以功能性磁振造影探討在跨感官語意判斷作業中功能語意關係的發展差異

Abstract

過去研究發現，孩童或成人處理具有功能語意關係(亦即出現在相同的時間、空間，或是具有因果關係的事物)的刺激時，皆會產生語意處理的加速現象。然而，很少有研究探討處理功能語意關係的發展差異，及同時控制刺激的語意關聯強度得以更清楚地觀察功能語意關係的處理。因此，本研究透過跨感官語意關聯判斷作業及功能性磁振造影，探討處理功能語意關係的神經機制及其發展的變化。本研究共有十八位孩童與十八位成人參與者，他們必須判斷先呈現的視覺刺激字及後呈現的聽覺刺激字是否有語意相關，其中相關的字對又分為高功能關係(如:船─港)及低功能關係(如:錢─稅)。行為結果發現僅有成人組出現功能語意關係的促進效果，孩童組則無此促進效果。腦影像結果發現相較於處理高功能語意字對，成人組在處理低功能語意字對時，需要活化更多的左前側顳中迴(MTG)，表示需要更多的資源進行功能語意關係整合。在發展變化的比較中，相較於孩童在處理低功能語意字對時，成人活化較多的左前側顳中迴(MTG)及右側視丘(thalamus)。研究結果顯示，成人活化更多的顳中迴藉以更有效率地整合及聯結功能關係訊息。成人也會活化更多的視丘藉以調節大腦皮質區域，降低聽覺刺激同音字的激發閾值。

Past studies have found the thematic relation, which held together by external relations, unifying scenes or events, can speed up semantic processing in either children or adults. However, few studies examine developmental changes and control semantic association to observe the process of thematic relations. Therefore, this thesis is designed to examine the neural correlates of the thematic effect and the developmental differences in processing thematic relations. A cross-modal semantic judgment task was used in functional magnetic resonance imaging (fMRI). Eighteen children and eighteen adults participated in this study. They were asked to determine whether a written character and a subsequent spoken character were related in meaning in an MRI scanner. The character pairs were divided into strong (e.g., ship - port) and weak (e.g., money - tax) thematic relations. The behavioral results showed a thematic effect in adults but not in children. The imaging results showed greater activation in left anterior MTG for the weak as compared to the strong thematic relation in adults. Greater activation in the MTG may suggest a greater demand on integrating thematic features. Moreover, developmental increases in activation were found in left anterior MTG and right thalamus for the weak as compared to the strong thematic relation. In comparison with children, greater MTG activation in adults suggests that they may efficiently integrate and associate thematic related information. Greater thalamus activation in adults suggests a greater regulating mechanism to the cortical regions that decrease the threshold of the competing homophones of the auditory stimulus.