Cuttlefish watch 3D movies in peculiar new study on depth perception

Cuttlefish wearing 3D glasses aren't enjoying the latest superhero movie, but they are helping scientists better understand how they see when on the hunt for food. 

The octopus-like cephalopods can move their eyes independently from one another, which gives them a 360-degree field of vision. Each cuttlefish eye moves in slightly different positions to recognize objects at a distance. Scientists want to test cuttlefish to see if they use stereopsis, even though their eyes move differently than human eyes. 

Stereoscopic vision refers to the ability to see with both eyes in similar but slightly different ways. Stereopsis allows humans to judge distance and have true depth perception by extracting information from the left and right eyes and then letting our brains do some complex processing. 3D glasses also use this technique to create the illusion of depth.

University of Minnesota researchers led by Trevor Wardill and his colleague Rachael Feord at Cambridge University wanted to test whether cuttlefish also use stereopsis to see distances -- and so they outfitted the creatures with miniature 3D glasses. 

Getting tiny 3D glasses to stay on cuttlefish wasn't so easy, but a superglued Velcro strip on the glasses secured them to the test subjects. The scientists then placed the cuttlefish wearing 3D glasses in a tank with an underwater movie screen playing moving images of shrimp.

The cuttlefish saw shrimp on film moving along in slightly different positions with each eye. By making the shrimp film images seem nearer or further away, the cuttlefish wearing 3D glasses would change their striking distance before making a sudden move at the shrimp.

"If you have the images a long way apart, the cuttlefish think the shrimp is really close and they back up and try to shoot their tentacles right in front of them," Wardill told The Guardian on Wednesday. "But if you flip the images around and make the shrimp look like it's behind the screen, they'll swim right into it." 

The study, published in the journal Science Advances on Wednesday, concludes that cuttlefish do indeed use stereopsis. However, the way vertebrates, like humans, and cuttlefish use stereopsis in different ways -- processing images in the brain happens in a different way. These findings may be applied to real-world engineering issues. 

"Creatures like cuttlefish or mantises may seem outlandish, but understanding them will help us come up with varieties of machine vision which are most appropriate for different situations, say for a flying drone versus a robot vacuum cleaner versus a security camera," Newcastle University professor Jenny Read -- who wrote her own study on stereopsis in praying mantises -- told The Guardian. "They are amazing examples of evolved engineering, and we have so much to learn from them."

As expected, social media reaction of cuttlefish wearing 3D glasses to study stereopsis proved to be as entertaining as the study itself. 

"My wishlist now is for every species to have their own cute set of 3D glasses to study their stereo vision," one Twitter user wrote. 

"Love that Trevor Wardill's study into binocular vision in cuttlefish involved Velcroing 3D glasses onto them. I think they suit them!" another user tweeted.

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