ABSTRACT
Dyslexia is both common in its occurrence and profound in its consequence; the student struggles to read and spell, and the achievement gap between typical and dyslexic learners widens at each literacy stage. An exploration of its neurological etiology illuminates the character of this learning challenge, as does an investigation of the spoken and written language interface. The cultural invention of written language is based on the spoken-language systems, which represent the linguistic and neurological substrates of the written form. Spoken language is a natural and evolved capacity; we are prewired to acquire and to process speech but are not prepared in the same way to process print. Reading and spelling utilize neural structures designed for spoken-language processes; in addition, the created orthographic system is used to encode spoken-language output in print form. The phoneme is the minimal phonological unit of natural language, but the speaker and the listener need not be aware of the phonemic composition of the speech stream in order to speak and apprehend. The reader/speller, however, must segment phonemes to map them to graphemes; dyslexia’s core phonological processing deficit vitiates that phonemic segmentation capacity and inhibits reading and spelling.
