健康與自閉症青少年之中文語意知識

Abstract

目的：瞭解語意處理的發展變化對於探討語意知識發展具有其重要性。過去關於健康青少年語意發展的研究，皆採用橫斷式取向觀察年齡變化的差異，而且沒有將語意關聯與類別語意關係對於語意處理的影響清楚區分。此外，神經發展障礙的自閉症疾病，其主要臨床症狀為溝通障礙與語意處理能力缺失，已被證實在進行語意處理時會伴隨著異常神經活動。然而，對於自閉症青少年與健康青少年在處理語意關係時，是否在神經機制上也有著異同表現的知識仍然缺乏。此論文藉由行為測量與功能性磁振造影（fMRI），檢驗健康青少年的語意關聯與類別語意關係的發展變化，並進一步地比較自閉症青少年處理語意關聯與類別語意關係時對應的神經活動表現。方法：實驗一採縱貫式取向，正交地操弄語意關聯（高、低）與類別語意關係（高、低）兩個變項，以檢驗16位10到14歲青少年參與者語意知識的發展。參與者在進入fMRI後，判斷依序出現的視覺中文字對是否具有意義關係，在間隔兩年後，再次進行相同作業。實驗一更進一步的檢驗第一次的行為表現是否能預測兩年後的神經活化變化。實驗二以fMRI檢驗31位自閉症青少年與36位年齡、性別、慣用手與智力配對的健康青少年在進行語意處理時相對應的神經活動表現，參與者需判斷視覺呈現的中文字是否具有語意關係。分析判斷結果時將語意相關字對，依照語意關聯與類別語意關係的評分視為一連續性的刺激（item-level）參數調節變項。結果：實驗一，在弱語意關聯字對的表現，第二次比第一次有較多的神經生理反應，顯現在左顳中回（middle temporal gyrus）與左額下回（inferior frontal gyrus）有較多的活化反應，而第一次的行為正確率表現也預測了第二次的左額下回活化反應。推論處理越精緻化的語意表徵時，需要更仔細的選擇適當的語意表徵。此外，高類別語意關係字對則是在左枕-顳葉皮質區（occipito-temporal cortex）與左楔前葉（precuneus）有較多的活化，而第一次的行為正確率表現則預測了第二次的左楔前葉活化反應。推論較為精緻化的語意屬性能完整的整合語意訊息。實驗二，相較於健康青少年，自閉症青少年在進行語意關係判斷時，隨著語意關聯性減弱，在左楔狀葉（cuneus）有明顯的活化反應，而健康青少年則是在隨著語意關聯性減弱，在左額下回與左顳中回有較明顯的活化反應；隨著類別語意關係增加，在左楔前葉（precuneus）與左枕-顳葉皮質區（occipito-temporal cortex）有明顯的活化反應。根據結果推論自閉症青少年與健康青少年在處理語意關係時的神經生理反應層次不同。自閉症青少年仰賴使用較低層次的視覺處理來進行語意處理，而健康青少年有著較精緻化的語意表徵，以較高層次的提取能力選擇適當語意表徵，對於語意屬性的掌握也較為精熟，得以將類別知識進行整合。

To understand the developmental changes of semantic processing in autism spectrum disorders (ASD) and typical development (TD) youths is crucial to know the nature of the organization of semantic knowledge. However, the distinction of semantic knowledge including association strength and categorical relatedness has not been made clear in the literature for these two groups. In Experiment 1, using a longitudinal approach for the TD group, I orthogonally manipulated association strength (strong, weak) and categorical relatedness (high, low) to examine the developmental changes in activation of sixteen 10- to 14-year-old children over a two-year interval. Moreover, I examined whether initial behavioral performance (Time 1) predicted brain activation changes (Time 2-Time 1). Experiment 2 used fMRI to examine the neural correlates of semantic processing in thirty-one male youths with ASD and thirty-six TD youths. The association strength and categorical relatedness were item-level parametric modulators as two continuous variables. In Experiment 1, for Time 2-Time 1, the weak versus strong association strength produced greater activation in the left middle temporal gurus (MTG, BA 21) and inferior frontal gyrus (IFG, BA 45) as well as accuracy (Time 1) predicted activation changes in the IFG, suggesting more elaborate semantic representations that require greater engagement of selection processes. Moreover, the high versus low categorical relatedness produced greater activation in the left occipito-temporal cortex (OTC, BA37) and precuneus (BA 30) as well as accuracy (Time 1) predicted activation changes in the precuneus, suggesting more elaborate features of categorical knowledge that allow complete integration. In Experiment 2, for group comparisons, the ASD group showed greater activation in the left cuneus (BA 7) for the weaker association strength. The TD group showed greater activation in the left IFG and MTG for the weaker association strength, and greater activation in the left precuneus and left OTC for the higher categorical relatedness as compared to the ASD group. The ASD group may use lower-level visual processing during semantic processing. The TD group showed higher-level controlled processes of more elaborate semantic representations for selection processes and more elaborate features of categorical knowledge for integration.