Neural Speech Tracking Across the First 62 Days of Life: Effects of Language Background and Cognitive Maturation

Newborns recognise familiar language patterns experienced in utero and discriminate them from unfamiliar ones. It is as yet unclear which neural mechanisms are responsible for such early language-specific behavior. Here we focus on neural speech tracking and test whether it shows language-specific attunement in newborns and one-to-two month olds. Infants listened to infant-directed stories in their native language (Czech) and an unfamiliar language (Russian) while their EEG was recorded. First, we examined whether neural speech tracking differed between infants predominantly exposed to Czech and infants exposed primarily to other languages. Second, we assessed developmental changes by combining these data with a previously collected cohort of newborns, yielding a continuous sample spanning 1-62 days of age. Neural speech tracking was assessed in stimulus-derived delta and theta frequency bands in terms of oscillatory power and accuracy of EEG-to-speech envelope reconstruction using the backward multivariate temporal response functions. Czech-exposed infants had stronger cortical tracking of Czech speech than infants exposed to other languages. Within the Czech-exposed group, native Czech elicited stronger neural tracking than unfamiliar Russian, particularly in the delta band, indicating early language-specific tuning to the prosodic-word structure. Across the combined Czech-exposed sample, this native-language advantage gradually decreased with age, suggesting that neural speech tracking of the slow rhythms undergoes rapid reorganization during the first two months of life. These findings demonstrate that language-specific neural speech tracking is detectable from the earliest weeks of life and is jointly shaped by early, perinatal language experience as well as cognitive maturation.