Cats Have Super, Psychedelic Vision

Psychedelic stripes, colors and patterns on flowers, birds and bugs are just some of the things that cats can see that humans cannot.

Given their sleek ways, cats have long been a symbol of mysticism, and now the reputation gets a boost from new research that finds common house cats see things that are invisible to us.

Everything from psychedelic stripes on flowers to flashy patterned feathers on birds are likely detectable by cats and certain other animals, while humans remain oblivious to such things. We are also -- perhaps luckily -- missing out on seeing a whole world of urine markers blanketing the landscape.

The secret behind the feline vision "superpower" is ultraviolet light (UV) detection. A new paper, published in the Proceedings of the Royal Society B, found that cats, dogs and certain other animals see this form of light that is usually invisible to humans.

"There are many examples of things that reflect UV, which UV sensitive animals could see that humans can't," co-author Ronald Douglas told Discovery News. "Examples are patterns on flowers that indicate where nectar is, urine trails that lead to prey, and reindeer could see polar bears as snow reflects UV, but white fur does not."

A reindeer, a cat and a dog could therefore probably see a white-furred animal, such as a bunny, hopping through a snow blizzard, while most people would just see a blur of all white.

Douglas, a professor of biology at City University London specializing in the visual system, and co-author Glen Jeffery, a professor of neuroscience at University College London, determined that cats, dogs, rodents, hedgehogs, bats, ferrets and okapis all detect substantial levels of UV.

"It has been known for nearly a hundred years that many invertebrates, such as bees, see UV," Douglas said, adding that birds, fish, and some reptiles and amphibians were added to the list in more recent decades.

"However," he added, "it was assumed that most mammals do not see UV because they have no visual pigment maximally sensitive in the UV and (instead possess) lenses like those of man, that prevent UV reaching the retina."

He explained that visual pigments are the substances that absorb light and turn it into the electrical activity that nerve cells transmit. They turn out not to be always necessary for UV sensitivity. Instead, the "ocular media" (transparent parts of the eye like the cornea and crystalline lens) in certain animals transmits UV wavelengths.

The ability allows more light to reach the retina, "which would be good for a nocturnal cat," Douglas said.

The skill might also help to explain why cats become obsessed with unusual objects, like sheets of paper.

Man-made optical brighteners are sometimes added to paper, fabrics, laundry detergents, cosmetics and shampoos to make them appear brighter. Since optical brighteners absorb light in the UV spectrum, they might appear different, or stand out more, to UV-sensitive animals.

Certain people, such as those who have had their lenses replaced during cataract surgery, can see at least some UV, but most humans cannot.

"We do all assume that it (UV) may be harmful," Jeffery told Discovery News. "I work a lot in the Arctic where UV levels can be very high, particularly in spring and early summer when there is still a lot of snow and ice. These surfaces reflect 90 percent of the UV, so the animals are exposed from above and below. If you do not have snow goggles on, your eyes hurt within 15 minutes."

Studies on reindeer, however, find that repeated exposure to UV doesn't bother them at all.

Cats, reindeer and other animals built to detect UV might be protected from this visual damage in some way. It's also thought that UV light tends to create more blurry images.

"Now, if there is one thing humans are good at, it's seeing detail," Douglas said. "Perhaps that's why they have a lens that removes the UV. If they didn't, the world would appear more blurred."

The secret behind the feline vision "superpower" is ultraviolet light (UV) detection.

Animals and insects see the world in unique ways. From fish, to dogs, to birds to shrimp, super-eyesight allows them to thrive in places others can't.

Dung beetles, for example, have internal compasses that are sensitive to the sun, Marie Dacke of Lund University and her colleagues have determined. In a paper published in the latest Philosophical Transactions of the Royal Society B, she and her team explain that solar cues and skylight help guide where the beetles roll their coveted balls of poop.

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Siberian huskies evolved colorful, almond-shaped eyes to see in low light, desolate northern regions. A quirk of genetics is that an individual dog may have two differently colored eyes. A single eye may also feature two colors. It's known as a "parti" or "split" eye.

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Chameleons can rotate and focus their eyes separately to look at two different objects at the same time, according to the San Diego Zoo. This gives chameleons a full 360-degree view around their body.

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Ants have vision "superpowers," interactive media designers and artists Chris Woebken and Kenichi Okada believe. Using their ant apparatus, humans can see as ants do by placing microscope antennas on their hands (ants have these on their heads) that transmit a 50-fold magnified view of wherever the person's hand is resting.

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Imagine if you spent most of the day looking up from below. That is what escolar, a large and mysterious deep-sea fish, do, according to a new study by Eric Warrant of the University of Lund and colleagues. Escolar use this technique to "sit and wait" for prey, hoping something tasty will swim over them.

Shrimps have some of the most complex visual systems in the animal kingdom. Justin Marshall of the University of Queensland and his team found that some shrimp stare down prey before attacking with a movement that is so swift that it actually boils water in front of the shrimp. (The other temperate water surrounding the shrimp prevents it from cooking itself to death!)

Most animals, including humans, have round pupils, but the eyes of goats (toads, octopi and a few others too) tend to be horizontal and rectangular with rounded corners. This broadens the horizon that they see, enabling them to better spot predators.

Bird eyes, such as those of the eagle seen here, feature oil droplets located in the front, Doekele Stavenga of the University of Groningen and colleagues have discovered. The droplets serve as "microlenses" that help to filter and direct light.

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The eyes of certain animals, such as raccoons and cats, glow in the dark. Their eyes have a light-reflecting surface, known as the tapetum lucidum, which makes this possible. Depending on the animal, the glow takes on certain colors. Cats tend to have eyes that glow green. Miniature schnauzer eyes will sometimes glow turquoise, according to Colorado State University ophthalmologist Cynthia Powell.

Cuttlefish, a type of mollusk, are the transformer visionaries of the animal kingdom. They reshape their entire eyes to adjust to what they see. Humans and many other species, in contrast, usually just reshape their eye lenses to get a better look at something.

Giant squid have the largest eyes in the world, according to the Smithsonian National Museum of Natural History. At up to 10 inches in diameter, the human head-sized eyes help giant squid to see in deep water. It's believed that they can detect a moving sperm whale from 394 feet away.

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We create a mental map of our surroundings in our brain. As Michael Land of the University of Sussex explains, "To interact with objects in the world we need to know where they are, whether they are in our field of view or outside it. Objects in memory have to move in the brain as we move through the world, otherwise they would be not be in the right place."