Dogs have the ability to distinguish vocabulary words and the intonation of human speech using brain regions similar to those that humans use.
The surprising results from a study conducted by Dr. Attila Andics and his team based in Hungary note that vocabulary learning "does not appear to be a uniquely human capacity that follows from the emergence of language, but rather a more ancient function that can be exploited to link arbitrary sound sequences to meanings."
"Both what we say and how we say it matters to dogs," said Dr. Andics, a research fellow at Eotvos Lorand University, a Hungarian public research university based in Budapest, who studies language and behavior in dogs and humans.
Dr. Andics, Adam Miklosi and several other colleagues reported in a paper to be published this week in the journal Science that different parts of dogs' brains respond to the meaning of a word, and to how the word is said, much as human brains do.
Parts of a dog's left hemisphere react to meaning and parts of the right hemisphere to intonation or the emotional content of a sound. Surprisingly, the study showed only a word of praise said in a positive tone really made the reward system of a dog's brain light up.
Dr. Andics and his colleagues explored whether dogs also depend on both words and intonation. Dogs were exposed to recordings of their trainers' voices as the trainers spoke to them using multiple combinations of vocabulary and intonation, in both praising and neutral ways.
For example, trainers spoke praise words with a praising intonation; praise words with a neutral intonation; neutral words with a praising intonation and neutral words with neutral intonation.
Researchers used fMRI to analyze the dogs' brain activity as the animals listened to each combination. Their results revealed that dogs process vocabulary, recognizing each word as distinct, and further, that they do so in a way similar to humans, using the left hemisphere of the brain regardless of intonation.
Also like humans, dogs process intonation separately from vocabulary in auditory regions in the right hemisphere of the brain. And also like humans, dogs relied on both word meaning and intonation when processing the reward value of utterances.
Thus, dogs seem to understand both human words and intonation.
The authors note it's possible that selective forces during domestication could have supported the emergence of the brain structure underlying this capability in dogs, but this rapid evolution of speech-related hemispheric asymmetries is unlikely. Humans, they say, are only unique in their ability to invent words.