A multidisciplinary approach to understanding developmental dyslexia within working-memory architecture: genotypes, phenotypes, brain, and instruction.

A unifying theoretical framework of three working memory components provides a systems perspective for discussing past and new findings in a 12-year research program that point to heterogeneity in the genetic and brain basis and behavioral expression of dyslexia: (a) codes for word-form storage and processing, (b) time-sensitive phonological and orthographic loops for maintaining information in working memory or outputting it, and (c) executive functions for language (e.g., rapid automatic switching of attention). Results, which span the genetic to neurological to behavioral levels of analysis, point to possible impairment in any one or combination of these working memory components in individuals with dyslexia. A DNA variation on chromosome 15 may be linked with the phonological word-form in the first working-memory component. A DNA variation on chromosome 6 may be linked with slow rapid automatic switching, inattention ratings, and impaired goal-directed activity ratings in the third working-memory component. Brain and behavioral findings support (a) Triple Word Form Theory: phonological, orthographic, and morphological word-forms and their parts contribute to learning to read and spell words; and (b) Cross-Word Form Mapping: in the process of learning to read and spell words children compute the inter-relationships among the three word-forms and their parts. However, children with dyslexia may require more focus on the morphological word-form and its parts and their relationships with the other two word-forms and their parts than do normal readers. Also, children with dyslexia have unusual difficulties in sustaining phonological loop function in working memory over time; their impaired orthographic loop function may interfere with learning to write alphabet letters and spell, which may be as impaired as word decoding and reading. Impaired executive functions may interfere with the efficiency of working memory in processing oral and written language.