左中部梭状回枕颞沟内皮质对汉字加工的必要性、选择性和作用性质

PSYCH OpenIR > 中国科学院心理研究所回溯数据库(1956-2010)

	左中部梭状回枕颞沟内皮质对汉字加工的必要性、选择性和作用性质
其他题名	The necessity, selectivity and function properties of the left mid-fusiform cortex in occipitotemporal sulcus for Chinese character processing
	单春雷
	2008-05-14
摘要	对熟练阅读者的脑功能成像研究显示，左中部梭状回枕颞沟内皮质（LMFC-OTS）对视觉词汇有稳定性的激活。神经心理学研究也提示左半球腹侧枕颞区损害可以导致视觉词汇加工障碍。基于这些实验性观察和理论上的思考，有研究者假定LMFC-OTS负责快速、平行、整体地提取字母串的抽象表征，并把这小块皮质称为“视觉词形区” （VWFA）。然而，脑功能成像技术本身基本上是相关性的而不是因果性的方法；而以往研究中导致视觉词形加工障碍的左半球腹侧枕颞区病灶通常包含了LMFC-OTS以外的其它脑区。鉴于这些局限，尚有三个基本问题没有得到恰当的回答。即LMFC-OTS是否对视觉词汇加工必要？该皮质是否对视觉词汇加工具有选择性而对非视觉词汇刺激的加工不必要？该皮质对视觉词汇加工的作用性质是什么？本论文通过对4位左梭状回不同程度损伤的特殊病例进行一系列的神经心理学、脑结构和功能性磁共振的实验，力图回答上述三个问题。必要性：通过对磁共振脑结构像的细致分析发现，4位患者的脑梗死病灶在LMFC-OTS有所分离。具体地说，有1位患者该处皮质受损，3位患者该处皮质保留。神经心理学研究发现，LMFC-OTS损伤的患者汉字朗读、识别严重障碍，出现纯失读；LMFC-OTS保留但由于胼胝体压部损害导致左视野信息至该皮质的传入通路中断的患者对左视野呈现的汉字出现严重加工障碍，即左视野失读；而LMFC-OTS正常的患者汉字加工完全正常。功能性磁共振成像（fMRI）结果显示，纯失读患者对于汉字、左视野失读患者对于左视野汉字在LMFC-OTS无激活；然而，左视野失读患者对于右视野汉字，以及LMFC-OTS保留的两患者对于汉字在LMFC-OTS有正常激活。这些实验结果一致表明，LMFC-OTS对汉字的加工是必要的。选择性：我们通过系统检查患者加工视觉词汇及非视觉词汇刺激（视觉及听觉词汇；视觉词汇及非词汇的视觉刺激如面孔、物体、颜色和数字）检验LMFC-OTS对视觉词汇加工的选择性。结果显示，纯失读患者听觉词汇加工（词汇表达、听理解、复述）完全正常；对非词汇视觉刺激（面孔、物体、颜色、数字）的识别也完全正常。尽管对面孔、物体、颜色有一定程度的命名受损（数字朗读正常），但显著轻于LMFC-OTS未受损的患者或无显著差异。这些数据提供了强有力的证据表明LMFC-OTS对非视觉词汇的加工不必要，故具有视觉词汇加工的选择性。作用性质：通过多层次、不同性质的汉字加工任务，包括汉字朗读、语音判断、语义判断、字形抽象表征（字素）异同判断、词汇判断、字形异同判断；以及听写、抄写、自发书写等检查，我们试图揭示LMFC-OTS损伤导致的最关键的汉字加工障碍，从而证明LMFC-OTS对汉字加工的最本质作用。结果表明，LMFC-OTS损伤患者除汉字朗读、语音/语义判断异常外，尚不能正常完成具有不同字形表面特征（宋体/草体/手写体、简/繁体字、笔画/整字方向等不同）的两个字（包括独体字和合体字）是否有同一抽象表征（字素）的判断。最初检查合体字和独体字的抽象表征均无法正常提取。抄写合体字时表现为“看一笔划写一笔划”的非常缓慢的临摹（30秒/字），无法按整字甚至无法按部件（独体字）进行抄写。随着病情的恢复，第二次复查时（5月后），患者能够完成独体字的抽象表征异同判断，而合体字仍无改善。但是，患者抄写合体字却演变为“按整部件（独体字）”进行抄写。此外，抄写和字形抽象表征判断能力的发展似乎是比较同步的，这种现象反映了纯失读患者LMFC-OTS损害后无法从汉字次级单元提取出上级单元的抽象表征，尤其对于从大的次级单元提取出整字（部件/独体字－合体字）的抽象表征更困难，损伤后难以恢复。因此，LMFC-OTS似乎承担了多层级的（尤其是高层级的）视觉词形抽象表征的提取。这种词形抽象表征的成功提取似乎不依赖于音义的正常通达，因为患者在能够正常完成独体字抽象表征异同判断时，其对独体字的朗读及语义加工能力仍明显受损。然而，也有可能是抽象表征同其相关的信息如语音、语义信息的交互作用也受损。综上所述我们得出结论：1、左中部梭状回枕颞沟内皮质对汉字加工是必要的；2、该皮质对汉字加工具有选择性；3、该皮质的关键作用在于提取多级的视觉词形抽象表征，并可能向语音、语义加工系统传递。
其他摘要	A number of functional neuroimaging studies with skilled readers consistently showed activation to visual words in the left mid-fusiform cortex in occipitotemporal sulcus (LMFC-OTS). Neuropsychological studies also showed that lesions at left ventral occipitotemporal areas result in impairment in visual word processing. Based on these empirical observations and some theoretical speculations, a few researchers postulated that the LMFC-OTS is responsible for instant parallel and holistic extraction of the abstract representation of letter strings, and labeled this piece of cortex as “visual word form area” (VWFA). Nonetheless, functional neuroimaging studies alone is basically a correlative rather than causal approach, and lesions in the previous studies were typically not constrained within LMFC-OTS but also involving other brain regions beyond this area. Given these limitations, it remains unanswered for three fundamental questions: is LMFC-OTS necessary for visual word processing? is this functionally selective for visual word processing while unnecessary for processing of non-visual word stimuli? what are its function properties in visual word processing? This thesis aimed to address these questions through a series of neuropsychological, anatomical and functional MRI experiments in four patients with different degrees of impairments in the left fusiform gyrus. Necessity: Detailed analysis of anatomical brain images revealed that the four patients had differential foci of brain infarction. Specifically, the LMFC-OTS was damaged in one patient, while it remained intact in the other three. Neuropsychological experiments showed that the patient with lesions in the LMFC-OTS had severe impairments in reading aloud and recognizing Chinese characters, i.e., pure alexia. The patient with intact LMFC-OTS but information from the left visual field (LVF) was blocked due to lesions in the splenium of corpus callosum, showed impairment in Chinese characters recognition when the stimuli were presented in the LVF but not in the RVF, i.e. left hemialexia. In contrast, the other two patients with intact LMFC-OTS had normal function in processing Chinese characters. The fMRI experiments demonstrated that there was no significant activation to Chinese characters in the LMFC-OTS of the pure alexic patient and of the patient with left hemialexia when the stimuli were presented in the LVF. On the other hand, this patient, when Chinese characters were presented in right visual field, and the other two with intact LMFC-OTS had activation in the LMFC-OTS. These results together point to the necessity of the LMFC-OTS for Chinese character processing. Selectivity: We tested selectivity of the LMFC-OTS for visual word processing through systematically examining the patients’ ability for processing visual vs. auditory words, and word vs. non-word visual stimuli, such as faces, objects and colors. Results showed that the pure alexic patients could normally process auditory words (expression, understanding and repetition of orally presented words) and non-word visual stimuli (faces, objects, colors and numbers). Although the patient showed some impairments in naming faces, objects and colors, his performance scores were only slightly lower or not significantly different relative to those of the patients with intact LMFC-OTS. These data provide compelling evidence that the LMFC-OTS is not requisite for processing non-visual word stimuli, thus has selectivity for visual word processing. Functional properties: With tasks involving multiple levels and aspects of word processing, including Chinese character reading, phonological judgment, semantic judgment, identity judgment of abstract visual word representation, lexical decision, perceptual judgment of visual word appearance, and dictation, copying, voluntary writing, etc., we attempted to reveal the most critical dysfunction caused by damage in the LMFC-OTS, thus to clarify the most essential function of this region. Results showed that in addition to dysfunctions in Chinese character reading, phonological and semantic judgment, the patient with lesions at LMFC-OTS failed to judge correctly whether two characters (including compound and simple characters) with different surface features (e.g., different fonts, printed vs. handwritten vs. calligraphy styles, simplified characters vs. traditional characters, different orientations of strokes or whole characters) had the same abstract representation. The patient initially showed severe impairments in processing both simple characters and compound characters. He could only copy a compound character in a stroke-by-stroke manner, but not by character-by-character or even by radical-by-radical manners. During the recovery process, namely five months later, the patient could complete the abstract representation tasks of simple characters, but showed no improvement for compound characters. However, he then could copy compound characters in a radical-by-radical manner. Furthermore, it seems that the recovery of copying paralleled to that of judgment of abstract representation. These observations indicate that lesions of the LMFC-OTS in the pure alexic patients caused several damage in the ability of extracting the abstract representation from lower level units to higher level units, and the patient had especial difficulty to extract the abstract representation of whole character from its secondary units (e.g., radicals or single characters) and this ability was resistant to recover from impairment. Therefore, the LMFC-OTS appears to be responsible for the multilevel (particularly higher levels) abstract representations of visual word form. Successful extraction seems independent on access to phonological and semantic information, given the alexic patient showed severe impairments in reading aloud and semantic processing on simple characters while maintenance of intact judgment on their abstract representation. However, it is also possible that the interaction between the abstract representation and its related information e.g. phonological and semantic information was damaged as well in this patient. Taken together, we conclude that: 1) the LMFC-OTS is necessary for Chinese character processing, 2) it is selective for Chinese character processing, and 3) its critical function is to extract multiple levels of abstract representation of visual word and possibly to transmit it to phonological and semantic systems.
关键词	左中部梭状回枕颞沟内皮质视觉词形区汉字纯失读左视野失读视觉词形抽象表征功能性磁共振成像
学位类型	博士
语种	中文
学位授予单位	中国科学院心理研究所
学位授予地点	心理研究所
文献类型	学位论文
条目标识符	http://ir.psych.ac.cn/handle/311026/4644
专题	中国科学院心理研究所回溯数据库(1956-2010)
推荐引用方式 GB/T 7714	单春雷. 左中部梭状回枕颞沟内皮质对汉字加工的必要性、选择性和作用性质[D]. 心理研究所. 中国科学院心理研究所,2008.

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