with a single “multi-terrain pattern” that includes green, brown
© ESTATE OF EDWARD WADSWORTH. ALL RIGHTS RESERVED, DACS 2013/BRIDGEMAN ART LIBRARY
INVISIBLE During both world wars, cubism was camouflage
and sandy yellow, following field trials indicating this print was better at concealing soldiers. “Cynics may say this is just a cost-cutting exercise,” says Webster. “But maybe they’ve worked out how to get the most out of disruptive colouration.” In fact, the military has a long history of using conspicuous patterns to fool observers. During both world wars, several US and British ships were painted with striking black-and-white geometric patterns. Some looked like floating checkerboards, others like Cubist zebras. Rather than hiding the vessels, these gaudy designs, known as “dazzle camouflage” in the UK and
ALL-SEEING EYES
Hypercolour Most of us don’t think of ourselves as colour-blind. But compared to the many animals blessed with superior colour vision, that’s exactly what we are. Strictly speaking, colours do not exist. Our brains generate the perception of colour by comparing the responses of colour-receptor cells in the eye tuned to different wavelengths. People with mutant receptors – which are surprisingly common – perceive light of a specific wavelength very differently. What’s more, the number of different colours we can distinguish depends on how many types of colour receptors we have. Early fish had four, which is why they and most of their descendants – including amphibians, reptiles and birds – have excellent colour vision. But during the many millions of years that early mammals spent hiding from the dinosaurs and coming out only at night, they lost two colour receptors.
40 | NewScientist | 22 March 2014
Most mammals therefore have poor colour vision. Our primate ancestors later re-evolved a third colour receptor, so humans can see hundreds of thousands of hues that are invisible to dogs or horses. But with a fourth receptor we would be able to see millions more – as a few people can. As many as 1 in 10 women have mutated receptors for red light in their eyes, as well as the normal one, effectively giving them four receptors in all. Neuroscientist Gabriele Jordan at Newcastle University in the UK has tested the perception of these women. Most have normal vision but one woman could see more colours than the rest of us. Jordan’s team has since identified others with this ability too. What it’s like for these people, of course, the rest of us can only imagine.
vision thanks to colour receptors optimised for detecting it, but at the cost of poorer vision at the red end of the spectrum. UV vision is used for different purposes by different species, from kestrels detecting the urine trails of prey to reindeer spotting polar bears. Reindeer were thought rare among mammals in having UV vision, but Ron Douglas of City University London reported this year that many mammals, including hedgehogs, cats, ferrets, seals, pigs and rabbits have lenses that let UV through. A few people can see into the near-UV spectrum. What do they have that the rest of us don’t? Well,
Sight beyond sight Our colour vision stretches from the longer wavelengths we see as red to the shorter wavelengths we see as violet. But ultraviolet vision is fairly common among insects, fish, reptiles and birds, especially those with smaller eyes that filter out less UV light. Bees have excellent UV
DOUG PERRINE/NATUREPL
Other animals perceive much that we can’t
actually, it’s what they don’t have. The receptors in our retinas can detect UV but wavelengths shorter than 400 nanometres are normally filtered out by the eye’s lens. People who develop cataracts and have their lens replaced with a UVtransparent one sometimes start seeing UV as a bluish or purplish glow. The painter Monet may have started seeing UV after a cataract operation at age 82, influencing his famous series of water lily pictures. The US defence department is working on several devices that people could wear to extend what they can see beyond the visible spectrum.
The colour of night Until recently, we thought nocturnal animals see at night the same way that we do – in shades of grey. But it turns out that several can see colours in the dark. Our colour vision depends on comparing the responses of three kinds of cone cells tuned to different wavelengths, but this works only when there is plenty of light. In dimmer conditions, we rely on rod cells that are far more sensitive to light but, because there is only one type of rod cell, they cannot help us to distinguish colour. Many nocturnal animals have the same two-part system as us, but max out on rods at the expense of cones, sacrificing colour perception in good light for better detail at night. Some animals do see colour in the dark, Almut Kelber of Lund University in Sweden discovered a few years ago. In the case of geckos, it happened by a kind of evolutionary accident. Their ancestors lost their rod cells altogether during millions of years as die-hard diurnal creatures, so maxing out on rods was not an option when they started to become nocturnal. Instead, their cone cells
“Bold make-up p and d bizarre iz hairstyles might gh thwart thwart art facial recognition” on The army is not alone in wanting to exploit Thayer’s insights. Governments’ efforts to keep an eye on their citizens are changing rapidly, and this year the Janus programme, run by the US intelligence community, will start collecting photographs from social media websites and public video feeds, to identify faces in the images by using algorithms that match them to
grew bigger to work better in low light – becoming 350 times as sensitive as human ones. This ability to distinguish far subtler shades of colour gave them the ability to see colour in the dark. The superpower comes with a trade-off, though. The bigger the cone cells, the less detail they can resolve, and so geckos have grainy vision in all light. Kelber and others have also found colour night-vision in a handful of insects, including hawkmoths and nocturnal carpenter bees, which use it to find flowers in the dark. There may be many more species that see colour at night, says Kelber, who is now studying frogs and toads. These discoveries have inspired those trying to develop better cameras. A team at Toyota’s R&D centre in Belgium is working on night-vision systems that use ordinary camera sensors to produce a much better image in low light by mimicking the way night-flying dung beetles process signals. Toyota wants to provide drivers with a better view of the road ahead at night, but this kind of technology might one day make colour night-vision systems widely available.
those on existing web profiles. Face recognition could also feature in drones, which are set to become a common feature outside war zones. Alarmed by the steady rise in surveillance, New York-based artist Adam Harvey aims to thwart facial recognition technologies by being conspicuous. The bold make-up and bizarre hairstyle showcased in his CV Dazzle project are certainly eccentric; whether they can foil an AI system is another matter. But it’s tempting to think that Thayer would have approved. ■ Ed Yong is a writer based in London
This is just a pigment of your imagination
BURKART/PLAINPICTURE
“razzle-dazzle” in the US, were supposed to make it harder for the enemy to judge a ship’s speed, size and bearing. There was scant evidence to support the idea, so Cuthill decided to test it. He found that people consistently underestimated the speed of on-screen dazzle patterns, such as checks and zigzags, by around 7 per cent – but only when the patterns moved quickly. Large warships are probably too slow to benefit from this “motion dazzle” illusion, he concludes, but it could allow a speeding Land Rover to evade enemy fire. Conspicuous markings might, likewise, help a fleeing zebra elude a pursuing lion.
Eyes in the back of our head Our forward-facing eyes move in unison, allowing us to judge distances accurately and see through solid objects. But with a little help from technology and our highly adaptable brains, we can swap these abilities for the 360-degree vision of a fly or the independently moving eyes of a chameleon. You can have a fly’s all-around vision using a head-mounted panoramic camera that beams a 360-degree view of the world onto a screen. According to its inventors at the ESIEA engineering school in Paris, France, “FlyVIZ” takes 15 minutes to get used to, doesn’t make you dizzy and enables wearers to dodge balls thrown from behind, grab objects they wouldn’t normally
see and walk backwards while navigating doorways with ease. The device is an unwieldy prototype at present but potential beneficiaries could include police, security guards and, perhaps, even teachers. Another group, led by Fumio Mizuno at the Tohoku Institute of Technology in Sendai, Japan, is working on a different kind of 360-degree vision based on chameleon eyes. Two cameras move independently to provide totally non-overlapping views. In experiments, 11 out of 12 volunteers could make sense of this strange view of the world even though it is so different from our own. ■
Caroline Williams is a freelance writer based in Godalming, UK
22 March 2014 | NewScientist | 41