Data_Sheet_1_Merge-Generability as the Key Concept of Human Language: Evidence From Neuroscience.pdf

Ever since the inception of generative linguistics, various dependency patterns have been widely discussed in the literature, particularly as they pertain to the hierarchy based on “weak generation” – the so-called Chomsky Hierarchy. However, humans can make any possible dependency patterns by using artificial means on a sequence of symbols (e.g., computer programing). The differences between sentences in human language and general symbol sequences have been routinely observed, but the question as to why such differences exist has barely been raised. Here, we address this problem and propose a theoretical explanation in terms of a new concept of “Merge-generability,” that is, whether the structural basis for a given dependency is provided by the fundamental operation Merge. In our functional magnetic resonance imaging (fMRI) study, we tested the judgments of noun phrase (NP)-predicate (Pred) pairings in sentences of Japanese, an SOV language that allows natural, unbounded nesting configurations. We further introduced two pseudo-adverbs, which artificially force dependencies that do not conform to structures generated by Merge, i.e., non-Merge-generable; these adverbs enable us to manipulate Merge-generability (Natural or Artificial). By employing this novel paradigm, we obtained the following results. Firstly, the behavioral data clearly showed that an NP-Pred matching task became more demanding under the Artificial conditions than under the Natural conditions, reflecting cognitive loads that could be covaried with the increased number of words. Secondly, localized activation in the left frontal cortex, as well as in the left middle temporal gyrus and angular gyrus, was observed for the [Natural – Artificial] contrast, indicating specialization of these left regions in syntactic processing. Any activation due to task difficulty was completely excluded from activations in these regions, because the Natural conditions were always easier than the Artificial ones. And finally, the [Artificial – Natural] contrast resulted in the dorsal portion of the left frontal cortex, together with wide-spread regions required for general cognitive demands. These results indicate that Merge-generable sentences are processed in these specific regions in contrast to non-Merge-generable sentences, demonstrating that Merge is indeed a fundamental operation, which comes into play especially under the Natural conditions.自生成语言学（generative linguistics）创立以来，各类依存模式在学界已有广泛讨论，尤其是与基于“弱生成性”的层级体系——即所谓乔姆斯基层级（Chomsky Hierarchy）——相关的依存模式。然而人类可通过人工手段在符号序列（例如计算机编程）中构建任意可能的依存模式。学界早已普遍观察到人类语言语句与通用符号序列之间的差异，但此类差异何以存在的问题却极少被提出。本研究针对该问题展开探讨，并基于“可合并生成性（Merge-generability）”这一新概念提出理论解释：即某一特定依存关系的结构基础是否由核心操作“合并（Merge）”所提供。在我们的功能磁共振成像（functional magnetic resonance imaging, fMRI）研究中，我们以日语（一种允许自然无界嵌套结构的SOV型语言）的语句为材料，测试了名词短语（noun phrase, NP）-谓词（predicate, Pred）配对的判断任务。我们进一步引入两个伪副词，它们可人工强制构建不符合合并生成结构的依存关系，即非可合并生成性结构；借此我们能够操控可合并生成性的状态（自然或人工）。通过这一新颖实验范式，我们获得了如下结果：其一，行为数据清晰显示，相较于自然条件，人工条件下的NP-Pred匹配任务难度更高，这一现象反映出可随词汇数量增加而变化的认知负荷。其二，在[自然条件减人工条件]的对比中，我们观察到左侧额叶皮层、左侧颞中回以及角回出现局部激活，表明这些左侧脑区在句法加工中具有特异性。由于自然条件始终较人工条件更为简单，因此任务难度带来的任何激活均已从这些脑区的激活信号中完全排除。最后，[人工条件减自然条件]的对比则激活了左侧额叶皮层的背侧部分，以及广泛参与通用认知需求的脑区。上述结果表明，可合并生成性语句与非可合并生成性语句分别在上述特定脑区中进行加工，证实合并（Merge）确实是一项核心操作，尤其在自然条件下发挥关键作用。