It may not quite be X-ray vision but it is the kind of ability that brings to mind superheroes or gifted mutants.
Humans have eyes that can sense a third property of light besides colour and brightness. And despite being better at it than any other vertebrate tested to date, most people have no idea they possess the skill.
A new study shows that humans are surprisingly good at detecting polarised light, something most commonly associated with bees and other insects, as well as octopuses and cuttlefish.
Far back in our past it may have provided us with a navigational aid, scientists believe.
Today, it could point towards new methods of screening people at risk of age-related macular degeneration (AMD), a leading cause of blindness.
Polarised light consists of light waves that are oscillating in a particular direction, much like a skipping rope being shaken up and down or from side-to-side.
Some animals, especially invertebrates, employ polarised light to navigate, find water, detect prey or predators, or for communication.
The new evidence suggests that humans use it too - or at least our ancestors did.
Dr Shelby Temple, from the Ecology of Vision Group at the University of Bristol, who led the research, said: "Generally, light is a mixture of polarisations. But sometimes - for example in parts of the sky, on your computer screen and in reflections from water or glass - a large percentage of the waves are oscillating in the same orientation and the light is strongly polarised."
Tests carried out on 24 volunteers by the Bristol team found that participants had an average polarisation sensitivity threshold of 56 per cent.
Some could detect light that was less than 25 per cent polarised - a performance not on a par with a cuttlefish but still better than that of any other vertebrate tested so far.
But most of us have to be taught how to tap into our super-vision.
The key is to watch out for "Haidinger's brushes", a subtle short-lived visual effect that occurs when we look at polarised light.
Haidinger's brushes, named after their 19th century discoverer Wilhelm Karl von Haidinger, appear as a faint pattern of yellow and blue bow-tie shapes that fade after less than five seconds.
They can be observed by looking at a region of blue sky approximately 90 degrees from the sun, especially around sunset or sunrise, or at a white region on a liquid crystal display.
"You can see Haidinger's brushes if you look at a blank white portion of an LCD screen on a computer, tablet or phone," said Dr Temple.
"Tilt your head from side to side and faint yellow brushes should become visible."
Although the effect quickly fades, it can be maintained by rotating the eye around the primary visual axis relative to the light field - in other words, by tilting the head.
Share
