Victoria Ratcliffe's research shows how dogs process the information in speech in a similar way to humans

Dog owners often claim their pets understand everything they say. Now a new University of Sussex study shows that our canine friends do actually process human speech in a similar way to us.

Mammal communication researchers in the School of Psychology tested more than 250 dogs to see how they responded to a set of spoken commands, and found that, like humans, dogs use different parts of the brain to process the verbal components of a familiar sentence and the emotion or intonation of the speaker.

Doctoral candidate Victoria Ratcliffe and Dr David Reby, whose study is published today (26 November) in Current Biology, stress, however, that their research does not suggest dogs could understand the full complexity of human speech, only that their perception of speech parallels that of humans.

Miss Ratcliffe says: “Humans mainly use the left hemisphere of their brain to process the verbal content of speech and the right hemisphere to process the characteristics of the voice - whether it’s familiar, male or female -  and its emotional content.

“Previous studies have shown that other mammals also have hemispheric biases when processing their own species’ vocalisations, but no one had ever looked at whether biases existed in domesticated animals in response to the different components of human speech.”

The researchers enlisted the help of dogs and their owners in Brighton (including dog walkers in Stanmer Park, and dogs at Brighton’s RSPCA centre) for the study.

Individual dogs were simultaneously played a human speech sound through speakers on both the left and the right of them, the significance being that the right ear sends information to the left-hand side of the brain, and vice-versa.

If the dog turned toward the left speaker, it would mean that the information they were listening to in the sound was primarily being processed in the right side of the dog’s brain. If it turned to the right, the information was being processed in the left side of the brain.

The results showed that when the speech was meaningful for the dogs (such as the command “come on then”), but the voice features such as gender or intonation had been attenuated or removed, the dogs were more likely to turn to the right, therefore showing a left-hemispheric bias.    

But if the command was in a foreign language, or if the phonemes were put into the wrong order (“thon om ken”), so the sound ceased to be meaningful to the dog, the reverse bias was observed.

Miss Ratcliffe says: “Although we cannot say to what extent they understand the complexity of the verbal content, our study does suggest that dogs pay attention to this information in human speech and that they perceive its content in a way that broadly parallels human perception.”

Dr Reby says: “We would like to investigate if dogs show these similarities to humans because they have been selected to respond to human verbal commands during domestication, or if wild animals would also display these asymmetries if they were exposed to similar levels of speech during their development.

“This would advance our understanding of the evolution of speech perception in humans by revealing whether hemispheric specialisations for processing its different communicative components are uniquely human or instead shared with other mammals.”