OSU Working Papers in Linguistics 47, 1-19 Discriminating Between Syntactic and Semantic Processing: Evidence from Event-related Potentials

By measuring the event-related brain potentials (ERPs) elicited during a visual word-by-word presentation of sentences containing either a syntactic incongruity, semantic incongruity, or a combined syntactic and semantic incongruity, I investigated whether the N400 and P600 waveforms are discrete components reflective of independent semantic and syntactic processing or simply sub-parts of a larger wave caused by general sentential processing difficulty. Words that were syntactically inconsistent with the sentence structure elicited a P600 potential, while words that were semantically inconsistent elicited an N400 potential. Words that caused both a syntactic and semantic violation of the sentence in which they appeared evoked both a P600 and an N400 waveform. The results support the hypothesis that the N400 and P600 are independent waveforms, suggesting that the brain is capable of responding specifically to anomalies at both the syntactic and semantic levels. These findings are used to evaluate the functionality of three currently popular descriptions of the relationship between the syntactic and semantic levels of the human language processor. 1This research was made possible through funding provided by the Ohio State University Center for Cognitive Science, lhe Department of Psychology, and the Department of Linguistics. My appreciation is extended to my collaborators, Dr. Harvey Shulman and Dr. Julie Boland, for their guidance and support during this project, and to Dr. Peter Culicover for his comments and suggestions on earlier drafts of this paper. Thanks also to Rob Tigner, Christina Pencheff, Karen West, Maria Miles, and Angie Wascovich for their assistance in collecting and analyzing the data. All errorS are mine. Questions should be sent via electronic mail to damcllk@ling.ohio-state.edu. 2 KIM AINSWORTH-DARNELL Language comprehension is an intricate process, involving the evolution of a linguistic stimulus from a string of phonological or orthographic code into coherent, hierarchical structure that can be interpreted in terms of stored lexical and pragmatic knowledge. Developing a clear blueprint of the mechanisms that allow this process to talce place has been a focus of psycholinguistic research for decades. In particular, there has been substantial debate concerning the relationships between the various levels of processing that compose the language comprehension system. Do the mechanisms that extract the different levels of linguistic representation from the stimulus act in isolation from one another? Or are the processing tiers interconnected, influencing one another during the application of their respective operations? Essentially, . the· debate concerning the architecture of the. language processor concerns the sequence in which processes . from different levels cooperate. According to the serial autonomous view, language comprehension is strictly a bottom-up process, with processes at each level of representation operating in turn. The output of a lower level process serves as the input for the next level of computations. Word recognition processes, for example, generate the mental representations necessary for syntactic rules to be applied. Interactive views, on the other hand, hold that different kinds of linguistic knowledge can be applied simultaneously. Contextual information, then, might be used to guide the development of sentential structure by helping to select the syntactic rules that should be applied to a given string. The distinction between computationally autonomous, or modular, processes as in Fodor (I 983) and non-modular, or interactive, processes has played a key role in this debate. Within the literature on sentence processing, most"ofthe focus has been on the syntactic level and the question of whether it is computationally independent from other parts of the grammar. Syntactic processing is a reasonable candidate for a modular process because the development of sentential structure could take place within. a singular and narrowly defineddomain. This is how Fodor (1983) defined peripheral processes. Peripheral processes are special purpose routines for inputting and outputting information. They can be distinguished from central processes like problem-solving and reasoning, which are general purpose cognitive processes, and therefore would not be computationally autonomous. The semantic level of processing, where. meaning is determined, is seen as more central to human cognition, and thus less likely to be purely linguistic (Fodor, 1983). Functionally, an autonomous syntax module in the language processor results in . an architecture like that shown in Figure I. Here, hierarchical structure is applied to incoming lexical information without recourse to contextual or pragmatic · knowledge; thematic roles and word meanings are considered separately from structural function. 3 DISCRIMINATING BBTWBEN SYNTACTIC AND SEMANTIC PROCESSING