Longitudinal trajectories of the neural encoding mechanisms of speech-sound features during the first year of life

Abstract

Infants quickly recognize the sounds of their mother language, perceiving the spectrotemporal acoustic features of speech. However, the underlying neural machinery remains unclear. We used an auditory evoked potential termed frequency-following response (FFR) to unravel the neural encoding maturation for two speech sound characteristics: voice pitch and temporal fine structure. The FFR was elicited by a two-vowel stimulus (/oa/) in a sample of 41 healthy-term neonates, tested at birth and retested at the ages of six and twelve months. Results revealed a reduction in neural phase-locking time to the stimulus envelope from birth to six months, remaining stable thereafter. While neural encoding of voice pitch remained consistent, temporal fine structure encoding matured rapidly from birth to six months, without further improvement from this age onwards. Results highlight the critical importance of the first six months in the maturation of neural encoding mechanisms, crucial for phoneme discrimination during early language acquisition.