Many deaf and hard-of-hearing (DHH) children struggle with reading and the severity of the impairment for some children increases with age. Despite this, we know very little about the brain mechanisms for successful reading in DHH children, or whether reliance on certain mechanisms differs with communication mode. We do not know why some DHH children are good readers and other are not. We take advantage of the large individual differences in reading skill to determine how better reading relies on different mechanisms and whether this varies with communication modes. This project uses functional magnetic resonance imaging (fMRI) in 10- to 15-year-old hearing children as well as in DHH children with predominant signed language, predominant oral language, or bimodal language. The innovative longitudinal approach follows children two years later and allows an investigation of how reading gains are related to brain changes over time and whether this varies with age. The overarching theory of reading acquisition is the Triangle Model which has three representational systems, including orthography (spelling), phonology (sound) and semantics (meaning), as well as pathways for mapping between these systems. A fundamental strength of this project is extending the well-developed Triangle Model to formulate the first neurocognitive model of reading in DHH children. Our project tests critical assumptions of the Triangle Model including the nature of orthographic representations, of orthographic to phonological mapping and of orthographic to semantic mapping. We test how these components are related to skill and developmental change over time in DHH children with different communication modes. Another innovative aspect of the project is the use of `localizer' fMRI tasks to independently identify regions associated with phonological mechanisms in temporo-parietal cortex during speech reading, signed language and spoken phonology, as well as regions associated with semantic mechanisms in middle temporal gyrus. The use of independent localizer tasks provides fundamental advances in our understanding of the underlying neural mechanisms involved in skilled reading in DHH children. Children also complete two reading fMRI tasks, one involving rhyming judgments and the other involving meaning judgments to words presented visually. Not only do we examine how phonological and semantic mechanisms are related to reading, but our novel approach also examines connectivity of these regions with fusiform cortex involved in orthographic processing. In addition to the fMRI measures, all children complete an extensive battery of state-of-the-art behavioral tests measuring signed language, oral language and reading. The focus of the project is on individual differences on word decoding as this is a critical building block to reading, but we also examine behavioral differences in reading comprehension.
This investigation of the brain basis of reading in deaf and hard-of-hearing (DHH) children develops and tests a neuro-cognitive model of acquisition. Understanding precisely how the underlying mechanisms are related to reading skill and changes over time, and whether this varies with communication mode, has implications for identification and intervention of reading difficulties in DHH children through future work targeting these mechanisms.
