| dc.description.abstract | 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. | en_US |