Attenuated brain responses to speech sounds in moderate preterm infants at term age

Recent findings have revealed that very preterm neonates already show the typical brain responses to place of articulation changes in stop consonants, but data on their sensitivity to other types of phonetic changes remain scarce. Here, we examined the impact of 7-8 weeks of extra-uterine life on the automatic processing of syllables in 20 healthy moderate preterm infants (mean gestational age at birth 33 weeks) matched in maturational age with 20 full-term neonates, thus differing in their previous auditory experience. This design allows elucidating the contribution of extra-uterine auditory experience in the immature brain on the encoding of linguistically relevant speech features. Specifically, we collected brain responses to natural CV syllables differing in three dimensions using a multi-feature mismatch paradigm, with the syllable/ba/ as the standard and three deviants: a pitch change, a vowel change to/bo/ and a consonant voice-onset time (VOT) change to/pa/. No significant between-group differences were found for pitch and consonant VOT deviants. However, moderate preterm infants showed attenuated responses to vowel deviants compared to full terms. These results suggest that moderate preterm infants' limited experience with low-pass filtered speech prenatally can hinder vowel change detection and that exposure to natural speech after birth does not seem to contribute to improve this capacity. These data are in line with recent evidence suggesting a sequential development of a hierarchical functional architecture of speech processing that is highly sensitive to early auditory experience.