Dogs Understand Human Words and Intonation

Do dogs process speech in the same ways that humans do? | Produced by Attila D. Molnár,

Dogs have the ability to distinguish words and the intonation of human speech through brain regions similar to those that humans use, a study in the 2 September issue of Science reports.

The results reveal important insights into the neural networks needed to understand speech, hinting that perhaps both humans and dogs may have relied on similar networks that were already in place before language evolved, and later adapted to process speech.

Words are the basic building blocks of human language, but they are hardly ever found in nonhuman vocal communication. Intonation is another way that information is conveyed through speech. For example, praises tend to be conveyed with higher and more varying pitch. Humans use both words and intonation to understand speech.

And many of us do not just use language to communicate among our peers.

"We humans also love talking to dogs all the time. We praise them, call them," said Attila Andics of Eötvös Loránd University, lead author of the study. "But quite little is known about what dogs get out of all of this, of how dogs interpret our words. Do they process the tone of our words only or do they process the words as well?"

In their study, Andics and his colleagues sought to answer this question. Magnetic resonance imaging can be used to measure brain activity, but the process requires the subject to lie still, in a tightly enclosed area. Sometimes humans with a fear of small spaces have trouble lying in such machines, but remarkably the researchers, with dogged effort, were able to recruit some well-trained canines who were comfortable in the machines.

Study participant Barack on the scanner bed. | Enikő Kubinyi

While the MRI machine captured their brain activity, the dogs were exposed to recordings of their trainer speaking in different combinations of words and intonation, in both praising and neutral ways. For example, trainers said words like "super" or "however" in a high-pitched, cheery voice, as well as a neutral tone. The results reveal that, regardless of intonation, dogs process vocabulary, recognizing distinct words. What's more, they do so in a way similar to humans, using the left hemisphere of the brain.

Also like humans, the researchers found that dogs process intonation separately from vocabulary, in auditory regions in the right hemisphere of the brain.

Furthermore, monitoring of the reward regions of the brain revealed that the dogs responded best when praising words were used in combination with praising intonation.

"This shows … that dogs not only separate what we say from how we say it, but also that they can combine the two for a correct interpretation of what those words really meant," Andics said.

The authors note that it is possible that selective forces during domestication could have supported the emergence of the brain structure underlying this capability in dogs, but such rapid evolution of speech-related hemispheric asymmetries over a relatively short time period is unlikely. Therefore, they suggest that a more ancient brain function exists in both dogs and human that has been exploited to link arbitrary sound sequences to meanings.