| Reading is an acquired skill; unlike spoken language acquisition it has to be taught and there are significant individual differences in how well people read. The suite of neuroimaging studies described in this dissertation share an underlying theme of how the brain supports reading fluency and expertise. The first experiment explored a basic component of reading, letter identification. Participants matched a target letter with two alternatives. Conditions included same-case (a-a), mixed-case (a-A), and Korean letter matching across two levels of difficulty. Across the ventral visual stream, Korean letters produced the greatest signal activation. The mixed and same-case conditions activated the ventral stream to a lesser extent and were indistinguishable from one another. Additional activation (mixed>same>Korean and hard>easy) was observed in left perisylvian area reflecting phonological processing. Thus letter categorization depends on phonological information in letter names, rather than a ventral visual area dedicated to abstract representations of letters. The second set of experiments gathered function snapshots of early word-processing that occur within the first few hundred milliseconds of processing. Words with varying frequencies were presented for short durations via gated masking to leverage brain activation information about the time course of word processing. This method failed to distinguish between factors of interest. The long mask presentation may have generated extra-strong visual activity, obscuring subtle differences between conditions. Moreover, it was assumed that the mask limited processing, however, it may not have completely extinguished processing. In the third experiment, children diagnosed with Specific Language Impairment (SLI) participated in a combined behavioral and neuroimaging study to explore the disorder's consequences on reading organization. Two control groups were used: the standard age-matched group and a group of younger typically developing children with comparable language and reading skills. The results suggest that when equated for language skills, children with SLI still employ differential neural processing strategies to overcome their severe phonological weakness.{09}Together, these three experiments yield a more detailed picture of the neural computations that support reading and literacy. |
