左侧额中回参与汉字视觉空间分析的fNIRS证据

fNIRS evidence for left middle frontal gyrus involved in visual-spatial analysis of Chinese characters

左侧额中回(MFG)是汉字阅读脑机制研究发现的一个典型脑区,它表现出在汉字阅读中的特异激活,一种普遍的解释认为其负责了汉字独特的视觉空间加工。但是,该解释没有得到直接的证据支持。本研究操纵汉字材料的视觉呈现空间频率,使用功能性近红外光谱成像(fNIRS)技术对此问题进行探讨。通过构建3(字类型:真字、假字和非字)×3(空间频率:完整频谱、低空间频率和高空间频率)的重复测量实验设计,记录被试在完成重复刺激检测的one-back任务时MFG的血氧浓度变化。结果发现左侧MFG表现出显著的字类型主效应,即假字比真字和非字需要更多MFG的激活;而且,左侧MFG还表现出显著的字类型与空间频率的交互作用,即在低空间频率条件下假字比真字和非字具有更强的MFG激活,而在另两种频率条件下并没有发现字类型的显著激活差异。结果表明左侧MFG的确对汉字的空间信息敏感,尤其是在需要更多字形/正字法加工的假字条件下以及对低空间频率信息的加工上都需要更多MFG的激活。研究结果为左侧MFG参与汉字正字法信息的视觉空间加工提供了直接的证据。

The left middle frontal gyrus(MFG)is a typical region identified in the brain mechanism of Chinese character reading.A common view suggests that the MFG is responsible for visual-spatial processing in reading Chinese characters,since the Chinese writing system has extremely complex structures.However,this explanation has not received direct evidence.Moreover,which kind of visual-spatial analysis underlying the MFG's activation is not clear.The current functional Near-Infrared Spectroscopy(fNIRS)study examined the functional role of the MFG in Chinese character reading by directly manipulating the spatial frequency characteristics of the Chinese character materials.The experiment adopted a 3(characters type:Real,Pseudo,and Artificial character)by 3(spatial frequency:Full,Low,and High spatial frequency)within-participant factorial design.All Real characters were phonograms containing two components:phonetic and semantic radicals.The phonetic radical was not pronounceable and meaningless.The semantic radical was not pronounceable and meaningful that can provide the meaning category.The Pseudo characters were created by switching the position of radicals from Real characters.The Artificial characters were scrambled strokes from Pseudo characters.Each type of character was presented in three ways with different spatial frequencies:Full,Low,and High spatial frequency.In the Full spatial frequency,items were typical stimuli.In the Low and High spatial frequency,items were spatially filtered by Gaussian filter to remain the low/high spatial frequency features.Each type of character has 60 stimuli.All 540 stimuli for nine conditions were presented in 6 runs.Each run contained 1~2 blocks for each condition and lasted for about 8 minutes.Thirty-one participants took part in the experiment to perform a one-back task in each block by detecting whether the current stimulus was the same as the previous one.Meanwhile,a multi-channel fNIRS system was used to record brain activity at the left MFG.The results found a significant main effect of character type at left MFG.The activation of MFG was stronger for Pseudo characters than for Real and Artificial characters.The left MFG also showed a significant interaction between character type and spatial frequency.The difference among the three types of characters was significant for Low spatial frequency but not for Full and High spatial frequency.For materials presented in Low spatial frequency,Pseudo characters elicited more robust activation than Real and Artificial characters.These results suggested that the left MFG was sensitive to the spatial information of Chinese characters,especially for materials presented in low spatial frequency and for materials that required more graphemic/orthographic processing.In sum,the finding provided direct evidence that the left MFG engaged in visual-spatial processing in Chinese character reading.