Federmeier K D, Segal J B, Lombrozo T, Kutas M
Departments of Cognitive Science and Neurosciences, University of California San Diego, La Jolla, California 92093-0515, USA.
Brain. 2000 Dec;123 Pt 12:2552-66. doi: 10.1093/brain/123.12.2552.
Recent neuropsychological and imaging data have implicated different brain networks in the processing of different word classes, nouns being linked primarily to posterior, visual object-processing regions and verbs to frontal, motor-processing areas. However, as most of these studies have examined words in isolation, the consequences of such anatomically based representational differences, if any, for the processing of these items in sentences remains unclear. Additionally, in some languages many words (e.g. 'drink') are class-ambiguous, i.e. they can play either role depending on context, and it is not yet known how the brain stores and uses information associated with such lexical items in context. We examined these issues by recording event-related potentials (ERPs) in response to unambiguous nouns (e.g. 'beer'), unambiguous verbs (e. g. 'eat'), class-ambiguous words and pseudowords used as nouns or verbs within two types of minimally contrastive sentence contexts: noun-predicting (e.g. 'John wanted THE [target] but.') and verb-predicting ('John wanted TO [target] but.'). Our results indicate that the nature of neural processing for nouns and verbs is a function of both the type of stimulus and the role it is playing. Even when the context completely specifies their role, word class-ambiguous items differ from unambiguous ones over frontal regions by approximately 150 ms. Moreover, whereas pseudowords elicit larger N400s when used as verbs than when used as nouns, unambiguous nouns and ambiguous words used as nouns elicit more frontocentral negativity than unambiguous verbs and ambiguous words used as verbs, respectively. Additionally, unambiguous verbs elicit a left-lateralized, anterior positivity (approximately 200 ms) not observed for any other stimulus type, though only when these items are used appropriately as verbs (i.e. in verb-predicting contexts). In summary, the pattern of neural activity observed in response to lexical items depends on their general probability of being a verb or a noun and on the particular role they are playing in any given sentence. This implicates more than a simple two-way distinction of the brain networks involved in their storage and processing. Experience, as well as context during on-line language processing, clearly shapes the neural representations of nouns and verbs, such that there is no single neural marker of word class. Our results further suggest that the presence and nature of the word class-based dissociations observed after brain damage are similarly likely to be a function of both the type of stimulus and the context in which it occurs, and thus must be assessed accordingly.
最近的神经心理学和影像学数据表明，不同的脑网络参与了不同词类的处理，名词主要与后部的视觉对象处理区域相关联，而动词则与额叶的运动处理区域相关。然而，由于这些研究大多是孤立地研究单词，这种基于解剖学的表征差异（如果有的话）对句子中这些词项处理的影响仍不清楚。此外，在一些语言中，许多单词（如“drink”）在词类上是模糊的，即它们可以根据上下文扮演任何一种角色，目前尚不清楚大脑如何在上下文中存储和使用与这些词汇相关的信息。我们通过记录事件相关电位（ERP）来研究这些问题，这些电位是对明确的名词（如“beer”）、明确的动词（如“eat”）、词类模糊的单词以及在两种最小对比句子语境中用作名词或动词的伪词的反应：名词预测（如“John wanted THE [目标词] but.”）和动词预测（“John wanted TO [目标词] but.”）。我们的结果表明，名词和动词的神经处理性质是刺激类型及其所扮演角色的函数。即使上下文完全确定了它们的角色，词类模糊的词项在额叶区域与明确的词项相比仍有大约150毫秒的差异。此外，虽然伪词用作动词时比用作名词时引发更大的N400，但明确的名词和用作名词的模糊词分别比明确的动词和用作动词的模糊词引发更多的额中央负波。此外，明确的动词会引发一种左半球偏侧化的前部正波（约200毫秒），其他任何刺激类型都未观察到这种情况，不过只有当这些词项被恰当地用作动词时（即在动词预测语境中）才会出现。总之，观察到的对词汇项的神经活动模式取决于它们作为动词或名词的总体概率以及它们在任何给定句子中所扮演的特定角色。这意味着参与其存储和处理的脑网络不仅仅是简单的二元区分。经验以及在线语言处理过程中的上下文显然塑造了名词和动词的神经表征，因此不存在单一的词类神经标记。我们的结果进一步表明，脑损伤后观察到的基于词类的分离的存在和性质同样可能是刺激类型及其出现的上下文的函数，因此必须相应地进行评估。
