Event-related potential indices of auditory vowel processing in 3-year-old children

Objective: To determine the ERP characteristics and ERP indices of central speech sound encoding and discrimination in young children. Methods: Auditory sensory event-related potentials (ERPs) and the ERP index of auditory sensory discrimination (the mismatch negativity, MMN) were elicited by vowel stimuli in 3-year-old children. In an oddball paradigm, the standard stimulus was vowel /a/, one deviant stimulus was vowel /o/ (the across-category change), and the other was nasalized vowel /a/ (within-category change). In addition, the ERP changes occurring during the 14 min uninterrupted recording were examined. Results: As indexed by the sensory P1, N2, and N4 peaks, the 3-year-old children's transient neural encoding of vowels was comparable to that earlier registered in 1-year-old children but also showed vowel-specific characteristics observed in school-age children. The 3-year-old's MMN was comparable in amplitude to the school-age children's MMN and appeared to be sensitive to the across-category aspects of vowel changes. However, its latency was longer in the 3-year-olds than in school-age children. Among the sensory ERPs, only the N4 peak showed significant diminution during the experiment. The across-category change MMN diminished after 10 min of the recording, however, over the frontal areas only. Conclusions: In the 3-year-old children, the sensory processing of vowels exhibited transitional characteristics between those observed in infants and school-age children. The auditory sensory discrimination in the 3-year-olds appeared to be sensitive to the phonemic aspects of stimulus change. The frontally-predominant MMN diminution during the experiment might indicate the greater refractoriness of its frontal-lobe generators. In general, the auditory sensory ERPs show distinct maturational profiles from that of the MMN. (C) 2003 International Federation of Clinical Neurophysiology. Published by Elsevier Science Ireland Ltd. All rights reserved.