Experts found that the human eyes, aside from color and brightness, possess the third property of light: polarization. Majority of the population, including scientific professionals, do not know that humans have this super sense. However, because of a study originally conducted to test the visual abilities of octopuses and cuttlefish, this concept has finally found evidence.
The study conducted by an expert team from the University of Bristol involved the creation of special filters that allow varying percentages of polarized light from zero to 100 percent. The study participants were subjected to Haidinger's brushes and made them used the special filters to assess their minimum percentage of polarization upon exposure.
The researchers led by Dr Shelby Temple, a Research Associate from the Ecology of Vision Group in Bristol's School of Biological Sciences, found that 56 percent is the average threshold at which the 24 participants become sensitive to polarization. Although some subjects were able to see the Haidinger's brushes even if the light was just 25 percent polarized, the researchers said this is better than the other vertebrates they have evaluated so far.
"Haidinger's brushes usually fade in a couple of seconds as your brain processes them out," says Dr Juliette McGregor, one of the lead authors of the study, who is now part of the University of Leicester. "This is one of the reasons that few people notice them day to day, and why they have previously been fairly difficult to study."
McGregor adds that the findings show that the cornea has significant impact to how an individual see a polarized light. The optical properties that the cornea has may vary depending on the individual and this may be the reason why different people claim varied reports regarding their perception of the Haidinger's brushes.
How an individual sees Haidinger's brushes may be linked to the composition of the carotenoid elements in the macula, which is the pigmented covering that shields the center of the retina. Low carotenoid pigment density is said to increase the risk of developing Age-related Macular Degeneration (AMD). With this, the researchers are looking at developing diagnostic tools that can help to identify individuals who are at a high risk of developing AMD. AMD, at present, is the most prevalent cause of blindness in developed nations.
The electromagnetic waves of ordinary light move in all types of direction. Polarized light, on the other hand, is filtered so it oscillates in one direction only. Light becomes polarized when a transparent object such as glass, serve as a medium for reflection. In the natural environment, refraction in the sky is an example of polarized light.
"As 2015 is the UNESCO International Year of Light, we are delighted to have been able to use twenty-first century technology to gain new insight into an effect that has interested and entertained scientists for more than 160 years," McGregor closed.
Photo: Helga Birna Jónasdóttir | Flickr
