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If you talk to your dog, you’re in the majority: 84% of pet owners talk to their dogs. Maybe it’s just to ask for certain behaviors, or maybe it’s entire conversations. Either way, have you ever wondered how many words your dog can understand? Do they know the meaning of those words, or do they just remember that certain sounds lead to certain outcomes, like “walk” leading to a trip outside? Recent research is shedding new light on if dogs can truly understand human language, and the truth might surprise you.

Dogs Recognize Different Languages

People talking isn’t just noise to your dog’s ears. According to a study in the journal NeuroImage, dogs recognize words they haven’t been formally taught. By placing dogs in MRI machines, scientists showed that dogs can tell the difference between nonsense sounds and human language. They can even tell familiar languages and unfamiliar ones apart. The scans showed that dogs process speech in two steps – first, their brain determines whether the sound they hear is speech, then it decides if it’s a language they’re familiar with.

Woman talking to Shetland Sheepdog puppy
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Dogs May Not Recognize the Details of Human Speech

Even though they can recognize familiar and unfamiliar languages, they can’t always tell apart similar sounds. A Royal Society Open Science study found that dogs struggle to distinguish phonetic details when they’re listening to people speak. For example, “stay” and “shay” would both result in your dog staying still.

The researchers used electroencephalography (EEG), a non-invasive way of recording electrical activity in the brain, on awake, cooperating dogs. They discovered instruction words the dogs already knew, like “sit” or “down,” weren’t distinguished in the dogs’ brains from similar-sounding nonsense words. However, that doesn’t necessarily mean the dogs don’t hear the difference. They just might not consider the difference important.

Dogs May Understand the Meaning of Words

But what about “Chaser,” known as the smartest dog in the world? She was a Border Collie that knew over 1,000 proper nouns. She was able to retrieve hundreds of toys from another room by their name alone. She must have had a mental representation of what each name or word represented. Was she an exceptional canine genius, or can other dogs use toy names as object labels too?

When other dogs were tested like Chaser and asked to fetch their toys, they didn’t perform any better. So, researchers in the Neuroethology of Communication Lab of the Eötvös Loránd University decided to try a different approach. Using non-invasive EEG technology, the scientists recorded brain activity in dogs to see if certain words stood for certain objects in their minds. In other words, did hearing the word activate a matching mental representation? 18 dogs (including Border Collies, an Akita, a Toy Poodle, a Pumi, a Labrador Retriever, and mixed breeds, among others) and their owners participated in the study. The results were published in the journal Current Biology.

English Cocker Spaniel meeting a man outdoors.
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The owners would say a word for a toy the dog knew and then show the dog an object. Sometimes the object was the matching toy and at other times the object was a mismatch. For example, the owner might tell the dog to look at the ball but show the dog a Frisbee. The dogs were awake and had small metal electrodes taped to their heads, so their brain activity could be recorded while they watched and listened to their owners. The brain recordings showed one pattern when the object was a match and a different pattern for the mismatch. This is similar to what is seen in humans and is considered evidence that humans understand words. So it looks like Chaser, as incredible as she was, isn’t as unique as once thought. Dogs have the capacity to understand words as object labels just like us.

According to Lilla Magyari, PhD, a cognitive neuroscientist at the University of Stavenger, Norway, and one of the researchers, this specific study was particularly challenging. Canine EEG experiments are usually easy to run and can be done with untrained dogs. In this study, it was difficult to find dogs that knew at least five object names. On top of that, the dogs couldn’t play with the toys. They had to lie motionless and watch their owner show them the toy, then put it away. Some dogs couldn’t manage, others just needed a bit of training beforehand, and some were very calm and accepted the task. “This required an enormous amount of self-control from them,” Dr. Magyari said, “and we are very grateful to them and their owners for their persistence.”

Does a Dog’s Vocabulary Matter?

The results were influenced by how well the dogs knew the words, at least according to their owners, with a greater difference in brain activity for words the dogs knew better. But Dr. Magyari says older dogs with more experience with human language didn’t show greater brain activity difference than younger dogs. However, she said, “In our sample, there was also no relationship between the dog’s age and the number of words they knew.”

In terms of the earlier research on phonetic details, Dr. Magyari wouldn’t expect dogs to react differently to words they know and similar-sounding nonsense words, such as “Frisbee” and “bisbee.” Both should show the mismatch reaction if the dog was shown a ball, for example. But she believes it’s possible that this mismatch reaction could be modified by the number of object labels a dog understands. “When a dog has a lot of toys, then the dog has more opportunities to hear different words for them, perhaps learn those words and this may give them an opportunity to realize that phonological details in a word matter. A comparison between dogs with high and low vocabulary could shed light on this issue in the future,” she explains.

Is This Ability Unique to Dogs and Humans?

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This type of referential understanding of words has yet to be found in any other species besides humans. There could be several reasons why that is. The first could be based on dogs’ evolutionary history. According to Marianna Boros, PhD, cognitive neuroscientist and postdoctoral researcher at the Neuroethology of Communication Lab and one of the study’s authors, dogs have been selected for over 5,000 generations to cooperate and communicate with humans. That domestication process could’ve played a role in their capacity to understand object words. However, she says it’s also possible their rich contact with objects and human speech is another important factor.

Finally, it’s possible that this capacity is generally present in mammals, including non-domesticated species. Dr. Boros explains that whether animals can understand that words or symbols stand for things or concepts has been a topic of scientific debate, although there have been reports from wild species that support the idea. However, all the evidence prior to this study was based on the animals’ behavior, not their mental processes. “But in our study, we were able to show that dogs activate the mental representation of the object when they hear its name. To confirm previous behavioral reports, more species should be tested in the future,” she notes.

EEG testing on other species isn’t the only area for future study. Dr. Boros says the current research’s proof of a marker in a dog’s brain activity when there’s a mismatch in expectations opens other doors for testing dogs’ knowledge about their environment. For example, does this mismatch occur in other semantic contexts outside of object labels? Chaser knew adjectives like bigger and smaller. Do other dogs understand those concepts? What about exploring physical and social cognition? By looking at brain activity, we have a new window into the dog’s mind.