Some cuttlefish absolutely refuse to wear 3-D glasses.
These relatives of squid and octopuses have blimplike bodies that end in a ring of eight arms topped by two prominent eyes. It’s not hard to mount a pair of specs in front of those eyes, but a cuttlefish’s arms are so dexterous that, if it’s displeased with its new accoutrements, it can just yank them off. “And indeed, that happened a lot,” says Trevor Wardill from the University of Minnesota, who spent the better part of a recent summer trying to accessorize the animals. “But about 20 to 30 percent didn’t seem to be bothered. Everyone was very surprised.”
Together with his colleagues Paloma Gonzalez-Bellido and Rachael Feord, Wardill used the glasses to show different images to each of a cuttlefish’s eyes. By doing that, they proved that these animals have stereopsis—that is, their brains can work out how far away objects are by comparing the slightly divergent images perceived by each of their eyes. It is an ability that humans and a few other animals share. But, as is the norm with cuttlefish, they manage the task in an odd and surprising way.
Stereopsis comes so naturally to us that we take it for granted. It’s actually a difficult computation that doesn’t happen automatically for every creature with a pair of forward-facing eyes. “It’s thought that animals need a fancy brain to do that calculation,” says Wardill. Indeed, after scientists rigorously confirmed that humans have stereopsis in 1838, it took another 132 years to do the same for another animal. Macaque monkeys came first, followed by cats, horses, sheep, owls, falcons, and toads.