A Role for Declarative and Procedural Memory in Language

人类语言依赖于一本单词词典(心理词典)和规则，这些规则规定了如何将这些单词组合成更大的单词、短语和句子(心理语法)。这两种基本语言能力的计算和大脑基础仍然没有得到很好的理解。本项目研究了一种新的观点，即学习和使用这两种语言能力依赖于另外两个通用记忆系统，它们的神经基础得到了相对较好的研究。具体地说，它假设单词的习得和使用依赖于先前证明的学习和使用事实知识(如斑马是什么以及它生活在哪里)的“陈述性记忆”颞叶大脑回路。还假设语法规则的习得和使用依赖于“程序性记忆”，即先前被证明是学习和表达运动和认知“技能”的左额叶/基底节脑回路，例如骑自行车。在这种“陈述性/程序性”的语言观中，词汇和语法与不同的通用系统相联系，每个系统都负责一套特定的语言和非语言功能。陈述性/程序性观点与之前提出的关于语言的计算机制和神经机制的两种主要理论形成了鲜明对比。它认同传统的“二元系统”理论，即词汇和语法依赖于不同的系统，但它与他们所声称的这些系统只对语言负责的观点不同。相反，虽然陈述性/程序性观点与“单一系统”理论一致，即两种语言能力依赖于通用的大脑回路，但它与他们的主张背道而驰，即这两种能力都与大脑中广泛分布的单一系统有关。为了区分这三种观点，该项目将重点放在语言上的一个简单区别：过去时和语言其他方面的规则和不规则转换之间的区别。在这一区别中，词汇和语法可以进行对比，而其他心理相关因素保持不变。不规则变换至少部分是任意的(例如，唱和、带来)，因此必须依赖于记忆，而规则变换是可预测的(例如，动词+-ed)，因此可以通过语法规则来计算。因此，在非规则(词汇)、事实和颞叶回路之间，以及在正规(语法)、技能和额叶/基底节回路之间，可以预测出联系。大脑损伤局限于特定的颞叶区域的患者(例如，后部失语症)应该更多地与非正规患者打交道，而不是与事实打交道，而不是与技能打交道。仅限于特定左额/基底节结构受损的患者(如“前部失语症”)应该表现出相反的模式。如果陈述性和程序性记忆系统确实在词汇和语法中发挥作用，那么来自人类和动物这两个大脑记忆系统的神经、计算和发展基础的大量研究数据将有助于我们对语言的理解。相反，基于我们对语言结构、处理和习得的知识，研究这两种记忆系统的新方法将成为可能。对词汇和语法的测试，例如在拟议的项目中使用的测试，可能会成为这两个大脑系统的有用探测器。除了认知科学基础知识的进步外，动物和人类对这两个大脑系统的研究对我们理解语言的贡献应该会为后天和发育性语言障碍的诊断和治疗带来新的临床方法。

Human language depends upon a dictionary of words (the mental lexicon) and rules which specify how those words are put together into larger words, phrases, and sentences (the mental grammar). The computational and brain bases of these two fundamental language capacities are still not well understood. This project investigates the novel view that the learning and use of the two language capacities depends upon two more general-purpose memory systems whose neural foundations are relatively well studied. Specifically, it is hypothesized that the acquisition and use of words depends upon "declarative memory" temporal-lobe brain circuits previously shown to underlie the learning and use of fact knowledge, such as what a zebra is and where it lives. It is also hypothesized that the acquisition and use of grammatical rules depends upon "procedural memory" left frontal/basal-ganglia brain circuits previously shown to underlie the learning and expression of motor and cognitive "skills," such as riding a bicycle. On this "declarative/procedural" view of language, lexicon and grammar are linked to distinct general-purpose systems, each responsible for a particular set of language and non-language functions. The declarative/procedural view contrasts with the two main classes of previously proposed theories regarding the computational and neural mechanisms of language. It shares the perspective of traditional "dual-system" theories that lexicon and grammar depend upon distinct systems, but it diverges from their claim that these systems are responsible for language alone. Conversely, while the declarative/procedural view agrees with "single-system" theories that the two language capacities depend upon general-purpose brain circuitry, it diverges from their claim that both capacities are linked to a single system with a broad distribution in the brain. To distinguish the three views, the project will focus on a simple distinction in language: between regular and irregular transformations in past tense and in other aspects of language. In this distinction lexicon and grammar can be contrasted, while other psychologically relevant factors are held constant. Irregular transformations are at least partially arbitrary (e.g., sing-sang, bring-brought), and therefore must depend upon memory, whereas regular transformations are predictable (e.g., verb + -ed), and so could be computed by a grammatical rule. Thus links are predicted among irregulars (lexicon), facts, and temporal-lobe circuits, and among regulars (grammar), skills, and frontal/basal-ganglia circuits. Patients with brain damage limited to particular temporal-lobe areas (e.g., "posterior aphasics") should have more trouble with irregulars than regulars, and with facts than skills. Patients with damage limited to particular left frontal/basal-ganglia structures (e.g., "anterior aphasics") should show the opposite pattern. If indeed the declarative and procedural memory systems play a role in lexicon and grammar, then data from numerous investigations of the neural, computational, and developmental underpinnings of the two brain memory systems in humans and in animals will contribute to our understanding of language. Conversely, new approaches to the study of the two memory systems will become possible on the basis of our knowledge of language structure, processing, and acquisition. Tests of lexicon and grammar, such as those used in the proposed project, may become useful probes of the two brain systems. In addition to the advancement of fundamental knowledge in cognitive science, the contributions of animal and human studies of the two brain systems to our understanding of language should lead to new clinical approaches for the diagnosis and treatment of acquired and developmental language disorders.