When humans roll their eyes, it's because they think something is absurd, but for a mantis shrimp it's all good: eye-rolling just means it's trying to see better.
That's the thrust of a new study in the journal Nature Communications by researchers from the University of Bristol.
The scientists were looking for a reason behind the mantis shrimp's eye movements. The creatures watch the world not with a fixed gaze (though they will do that occasionally) but with a series eye rotations that even occur independent of each other.
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Many animals make sure to stabilize their sightlines – their eyes, heads and bodies moving together to make sure what they're looking at isn't blurry.
But mantis shrimp, with four times the photoreceptors of humans, are nearly alone in their eye-rolling ways. What do they get out of it?
The researchers captured images of mantis shrimp eyes, as the darting orbs reacted to various light sources. They determined that the eye-rolls are actually a way for the creatures to enhance their ability to see polarized light, reducing glare and improving the contrast of objects around them.
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The scientists call the capability "dynamic polarization vision" and say their study is the first to document the feature in any animal.
"We have known for a while that mantis shrimp see the world very differently from humans," said study co-author Nicholas Roberts in a statement.
"They can use 12 different color channels -- we use only three -- and can see the polarization of light," he added. "But the eye movements of mantis shrimp have always been something of a puzzle."
Other than it's being simply neat, why should we care? The scientists say their findings may be of use in the field of robotics, where automated visual recorders, such as undersea robotic cameras, could one day mimic the mantis shrimp's vision and provide low-cost, high-performance imagery.
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