Dogs also prefer consonants: how our language shapes their brain

Everything is contagious, even the way we listen and understand. For humans, consonants usually carry more information than vowels. This pattern appears in many languages: when a sentence is stripped down to its bones, those bones are more recognizable if consonants dominate. That is why Spanish has 23 consonants and five vowels, a ratio that holds in almost every language. It is also why people drop vowels when they want to save characters in a message. Our brains fill in the gaps more effectively.

Until now this was thought to be a uniquely human trait. But a study published Thursday in the journal Science has shown that dogs have developed the same consonant preference bias. “They make a very useful model for investigating these questions because, unlike laboratory animals, they hear human speech daily,” said Attila Andics, lead author and neuroethologist at Loránd Eötvös University in Hungary.

In the study the researchers directly compared electroencephalographic responses in the brains of 20 adults and 20 pet dogs while they listened to continuous streams of nonsensical three-syllable words. The words followed patterns based on either consonants or vowels, while a third set had no consistent pattern. “We found striking similarities in how both species processed these speech sequences,” said Dorottya Rácz, co-author of the study. “Like humans, dogs’ brains segmented the continuous speech stream into words more effectively when the recurring pattern — that is, the word’s skeleton — was made up of consonants.”

This suggests that mere regular exposure to speech can reshape brain function and that certain language-processing biases, previously observed only in humans, can develop without complex linguistic abilities. “And that is what makes this study interesting,” said Juan Manuel Toro, professor at the Center for Brain and Cognition at Pompeu Fabra University. “Because it shows this bias is not exclusively human. Domestic dogs are exposed to human language from birth, and this study demonstrates that that experience is enough for them also to ‘focus’ on consonants to identify words.”

It so happens that Toro presented a study last year showing that ChatGPT had likewise developed a consonant-preference bias. His study is, in fact, cited as a reference in the paper led by Andics.

“These models are trained on enormous amounts of text and learn to detect regularities within it,” Toro explained. In this way they end up detecting that consonants provide more information than vowels for identifying words. The researchers asked ChatGPT to determine which of two pseudowords — one with a vowel change and the other with a consonant change — more closely resembled a target word. They observed that the model relied more on consonants than vowels when assessing similarity between words, in both Spanish and English. “The results with dogs and with artificial intelligence language models point to the idea that experience with language allows this consonant bias to emerge.”

Consonant preference began to be studied 20 years ago in infants. It was the strategy they used to begin recognizing words, a strategy we retain into adulthood. Other studies have pointed to prosody (the rhythm of speech) as another particularly useful tool for children when they start to understand adults. Toro studied that too — in rats. “What we showed is that rats displayed the same pattern of responses. This suggested that the mechanism infants use to process the prosody of language comes from mechanisms we share with other animals and that evolved long ago.”

Human language is an extremely complex communication system. It is, in a way, a mystery. Before their first birthday, infants begin to develop a system that will allow them to express an infinite number of ideas by combining a small set of sounds. It is like acquiring the pieces of a puzzle with infinite combinations — a puzzle with which you can build worlds and explain feelings. With it we can explain ourselves to the world and perhaps understand it a little better. One of the biggest problems in the study of language is understanding its biological foundations. It is unknown whether it is an exclusively human ability, whether we are hardwired for it, or whether it is cultural and learned. Today, animal studies are helping to understand how humans acquire and process language.

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