語言轉換與語言混合之功能性磁振造影研究
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2017
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對於雙語及多語人士可以輕鬆地進行語言轉換(language switching)及語言混合(language mixing)的現象一直是語言學家感興趣的議題，其背後的神經機制更是神經語言學家所感興趣的。本研究旨在探討健康成人在語言轉換及語言混合上的神經機制是否有差異，以補足先前文獻對此議題的探討。此外，本研究也進一步探討語言轉換及語言混合的方向性(從優勢的語言(L1)至非優勢語言(L2)或相反)在處理歷程上的差異。此實驗採用功能性磁振造影(fMRI)技術的區塊設計(block design)，操弄三個因子：語言(中文及英文)、語言轉換或語言混合以及語言轉換的方向。23位中文為母語、英文流利的受試者參與此實驗。正式實驗中，受試者必須在MRI機器內仔細聆聽所播出的音檔。實驗結果發現語言轉換及語言混合活化的腦區非常類似，尤其在顳葉顳上迴(superior temporal gyrus)及額葉腦迴區(inferior frontal gyrus)上的活化最強，研究結果與先前探討病人上所得到的結論似乎相反。實驗結果進一步顯示有語言轉換及混合的操弄相較於無任何操弄的情況下的腦區更為活化，這表示受試者在處理語言轉換及混合的句子下需要更多的認知功能處理。在語言轉換方向上，大腦活化從中文轉至英文比起英文轉至中文來得強。此結果顯示從優勢的語言（L1）轉換/混和至非優勢語言（L2）在處理歷程上是比較困難的。總結，此研究顯示語言轉換及語言混合在大腦活化上並無明顯差異，但在語言轉換的方向上具有顯著差異。
Bilinguals and multilinguals often switch and mix languages with automaticity, but was it really that easy? The aims of the current study were to investigate the underlying neuronal mechanisms for switching and mixing in healthy individuals as few study attempts to differentiate between these two phenomena. We then examined the processing cost of language switching and mixing in both directions (L1 to L2 or L2 to L1). A block fMRI design was adopted and the experimental materials were in Mandarin or in English, with the manipulation of switching or mixing and also the switching/mixing directions. Twenty-three proficient Mandarin-English bilinguals were recruited. They were instructed to listen to the auditory stimuli inside the MRI machine. The results revealed that the comprehension of language switching and mixing sentences activated very similar brain regions, with fairly strong activations in superior temporal gyrus (STG) and inferior frontal gyrus (IFG), which was drastically different from their clear distinction in language production in patient research. However, higher activations were found in the switched and mixed conditions compared to the non-switched/mixed conditions, indicating that higher cognitive effort was required in processing the switching and mixing conditions. As for switching direction, switching/mixing from Mandarin to English induced stronger brain activation than switching/mixing from the other way around, revealing that higher processing cost was required to process a switch/mix from a more dominant to a less dominant language. In sum, the study showed that switching and mixing developed similar activity in the brain, while switching/mixing directions elicited different processing cost.
Bilinguals and multilinguals often switch and mix languages with automaticity, but was it really that easy? The aims of the current study were to investigate the underlying neuronal mechanisms for switching and mixing in healthy individuals as few study attempts to differentiate between these two phenomena. We then examined the processing cost of language switching and mixing in both directions (L1 to L2 or L2 to L1). A block fMRI design was adopted and the experimental materials were in Mandarin or in English, with the manipulation of switching or mixing and also the switching/mixing directions. Twenty-three proficient Mandarin-English bilinguals were recruited. They were instructed to listen to the auditory stimuli inside the MRI machine. The results revealed that the comprehension of language switching and mixing sentences activated very similar brain regions, with fairly strong activations in superior temporal gyrus (STG) and inferior frontal gyrus (IFG), which was drastically different from their clear distinction in language production in patient research. However, higher activations were found in the switched and mixed conditions compared to the non-switched/mixed conditions, indicating that higher cognitive effort was required in processing the switching and mixing conditions. As for switching direction, switching/mixing from Mandarin to English induced stronger brain activation than switching/mixing from the other way around, revealing that higher processing cost was required to process a switch/mix from a more dominant to a less dominant language. In sum, the study showed that switching and mixing developed similar activity in the brain, while switching/mixing directions elicited different processing cost.
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語言轉換, 語言混合, 語言轉換方向, 語句處理歷程, 功能性磁振造影, language switching, language mixing, switching direction, sentence processing, fMRI