人类语言能力的独特之处在于加工、处理层级结构。其他语言的相关研究认为左侧额下回（the left inferior frontal gyrus，LIFG）是承担复杂句法结构加工功能的关键脑区。然而，在汉语相关研究中，LIFG对汉语复杂句法结构加工的具体作用并不明确。同时，在自然语言中，关系从句是体现语言层级的典型句法结构，也是汉语二语者句法习得过程中的重难点。因此，本研究将带关系从句的复杂句作为复杂句法结构加工的研究材料，对LIFG在汉语一语者和以泰语为母语的晚期汉语二语者进行汉语复杂句法结构加工时潜在的因果致使性作用及其异同进行探究，并在此基础上深入探究可能影响LIFG发挥因果致使性作用的汉语二语学习者个体因素。

本文通过三项研究对上述问题进行了系统考察：

研究一采用经颅磁刺激技术（transcranial magnetic stimulation，TMS），通过分析汉语一语者句子理解任务和工作记忆任务的相关行为指标，考察抑制LIFG对汉语一语者复杂句法结构加工的影响。

研究二采用与研究一相同的实验范式，探究LIFG在汉语二语者加工复杂句法结构时是否具有因果致使性作用，并结合研究一的结果对比分析了LIFG在汉语一语者和二语者复杂句法结构加工时所起作用的异同。

研究三在研究二的基础上进一步探索了可能影响TMS调控效应的汉语二语学习者个体因素。

本文三项研究主要发现：

对汉语一语者而言，刺激LIFG后被试基于反应时计算得出的变异系数和峰度等行为指标发生了显著变化，说明被试加工复杂句法结构的稳定性受到影响，验证了LIFG对汉语一语者复杂句法结构加工具有因果致使性作用；

TMS抑制LIFG对汉语二语者的复杂句法结构加工亦产生了显著影响，其中加工质量（如正确率、d-prime值）和加工稳定性（如变异系数）相关指标都受到了调控，表明LIFG在汉语二语者进行复杂句法结构加工时也具有因果致使性作用；对比汉语一语者和二语者的TMS调控效应可以发现二者加工主语关系从句的稳定性都受到了显著影响，且二者之间存在显著差异；

通过回归分析考察学习者个体因素与汉语二语者TMS调控效应的关系发现，学习时长和使用频率能够有效影响并预测相关TMS调控效应。

综合上述结果，本研究得出以下结论：（1）LIFG在汉语一语者复杂句法结构加工中具有因果致使性作用；（2）类似地，汉语二语者同汉语一语者共享LIFG这一复杂句法结构加工核心脑区，但LIFG所发挥的因果致使性作用在两者之间存在一定差异，此外，相较于宾语关系从句，主语关系从句对汉语一语者和二语者而言似乎都更难加工，更易受到TMS的调控，且两组在主语关系从句加工的稳定性上存在不同的TMS调控效应；（3）与初始习得年龄、二语熟练度等因素相比，学习时长和使用频率似乎更能预测汉语二语者加工复杂句法结构时的TMS调控效应。

本研究围绕“左侧额下回对汉语一语者与二语者复杂句法结构加工的因果致使性作用及其异同”这一核心论题展开，采用TMS技术验证了对汉语一语者和二语者进行复杂句法结构加工具有因果致使性作用的核心脑区——LIFG，同时分析了LIFG在汉语一语者和二语者进行复杂句法结构加工时所起作用的异同，并对影响汉语二语复杂句法结构加工神经调控效果的学习者个体因素进行了考察，为优化语言加工认知神经模型、补充二语习得理论、指导汉语国际教育实践提供了来自神经调控的证据。

The uniqueness of human language ability lies in its processing of hierarchical structures. In previous studies on other languages, LIFG has been found to play a crucial role in complex syntactic processing. However, the specific role of LIFG in complex syntactic processing in Chinese is not yet clear. Moreover, relative clauses are crucial in reflecting linguistic hierarchies and pose challenges for second-language learners of Chinese. Therefore, the present study aims to investigate the causal role of LIFG in complex syntactic processing for both Chinese native speakers and late second-language learners of Chinese whose native language is Thai. Additionally, it examines similarities and differences between their performances. Furthermore, potential individual factors that may influence the causal effect of LIFG in second-language learners of Chinese are discussed.

This thesis systematically explored the above core topics through three studies:

Study 1 applied transcranial magnetic stimulation (TMS) to investigate the impact of inhibiting LIFG on syntactic processing in Chinese native speakers by analyzing behavioral measures during sentence comprehension and working memory tasks.

Study 2 used the same behavioral experiment as Study 1 to clarify the role of LIFG in complex syntactic processing among Chinese second-language learners. Additionally, by comparing the results of Study 1, Study 2 also examined the similarities and differences in the involvement of LIFG during syntactic processing between Chinese native speakers and second-language learners.

Study 3 further investigated individual factors that may exert an influence on the effects of transcranial magnetic stimulation (TMS) modulation among Chinese second-language learners, thereby expanding upon the groundwork laid by Study 2.

The three main findings of this thesis are as follows:

For Chinese native speakers, stimulation of LIFG resulted in significant changes in behavioral indicators such as coefficient of variation and kurtosis of response time. This indicated that the stability of complex syntactic processing was affected by the stimulation, providing evidence for a causal role of LIFG in complex syntactic processing for native speakers.

The inhibition of LIFG by TMS also significantly affected complex syntactic processing in Chinese second-language learners, modulating both processing quality (e.g., accuracy rate, d-prime value) and stability (e.g., coefficient of variation). This indicates that LIFG causally influences the processing of L2 complex syntactic structures. A comparison of the TMS modulatory effects between native and second-language learners of Chinese showed that the stability of processing subject relative clauses was significantly affected, and there were significant differences between them.

The relationship between individual factors and the TMS modualtion effect was investigated by regression analysis. It was found that learning duration and frequency of use can effectively influence and predict the TMS modualtion effect.

Based on the above results, this study drew the following conclusions: (1) LIFG plays a causal role in the complex syntactic processing of Chinese native speakers; (2) Similarly, Chinese second-language learners and Chinese native speakers share LIFG as the core brain region for processing complex syntactic structures, but there are some differences in the causal effects of LIFG between the two groups. In addition, compared with object-relative clauses, subject-relative clauses seem to be more difficult to process for both groups and are more easily-prone to be modulated by TMS. The two groups further exhibited different TMS modualtion effects on the stability of subject relative clauses processing. (3) Compared with the age of acquisition and proficiency level in the second language, learning duration and frequency of use seem to be more predictive of TMS modulation effects on Chinese second-language  complex syntactic structure processing.

This study focused on the core research topic of "The causal role of the LIFG in complex syntactic processing in Chinese native and second-language learners". TMS was applied to verify the core brain region, LIFG, which might play a causal role in processing the complex syntactic structures for both Chinese native speakers and second-language learners. At the same time, the differences and similarities of LIFG in the processing of complex syntactic structures between the two groups were analyzed, and the individual learner factors affecting the neuromodulation of complex syntactic structure processing in second-language learners were investigated, which provided further evidence from neuromodulation for optimizing the cognitive neural model of language processing, supplementing the theory of second language acquisition, and guiding the practice of international Chinese education.