Developmental dyslexia is characterized by the co-existence of visuospatial and phonological disorders in Chinese children

Developmental dyslexia is a neurological condition that is characterized by severe impairment in reading skill acquisition in people with adequate intelligence and typical schooling [1-3]. For English readers, reading impairment is critically associated with a phonological processing disorder [3-5], which may co-occur with an orthographic (visual word form) processing deficit [6], but not with a general visual processing dysfunction in most dyslexics [7]. The pathophysiology of dyslexia varies across languages [8]: for instance, unlike English, written Chinese maps visually intricate graphic forms (characters) onto meanings; pronunciation of Chinese characters must be rote memorized. This suggests that, in Chinese, a fine-grained visuospatial analysis must be performed to activate characters' phonology and meaning; consequently, disordered phonological processing may commonly co-exist with abnormal visuospatial processing in Chinese dyslexia. To test this hypothesis, we conducted an fMRI experiment in which 12 Chinese dyslexics, shown previously [9] to exhibit a phonological disorder, performed a physical size judgment measuring visuospatial dimensions. Compared with 12 control subjects, the dyslexics showed weaker activations in left intraparietal sulcus (IPS) mediating visuospatial processing. Analyses of individual dyslexics' performances further suggest that developmental dyslexia in Chinese is commonly associated with the co-existence of a visuospatial deficit and a phonological disorder.