Influences of semantic and syntactic context on open- and closed-class words

CYMA VAN PETTEN 0 MARTA KUTAS 0 0 University of California , San Diego, La Jolla, California Event-related potentials (ERPs) were recorded as subjects read semantically meaningful, syntactically legal but nonsensical and random word strings. The constraints imposed by formal sentence structure alone did not reduce the amplitude of the N400 component elicited by open-class words, whereas semantic constraints did. Semantic constraints also eliminated the word-frequency effect of a larger N400 for low-frequency words. Responses to closed-class words exhibited reduced N400 amplitudes in syntactic and congruent sentences, indicating that formal sentence structure placed greater restrictions on closed-class words than it did on open-class words. However, unlike the open-class results, the impact of sentence context on closed-class words was stable across word positions, suggesting that these syntactic constraints were applied only locally. A second ERP component, distinct from the N400, was elicited primarily by congruent closed-class words. - Much experimental effort has been devoted to demon strating that people are faster at identifying (or require less sensory information to identify) words that occur in an informative context than they are at identifying words that do not. In natural discourse, readers and listeners have several theoretically distinct sources of information that they may use in the transformation of a visual or acoustic signal into a meaningful representation. These include as sociations between individual words in long-term mem ory, semantic information derived from larger chunks of the ongoing discourse or real-world knowledge, syntac tic restrictions provided by the grammar of the language, the overall probability of occurrence of particular words based on their frequency of usage in the reader's/listener's experience with the language, and pragmatic cues. Psy cholinguistic research has attempted to describe how each source of information is used, addressing such questions as whether different cues are utilized serially or in parallel, whether they are allowed to interact or are kept distinct until a relatively late stage of processing, whether each type of information is applied to all words or only a subset, and whether or not different sources of information or vocabulary types are interpreted by distinct neural circuits. In the present experiment, we examined the impact of three potentially informative cues for the processing of A brief report of this study was presented at the 28th annual meeting of the Society for Psychophysiological Research, in October 1988. We are grateful to Jon Hansen for software support, to Jeff Elman. Liz Bates. Robert Proctor, and two anonymous reviewers for commenting on an earlier version of the paper, to Cathy Harris for helpful discussions, and to Steve Hillyard for making his facilities available for preparation of the manuscript. The work was supported by NSF Grant BNS83-00243 and NICHD Grant HD 22614. C. Van Petten was supported by an NSF graduate fellowship. M. Kutas was supported by Research Career De velopment Award MH 00322 from NIH. Correspondence should be ad dressed to Cyma Van Petten, Department of Psychology, University of Arizona, Tucson, AZ 85721. words in sentences: semantic context, syntactic context, and word frequency. In the analysis of contextual in fluences, open- and closed-class words were considered separately; the effect of frequency was evaluated only for open-class words. Our dependent measure was the event related brain potential (ERP) recorded as subjects read visually presented words. This physiological measure al lows the possibility of detecting qualitative differences in the ways in which people use different sources of infor mation to process individual words and the extent to which these may differ for the processing of open- and closed class words. The ERP, formed by averaging time segments of the electroencephalogram following similar stimuli, is typi cally decomposed into "components" based on the differential responsiveness of particular epochs of the waveform to different experimental manipulations. The first 150 msec (approximately) of the ERP response is primarily determined by the sensory characteristics of a stimulus (e.g., size, luminance, loudness, pitch, etc.), although selective attention can enhance these early com ponents (for recent reviews, see Hillyard, Woldorff, Man gun, & Hansen, 1987; Mangun & Hillyard, 1990). In con trast, later components of the ERPs are sensitive to a broader range of cognitive activities (for reviews, see Hill yard & Kutas, 1983; Hillyard & Picton, 1987; Johnson, 1988; Kutas, 1988; Kutas & Van Petten, 1988). It is im portant to note, however, that variations in the amplitude or latency of different ERP components have been linked to different cognitive processes. The possibility thus ex ists of finding qualitatively distinct ERP signatures of semantic versus syntactic processing or of open- versus closed-class word recognition. In the analysis of the present data, we will devote par ticular attention to the N400 component of the ERP, be cause it has already proved responsive to manipulations of linguistic variables. Most of our knowledge of the factors governing N400 activity concerns semantic con straints in the processing of individual words, presented visually (as printed words or American Sign Language) or aurally (e.g., see Kutas, Neville, & Holcomb, 1987; Kutas & Van Petten, 1988; Neville, 1985; Neville, in press). Relatively little research has assessed the sensi tivity of the N400 to syntactic constraints. The demon stration of a brain response that is differentially sensitive to semantic and syntactic factors could lend supporting data from the normal population to an idea that has been prominent in the aphasia literature: specialized neural sys tems subserve semantic and syntactic analyses (e.g., Jakobson, 1956; Zurif, 1980). The evidence that the N400 is sensitive to semantic vari ables has come from two basic paradigms. The first con sists of substituting a semantically anomalous word into an otherwise coherent sentence or text and observing an increase in the amplitude of this potential relative to con gruent control words (for visual modality, see Kutas & Hillyard, 1980a, 1980b, 198Oc; for auditory modality, see Holcomb, 1985; Karniski, Vanderploeg, Diehl, & Lease, 1988; McCallum, Farmer, & Pocock, 1984; Neville, 1985). The second consists of increasing the degree of semantic context relevant to a congruous word and ob serving a decrease in N400 amplitude. This paradigm, when applied to the final words of visually presented sen tences, yielded an inverse correlation between cloze prob ability and N400 amplitude of up to 94% (Kutas & Hill yard, 1984; Kutas, Lindamood, & Hillyard, 1984). With regard to the relationship between the N400 and syntactic constraints, only the first type of paradigm with anomalous words has (...truncated)