Insights into visual supersense provided by new study

An experiment originally designed to test the visual abilities of octopuses and cuttlefish has provided researchers with new insights into a human supersense – the ability to perceive the polarisation of light.

Animals, like bees and ants, use polarisation patterns in the sky as a navigation aid. But few people are aware that humans can perceive the polarisation of light with the naked eye too. We do so using ‘Haidinger’s brushes’, a subtle visual effect - which appears like a yellow bow tie at right angles to the polarization angle.

Dr Juliette McGregor from the Department of Cell Physiology and Pharmacology said: “Haidinger’s brushes usually fade in a couple of seconds as your brain processes them out. This is one of the reasons that few people notice them day to day, and why they have previously been fairly difficult to study.”

By using LCD screens capable of constantly refreshing the effect, the researchers were also able to make the first measurements of the dynamics of Haidinger’s brushes, confirming the prediction that some individuals would perceive a ‘flip-flop’ effect, as the polarisation angle is rotated.

Dr McGregor added: “This result shows that your cornea can dramatically affect how you perceive polarized light. As the optical properties of the cornea vary between individuals, this may partly explain why people often report their experience of seeing Haidinger’s brushes quite differently."

The ability to see Haidinger’s brushes is associated with the organisation of carotenoid pigments in the macula (a pigmented area that covers and protects the central part of the retina). The risk of acquiring Age-related Macular Degeneration (AMD) has previously been correlated with low carotenoid pigment density in the macula. The researchers are presently adapting their approach with the aim of developing a screening device to detect individuals at high risk of AMD, currently the leading cause of blindness in the developed world.

The study, published in the Proceedings of the Royal Society B was carried out in collaboration with Dr Shelby Temple while they were working at the University of Bristol