The goal of this project is to examine developmental and individual differences in the neural substrate for lexical processing in normal children (7-15 year olds) using fMRI (functional magnetic resonance imaging). We propose to examine these differences with lexical tasks designed to tap into intra-modal processing (auditory rhyming and visual spelling tasks), conversion between orthography and phonology during crossmodal processing (auditory spelling and visual rhyming tasks) and modal word comprehension (auditory and visual meaning tasks). This proposal has three specific aims. First, we will use a combination of a cross-sectional and longitudinal design in order to measure developmental changes in lexical processing across a wide age range in a relatively short amount of time. We expect that development will produce increased activation in unimodal areas consistent with the modality of input and decreased activation in posterior heteromodal areas. Second, we will examine whether the correlation between brain activation and individual differences in skill depends on developmental level. We expect that behavior will correlate with the cognitive components required by the lexical task for older children, but will weakly correlate with posterior heteromodal activation for younger children. Third, we will examine developmental differences in the overlap in activation between auditory and visual modalities of input and between the spelling, rhyming and meaning tasks. We expect that younger children will show more overlap in activation than older children between moralities and between tasks.
These specific aims also incorporate parametric manipulations and a simple versus complex baseline for each lexical task, so that we can more clearly relate differences in activation during tasks to either developmental or skill differences in lexical processing. Because few fMRI studies have directly examined developmental or individual differences in lexical processing, this project on a normative population will have implications for future studies on the neural basis of reading and language impairments in children.
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