Event-related brain potentials to grammatical errors and semantic anomalies

MARTA KUTAS 0 1 STEVEN A. HILLYARD 0 1 0 This research was supported by NSF Grant BNS80-05525 and Sloan Foundation Grant BI980-35. M. Kutas is sup ported by Research Scientist Development Award USPHS IK02MH0322!03. Thanks go to J. C. Phillips for technical as sistance and to J. C. Hansen for providing compu ter programs for data reduction and analyses. The author's mailing address is Department of Neurosciences, University of California at San Diego , La Jolla, California 92093 1 University of California at San Diego , La Jolla, California Event-related brain potentials (ERPs) were recorded while subjects silently read several prose passages, presented one word at a time. Semantic anomalies and various grammatical errors had been inserted unpredictably at different serial positions within some of the sentences. The semantically inappropriate words elicited a large N400 component in the ERP, whereas the grammatical errors were associated with smaller and less consistent components that had scalp distributions different from that of the N400. This result adds to the evidence that the N400 wave is more closely related to semantic than to grammatical processing. Additional analyses revealed that different ERP configurations were elicited by open-class ("content") and closedclass ("function") words in these prose passages. - monitoring and mispronunciation-detection tasks (Cole & Jakirnik, 1978, 1980; Marslen-Wilson & Tyler, 1980; Tyler & Marslen-Wilson, 1981). During reading, de pendent measures such as fixation or gaze durations (Ehrlich & Rayner, 1981; Just & Carpenter, 1980; McConkie, Zola, Blanchard, & Wolverton, 1982), number of regressive eye movements (Carpenter & Daneman, 1981 ; Carpenter & Just, 1981), and number and type of oral reading errors (Danks & Hill, 1981; Jacobson, 1973; Danks, Fears, Bohn, & Hill, Note 1) are likewise sensitive to deviations from context. It is clear that the buildup of linguistic expectancies and the specialized processing that is accorded out-of-context words are important factors in language comprehension. The role of contextual factors in language can also be investigated through scalp recordings of the electrical activity that is elicited in the brain by word presenta tions. This approach sterns from fmdings that several of the longer latency components of the event-related brain potentials (ERPs) are markedly sensitive to varia tions in stimulus expectancy for both verbal and non verbal material (reviewed in Donchin, Ritter, & McCallum, 1978, and Pritchard, 1981). In particular, a late positive wave elicited 300-500 msec after relevant but unpredictable stimuli (the P3 or P300 component) is augmented in amplitude for increasingly improbable or unexpected stimuli. The making of lexical or semantic decisions about unpredictable words is associated with late positive ERPs in a variety of circumstances (Friedman, Simson, Ritter, & Rapin, 1975; Kutas, McCarthy, & Donchin, 1977; Polich, Vanasse, & Donchin, 1981;Shelbume, 1972). Over the past several years we have recorded ERPs associated with the violation of semantic expectancies during a reading task in which grammatically simple sentences were presented one word at a time (Kutas & Hillyard, 1980a, 1980b, 1980c, 1982, in press; Kutas, Lindamood, & Hillyard, in press). The ERPs to the final words in the sentence were distinctly different according to whether the word completed the sentence in an appropriate, meaningful way or whether it was semantically anomalous to the preceding context. The ERPs following appropriate words showed a broad positive shift, which appeared to consist primarily of the resolution of a prior contingent negative variation (CNY), whereas the semantically incongruous words elicited an additional negativity peaking at around 400 msec over the posterior scalp (the N400). Control experiments showed that physically deviant stimuli such as words presented in boldface type (Kutas & Hillyard, 1980a, 1980b) or complex colorful pictures presented at the ends of these sentences (Kutas & Hillyard, in press) elicited late positive components of the P300 variety rather than a negative-going N400 component. Kutas and Hillyard (I980c) suggested that the N400 might be a physiological sign of the reader's continued processing of an unexpected semantic violation in attempt to arrive at a meaningful interpretation of the sentence. The present study was aimed at investigating whether the N400 effect is specific to semantically deviant words or whether it is elicited by a broader class of unexpected words, in particular, words that are gram matically incorrect. Several types of grammatical errors were chosen for study on the basis of their being im mediately evident upon presentation and yet preserving the meanings of the sentences in which they were em bedded. These violations consisted primarily of errors in word-boundary morphemes that designated either word number (singular vs. plural) or verb tense (past vs. present). If the N400 is associated specifically with semantically inappropriate words, then we would not expect grammatical errors to yield an N400. On the other hand, if the N400 is associated with violations of linguistic relationships at any level, it should be present for both types of deviant words. Another experimental goal was to determine whether the N400 could be elicited in a more natural reading situation. In our previous studies of this ERP, all the sentences used were seven words in length, successive sentences were unrelated to one another, and the se mantic anomalies were restricted to the terminal posi tion. The present experiment presented prose passages consisting of variable-length sentences, each passage dealing with a single topic. Semantic and grammatical anomalies occurred unpredictably at different serial positions within the sentences. The presence of semantic incongruities at inter mediate positions within sentences allowed tests of specific hypotheses about the relationship of the N400 effect to other types of ERPs. One possibility is that the N400 is simply a continuation of the CNY-like nega tivity that develops over the course of a sentence (Kutas & Hillyard, 1980c); following the anomalous word, the subject may be anticipating a further word that will better complete the sentence or resolve the ambiguity, and this expectation could prolong the CNV. In this view, the N400 could be seen as either an extension of the CNV or a postimperative negative variation (PINV) that follows the CNV under certain circumstances. The incongruities that occur at intermediate sentence posi tions test for the presence of the N400 effect without the confound of CNV extension and/or resolution effects that may follow terminal words. The intermediate semantic anomalies can also be used to examine the proposal that the N400 in the sentence reading task is actually the initial negative phase of a delayed N200-P300 complex (Polich et aI., 1981; Ritter, Ford, (...truncated)