Marta Kutas

Thirty Years and Counting: Finding Meaning in the N400 Component of the Event-Related Brain Potential (ERP)

We review the discovery, characterization, and evolving use of the N400, an event-related brain potential response linked to meaning processing. We describe the elicitation of N400s by an impressive range of stimulus types--including written, spoken, and signed words or pseudowords; drawings, photos, and videos of faces, objects, and actions; sounds; and mathematical symbols--and outline the sensitivity of N400 amplitude (as its latency is remarkably constant) to linguistic and nonlinguistic manipulations. We emphasize the effectiveness of the N400 as a dependent variable for examining almost every aspect of language processing and highlight its expanding use to probe semantic memory and to determine how the neurocognitive system dynamically and flexibly uses bottom-up and top-down information to make sense of the world. We conclude with different theories of the N400s functional significance and offer an N400-inspired reconceptualization of how meaning processing might unfold.

Expect the Unexpected: Event-related Brain Response to Morphosyntactic Violations

Arguments about the existence of language-specific neural systems and particularly arguments about the independence of syntactic and semantic processing have recently focused on differences between the event-related potentials (ERPs) elicited by violations of syntactic structure (e.g. the P600) and those elicited by violations of semantic expectancy (e.g. the N400). However, the scalp distribution of the P600 component elicited by syntactic violations appears to resemble that elicited by rare categorical events (ldquo;odd-balls”) in non-linguistic contexts, frequently termed the P3b. The relationship between the P600 and the P3b was explored by manipulating the grammaticality of sentences read for comprehension, as well as two factors known to influence P3b amplitude: odd-ball probability and event saliency. Oddball probability was manipulated by varying the frequency of morphosyntactic violations within blocks of sentences, and event saliency was manipulated by using two types of morphosyntactic violatio...

Event-related brain potentials to semantically inappropriate and surprisingly large words

Event-related brain potentials (ERPs) were recorded from young adult subjects as they silently read 160 different seven-word sentences, presented one work at a time. The sentences either ended normally or were completed by unexpected words that were either semantically inappropriate, physically deviant or both. These two types of deviations were associated with distinctly different ERP components - a late negative wave (N400) for semantic deviations and a late positive complex for physical deviations. A deviation along either one or these dimensions (semantic or physical) did not appear to alter the ERP effect of a concurrent deviation along the other. In addition, it was found that the ERPs elicited by the words during the reading condition were characterized by a left-greater-than-right asymmetry in a slow, positive component. This asymmetrical scalp distribution was most pronounced for right-handed subjects having not left-handers in their immediate family.

Event-related brain potentials to grammatical errors and semantic anomalies.

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 closed-class (“function”) words in these prose passages.

Interactions between sentence context and word frequency in event-related brain potentials

Event-related brain potentials (ERPs) were recorded as subjects silently read a set of unrelated sentences. The ERP responses elicited by open-class words were sorted according word frequency and the ordinal position of the eliciting word within its sentence. We observed a strong inverse correlation between sentence position and the amplitude of the N400 component of the ERP. In addition, we found that less frequent words were associated with larger N400s than were more frequent words, but only if theeliciting words occurred early in their respective sentences. We take this interaction between sentence position and word frequency as evidence that frequency does not play a mandatory role in wordrecognition, but can besuperseded by the contextual constraint provided by a sentence.

Who did what and when? using word-and clause-level erps to monitor working memory usage in reading

ERPs were recorded from 24 undergraduates as they read sentences known to differ in syntactic complexity and working memory requirements, namely Object and Subject Relative sentences. Both the single-word and multiword analyses revealed significant differences due to sentence type, while multiword ERPs also showed that sentence type effects differed for Good and Poor comprehenders. At the single-word level, ERPs to both verbs in Object Relative sentences showed a left anterior negativity between 300 and 500 msec postword-onset relative to those to Subject Relative verbs. At the multiword level, a slow frontal positivity characterized Subject Relative sentences, but was absent for Object Relatives. This slow positivity appears to index ease of processing or integration. and was more robust in Good than in Poor comprehenders.

Event-related brain potentials during initial encoding and recognition memory of congruous and incongruous words

Abstract Event-related brain potentials (ERPs) were recorded while subjects read statements followed by words that were either semantically congruous or incongruous with the preceding phrase, and during a subsequent recognition test. Congruous words yielded smaller N400s and better memory than did incongruous statements. In addition, the ERPs to correctly recognized old words were characterized by an enhanced late positivity (P650) relative to those elicited by correctly identified new words. A second experiment essentially replicated the results of the first. In addition, the amplitude of the late positive component (P650) elicited by final words on initial exposure was predictive of subsequent recognition; words that would be later recognized were associated with a larger P650 (whether they were incongruous or not) than were words that would not be recognized. These ERP data provide evidence that within 250 ms of the presentation of a congruous word and within 450 ms of an incongruous word, a significant portion of the brain processes which determine whether a word will or will not be recognized some time in the future have taken place.

Mass univariate analysis of event-related brain potentials/fields I: A critical tutorial review

Event-related potentials (ERPs) and magnetic fields (ERFs) are typically analyzed via ANOVAs on mean activity in a priori windows. Advances in computing power and statistics have produced an alternative, mass univariate analyses consisting of thousands of statistical tests and powerful corrections for multiple comparisons. Such analyses are most useful when one has little a priori knowledge of effect locations or latencies, and for delineating effect boundaries. Mass univariate analyses complement and, at times, obviate traditional analyses. Here we review this approach as applied to ERP/ERF data and four methods for multiple comparison correction: strong control of the familywise error rate (FWER) via permutation tests, weak control of FWER via cluster-based permutation tests, false discovery rate control, and control of the generalized FWER. We end with recommendations for their use and introduce free MATLAB software for their implementation.

Brain potentials during memory retrieval provide neurophysiological support for the distinction between conscious recollection and priming

Event-related brain potentials were recorded from subjects as they attempted to identify words displayed tachistoscopically. Words that had also been presented a few minutes earlier in a different context were identified more often than were words that had not been presented before. This priming effect was observed for words initially seen in an imagery task requiring size estimations as well as for words initially seen in an orthographic task requiring letter counting. Unlike priming, recall and recognition were much better for words repeated from the imagery task than from the orthographic task. Brain potentials elicited during word identification also differed as a function of task. Based on these differences, a potential from 500 to 800 msec was interpreted as an index of recollection processes. Earlier potentials may have indexed processing related to priming. These effects thus provide measures of the hypothetical processes underlying memory performance and demonstrate that recollection and priming are associated with distinct neural events.

Bridging the gap: Evidence from erps on the processing of unbounded dependencies

Since the early days of generative grammar, the study of unbounded dependencies such as wh-questions and relative clauses has occupied a central place in both syntactic theory and language processing research. The problem that such constructions pose is as follows. In a normal wh-question, a wh-phrase is typically displaced to the left periphery of a clause (What did you say to John?); this displaced constituent is often referred to as a filler. The vacant position (indicated in the previous example by a blank line) where it would ordinarily occur in an echo question (You said what to John?) is correspondingly referred to as a gap. Filler and gap are mutually dependent on each other since they share syntactic and semantic information essential for successful sentence interpretation. However, since sentence processing is a sequential operation, a filler cannot be assigned to its gap until some time after it has occurred. In other words, the filler must be held in working memory until such time as filler-gap assignment can take place. The intent of the research reported here was to examine the processing of unbounded dependencies in English as revealed in event-related brain potentials (ERPs). To this end, subjects were shown both grammatical and ungrammatical yes/no-questions (Did you say something to John?) and wh-questions. A number of comparisons made at various points in these questions showed that both the storage of a filler in working memory and its subsequent retrieval for filler-gap assignment were associated with an enhanced negativity between 300 and 500 msec poststimulus over left anterior sites. This effect of left anterior negativity (LAN) was independent of and orthogonal to the grammaticality of the eliciting condition. We show how this interpretation coincides with recent studies that demonstrate a correlation between left anterior negativity, working memory capacity, and successful language processing.