If you’ve ever wondered why your cat is staring at something like it’s the most fascinating thing ever when you don’t see anything interesting there, scientists may have an answer. It’s not so much that they’re “having a moment” or seeing paranormal activity as it is that they can actually see things we can’t.
According to a new study published in the Proceedings of the Royal Society B, cats, dogs and a few other animals have the ability to see ultraviolet (UV) light, which is invisible to the human eye. It’s been known that many animals can see ultraviolet wavelengths, including birds, fish, and some reptiles and amphibians, but it had been believed until now that most mammals couldn’t because the lenses of their eyes are similar to ours.
While we can see from red to violet on the color spectrum, our eyes block out UV wavelengths. As LiveScience explains, for animals with UV-transparent lenses, the ultraviolet light reaches the retina, which converts it into nerve signals that head to the brain where they’re processed by the visual system.
For the study, researchers from the City University London and the University College London examined the eyes of 38 different species to measure how much light could go through the lens to reach the retina. Animals with transparent lenses can process UV light and now dogs, cats, rodents, hedgehogs, ferrets and okapis have been added to the roster of animals who can see these wavelengths to some degree.
The ability to see ultraviolet light may serve a number of purposes for animals that range from helping them see at night and communicate with each other to helping them find food and avoid predators.
“There are many examples of things that reflect UV, which UV sensitive animals could see that humans can’t,” Ronald Douglas, co-author of the study, 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.”
According to Discovery, this might also explain explain why cats become obsessed with otherwise ordinary objects, like a sheet 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.
More interesting might be why some animals can see UV light, while others can’t. Blocking UV light is thought to protect the retina of the eye from damage and help improve the clarity of vision, but many animals, like reindeer, can see it and haven’t suffered any problems. For reindeer in the Arctic, the ability to see UV light helps them find lichen and see the urine markings of predators more clearly, which both appear black in their snow-covered world. Researchers are trying to figure out how they protect their eyes from damage, which could help us learn how to treat and protect our own.
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