The question of whether dogs really understand the words we say has long puzzled owners, and so far science has failed to provide clear answers.
But a new brainwave study published in Current Biology shows that hearing the names of their favorite toys actually activates dogs' memories of those objects.
"It definitely shows us that it's not unique for humans to have this type of referential understanding," first author Lila Magyari of Eotvos Lorand University in Hungary told AFP, explaining that until now researchers have been skeptical.
With a few notable exceptions, dogs do poorly on lab tests that require them to fetch objects after hearing their names, and many experts say it's not so much what we say but rather how and when we say things that piques our dogs' interest.
For example, if you call out "Go get the stick!" and the dog successfully fetches the object, this does not conclusively prove that he knows what the word "stick" means.
Even scientists who acknowledge that dogs do pay attention to our speech argue that instead of truly understanding what words mean, they respond to certain sounds with rote behavior.
In the new paper, Magyari and his colleagues apply a non-invasive brain imaging technique to 18 dogs brought to their lab in Budapest.
The test involves placing electrodes on the dogs' heads to monitor their brain activity. Their owners uttered words about the toys they were most familiar with -- for example, "Coon-coon, look at the ball!" -- and then showed them either the corresponding object or a different object.
After analyzing the EEG recordings, the team found different brain patterns when the dogs were shown matching and mismatched objects.
This experimental setup has been used for decades in humans, including infants, and is taken as evidence of "semantic processing," or understanding meaning.
The test also has the advantage that dogs are not required to bring anything to prove their knowledge.
"We found the effect in 14 dogs," says Mariana Boros, co-author of the first project, proving that this ability is not inherent to just "a few exceptional dogs." Even the four that "failed" may simply have been tested on the wrong words, she added.
Holly Ruth-Gutteridge, a dog behaviour specialist at the University of Lincoln in England, said the ability to fetch certain toys by name had previously been considered a "genius" quality.
The famous Border Collies Chaser and Rico were able to find and retrieve specific toys from large piles, but were considered exceptions, she said.
But the new study "shows that a whole range of dogs learn the names of objects in terms of brain response, even if they don't demonstrate it behaviorally," Ruth-Gutteridge said, adding that it was "another blow to the special and distinctive qualities of humanity."
The paper "provides further evidence that dogs may understand human vocalizations much better than we typically attribute to them," added Federico Rossano, a cognitive scientist at the University of California, San Diego.
But not all experts were equally enthusiastic. Clive Wynn, a canine behavior specialist at Arizona State University, said he was "split" on the results.
"I think the paper fails when it wants to make the big claim that they have demonstrated what they call 'semantic understanding,'" he said, although he praised the "ingenious" experimental setup as a new way to test the full range of dogs' "functional vocabulary."
For example, Wynn said, he has to spell out the word "w-a-l-k" when in front of his dog - lest his pet get excited about a walk there and then.
"Would Pavlov be surprised by these results?" asked Wynn, referring to the famous Russian scientist who proved that dogs can be conditioned to expect food when they hear a bell signaling feeding time. "I don't think it would be."/BGNES