Developmental dyslexia is defined as a reading skills acquisition impairment despite normal intelligence, normal visual acuity and adequate learning opportunities.
The cause of the dyslexia was still unknown. A substantial number of research have demonstrated that alphabetic language speaking children with dyslexia have deficit in visual-spatial attention, especially in rapid orienting of the attentional spotlight. And their visual-spatial attention is correlated with their phonological decoding deficit. Chinese, as a logographic language, is charaterized with several diffences to alphabetic languages. Chinese script is known as addressed phonology, which means that a Chinese character directly maps to a whole morpheme syllable.Thus, there is no letter-by-letter phonological decoding when reading Chinese.Besides, Chinese characters also have higher visual-spatial complexity than alphabetic language. There is more visual processing in reading Chinese than reading alphabetic language script. To date, few studies have explored the visual spatial attention of Chinese dyslexia. The present study adopted behavioral measurements and functional magnetic resonance imaging (fMRn technique to systematically investigate the visual spatial attention in Chinese dyslexic children and the relationship between the visual spatial attention and the Chinese reading skills.
The first research explored the covert attention and the overt attention of Chinese dyslexic children using the cue paradigm and the visual search paradigm respectively. The results showed that the Chinese dyslexic children only exhibited an impairment in overt attention, which was inconsistent with the results of the alphabetic language studies. The Chinese dyslexic children showed difficulties in orientation searching and the conjunction searching tasks, indicating that the Chinese dyslexic children have impairment in early visual processing of orientation and overt attention. We also found that the overt attention was correlated with multiple Chinese reading skills, such as the reading fluency, rapid naming and orthographic skill.
The second research explored the neural basis of the visual spatial attention in Chinese dyslexic children. Using the resting一state fMRI, the present research found that the Chinese dyslexia showed the abnomal amplitude of low-frequency fluctuation (ALFF) or regional homogeneity (ReHo) in several brain regions in dorsal attention network and ventral attention network. The results also showed that the strength of resting一state functional connectivity (RSFC) within the dorsal attention network and between the dorsal attention network and the ventral attention network was abnormal in Chinese dyslexia. The RSFCs between the brain regions in attention network and reading network was also abnormal in Chinese dyslexia. The RSFC between the dorsal attention network and the reading network was correlated with the reading fluency. The RSFC between the ventral attention network and the reading network was correlated with the rapid naming. The present research also found that the cortical thickness in brain regions of dorsal attention network increased in Chinese dyslexia. And the cortical thickness in those brain regions were correlated with the reading fluency and orthographic skill.
In conclusion, the Chinese dyslexia exhibits the impairment in visual spatial attention, but the impairment is restricted to overt attention. The Chinese dyslexia also exhibits both functional and structural impairment in dorsal and ventral attention network. In addition, the impairment in visual spatial attention was correlated with multiple Chinese reading skills, such as reading fluency and rapid naming.