二語語法處理的多重支援機制：事件相關電位研究

Multiple Scaffolding Mechanisms for L2 Syntactic Processing: An Event-related Potential Study

二語學習者往往無法以母語者所使用的認知神經資源來處理句法資 訊；為了彌補其不足，學習者常以處理語意的方式來理解句法，或是尋 求語言非優勢腦的協助。為更加瞭解這些替代處理模式，本研究結合分 視野呈現以及事件相關電位來量測華語學習者左右半腦的反應。在實驗 中，受試者需判斷以量詞為首的雙詞短語是否符合華語的語法結構。實 驗結果顯示，與母語者相比，華語學習者不僅正確率較低，即便是在正 確回答的題目裡，也誘發了和母語者不同本質的腦波反應。母語者只有 在右視野呈現（左腦優先處理時）有顯著的P600 效果，複製了以往母語 者的語法處理偏向左側化的研究發現。由於二語學習者的腦波反應呈現 很大的個體差異，因此整體而言，華語學習組並無呈現任何統計顯著的 效果。然而，當我們進一步對學習組的腦波與華語行為表現做相關分析 時發現，行為表現較佳的學習者在右視野呈現時誘發較小的N400 效果， 在左視野呈現（右腦優先處理時）也誘發較小的P600 效果。依據學習組 受試者的華語表現將他們分成四等份後，腦波反應清楚呈現出以下的變 化：隨著華語表現的進展，右視野呈現（左腦優先處理時）誘發的N400 效果會逐漸轉為P600 效果，而左視野呈現（右腦優先處理時）誘發的 P600 效果則逐漸轉為晚期出現的負向波效果。因此，我們的實驗結果不 僅支持了優勢腦中詞彙語意處理以及非優勢腦中語法結構處理這兩種鷹 架機制的存在，更點出其在語言學習時所扮演的過渡角色，顯示二語學習 者會逐漸減弱對這兩種鷹架機制的倚賴，以提升其二語語法的處理能力。

Native-like cognitive-neural mechanisms for syntactic processing have been shown to be less available for L2 learners. To compensate， learners may rely on lexical-semantic processing or the non-dominant hemisphere. To investigate these scaffolding effects， this study combined divided visual-fi eld (VF) and Event-Related Potential (ERP) techniques to assess L2 learners’ brain responses across the left and right hemispheres (LH and RH). Participants judged the grammaticality of Chinese two-word phrases starting with a classifier. Our data showed that， compared to native speakers， L2 learners were less accurate in grammaticality judgments and elicited qualitatively different brain responses even to correct trials. Replicating our previous findings on left-lateralized structural processing in native speakers， native participants in this present study showed a P600 grammaticality effect with RVF/LH presentation only. L2 learners showed remarkable intersubject variability in brain responses， and as a consequence， showed no statistically reliable ERP grammaticality effects. However， correlational analysis on individual learners’ brain responses and behavioral language performance revealed important correlations. Specifically， better language performance was associated with smaller RVF/LH N400 grammaticality effects and smaller LVF/RH P600 grammaticality effects. Quartile split based on participants’ language performance showed striking patterns， showing from bottom quartile to top quartile a gradual shift from an N400 grammaticality effect to a P600 grammaticality effect in the RVF/LH condition， and a P600 grammaticality effect to a later negativity effect in the LVF/RH condition. These results thus highlight the transitional roles of scaffolding mechanisms in language learning and suggest in particular that higher L2 syntactic processing co-occurs with less reliance on lexical-semantic processing in the dominant LH and disengagement of structural analysis from the non-dominant RH.