An international team of researchers has found that cuttlefish have the most acute polarization vision yet found in any animal by showing them movies on a modified LCD computer screen to test their eyesight.
A close up of a cuttlefish head, showing the well developed eye
Cuttlefish as well as squid and octopus see aspects of light – including polarized light – that are invisible to humans.
A study, published in the journal Current Biology, shows that cuttlefish are much more sensitive to polarization than it was previously thought.
“Just like color and intensity, polarization is an aspect of light that can provide animals with information about the world around them,” said lead researcher Dr. Shelby Temple of the University of Bristol, UK. “If you’ve ever put on a pair of polarized sunglasses glasses to cut the glare from water or the road, or gone to a recent 3D movie, then you’ve observed some aspects of polarized light.”
The team gave cuttlefish an eye exam, but instead of measuring their acuity they measured the smallest difference in the angle of polarization the cuttlefish could detect. Since the team could not ask the cuttlefish what they could see, they took advantage of the chameleon-like color changes that cuttlefish use for camouflage as a way of measuring whether the animals could detect the polarized stimuli.
“We modified LCD computer monitors to show changes in polarization instead of changes in color, and then played videos of approaching objects and watched for changes in skin color patterns to determine if the cuttlefish could see small changes in polarization contrast,” Dr. Temple explained. “Cuttlefish change color all the time and respond to the slightest movement so they are an excellent model.”
“Cuttlefish were much more sensitive than we expected. It was previously thought that polarization sensitivity was limited to about 10-20 degree differences, but we found that cuttlefish could respond to differences as small as one degree.”
In addition to measuring the limits of polarization vision in the cuttlefish, the team also modeled how underwater scenes might look to an animal that has such high-resolution polarization vision. Using colors instead of changes in polarization angle they created images of the polarized world that humans can see and showed that there is much more information available in the polarization dimension than was previously known.
“These extraordinary findings suggest that we need to reexamine how we have been measuring the visual world underwater,” said Justin Marshall, a co-author on the study and a professor at the University of Queensland. “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.”
