過去以拼音文字為刺激材料的寫字研究中，發現字形詞彙系統(orthographic lexicon)與字形緩衝區(graphemic buffer)分別在功能與神經機制上有雙重分離的現象。舉例來說，左側梭狀回(left fusiform gyrus)以及左側額中回與額下回的交接處(left inferior frontal junction)會受到字頻的高低而影響腦部活化程度，此腦區被認為負責字形詞彙系統的處理；另一方面，左側額上溝(left superior frontal sulcus)與左側頂上小葉(left superior parietal lobule)會受到字母長度的長短而影響腦部活化程度，這些腦區被認為負責字形緩衝儲存庫的處理。然而，以非拼音文字為刺激材料的寫字研究來說，對於字形詞彙系統與字形緩衝區是否有雙重分離的現象卻未進行詳盡地探討。因此，本研究目的在於操弄中文刺激材料中不同的語言變項(即字頻與筆畫數)來探討字形詞彙系統與字形緩衝區是否在功能上有分離現象，並進一步找出與這兩個系統各自相關的負責腦區。本研究實驗一在兩個寫字作業(抄寫與聽寫)以及兩個字詞辨識作業(視覺字詞辨識與聽覺字詞辨識)中操弄中文字的字頻與筆畫數，並以受試者對於刺激字的反應時間為實驗結果的指標，結果顯示在聽寫作業中的字頻效果顯著大於在聽覺字詞辨識作業中的字頻效果，此效果反映聽寫需要更多的字形詞彙系統的參與；然而，筆畫效果只存在於寫字作業，此效果反映寫字作業比字詞辨識作業多了字形緩衝區的處理。由實驗一可發現字形詞彙系統的處理會受到中文字字頻的影響，而字形緩衝區的處理會受到中文字筆畫數的影響，因此我們運用這兩個語言變項分別和兩個字形系統之處理相關的特性，在實驗二的想像寫字作業以及中文字辨識作業中操弄字頻與筆畫數，並透過功能性核磁共振造影技術進一步找出相對應腦區。結果顯示受試者在進行想像寫字作業與中文字辨識作業過程中，低頻字比起高頻字在左側梭狀回引發更高活化程度，反映此腦區負責中文字形表徵的處理，即字形詞彙系統的處理；另一方面，受試者在進行想像寫字作業過程中，多筆畫字比起少筆畫字在左側額中回(left middle frontal gyrus)與左側角回(left angular gyrus)引發更高活化程度，反映這些腦區在中文字書寫過程當中負責連續性的筆畫提取，即字形緩衝區的處理。本研究藉由行為與大腦反應的實徵證據，呈現出中文字書寫在字形詞彙系統與字形緩衝區的功能與解剖腦區上呈現雙重分離的現象。; Previous literature on writing has demonstrated a double dissociation of the underlying functional and neuronal mechanisms between the orthographic lexicon and the graphemic buffer in alphabetic languages. Specifically, the frequency of to-be-writtten stimuli correlated with the processing of the orthographic lexicon situated in the left fusiform gyrus and left inferior frontal junction, while the letter length of the to-be-written stimuli correlated with the processing of the graphemic buffer situated in the left superior frontal sulcus and left superior parietal lobule. Such dissociation has not been explicitly explored in non-alphabetic languages. In the present study, we investigated the functional dissociation between the orthographic lexicon and buffer in Chinese writing by identifying the distinct factors that affect these components selectively. We also investigated the anatomical dissociation between these two processes by identifying the separate brain regions that are associated with these components selectively. In Experiment 1, two linguistic factors, namely, the frequency and the stroke number of characters, were manipulated in two writing tasks: copy and dictation, as well as in two character recognition tasks: visual and auditory lexical decision. The effects of character frequency and stroke number on the durations from the onset of the stimuli till participants started to make responses (RTs) were compared among these tasks. We found that the frequency effect on RTs in the dictation task was stronger than that in the auditory lexical decision task, which suggested that the frequency effect in the dictation task reflected the involvement of the orthographic lexicon in addition to that of the phonological lexicon. The stroke number effect on RTs was significant and equivalent in the dictation and copy task, which suggested the involvement of the orthographic buffer in these two tasks. These findings confirmed that the orthographic lexicon and buffer was selectively sensitive to the manipulation of character frequency and stroke number, respectively. In Experiment 2, participants performed a mental writing task and a recognition task in which the frequency and the stroke number of Chinese characters were manipulated. Their brain responses were simultaneously recorded by functional magnetic resonance imaging (fMRI). It was found that characters with low frequency were associated with higher activation in the left fusiform gyrus than characters with high frequency across the mental writing and the character recognition tasks, which suggested this region to be the locus of the orthographic lexicon that represents the knowledge of character forms. It was also found that the stroke number correlated with the activations in the left middle frontal gyrus and left angular gyrus only in the mental writing task, which suggested these regions to be the loci of the orthographic buffer that represents the serial stroke selection in written production. The results from the two experiments in the present study revealed the functional and anatomical dissociation between the orthographic lexicon and buffer in writing Chinese characters.
