Neural processing of speech sounds at premature and term birth: ERPs and MMR between 32 and 42 weeks of gestation

Abstract

Prenatal listening experience reportedly modulates how humans process speech at birth, but little is known about how speech perception develops throughout the perinatal period. The present experiment assessed the neural event-related potentials (ERP) and mismatch responses (MMR) to native vowels in 99 neonates born between 32 and 42 weeks of gestation age (GA). The newborns had reliable ERPs to native vowels from conception age 36 weeks and 1 day (36+1). The ERPs reflected spectral distinctions between vowel onsets from conception age 36+6 and durational distinctions at vowel offsets from conception age 37+6. Starting at age 40+1, there was evidence of neural discrimination of native vowel length contrast, indexed by a reliably negative MMR response. The present findings extend our understanding of the earliest stages of speech perception development in that they pinpoint the ages at which the cortex reliably responds to the phonetic characteristics of individual speech sounds and discriminates a native phoneme contrast. Curiously, the age at which the brain reliably differentiates vowel onsets coincides with what is considered term age in many countries (37+0 GA). Future studies should investigate to what extent the perinatal maturation of the cortical responses to speech sounds is modulated by the ambient language