Dogs know words for their favorite toys

Dogs may know more than they let on. Pet dogs’ brains displayed neural signs of surprise when their owners showed them an unexpected toy. The findings, published March 22 in Current Biology, suggest that dogs create mental concepts of objects.

“Anyone who has ever interacted very much with a dog probably is not that surprised to know that dogs understand that your speech is referring to at least a few common objects,” says Ellen Lau, a neuroscientist at the University of Maryland in College Park. But some people may have assumed this sort of “understanding” is just a simple, almost reflexive reaction to the sound of the word. “It’s always great to have evidence like this coming out to make the argument against that,” Lau says.

Some unusually gifted dogs have stunning vocabularies. A famous border collie named Chaser knew more than 1,000 words for toys, for instance. Marianna Boros, a neuroscientist and ethologist at Eötvös Loránd University in Budapest, and colleagues wondered about dogs in the middle of the pack — the ones that don’t listen well enough to fetch specific toys from other rooms like Chaser did. “They can be bored or not willing to perform or be more interested in the other toy than the toy they’re supposed to fetch,” Boros says.

The researchers recruited 27 pet dogs (and their humans). This motley collection included a toy poodle, an Akita, a Labrador and some mixed breeds (though brain data for only 18 dogs made it into the final analysis). Boros and her colleagues asked the owners to bring five familiar toys to the lab. Once there, the team stuck electrodes to the pooches’ heads and asked the pups to do just two things: lie on a comfy mat and stay awake.

Every so often, the dogs would hear a recording of its owner saying things like, “Kun-Kun, look, the ball!” The dogs’ human was on the other side of a wall with a window. This electronic window could instantly change from opaque to translucent, allowing the dog to see through. Just after the audio played, the window would reveal the owner holding a toy. Sometimes the toy was the ball, but sometimes it was a different toy, such as a rope.

The electrodes monitored brain activity while the dogs listened and watched the window. Just after the surprise of seeing an unexpected object — a rope instead of a ball — an electrode picked up a larger-than-normal signal.

This signal indicates surprise, the researchers think, and suggests that the dog had already formed a mental concept and expectation of the ball after hearing that word. In fact, the signal was especially strong for a mismatch involving words that the dogs reportedly knew very well. “That suggests that it is really about understanding and knowledge of the word,” Boros says. “That was really exciting to see.”

Humans have this surprise signal, too. It’s called the N400 effect, and it occurs in the brain just after something unexpected happens. “There have been now thousands of human studies investigating and using this N400 effect,” Lau says. But there has been no evidence of a similar signal in dogs, until now.

This neural signal of surprise in the dogs’ brains wasn’t, well, surprising, Boros says. Scientists have previously found clues about how dogs process meaningful words, but the findings give a glimpse into the mental lives of dogs that didn’t exist before (SN: 8/30/16). “We can say that they know passively the words,” she says. “They understand more than they show signs of.”