Effects of Vocabulary Sizes on Semantic Processing to Chinese Characters between Fifth Graders and Adults
|Keywords:||語意;語音;字形;語意關聯強度;功能性磁振造影;孩童;semantics;phonology;orthography;semantic association strength;fMRI;children||Issue Date:||2009||Abstract:||
目的：目前探討中文識字能力的研究主要在字形處理及語音處理兩個取向，但尚未有語意處理與中文識字能力的關係的研究。因此，本研究以聽覺語意判斷作業進行三個行為實驗，探討五年級孩童及成人、五年級高/低識字能力孩童在語意處理上的差異。實驗四則透過功能性磁振造影(Functional magnetic resonance imaging, fMRI)探討10-21歲參與者聽覺語意處理之神經機制，以此對應實驗一至三所發現的語意處理的行為變化。方法：本實驗操弄三種語意關聯強度字對(高，低，無關語意)，要求參與者判斷中文字對是否具有語意關係。結果：實驗一至三的行為測量顯示，隨著語意關聯強度減弱，參與者的正確率都隨之下降，所需反應時間皆隨之增加。成人在高低語意判斷間的差異，較孩童在高低語意判斷間的差異來得大。高識字能力孩童較低識字能力的孩童，在高低語意判斷上都呈現較優的表現。實驗四的造影結果顯示，參與者在進行聽覺語意判斷時，對於高語意與低語意相關的字對，在左腦額下回(Inferior frontal gyrus, IFG, BA 45, 47)及左腦顳中回(Middle temporal gyrus, MTG, BA 21)有較多活化。隨著字對的語意關連強度越強，在左腦下頂葉(Inferior Parietal lobule, IPL, BA 39, 40)有較多活化。隨著字對的語意關連強度遞減，則是在左腦額下回(IFG, BA 45)有較多活化。年齡與語意相關字對在左腦顳中回(MTG, BA 21)及額下回(IFG, BA 45)的活化呈現正向相關，年齡與無語意相關字對在左腦額下回(IFG, BA 47)的活化呈現正向相關。結論：一、年齡與識字能力的差異，可以反映語意處理之間的差異，孩童較成人在搜尋和整合正確的語意特徵時，做出判斷反應上有困難。二、低識字能力孩童無法掌握字彙的字形、語音及語意的對應關係，因此在語意判斷作業的表現比高識字能力孩童差。三、參與者在處理中文語意時，透過左腦下頂葉(IPL, BA39, 40)整合相關語意特性，並透過左腦額下回(IFG, BA 45)對語意表徵進行提取及比對。四、孩童在發展的過程中，年齡愈大的孩童，會透過整合字彙的語音及語意，在語意相關的字對中的一群同音字裡選擇出正確的答案;在判斷無語意相關的字對時，則需要提取語意表徵進行語意關聯的判斷。
Purpose: Although many studies have focused on the effects of vocabulary sizes on orthographic and phonological processes to Chinese characters, few studies have explored the effects of vocabulary sizes on semantic processing. Experiments 1-3 used behavioral paradigms with an auditory semantic judgment to evaluate the differences between fifth graders and adults, as well as differences between fifth graders with different vocabulary sizes. In Experiment 4, functional Magnetic Resonance Imaging (fMRI) was used to examine the neural correlates of auditory semantic judgments to Chinese characters in a group of 10-21 year old Chinese participants. Methods: Semantic association strength was varied (stronger, weaker, and unrelated). Participants were asked to decide if two Chinese characters were semantically related. Results: In Experiments 1-3, lower accuracy and longer reaction time were found for weaker association, as compared to stronger association strength. The difference of stronger and weaker association strength was larger for adults than the difference of stronger and weaker association strength for fifth graders. Fifth graders with larger vocabulary sizes showed better performance for both stronger and weaker association strength, as compared to fifth graders with fewer vocabulary sizes. In Experiment 4, characters with stronger semantic association elicited greater activation in left inferior parietal lobule (IPL, BA 39, 40), and characters with weaker semantic association elicited activation in left inferior frontal gyrus (IFG, BA 45). Regarding developmental changes, increasing age was correlated with greater activation in left middle temporal gyrus (BA 21) and left IFG (BA 45) for related pairs, and in left IFG (BA47) for unrelated pairs. Conclusions: Effects of age and vocabulary sizes are related to semantic processing. Fifth graders show poorer search and integration of semantic features during semantic judgments as compared to adults. Fifth graders with fewer vocabulary sizes show deficient mappings among semantics, phonology, and orthography, producing poorer performance on meaning judgments as compared to fifth graders with larger vocabulary sizes. Characters with stronger semantic association elicited greater activation in left IPL(BA 39, 40) for semantic features integration, and characters with weaker semantic association elicited greater activation in left IFG (BA 45) for greater engagement of selection among homophones for Chinese characters. The developmental changes suggest greater integration of semantic and phonological processes to select the correct answer among homophones for related pairs, and demanding retrieval processes to judge unrelated pairs for older children.
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