These eyes don′t get dizzy | Global Ideas | DW | 04.05.2018
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Global Ideas

These eyes don't get dizzy

Do action movies at the theater make your head spin? Not a problem for the peacock mantis shrimp. And that's just for starters.

Most of us don't even need to get on a rollercoaster. Just watching a large-screen video shot by someone sitting in one will make us dizzy as the world seems to spin, rattle and shake all around us. There are even amusement parks that offer such virtual rides. Tell that to the peacock mantis shrimp. If it had shoulders, it would probably just give you an indifferent shrug.

So why doesn't the mantis shrimp care? Because the little sea creature has unique eyes that can do some amazing things.  

Are you looking at me?

For starters, they can see a lot more colors than we can. Whereas we have receptors for red, green and blue that our brain uses to put together the colorful world we see, mantis shrimp have 16 different kinds of color receptors. 

But let's get back to mobility. When we look at things, our eyes move in sync. When our right eye looks up, so does the left. And the overall movement of our eyes is rather limited. If we really want a change of perspective, we usually can't avoid moving our heads. 

Things are quite different for the mantis shrimp. Their eyes aren't deeply embedded in their heads like ours but stick out and can move up and down, left and right and even roll along their axis — all of it independently from one another.

But too much eye movement could get confusing, couldn't it? Apparently not for the mantis shrimp. A team of researchers from the University of Bristol recently put a peacock mantis shrimp (Odontodactylus scyllarus) through the paces and found that while they stabilize their vision by moving their eyes left and right, they rolled them (literally) at the same time. And no matter how much their eyes spun around, they could still reliably track a pattern that moved sidewise through their field of vision.

"It would be like you tipping your head on its side, then back to normal and all angles in between all while trying to follow the motion of a target," said Ilse Daly, lead author of the study, which was published in the Proceedings of the Royal Society B this week.

And keep in mind that their eyes can move independently from one another. So one of their eyes may be level while the other one is rolled 90 degrees to the side and their brain could still sort it out. 

The world spins but we don't care

Given how easily the shrimp mastered their test, the researchers upped the ante. They decided to make the world spin around the shrimp — virtually speaking.

"We expected that, in response to the world around them apparently rolling, mantis shrimp should roll their eyes to follow their surroundings," said Daly. But they didn't. 

"The mantis shrimp visual system seems entirely immune from any negative effects of rolling their eyes," she said in a statement. "Indeed, it appears as though rolling has absolutely no effect on their perception of space at all: up is still up, even when their eyes have rolled completely sideways. This is unprecedented in the animal kingdom.”

Considering how the world seems upside down so often these days, wouldn't it be nice to be a mantis shrimp sometimes?

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