Mantis shrimp vision is extraordinary, both in terms of their colour vision and their ability to see the polarisation of light.
Not only this, but they have extremely mobile eyes that never seem to stop moving. While most animals keep eye movements to a minimum to avoid blur, mantis shrimp apparently go out of their way to move their eyes as much as possible.
Each eye is capable of independent rotation in all three degrees of rotational freedom; pitch (up-down), yaw (side-to-side) and roll (twisting about the eye-stalk).
Like other animals, mantis shrimp do make stabilising side-to-side movements that help keep their vision steady as they move through the world, but a recent study found that even while stabilising in the horizontal direction, they can’t resist rolling their eyes.
This counter-intuitive behaviour has baffled researchers, since the whole point in stabilising the gaze is to keep the appearance of the world steady. But when eye-rolling transforms ‘up’ into ‘sideways’, the world gets very complicated.
Amazingly, this appears to have no effect on the mantis shrimp – no matter what position they’ve rolled their eyes to, or how quickly they’re rolling, mantis shrimp can still reliably and accurately follow the motion of a pattern that is moving sideways.
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