Dogs seem to have the ability – until now thought to be uniquely human – to spontaneously recognise words even when they are spoken by unfamiliar people with different voices, accents and pronunciation.
They also can recognise that someone is unfamiliar by the sound of their voice alone, according to a new study published in the journal Biology Letters.
A team of British and French researchers led by Holly Root-Gutteridge from the University of Sussex made this discovery while investigating how our all-important ability to perceive speech evolved.
“If you can’t recognise a word spoken by different people,” Root-Gutteridge says, “you can’t really use speech.”
Domestic dogs (Canis familiaris) present ready and willing volunteers to test how the ability to “normalise” speech across different speakers evolved because they are so responsive to human communication.
“They pay attention to it and show it by moving their heads and ears, or they gaze at the source, and they have lots of reasons to care about it,” says Root-Gutteridge.
In two experiments, the researchers played recordings of single syllable words produced by 13 men and 14 women, starting with “h” and ending with “d” but with different vowels, such as had, hid, heard, hood and heed, to 70 dogs and filmed their responses.
These words are not normally used as commands, so the dogs would not have had prior training with them. The speakers were also unknown to them and they were not encouraged or rewarded with treats and attention.
To establish whether the dogs recognised the same word across different speakers, or could discriminate an unfamiliar voice, the researchers observed how long they responded to each word.
Shorter responses meant the dogs habituated to a word, suggesting it was not novel to them, while longer responses indicated they perceived the word or speaker as new.
The recordings had six words in each, played with six-second intervals.
In the first version, the word didn’t change but the speaker did, so the dogs heard four people say “had”, then a fifth speaker say “hid”, then a sixth person say “had” again: “had, had, had, had, hid, had”.
In the second version, the dogs heard the same person say four different words, like “hid, heard, heed, had”, then a second person say a fifth word such as “heed” before the first person produced the sixth word.
“If the dogs recognised that a pattern had formed, they would show shorter responses over time to the sounds,” explains Root-Gutteridge, “then if they realised a pattern had been broken, their response would increase.”
And that’s indeed what they did.
“The biggest finding was that dogs can do this form of word recognition spontaneously,” says Root-Gutteridge. “We knew they could be trained to do it, but for speech it really needs to be spontaneous.”
She was also surprised at how good they were at realising when the speaker voice changed as some of the owners couldn’t even tell the speakers apart.
“This research shows that, despite previous assumptions, this spontaneous ability is not uniquely human and that dogs share this linguistic talent, suggesting that speech perception may not be as special to humans as we previously thought.”
To determine if this skill is a result of domestication, the researchers suggest that testing speech normalisation in captive grey wolves (Canis lupus) could settle the point.