Language Disorders Across Modalities:
The Case of Developmental Dyslexia
Pieter H. Been
University of Groningen
Developmental language impairment is a risk factor for other developmental disorders. Prospective studies following children with early developmental language impairment have shown a striking link with subsequent learning disabilities, especially developmental dyslexia (Bishop & Adams, 1990; Catts, 1993). In studies comparing dyslexic children with language-impaired children, both groups are specifically characterized by deficits in phonological analysis (Liberman et al., 1974; Wagner & Torgerson, 1987).
Indeed, converging evidence indicates that developmental dyslexia is a language disorder that often critically affects the phonological domain of language, although disturbances in the visual system also have been identified (Cornelissen et al., 1995; Eden et al., 1996; Lovegrove, Garzia, & Nicholson, 1990). The findings regarding visual problems are consistent with the processing of rapid information by the magnocellular pathway of the visual system. It has also been proposed that a slowed processing rate of acoustic cues may account for disturbances in phonological processing (Tallal, Miller, & Fitch, 1993). Increasing evidence indicates that rapid processing in general, across at least the auditory and visual modalities, is impaired in dyslexics. As far as the auditory modality is involved, a rapid temporal processing deficit may lead to problems with that part of language sounds (e.g., transients in some consonants, which require rapid processing). This may lead, in turn, to ambiguous entries in the phonological lexicon ultimately resulting in reading problems. As a matter of fact,