Our brain simultaneously follows two essential rhythms, that of syllables and that of (rapid) phonemes, to rebuild the meaning of sentences and understand speech, according to French researchers.
- How does the brain decipher speech? Researchers have discovered that the auditory cortex simultaneously follows two rhythms: that of syllables (slow) and that of (fast) phonemes.
- These pieces of the puzzle are treated together to reconstruct the meaning of the sentences. By studying 17 languages, researchers observed that these rhythms are universal, suggesting a biological mechanism common to humanity.
- These works could help to better understand language disorders, such as dyslexia, by identifying deficits in the perception of these essential rhythms.
Deciphering human speech is a real daily feat for our brain. But how does he manage to extract meaning from the continuous flow of sounds that constitutes speech? An Inserm and Aix-Marseille University team, in collaboration with the British University of Cambridge, recently answered this question by highlighting two key rhythms that the brain uses simultaneously: that of the syllables and that of phonemes . Their work was published in the journal Science Advances.
A two rhythms puzzle
Imagine that speech looks like a puzzle. The syllables, like “my” in “mom”, constitute the large pieces, while the phonemes – these individual sounds such as “M” or “A” – are the smallest. The syllables, produced at a slow pace, are perceived thanks to variations in sound amplitude, while the phonemes, much faster, manifest themselves by steep changes in the spectral content of sounds. The brain decodes these two elements simultaneously to rebuild the meaning of the sentences and understand speech.
To explore these mechanisms, the team of Benjamin Morillon, research director at Inserm, analyzed the brain activity of eleven participants equipped with intracranial electrodes. These subjects listened to 315 sentences in French, broadcast at different speeds and containing a fixed number of words, but various numbers of syllables and phonemes. The results are clear: the hearing cortex (a region of the brain responsible for treating sounds) simultaneously follows the slow rhythms of the syllables and the rapid rhythms of phonemes to segment the continuous speech signal.
A universal mechanism in humans
Importantly, by studying 17 different languages, the researchers found that these rhythms are present in all languages. “This universality suggests the existence of a biological mechanism for production and perception of speech common to all humans”says Benjamin Morillon in a press release. This discovery confirms that the treatment of speech is based on fundamental principles shared by humanity.
“These discoveries open up new perspectives in understanding language disorders, such as dyslexia, specifies the researcher. A deficit in the capacity of the brain to follow these two rhythms could, for example, explain certain difficulties of oral comprehension. “ These advances could one day make it possible to improve the diagnosis and therapeutic interventions for people affected by these disorders.
