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

Abstract

AbstractInfants learn to recognize the sounds of their mother language very early in development, exhibiting a remarkable ability to process the fine-grained spectrotemporal characteristics of speech. However, the neural machinery underlying this ability is not yet understood. Here, we used an auditory evoked potential termed frequency-following response (FFR) to unravel the maturational pattern of the neural encoding of two speech sound characteristics: voice pitch and temporal fine structure, during the first year of life. The FFR was elicited to a two-vowel stimulus (/oa/) in a sample of 41 healthy-term neonates that were tested at birth and retested at the ages of six and twelve months. Results revealed a shortening of neural phase-locking time to stimulus envelope from birth to six months, with no further difference between six and twelve months. While neural encoding of voice pitch was similar across age, encoding of the stimulus temporal fine structure exhibited a rapid maturation from birth to six months, without further improvement from this age onwards. Results highlight the first six months of age as a crucial period in the maturation of the neural encoding mechanisms of the temporal fine structure of speech sounds, essential for phoneme discrimination during early language acquisition.