Changes in auditory evoked responses at different levels of linguistic processing in adults and school-age children: An MEG study.

While the development of speech processing begins early in life, adult-level language proficiency takes a significant amount of time to emerge. How children comprehend speech with their immature auditory systems and how they gradually achieve adult-like language proficiency remains poorly understood. The present study used magnetoencephalography (MEG) to examine developmental changes during auditory processing of language in school-age children and adults at multiple levels of representation. Twenty-one children (ages 7-15 years) and twenty-five adults (ages 18-40 years) listened to repeated sounds (e.g., "mmm mmm"), one-word sounds (e.g., "mmm glass"), and adjective-noun phrases (e.g., "green glass") and afterwards selected a matching picture at the end of each trial. Our results show that at the basic sound level, both children and adults exhibited adaptation to repeated sounds. At the word level, children's N100m responses to lexicality in the left hemisphere correlated with their age, suggesting an enhancement in the efficiency of phonological processing with increasing age. Finally, at the phrase level, children showed increased N400m responses to words in phrasal contexts than to those without a context in the right temporal lobe. This suggests greater involvement of right hemisphere in children during phrase-level speech comprehension.