Numerous studies have reported an association between speech processing deficits and language impairments in young children (e.g. Tallal, et al., 1991). However, the causal relationship between these deficits remains unclear. A first step towards clarifying the nature of this relationship is to determine whether speech sound processing abilities in infants and toddlers correlate with later language processing abilities (Trehub &Henderson, 1996). Thus, the principal aim of this project is to determine the relationship between the brain's speech discrimination abilities in the first few years of life and later language development. Event-related potentials (ERPs) will be used to provide an index of neural processes that underlie discrimination of short, phonetically similar, vowel contrasts (I vs. E and blp vs. bEp) by infants and toddlers between the ages of 3 and 12 months. We have chosen these vowel contrasts because children with poor language skills have difficulty processing brief vowels (preliminary study 1;Stark and Heinz, 1996;Leonard, et al., 1992). A sub-group of the infants will be from bilingual Spanish-English households, because research suggests that exposure to a different distribution of speech sounds and syllable structures during development will affect development of phonological categories. ERP measures, such as peak latency, amplitude, topography of components that index discrimination will be related to behavioral measures of speech and language competence obtained at 6, 12, 18, 24, and 36 months of age in a longitudinal study. In a cross-sectional design, we will examine changes in the ERP manifestations of brain discrimination and changes in behavioral discrimination of these speech contrasts from 3 months to 10 years of age and in adults. The goal of this cross-sectional investigation is to provide information about the relationship between brain and behavioral discrimination that we cannot obtain in the longitudinal design.
The Specific Aims of this study are 1) To determine the relationship between the development of speech perception in the first year of life and later speech and language development measures;2) To determine the relationship between brain and behavioral indices of discrimination of the vowel contrast from 3 months to 10 years of age, and 3) To determine the effect of the input (monolingual vs. bilingual) on speech discrimination using brain and behavioral indices of processing of these stimuli.
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