中文語意處理之神經有效性連結

Effective Connectivity in Semantic Judgments of Chinese Characters

范利霙(Li-Ying Fan)

指導教授 ： 周泰立

共同指導教授 ： 曾文毅(Wen-Yih Isaac Tseng)

國立臺灣大學/理學院/心理學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.01987

摘要

目的:本研究利用功能性磁振造影(fMRI)、動態因果推論模型(DCM) 、階層式模型比較及擴散頻譜磁振造影(DSI)，探討中文語意處理的神經機制，所有受試者需要判斷視覺呈現的中文字對是否在意義上相關。方法: 在實驗一和實驗二，將利用DCM計算不同腦區之間的動態連結，並找出最適當的模型來解釋不同腦區間的連結。受試者皆為正常大人，並採用兩種刺激字對，分別為語意相關組與語意無關組。實驗三則利用Bayesian Model Selection (BMS) and Bayesian Model Averaging (BMA)找出最適當的模型，並探討發展上不同腦區間神經動態連結之差異。受試者分別為17位的正常大人及17位的孩童，而刺激字對將依照語意關聯強度區分成三組字對（高語意、低語意、無關語意）。實驗四結合DCM及DSI，進一步探討不同腦區之間的神經動態連結及白質纖維結構上之發展差異。結果:在功能性磁振造影的結果顯示，實驗一和實驗二皆發現共同的活化腦區於左腦腹側下額葉(IFG, BA 45, 47)及左腦中顳葉 (MTG, BA 21)。而實驗三和實驗四在大人及孩童組皆發現在左腦腹側下額葉，左腦中顳葉及左腦梭狀回(FG, BA 37)，會產生顯著的神經活化。而在實驗四中的擴散頻譜磁振造影結果顯示，成人在inferior frontal-occipital fasciculus (IFOF)的非等向性指標(generalized fractional anisotropy, GFA)較孩童高。在動態因果推論模型推論出的有效性連結，實驗一發現從左腦腹側下額葉到左腦中顳葉的顯著調節效果(modulatory effects)、從左腦中顳葉到左腦腹側下額葉的顯著調節效果及從左腦梭狀回到左腦中顳葉的顯著調節效果。在實驗二最適當的模型中，發現兩條顯著調節效果，分別從左腦腹側下額葉到左腦中顳葉和從左腦梭狀回到左腦中顳葉。實驗三亦發現兩組都有從左腦梭狀回到左腦中顳葉有顯著的調節效果。同時，也發現成人組比孩童組，在左腦梭狀回到左腦腹側下額葉的調節效果呈現更顯著的影響。實驗四主要發現成人相較於比孩童的發展變化，是從左腦梭狀回到左腦腹側下額葉的調節效果。結論:首先，左腦腹側下額葉到左腦中顳葉的顯著調節效果，推論為左腦腹側下額葉負責從上到下提取語意表徵的歷程。同時，從左腦中顳葉到左腦腹側下額葉的顯著調節效果，推論左腦中顳葉負責提供語意記憶中相關的表徵聯結，協助左腦腹側下額葉進行提取。再者，從左腦梭狀回到左腦中顳葉的顯著調節效果，推論左梭狀回將字形訊息藉由從下到上的歷程，傳送至左腦中顳葉處理語意表徵訊息。最後，在成人組發現從左腦梭狀回到左腦腹側下額葉調節效果及弱相關語意組有較強的調節效果。總結，在中文語意處理的發展歷程中，相較於孩童，成人有較顯著的左腦腹側下額葉及中顳葉的腦區活化，較成熟的腹側白質纖維束(IFOF)，及較強的左腦梭狀回到左腦腹側下額葉的調節效果。表示隨著年齡增長，腹側腦區及連結的成熟，使成人有較好的字形至語意的對應歷程，亦能更有效的進行中文語意的處理。

關鍵字

有效性連結 ； 語意 ； 動態因果推論模型(DCM) ； 擴散頻譜磁振造影(DSI)

並列摘要

Purpose: functional magnetic resonance imaging (fMRI), dynamic causal modelling (DCM) hierarchical model comparisons, and diffusion spectrum imaging (DSI) were used to investigate the effective connectivity and structural connectivity during semantic judgments to visual Chinese characters. All participants were asked to indicate if character pairs were related in meaning. Methods: In Experiments 1 and 2, the use of DCM was to examine the directional influences among brain regions, and to seek for the optimal model in the semantic network by hierarchical model comparisons. In adult participants, the experimental stimuli were character pairs that included semantically-related and semantically-unrelated pairs. In Experiment 3, Bayesian Model Selection (BMS) and Bayesian Model Averaging (BMA) were used to seek for the optimal model. In 17 children (10- to 13-year-olds) and 17 adults, the experimental stimuli included high association, low association, and unrelated pairs. In Experiment 4, fMRI, DSI and DCM were used to study the developmental changes of neural correlates, structural connectivity, and effective connectivity during semantic judgment. Results: In conventional fMRI analysis, common activation was found in left ventral inferior frontal gyrus (IFG, BA 45, 47), left posterior middle temporal gyrus (MTG, BA 21) in Experiments 1 and 2. In Experiment 3, both groups showed greater activation in left ventral IFG, left MTG, and left fusiform gyrus (FG, BA37). In Experiment 4, compared to children, adults showed greater activation in the left ventral IFG and MTG, and adults had significantly greater structural connectivity in the left ventral pathway (inferior frontal occipital fasciculus, IFOF) than children. As for effective connectivity from DCM analyses, significant modulatory effects were found from left ventral IFG to left MTG, from left MTG to left ventral IFG, and from left FG to left MTG in Experiment 1. In Experiment 2, the results of the optimal model showed significant modulatory effects from ventral IFG to MTG and from FG to MTG. In Experiment 3, a significant bottom-up effect was found from FG to MTG. Moreover, a bottom-up effect from FG to ventral IFG was stronger than a top-down effect from ventral IFG to FG in adults, and that the bottom-up effect from FG to ventral IFG was stronger in adults compared to children. In Experiment 4, adults showed significantly stronger bottom-up connection from FG to ventral IFG than children in the related condition. Conclusion: First, the modulatory effects from left ventral IFG to left MTG suggested top-down influences of the frontal cortex on retrieval of semantic representations. Second, the modulatory effects from left MTG to left ventral IFG suggested the role of MTG on providing relevant associations in verbal semantic memory for ventral IFG to perform retrieval. Third, the modulatory effect from left FG to left MTG suggested bottom-up orthographic influences on semantic representations. The most important finding was the bottom-up effect from FG to ventral IFG in adults, implying developmental changes in semantic processing. In conclusion, our findings suggest that age-related maturation in brain activation (ventral IFG and MTG) and structural connectivity (IFOF) might be associated with the bottom-up influence of orthographic representations on retrieving semantic representations for processing Chinese characters.

並列關鍵字

effective connectivity ； structural connectivity ； semantics ； dynamic causal modelling (DCM) ； Diffusion spectrum imaging (DSI)

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