Known to respond to command words such as "sit", dogs have now been found to conjure up mental representations when they hear known words referring to objects such as a ball, according to a new research that analysed their brain activity.

The researchers said it did not matter how many object words a dog understood -- known words activated mental representations anyway.

This suggested that the ability is generally present in dogs and not just in some exceptional canines knowing the names of many objects, they said.

"Your dog understands more than he or she shows signs of," said Lilla Magyari from Hungary's Eötvös Loránd University and co-first author of the study published in the "Current Biology" journal.

"Dogs are not merely learning a specific behaviour to certain words but they might actually understand the meaning of some individual words as humans do," Magyari said.

The finding that dogs may have a general capacity to understand words in a referential manner, as humans do, can reshape the way scientists think about humans' uniqueness in using and understanding language, the researchers said.

It also has important implications for theories and models of language evolution, they said.

For the study, the researchers recruited 18 dog owners and had them say words for toys that their dogs knew.

The dogs were then presented with objects -- sometimes matching the word their owner said and sometimes not -- and their brain's electrical activity was measured.

The brain activity recordings showed differences in patterns when the dogs were shown matching objects against those when shown non-matching ones, the researchers said and added that this was evidence of dogs understanding words.

They also found a greater difference in the brain activity patterns for words that the dogs knew better.

While the team also thought that dogs' ability to understand words depended on them having a large vocabulary of object words, the results showed otherwise.

"Because typical dogs learn instruction words rather than object names, and there are only a handful of dogs with a large vocabulary of object words, we expected that dogs' capacity for referential understanding of object words will be linked to the number of object words they know; but it wasn't," said Magyari.

The researchers now want to know if this ability to understand words through mental representations is specific to dogs or is present in other mammals as well.

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