The last time you saw a film in 3D, you probably weren’t grabbing for a tasty meal that seemed to hover just in front of you. But that’s exactly what happened when scientists put 3D glasses on cuttlefish and showed them a movie—all in the name of science.
The experiment may sound bizarre, but it actually led to an exciting discovery about the eyes of these invertebrates. Octopus and squid, cousins of cuttlefish, see only in two dimensions, so they lack depth perception. But since cuttlefish eyes often focus synchronously and their field of vision overlaps, biologists suspected cuttlefish might have 3D vision like humans. So they tested this hypothesis.
After carefully gluing red and blue shades on a cuttlefish’s brow, scientists returned it to a tank and projected a video of shrimp on the tank wall. The video made the shrimp appear to hover at different distances from the cuttlefish, just as 3D movies for humans can make objects appear closer or further away.
When cuttlefish hunt, they thrust out tentacles that have suckers on the tips, but they only succeed if they’re just close enough for the suckers to strike the prey without overshooting. When the shrimp in the video appeared close, the cuttlefish backed up a bit before springing its tentacles forward to capture it. When the shrimp appeared further away, the cuttlefish moved forward before attacking. And when scientists altered the video to make the shrimp appear invisible to one eye, the cuttlefish hesitated before doing anything, as though it was struggling to gauge its distance from its prey.
As with most scientific questions, the answer to whether cuttlefish see in 3D has led to many more questions, starting with how and why. Only more experiments will tell.