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Polarization vision keeps cuttlefish safe

BioPhotonics
Apr 2012

Cuttlefish may be colorblind, but they can see things we can’t – in fact, they have the most acute polarization vision yet found in any animal. And that special power gives them an advantage in survival and hunting situations.

“Just like color and intensity, polarization is an aspect of light that can provide animals with information about the world around them,” said Shelby Temple of the Ecology of Vision Laboratory at the University of Bristol in the UK.


On the left is an image of a shrimp as humans see it. On the right is an interpretation of how the shrimp might look to a cuttlefish or octopus – animals that see polarization angles but not color. The false colors in the image on the right represent the various polarization angles as provided in the colored triangle in the top left. Courtesy of Shelby Temple, University of Bristol.


Temple and colleagues believe that the polarization vision may provide the animals with a source of contrast information that serves as an alternative to color vision and that is just as fine-scale.

“Cuttlefish are much more sensitive than we expected,” Temple said. “It was previously thought that polarization sensitivity was limited to about 10° to 20° differences, but we found that cuttlefish could respond to differences as small as 1°.”

To determine whether the creatures could see small changes in polarization contrast, the researchers showed them movies – videos of approaching objects – on a modified liquid crystal display computer monitor that displayed changes in polarization rather than changes in color.


A recent study of the mourning cuttlefish (Sepia plangon) revealed that the animal has high-resolution polarization vision. The findings could lead to revisions in our approach to marine study and exploration. Courtesy of Shelby Temple.


The cuttlefish’s chameleonlike ability to change color to camouflage themselves showed that they could detect the polarized stimuli. “Cuttlefish change color all the time and respond to the slightest movement, so they are an excellent model,” Temple said.

The team then monitored the cuttlefish for changes in skin-color patterns to determine whether they could see the small changes in polarization contrast as shown in the videos. Instead of measuring visual acuity, the researchers measured the smallest difference in the angle of polarization that the cuttlefish could detect.

They also modeled how underwater scenes might look to an animal with high-resolution polarization vision. Using colors instead of changes in polarization angle, they created images of the polarized world that humans can see – providing a glimpse of the information available to animals with this kind of vision.


Shown is a close-up view of a cuttlefish eye. The colorblind animal visually experiences the aquatic world through polarization angles. Courtesy of Justin Marshall, University of Queensland, and Shelby Temple.


The findings, published recently in Current Biology, could someday result in changes in our approach to underwater exploration and study. “Cuttlefish may be using the polarization of light much like we use color, which means we may need to look at camouflage and communication underwater in a whole new way,” said co-author Justin Marshall of the University of Queensland in Brisbane, Australia.


GLOSSARY
polarization
With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam...
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