Milly: Polarization Paradise 2

Enjoying myself on my latest research cruise off
the coast of the UK. Photo: Zan Boyle.

Lizard Island, a tiny island on the Great Barrier Reef in Australia, famous for its abundance of bison lizards and known amongst scientists as a prime spot for marine science. The tranquil, aquamarine waters surrounding the island come as a welcome change from the turbid, brown, worm infested Atlantic I spent so long staring at during my last trip. My mud sieving days are over, instead, I'll be collecting animals from the reef and testing their polarization vision. "Do you make them wear sunglasses?". Sometimes I regret talking about science with my friends. No sunglasses, but plenty of polaroid and LCD screens.

Cats love to be breaded. Photo: web.

Sick of your office judging you for spending your lunch break perusing breadedcats.com? All you need to do is tweak your computer screen and you can hide your cat compulsions from the world. If you were to remove the front layer of an LCD screen, it would appear blank, but those loaf wearing cats are still there, all you need is a piece of polaroid to bring them back. LCD screens work by emitting polarized light at different angles. By putting a piece of polaroid in front of this system, changes in polarization angle alters the amount of light the viewer can see. The polaroid works by blocking light polarized at one angle (appearing black) and transmitting it at a perpendicular angle (appearing white). To the people working in my lab, I looked like very stange, sitting at a blank screen with sunglasses on...but little did they know, breadedcats.com.

So, if we want to test the ability of animals to see polarized light, what better than to use an LCD screen that allows us to create any image we want, and show it as a polarization signal. We will be testing cuttlefish, animals with a fascinating visual system, lacking colour vision entirely but possessing an extremely sensitive polarization visual system. Using LCD screens, a member of our lab, Dr Shelby Temple has discovered that cuttlefish can distinguish surprisingly low differences in polarization angle, far better than what we thought possible but how they are able to do this remains a mystery.

A cuttlefish showing off it's polarization pattern visible
here in a false colour image. Photo: Shashar et al., 1996.

You might be wondering what benefit detecting different angles of polarized light gives an animal living on the reef. Cuttlefish, like mantis shrimps, are able to signal by polarizing the light reflecting off their bodies. Scientists think that this could allow them to signal covertly to other members of their species without alerting prey or predators nearby, pretty nifty. To do this, mantis shrimps have an exoskeleton with special optical properties due to its structure. Cuttlefish however have a mechanism that allows them to control the polarization patterns they produce. Specialised pigment cells, iridophores, under control of the neural system are able to undergo ultrastructural changes in seconds, producing a changing polarization signal all over the body. All of this on top of changing colour and iridescence. The cuttlefish is an underwater disco.

So in in a nutshell, one of our projects will involve using LCD screens to display polarized stimuli to marine animals in tanks, and judging their responses to get a further insight into the mysterious world of polarization vision! More later...