Despite not being able to talk, dogs process speech in the same way as humans do, according to a new study.
Both dogs and human brains separately process the intonation – how a voice rises and falls – and the meaning of the words spoken.
Hungarian researchers used functional MRI – measures brain activity by detecting changes associated with blood flow – on awake dogs.
They found dogs process intonation mostly in the brain’s lower subcortical regions, and recognised the actual meaning of words in cortical regions, like humans.
‘Exploring speech processing similarities and differences between dog and human brains can help a lot in understanding the steps that led to the emergence of speech during evolution,’ said study author Anna Gábor at Eötvös Loránd University in Budapest, Hungary.
‘Some years ago, we discovered that dog brains, just as human brains, separate intonation and word meaning – but is the hierarchy also similar?
‘To find out, we used a special technique this time – we measured how dog brain activity decreases to repeatedly played stimuli.’
Dogs are well-known to have a sensitivity to human communicative signs, including vocal signals.
Both intonation and the meaning, or lexicality, of the words carry information for our canine companions.
When we praise dogs with a high toned voice, they may notice the positive intent and appear happy.
Dogs can respond to various words and phases, such as sit, lie down, play dead, wait or heel – but it’s not just the intonation that carry their meaning.
Many dogs still recognise the word or phase and respond in turn even if we’ve changed the intonation.
However, researchers have known very little about on what is going on in doggy brains during these interactions.
Hungarian researchers measured the awake, cooperative dogs’ brain activity via functional magnetic resonance imaging (fMRI).
Dogs listened to familiar praise words or phrases – ‘clever’, ‘well done’, ‘that’s it’ – and unknown, neutral terms – ‘such’, ‘as if’, ‘yet’ – both in praising and neutral intonation.
‘During brain scanning, sometimes we repeated words, sometimes intonations,’ said Gábor.
‘Stronger decrease in a given brain region to certain repetitions shows the region’s involvement.’
The results show that dog brains, just like human brains, process speech hierarchically – intonation at lower stages, mostly in subcortical regions, while known words are processed at higher stages, in cortical regions.
Repeating the same intonation led to activity decreases, mostly in ancient subcortical brain regions.
While repeating known words led to activity decreases in higher-stage auditory cortical brain regions.
Simpler, emotionally loaded cues, such as intonation, are typically analysed at lower stages, while more complex, learnt cues, such as word meaning, are analysed at higher stages in multiple species, including humans.
Interestingly, older dogs distinguished words less than the younger dogs in the study.
‘Although speech processing in humans is unique in many aspects, this study revealed exciting similarities between us and a speechless species,’ said study author Attila Andics at Eötvös Loránd University.
‘The similarity does not imply, however, that this hierarchy evolved for speech processing.
‘Instead, the hierarchy following intonation and word meaning processing reported here and also in humans may reflect a more general, not speech-specific processing principle.
‘What our results really shed light on is that human speech processing may also follow this more basic, more general hierarchy.’
The research team previously found that dogs separately analyse lexical and intonational cues to decipher meaning, published in Science in 2016.
Doggy methods to separately analyse and integrate word meaning and intonation suggest that this capacity can evolve in the absence of language, the team said.
This new study has been published in Scientific Reports.