Attention, dog owners! Your pets probably know when you’re praising them — and not just by the tone of your voice. New data suggest that dogs’ brains not only respond to the tone of human speech, but can also distinguish between positive and neutral words. The findings will be published in the 2 September issue of Science1.
The study “provides the first evidence from inside a dog’s brain that there’s processing that depends on the meaning of a word and not just the tone of voice in which it is said”, says Clive Wynne, a behavioural scientist who studies dogs at Arizona State University in Tempe.
In the study, Attila Andics, a neuroscientist at Eötvös Loránd University in Budapest, and his colleagues scanned the brains of 13 family dogs of 4 different breeds while the canines listened to a series of praising or neutral words. Different areas of the animals’ brains lit up depending on the tone and meaning of the words.
Over several months, the team had trained the dogs to lie in a functional magnetic resonance imaging (fMRI) scanner and remain completely still for two 7-minute brain-scanning sessions. The dogs were not restrained and could leave the scanner whenever they chose.
Once the dogs were inside the scanner, the researchers played recordings of Hungarian words spoken in both a neutral and a positive tone. They included praising words meaning “that’s it”, “clever” and “well done”, and neutral words meaning “as if”, “such” and “yet”.
The left hemisphere of the dogs’ brains responded more strongly to the meanings of words, much like human brains do2. Praising words, regardless of intonation, were associated with a greater response in the left hemisphere than in the right. Neutral words produced no such difference.
Parts of the right hemisphere, meanwhile, picked up on the emotional information conveyed by the intonation, regardless of a word’s meaning. The researchers found that words delivered in a praising tone were associated with stronger coordination of activity between certain auditory regions and areas involved in reward processing.
Praising words delivered in a positive tone elicited especially strong responses in the brain’s primary reward regions. All other combinations of word meaning and intonation provoked roughly equal, smaller responses in the dogs’ brains.
“Dogs seem to care both what we say and how we say it,” says Andics. “They not only separately process word meaning and intonation, but are also able to combine these two types of information as we see in reward processing.”
He cautions that dogs probably don’t fully understand language as humans do. Still, the study results suggest that dogs can derive some semblance of meaning from different words.
But Terrence Deacon, an evolutionary anthropologist at the University of California, Berkeley, notes that although the hemispheric differences in the study were convincing, the results in the reward centres were less so. “It’s such a small area and overlaps with so many different areas that I’m a little suspicious that it’s probably not a strong finding,” he says.
Others urge even greater caution in interpreting the results. Gregory Berns, who studies brain activity in dogs and people at Emory University in Atlanta, Georgia, faults the relatively small number of animals and the reporting of only averaged data. Berns argues that the authors failed to test whether individual dogs had inherent biases to greater activity in one hemisphere over the other, independent of language. Variability in even a single dog could have skewed the averaged results, he says.
But David Reby, a psychologist at the University of Sussex, UK, calls the work “an elegant study”, noting that it corroborates his own behavioural findings in dogs3.
The question that Reby wonders about, though, is whether the division of language-processing work between the two hemispheres arose in dogs from selective breeding for animals that efficiently processed human speech, or whether it is an inherent trait. In the future, studying brain activation in wolves — which can be tamed but not domesticated — could help to answer this question, he says.
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