Seeing polarised light is link to ancient ancestors

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, a skill most commonly associated with bees and other insects, as well as octopuses and cuttlefish.

Scientists believe that, in our past, it may have provided us with a navigational aid. Today, it could point towards new methods of screening for age-related macular degeneration, 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 Bristol University, 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.”

The Bristol team found that participants in its study had an average polarisation sensitivity threshold of 56 per cent.