Functional Specialization of Semantic Processing to Chinese Characters: Developmental Studies

閱讀發展歷程伴隨著大腦的成熟變化。然而，至今對於閱讀發展的神經機制尚未完全了解。本論文以行為測量及功能性磁振造影（fMRI），檢驗處理中文字的字音、字形及語意表徵時的發展變化。實驗一以fMRI進行縱貫發展研究，探討在整字的層次上，處理中文語意對應的發展神經機制。在弱語意相關字對中，孩童在兩次施測間，顳中回（middle temporal gyrus）的活化增加相較於青少年的活化增加更多，反映出發展相關的語意表徵連結強化。實驗二以fMRI進行橫斷發展研究，呈現視覺相似作業及視覺不相似作業，檢驗在整字及部件的層次上，字形和語意之間的交互作用所對應的神經機制。隨著年齡增加，在強語意相關字對，視覺相似作業比視覺不相似作業在角回（angular gyrus）有更多活化，反映出共有的語意部件能促進整合字對共享的語意特徵。實驗三以行為測量進行縱貫發展研究，呈現跨感官語意作業，探討語意、字形及語音在整字和部件層次的對應關係。孩童在高語意透明度相對於低語意透明度，在強語意關聯強度下有較好的表現。相對於第一次施測，第二次施測時的高語意透明度與低語意透明度之間的差距減少。推論孩童隨著年齡增加，其語意判斷由部件處理轉變為整字處理的發展上的變化。透過這篇論文能幫助我們更了解孩童的字彙辨識系統。Reading development is associated with maturational changes in the brain. However, the neural mechanisms of reading development are not fully understood. This thesis used behavioral measures and functional magnetic resonance imaging (fMRI) to investigate developmental changes in orthographic, phonological, and semantic representations for reading Chinese characters. Experiment 1 used a longitudinal fMRI approach to explore the neural substrates of semantic processing to written Chinese characters in the lexical level. The results demonstrated that processing weak association pairs produced greater activation in posterior middle temporal gyrus, reflecting a greater developmental increase between time 1 and time 2 for the children as compared to that for the adolescents. The developmental increase indicates greater improvements of accessing semantic representations via enhanced interconnections for weaker association pairs. Experiment 2 used a cross-sectional fMRI study with two visual tasks (visually-similar task vs. visually-dissimilar task) to investigate the interaction of semantic and orthography in both the lexical and sublexical levels. The results showed a greater developmental increase in left angular gyrus (BA 39) activation in the visually-similar compared to the visually-dissimilar task for strong association pairs. The results suggest that shared semantics at the sublexical level facilitates the integration of overlapping features at the lexical level in older children. Experiment 3 used a behavioral study with a cross-modal paradigm to demonstrate the relationship among semantic, orthography, and phonology in both the lexical and sublexical levels. Children performed better on accuracy for high relative to low transparency in the strong association. Moreover, the results showed a reduced difference in accuracy for high than for low transparency for time 2, compared to that of time 1. These findings demonstrate developmental changes from a focus on radical components (i.e., sublexical processing) to a focus on whole characters (i.e., lexical processing). The findings in this thesis will advance our understanding of the functional architecture of word recognition systems in children