Speech Processing Development in Infants: A Longitudinal ERP Study of Native and Nonnative Consonant Discrimination

Abstract

BackgroundPerceptual attunement theory predicts that during the first year of life, infants neural responses to native speech sounds should strengthen while responses to nonnative contrasts diminish. However, few longitudinal studies have directly tested these predictions using within-subject designs. MethodsWe recorded auditory event-related potentials (ERPs) from 84 typically developing infants at three time points (3, 6, and 12 months) using an oddball paradigm with native (/ba/-/da/) and nonnative (dental vs. retroflex /a/) consonant contrasts. We examined developmental trajectories of the mismatch response (MMR) and obligatory components (P1, N1, P2) using linear mixed-effects models, with Session x Language interactions testing differential development for native versus nonnative contrasts. Center of mass analysis characterized spatial reorganization of ERP topography across development. ResultsContrary to perceptual attunement predictions, most ERP measures showed similar developmental trajectories for native and nonnative consonants. Of 14 interaction tests, only N1 latency for deviant waveforms showed a significant Session x Language interaction (p = 0.046, p{superscript 2} = 0.025). Significant main effects of Session on multiple measures confirmed ongoing auditory maturation. Center of mass analysis revealed systematic spatial reorganization: P1 showed posterior migration and leftward shifts (0.078 units displacement), while N1 and MMR exhibited anterior shifts, with nonnative consonants showing larger spatial reorganization for N1 (0.099 units vs. 0.058 units for native). ConclusionsRobust neural signatures of perceptual attunement for consonants may be more subtle, later-emerging, or stimulus-specific than commonly assumed. The dissociation between stable amplitude and migrating generators suggests that spatial location may be as important as response magnitude for characterizing auditory maturation during early infancy. Practically, equivalent neural responses to native and nonnative consonant contrasts should not be interpreted as evidence of atypical development; rather, indices of general auditory maturation may be more reliable markers of healthy development during the first year.