For an animal that can’t speak, dogs interact with human language in impressive ways. The average dog can not only learn about 165 words spoken by humans, but also can interpret the meaning and emotions in your voice by using multiple parts of their brain that neuroimaging research has associated with tone and vocabulary.
But exactly how well can dogs parse human language? A recent fMRI study shed new light on the canine brain by testing whether dogs can differentiate between different languages. The results suggest that dogs can distinguish real speech from gibberish and also differentiate the language spoken by their owners from a foreign language.
Published in the journal NeuroImage, the study aimed to measure the brain activity of family dogs as they heard two different languages, as well as nonsense speech. To do that, the researchers trained 18 dogs of various breeds to remain still inside of an fMRI machine while female speakers read aloud passages from the French novella The Little Prince.
The speakers were two women with similar voices, one of whom spoke Spanish and the other Hungarian — languages that have different stress patterns but are rhythmically similar. When the dogs heard a familiar language (i.e., the language spoken by their owners), they displayed brain activity that was noticeably different from the activity produced while hearing the foreign language. Specifically, language familiarity was represented in the ventral (caudal and rostral) parts of the auditory cortex.
“The present study provides the first evidence of distinct brain activity patterns for two languages in a non-human species,” the researchers noted.
Another part of the study tested whether dogs could tell the difference between natural speech from nonsense speech, which was generated by scrambling the audio clips of the passages read by the speakers. The results suggest dogs can: fMRI showed distinct patterns in the bilateral near-primary auditory cortical regions while they listened to natural and unnatural speech clips.
What’s more, the original language of the scrambled clips didn’t matter; dogs recognized the gibberish either way. Interestingly, longer-headed dogs seemed better able to discern natural speech from unnatural speech, while older dogs were better able to discern a familiar language from an unfamiliar one, indicating that dogs become more familiar with a certain language over time.
The fact that dogs detect familiar and natural speech puts them in the same class as human infants, who even in their preverbal stages can recognize the language of their parents and can even discern between two languages that are rhythmically similar. But while humans have evolved neural processes fine-tuned to recognize speech, dog brains might simply be responding to the “naturalness” of the sounds they hear, the researchers noted.
However, given that dogs have been domesticated for millennia, they could have over time picked up some slight edge in language processing compared to other animals. After all, human speech is highly relevant to dogs, who use it to identify speakers, estimate human emotions, and detect action cues. But whether dog brains possess unique language-processing mechanisms is a question for future research.