for the degree of Doctor of Philosophy
at The University of Hong Kong
Previous studies found that children’s reading performance was associated with their verbal working memory ability, and that dyslexics were inferior in phonological working memory tasks compared to the normal readers. The present study includes a behavioral experiment and an experiment using functional magnetic resonance imaging (fMRI) to investigate the role of phonological working memory in the reading of the normal and dyslexics. In experiment one, thirty-five 4th graders and sixty-one undergraduates from Mainland China received a battery of tests measuring seven cognitive constructs, including phonological awareness, visual processing, orthographic processing, naming speed, morphological awareness, pinyin knowledge as well as phonological working memory. Regression analyses showed that phonological working memory was the only significant predictor of Chinese reading performance in both children and adults. After controlling for the effects of IQ, age, phonological awareness, naming speed and pinyin knowledge, it remained significant in accounting for variance in adults’ Chinese reading performance. In contrast to previous literature, phonological awareness, visual and orthographic skills as well as morphological awareness were found to be unimportant for Chinese reading. Naming speed proved to be a significant predictor of reading ability across languages, as it was one of the most important factors influencing reading in Chinese adults. Phonological awareness (phoneme awareness) and naming speed were the two best predictors for the subjects’ second language (English) ability. Interestingly knowledge of pinyin could account for variance of reading performance in both Chinese and English languages for skilled readers.
Based on these findings of phonological working memory’s unique contribution to Chinese reading development, an fMRI study was conducted to examine different neural connectivity for phonological working memory in normal and dyslexic children. Brain activation mapping of all children contrasting the 2-back working memory task and a control task revealed a general network for phonological working memory, which is similar with previous findings on alphabetic readers. Direct group comparisons showed that during the phonological working memory task, normal children had significantly greater neural responses in the left middle frontal gyrus, left inferior frontal gyrus, left premotor areas and left posterior parietal regions, which were defined as regions of interests for the functional connectivity analyses. Seed-regions based analyses found group differences in the seed regions of the left middle frontal gyrus and left premotor areas. Meanwhile interregional correlation of brain signals from these ROIs revealed significant group differences in the connection between anterior and posterior regions during resting and phonological working memory conditions. The neural connectivity strength between the left middle frontal gyrus and the left premotor areas had a strong linear correlation relationship with the children’s reading ability. In summary, the findings from the behavioral and the fMRI experiments not only provided strong support to the unique role of phonological working memory in learning to read, but also revealed the aberrant brain connectivity underlying dyslexics’ working memory deficits which is consistent with previous functional and anatomical findings of disconnection between anterior and posterior brain regions in dyslexics of alphabetic languages.