Neural mechanisms underlying the sensitive period for phonetic learning in infants at-risk for Developmental Language Disorder

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Project Summary/Abstract The sensitive period for phonetic learning, which occurs between 6~12 months of age, is demonstrably one of the earliest milestones for language acquisition, as infants’ speech processing during this period can reliably predict later language skills. Most recently, my work has shown for the first time that neural processing of speech during this period can predict not only individual grammar skills at 6 years, but also the risk of developing speech and language disorders in typically developing infants. This result suggests an important clinical relevance of the sensitive period and demonstrates a crucial need to further understand the underlying neural mechanisms of the sensitive period, particularly whether it may already be altered in infants at high-risk of developing language disorders, such as the developmental language disorder (DLD). Elucidating the neural mechanism would not only allow for the expansion of theories to encompass atypical language development, but more importantly, help identify early markers for language disorders and aid in the development of targeted early interventions. Specifically, the sensitive period is characterized by a divergence in speech processing, whereby infants’ sensitivity for native speech contrasts improves while sensitivity for nonnative speech contrasts declines. It is theorized to be a specialization process for the native language, where less native language specialization is associated with slower language growth. However, behavioral and functional neuroimaging studies have only investigated typically developing infants (Low-Risk), but not infants with a family history of communication disorders (High-Risk). It is possible that differences already emerge during this period that separate High-Risk infants and these differences may underlie later language difficulties in the High-Risk population. The current Katz ESI proposal aims to shift the focus and specifically examine High-Risk infants with a family history of DLD and compare them with Low-Risk infants at ~6 (start), ~12 (end) and ~14 (delayed end of sensitive period) months of ages, with the central theoretical hypothesis that High-Risk infants would demonstrate a protracted sensitive period, or a lagged native language specialization than Low-Risk infants. Particularly, we examine both higher and lower levels of neural processes for speech, as well as in the link between the neural processes. The higher-level processes related to speech discrimination is indexed by the mismatch response (MMR) while lower-level sensory encoding of speech is indexed by the complex auditory brainstem response (cABR). Both measures will be obtained simultaneously with Magnetoencephalography (MEG). Together, the proposed study will help uncover neural mechanisms underlying atypical language development and perfectly aligns with the mission of NIDCD to conduct research in disordered processes of speech and language.