Scientists are showing 3D films to cuttlefish, and while we didn't learn what they think of Avatar, the research has taught us they process visual images in a way once thought restricted to vertebrates.
Cuttlefish, like their relatives squid and octopuses, are the closest thing to alien intelligences scientists can study. If great apes teach us about how our own minds work, these astonishingly smart invertebrates reveal the path not traveled, demonstrating there are other very different ways to organize brains that still work exceptionally well.
For any predatory species, depth perception is vital for prey capture. Even with their immensely flexible arms, cuttlefish can't reach if their prey is too far away, and can't afford to get so close they scare them off, so distance assessment is vital when sneaking up on a tasty crustacean.
Dr Trevor Wardill of the University of Minnesota wanted to know if cephalopods (the tentacled mollusks that include cuttlefish) use stereopsis, the method humans use to determine distance by comparing images from left and right eye.
To answer this, Wardill made the (no doubt very puzzled cuttlefish) wear 3D glasses and showed them a film of shrimp walking across a screen. In some cases, the shrimp was camouflaged by covering it in dots, and putting similar dots on the screen such that the shrimp was only visible by combining information from both eyes. The shrimp images to each eye were adjusted so their distance judgements would depend on the method used. Their prey-capture efforts confirmed they were indeed using stereopsis.
"When only one eye could see the shrimp, meaning stereopsis was not possible, the animals took longer to position themselves correctly. When both eyes could see the shrimp, meaning they utilized stereopsis, it allowed cuttlefish to make faster decisions when attacking,” Wardill said in a statement. “This can make all the difference in catching a meal." The cuttlefish normally achieved 91 percent attack success, but this fell to 56 percent when one eye was obstructed.
However, the cuttlefish operated their eyes independently, like chameleons, when they were further from their prey, indicating stereopsis is something they only turn on when preparing to pounce.
The cuttlefish were able to do some things much better than humans, specifically assessing distance when one eye was shown an image with dark and light reversed compared to the other, suggesting their stereoposis operates differently from ours. "While cuttlefish have similar eyes to humans, their brains are significantly different," Dr Paloma Gonzalez-Bellido, co-author of a Science Advances paper on the findings, added. "They do not seem to have a single part of the brain – like our occipital lobe – dedicated to processing vision. Our research shows there must be an area in their brain that compares the images from a cuttlefish's left and right eye and computes their differences."
Unlike other cephalopods, cuttlefish can rotate their eyes to a forward-facing position, where the overlap between them can reach 75 degrees, leading the authors to suspect they were using stereopsis in the first place. Their closest relatives, with eyes that point in different directions, probably rely on other methods.