Scientists Put 3D Glasses on Cuttlefish and Find Out They Use Human-Like Depth Perception to Hunt Prey

Trevor Wardill
Trevor Wardill

Researchers at the University of Minnesota recently constructed a miniature underwater movie theater, outfitted a group of cuttlefish with 3D glasses, and proceeded to show them short movies of shrimp—all to see if humans and cuttlefish have more in common than we previously thought.

Cuttlefish, squid-like cephalopods with an internal shell, ensnare prey with one swift snatch of their tentacles. If they under- or over-estimate their distance from whatever unsuspecting marine animal they’re eyeing, however, they’ll fail to grasp their prey and give away their position, too.

To find out how cuttlefish estimate distance so accurately, Trevor Wardill, assistant professor in the University of Minnesota’s Department of Ecology, Evolution, and Behavior, and his team devised an innovative study, published in the journal Science Advances. After placing 3D glasses over a cuttlefish’s eyes, they set it in front of a screen that showed offset images of two different-colored shrimp on a leisurely walk.

cuttlefish in 3d glasses
Trevor Wardill

If you’ve ever briefly taken off your 3D glasses during a movie, you’ve seen the offset—or partially overlapped—images that filmmakers use to create the illusion of depth. The process by which we perceive depth is called stereopsis, where our brain receives different images from our left and right eyes and combines that information to help us understand when some objects are closer to us than others. When you’re watching a 3D movie, your brain is combining the offset images, as seen differently by your left and right eyes, to make you think that flat images have depth, and some are closer than others.

And, as demonstrated in the experiment, the same thing happens with cuttlefish. The researchers varied the positioning of the offset images so the cuttlefish would either perceive the shrimp to be in front of or behind the screen. When the cuttlefish then struck out at their would-be prey, their tentacles ended up grasping at empty water (if they thought the shrimp was in front of the screen) or colliding with the screen (if they thought the shrimp was behind it). In other words, stereopsis allowed them to interpret how far away the shrimp was, just like humans would have done.

"How the cuttlefish reacted to the disparities clearly establishes that cuttlefish use stereopsis when hunting," Wardill said in a statement. "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. This can make all the difference in catching a meal."

But cuttlefish brains aren’t as similar to ours as their depth perception skills might imply.

“We know that cuttlefish brains aren’t segmented like humans. They do not seem to have a single part of the brain—like our occipital lobe—dedicated to processing vision,” Wardill’s colleague Paloma Gonzalez-Bellido said in the press release. “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 squids, octopuses, and other cephalopods, cuttlefish can rotate their eyes to look directly forward, so the experiment isn’t suggesting that all cephalopods can use stereopsis. It is, however, suggesting that we may have underestimated invertebrates’ capacity for what we consider complex brain computations—and overestimated how unique humans actually are.

Not-So-Fancy Feast: Your Cat Probably Would Eat Your Rotting Corpse

Tycson1/iStock via Getty Images
Tycson1/iStock via Getty Images

Cat enthusiasts often cite the warmth and companionship offered by their pet as reasons why they’re so enamored with them. Despite these and other positive attributes, cat lovers are often confronted with the spurious claim that, while their beloved furry pal might adore them when they’re alive, it won’t hesitate to devour their corpse if they should drop dead.

Though that’s often dismissed as negative cat propaganda spread by dog people, it turns out that it’s probably true. Fluffy might indeed feast on your flesh if you happened to expire.

A horrifying new case study published in the Journal of Forensic Sciences offers the fresh evidence. The paper, first reported by The Washington Post, documents how two cats reacted in the presence of a corpse at Colorado Mesa University’s Forensic Investigation Research Station, or body farm, where the deceased are used to further forensic science for criminal investigations.

The study’s authors did not orchestrate a meeting between cat and corpse. The finding happened by accident: Student and lead author Sara Garcia was scanning surveillance footage of the grounds when she noticed a pair of cats trespassing. The cats, she found, were interested in the flesh of two corpses; they gnawed on human tissue while it was still in the early stages of decomposition, stopping only when the bodies began leaching fluids.

The cats, which were putting away one corpse each, didn’t appear to have a taste for variety, as they both returned to the same corpse virtually every night. The two seemed to prefer the shoulder and arm over other body parts.

This visual evidence joins a litany of reports over the years from medical examiners, who have observed the damage left by both cats and dogs who were trapped in homes with deceased owners and proceeded to eat them. It’s believed pets do this when no other food source is available, though in some cases, eating their human has occurred even with a full food bowl. It’s something to consider the next time your cat gives you an affectionate lick on the arm. Maybe it loves you. Or maybe it has something else in mind.

[h/t The Washington Post]

Wolf Puppies Play Fetch, Too, Study Finds

Christina Hansen Wheat
Christina Hansen Wheat

It took thousands of years of selective breeding for wolves to become the Golden Retrievers you see at dog parks today. Domesticated dogs are very different from their wild counterparts, but according to a new study, they may have a surprising trait in common. Researchers found that some wolf puppies are willing to play fetch with total strangers, suggesting that following human commands is intrinsic to canines.

For their study in the journal iScience, researchers from Stockholm University in Sweden set out to find how domestication affects behaviors in young wolves. They raised litters of wolf and dog pups separately from 10 days old and placed them in various scenarios.

When the scientists tested how the wolf puppies would respond to a game of fetch, they expected to be ignored. Chasing a ball and bringing it back requires understanding human commands and obeying them—abilities that were thought to only have emerged in dogs post-domestication.

The first two wolf groups met expectations by showing little interest in the toy, but something different happened with the third set. Three eight-week old pups went after the ball and brought it back when they were encouraged to do so. This was the case even when the person giving the commands was someone they had never met before.

Even though most of the puppies didn't play fetch, the fact that those who did belonged to the same litter indicates a "standing variation" for a retrieving trait in wolves. "When you talk about a specific trait in the context of standing variation, it means that there is variation for the expression of this trait within a given population," co-author Christina Hansen Wheat tells Mental Floss. "For our study it suggests that, while probably rare, standing variation in the expression of human-directed behavior in ancestral populations could have been an important target for early selective pressures exerted during dog domestication." In other words, ancient people seeking to domesticate wolves might have focused on some wolves' innate ability to follow human commands.

The first dogs were domesticated as far back as 33,000 years ago. Over millennia, humans have selected for traits like loyalty, friendliness, and playfulness to create the modern dog, but these new findings could mean that the dog's earliest canine ancestors were genetically predisposed toward some of these behaviors.

"All three litters were brought up under identical and standardized conditions across years," Hansen says of the pups in the study. "With this significant effort to control the environmental conditions, it is likely that the differences in behavior across litters to some extent have a genetic basis."

After raising the dog and wolf litters for three years and completing that part of their study, the researchers will continue to analyze their data to see if there are any other adorable (or weird) traits the two groups share.

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