"We discovered that these Gifted Word Learner dogs can extend labels to items that have the same function or that are used in the same way," says author Claudia Fugazza of Eötvös Loránd University, Budapest, Hungary. It's like a person calling both a traditional hammer and a rock by the same name, says Fugazza.

"The rock and the hammer look physically different, but they can be used for the same function," she says. "So now it turns out that these dogs can do the same."

The studies took place in the dogs' natural home environments with their human owners. At the beginning, the dogs spent time getting familiar with verbal labels for two functional groups of objects: pull and fetch. Their owners used these words with specific toys and played with them accordingly even though the toys didn't share any similar physical features.

Next, the dogs were tested to see if they had learned to connect the functional labels to the correct group of toys before playing with more novel toys in the two distinct categories. However, this time, their owners didn't use the "pull" and "fetch" labels for the dogs.

The team found that the dogs were able to extend the functional labels they'd learned previously to the new toys based on their experience playing with them. In the final test, the dogs showed that they could successfully apply the verbal labels to the toys by either pulling or fetching accordingly, even when their owners hadn't named them.

"For these new toys, they've never heard the name, but they have played either pull or fetch, and so the dog has to choose which toy was used to play which game," Fugazza says. "This was done in a natural setup, with no extensive training. It's just owners playing for a week with the toys. So, it's a natural type of interaction."

The authors note that the dogs' ability to connect verbal labels to objects based on their functional classifications and apart from the toys' physical attributes suggests that they form a mental representation of the objects based on their experience with their functions, which they can later recall. These findings provide insight into the evolution of basic skills related to language and their relationship to other cognitive abilities, including memory, the researchers say.

More research is needed to understand the scope and flexibility of dogs' language categorization abilities. The researchers suggest future studies to explore whether dogs that don't learn object labels may nevertheless have an ability to classify objects based on their functions.

"We have shown that dogs learn object labels really fast, and they remember them for a long period, even without rehearsing," Fugazza says. "And I think the way they extend labels also beyond perceptual similarities gives an idea of the breadth of what these labels could be for dogs."

This work was supported by National Brain Research Program NAP 3.0 of the Hungarian Academy of Sciences, MTA-ELTE Comparative Ethology Research Group, and TRIXIE.