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What the Cuttlefish Sees

Shrimp in Natural and Polarized light

A Shrimp - As We See it vs. How They See It. Courtesy Dr Shelby Temple, University of Bristol

Dr. Shelby Temple  at the University of Bristol and colleagues are doing some fascinating work with the visual systems of cuttlefish, animals that – despite their name – are most closely related to squid and octopi.  The cuttlefish are color-blind, so at first the second, rainbow-colored image might be a bit puzzling.  According to Temple, the cuttlefish are sensitive to differences in angle of polarization as small as a degree.  Explaining polarization is a bit tricky, because quite frankly you are blind to it.    Light can have an orientation (although it doesn’t necessarily need to have one) in addition to the other factors of light that your eyes actually are sensitive to, intensity and color (and if you are blind or color-blind, I apologize for my insensitivity).    In order to demonstrate this, purchase some polarized sun glasses or take some glasses home from your next 3D movie.  Look at a polarized light source (your monitor or TV, if they are LCD, are the closest), slowly cock your head, and note that the light appears to get brighter and darker.  You could measure the angle of polarization by noting at which angle your head is cocked when the light is at its brightest or, conversely, at its darkest.  If you had multiple sources at different orientations (take one of your TVs and rotate it on its side) you wouldn’t be able to turn your head so that everything was bright simultaneously.  And turning your head to take multiple measurements of the same scene is a waste of time and energy.  The cuttlefish doesn’t need to turn its head.  At every point in its visual field, it can measure this angle automatically.  To attempt to represent what it might see using this super-power, we have the rainbow shrimp.  Each color represents a slightly different angle of polarization.  However…

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