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

Abstract

Developmental dyslexia is a neurological condition that is characterized by severe impairment in reading skill acquisition in people with adequate intelligence and typical schooling. For English readers, reading impairment is critically associated with a phonological processing disorder, which may co-occur with an orthographic (visual word form) processing deficit, but not with a general visual processing dysfunction in most dyslexics. The pathophysiology of dyslexia varies across languages: 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 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.

Selective transfer of visual working memory training on Chinese character learning

“…This view is in line with several proposals consistently linking activity in the precuneus to visual imagery (Cavanna and Trimble, 2006;Fletcher et al 1995;Gardini et al 2009). It is also consistent with recent results demonstrating that normal reading children but not dyslexic children exhibited similar precuneus activation when asked to compare the physical size of two simultaneously presented Chinese characters (Siok et al, 2009). …”

“…Crucially, as those segments are visually more complex and cannot be converted into phonemes, additional visual-orthographic analysis and visual short-term storage are mandatory. While studies investigating visual working memory as a predictor for language learning, are scarce, a couple of developmental studies have examined determinants of reading ability in Chinese children focusing primarily on visual processing skills and phonological awareness (Ho and Bryant, 1997a;Huang and Hanley, 1995;McBride-Chang and Ho, 2005;Siok and Fletcher, 2001;Siok, Spinks, Jin, and Tan, 2009;Tong and McBride-Chang, 2010). Huang and Hanley (1995) reported that visual skills such as visual form discrimination and visual paired-associate learning predicted reading in native Chinese but not in native English children.…”

Universal brain systems for recognizing word shapes and handwriting gestures during reading

“…The observed large-scale network encompassed not only the known universal components of reading in occipitotemporal (4,5) and inferolateral frontal (5,8) regions, but also those brain regions previously proposed to represent culture-specific components of logographic reading, i.e., the left lateral prefrontal cortex around BA9 (15,17), left PMd (9), and bilateral PPC (13,16). Critically, however, this network showed no significant crosscultural difference between French and Chinese through its entire extent.…”

“…Reading of alphabetic scripts engages this multicomponent system with only small cultural variation depending on the degree of transparency (11) and grain size (12) of the orthographic system. However, beyond this shared left posterior network, several previous studies with normal (8,13,14) and dyslexic (15,16) Chinese participants defended a culture-specific model whereby logographic reading relies on unique cortical components (17). In a lateral prefrontal region within Brodman's area (BA) 9, just anterior to the precentral cortex, meta-analyses suggest a greater activation in Chinese compared with alphabetic readers (5,17), perhaps due to great demands on addressed phonology (17) or visuospatial working memory (18).…”

“…In a lateral prefrontal region within Brodman's area (BA) 9, just anterior to the precentral cortex, meta-analyses suggest a greater activation in Chinese compared with alphabetic readers (5, 17), perhaps due to great demands on addressed phonology (17) or visuospatial working memory (18). A posterior parietal region may also contribute to the visuospatial analysis of character layout (13,16). Finally, the acquisition of reading in Chinese has been proposed to depend heavily on a motor memory for writing gestures (19), in sharp contrast with the primary importance of phonological awareness in alphabetic literacy (20).…”