Periodic Reporting for period 5 - BabyRhythm (Tuned to the Rhythm: How Prenatally and Postnatally Heard Speech Prosody Lays the Foundations for Language Learning)
Reporting period: 2023-08-01 to 2024-05-31
The role of experience in language acquisition has been the focus of heated theoretical debates, between proponents of nativist views according to whom experience plays a minimal role and advocates of empiricist positions holding that experience, be it linguistic, social or other, is sufficient to account for language acquisition. Despite more than a half century of dedicated research efforts, the problem is not solved. The present project brings a novel perspective to this debate, combining hitherto unconnected research in language acquisition with recent advances in the neurophysiology of hearing and speech processing. Specifically, it claims that prenatal experience with speech, which mainly consists of prosody due to the filtering effects of the womb, is what shapes the speech perception system, laying the foundations of subsequent language learning. Prosody is thus the cue that links genetically endowed predispositions present in the initial state with language experience. The proposal links the behavioral and neural levels, arguing that the hierarchy of the neural oscillations corresponds to a unique developmental chronology in human infants’ experience with speech and language. The project uses state-of-the-art brain imaging techniques, EEG & NIRS, with monolingual full term newborns, as well as full-term bilingual, preterm and deaf newborns to investigate the link between prenatal experience and subsequent language acquisition. The project has led to the discovery that the neural architecture, in particular neural oscillations, for the processing of spoken language are already in place and operational at birth. Further and most importantly, they are modulated by prenatal experience. Indeed, newborns have been found to show evidence of learning and ongoing neural activation after listening to speech in the language heard prenatally even for several minutes after simulation, whereas this was not the case for unfamiliar languages. Furthermore, neural activation becomes increasingly specific to the native language. As an unexpected, but highly interesting finding, we observed that over development, infants' neural responses become highly specific to different levels of phonology that are most relevant for a given learning stage. Thus newborns show increased neural activation in frequency bands related to larger language units such as sentences, phrases and syllables, while 6-month-olds' brain activity is concentrated in faster frequency bands corresponding to individual language sounds.
In our work to date, we have shown that infants start learning the grammar of their native language earlier than previously believed, even before they utter their first words. We have also found that the brain already possesses the basic neural mechanisms needed for sophisticated speech processing in the form of neural oscillations, e.g. brain waves. We have found that at birth, these oscillations already exhibit the impact of the prenatally heard language, as newborns' brain activity remains heightened and shows traces of memory for several minutes after stimulation with the prenatally heard language, but not with unfamiliar languages. Furthermore, this prenatal impact is specific to the slower frequency bands such as theta corresponding to the frequencies characteristic of the speech signal heard prenatally. After several months of experience with their native language, infants then start showing neural activation specific to the characteristics of the native language in frequency bands (gamma) corresponding to the individual sounds of language. In summary, the main finding of the project is that the neural architecture for speech processing is already operational before birth, and prenatally heard language already sculpts the developing brain. These results were published in 47 scientific articles in peer-reviewed journals, as well as in a large number of talks and posters presented at international conferences. We have also disseminated our findings to stakeholders such as educators, paediatricians, parents etc. through targeted meetings and reports, as well as to the general public. The results have also been covered in the printed press world-wide.
In addition to the results already published (see above), we are expecting the publication of additional journal articles that are currently under review. We will also continue our dissemination work through outreach events.