Variation in the latencies and amplitudes of N400 and NA as a function of semantic priming

The purpose of this study was to determine whether the latencies of two event-related potential (ERP) components, the NA and N400, were sensitive to semantic priming. Subjects performed a semantic judgment task, which was designed in such a way that the N400 could be examined without overlap from the P3. Priming effects on the latencies of both NA and N400 were most apparent at frontocentral sites. The amplitude of NA was not significantly affected by priming. The amplitude of N400 was smaller for primed than for unprimed words, but the effect was significant only at centroposterior sites. Current source density (CSD) analyses performed on the ERP data suggested the activation of multiple generators in the N400 time region. The ERP and CSD data were consistent with the existence of two types of N400, a frontal N400 that varies in latency as a function of semantic priming, and a posterior N400 that varies in amplitude.     

The N400 as a function of the level of processing

In a semantic priming paradigm, the effects of different levels of processing on the N400 were assessed by changing the task demands. In the lexical decision task, subjects had to discriminate between words and nonwords and in the physical task, subjects had to discriminate between uppercase and lowercase letters. The proportion of related versus unrelated word pairs differed between conditions. A lexicality test on reaction times demonstrated that the physical task was performed nonlexically. Moreover, a semantic priming reaction time effect was obtained only in the lexical decision task. The level of processing clearly affected the event-related potentials. An N400 priming effect was only observed in the lexical decision task. In contrast, in the physical task a P300 effect was observed for either related or unrelated targets, depending on their frequency of occurrence. Taken together, the results indicate that an N400 priming effect is only evoked when the task performance induces the semantic aspects of words to become part of an episodic trace of the stimulus event.     

Cross‐modal symbolic processing can elicit either an N2 or a protracted N2/N400 response

A cross‐modal symbolic paradigm was used to elicit EEG activity related to semantic incongruence. Twenty‐five undergraduate students viewed pairings of visual lexical cues (e.g., DOG) with congruent (50% of trials) or incongruent (50%) auditory nonlexical stimuli (animal vocalizations; e.g., sound of a dog woofing or a cat meowing). In one condition, many different pairs of congruent/incongruent stimuli were shown, whereas in a second condition only two pairs of stimuli were repeatedly shown. A typical N400‐like pattern of incongruence‐related activity (including activity in the N2 time window) was evident in the condition using many stimuli, whereas the incongruence‐related activity in the two‐stimuli condition was confined to differential N2‐like activity. A supplementary analysis excluded stimulus characteristics as the source of this differential activity between conditions. We found that a single individual performing a fixed task can demonstrate either a protracted N400‐like pattern of activity or a more temporally focused N2‐like pattern of activity in response to the same stimulus, which suggests that the N2 may be a precursor to the protracted N400 response.     

Association and not semantic relationships elicit the N400 effect: electrophysiological evidence from an explicit language comprehension task

Language comprehension studies have identified the N400, an event-related potential (ERP) correlate of the processing of meaning, modulation of which is typically assumed to reflect the activation of semantic information. However, N400 studies of conscious language processing have not clearly distinguished between meaning derived from a semantic relationship and meaning extracted through association. We independently manipulated the presence of associative and semantic relationships while examining the N400 effect. Participants were asked to read and remember visually presented word pairs that shared an association ( traffic – jam ), an association+semantic relationship ( lemon – orange ), a semantic relationship alone ( cereal – bread ), or were unrelated ( beard – tower ). Modulation of the N400 (relative to unrelated word pairs) was observed for association and association+semantic word pairs but not for those that only shared a semantic relationship.     

单个汉字结尾笔画事件相关电位N400的研究

目的通过分别研究单个简单汉字结尾笔画匹配与非匹配以及单个复杂汉字结尾笔画联想正确与联想错误事件相关电位N400的变化，探讨正常人单个汉字结尾笔画事件相关电位N400的特征。方法对10名23岁．26岁右利手健康受试者，分别进行单个简单汉字结尾笔画匹配与非匹配的ERP实验，以及单个复杂汉字联想正确与联想错误的ERP实验。结果无论是单个简单汉字结尾笔画非匹配时还是单个复杂汉字联想错误时均可以诱发出波形较宽大而且走向明显向负的N400，其波幅均在中央顶部偏高，但两实验的诱发电位也有明显的差别。结论单个简单汉字结尾笔画匹配与非匹配的N400以及单个复杂汉字结尾笔画联想正确与联想错误的N400与字词认知中的语义密切相关，而且作为象形文字的汉字与作为拼音文字的西文在认知过程中存在差异。     

Semantic priming and stimulus degradation: Implications for the role of the N400 in language processing

Two experiments explored the effects of stimulus degradation on behavioral and event-related potential (ERP) measures of semantic priming. The primary goal was to help elucidate the psychological processes that underlie the N400 component. In both experiments, subjects made speeded lexical decisions to words and pseudowords preceded by either semantically related or unrelated prime words. In one block of trials, the target stimuli were intact, and in a second block they were degraded by removing a random 33% of the elements making up each letter of the target (Experiment 1) or by overlaying a matrix of dots on the target (Experiment 2). In both experiments, subjects responded faster and more accurately to related targets than to unrelated targets (behavioral semantic priming effect), and this priming effect was greater when the target was degraded. However, although the N400 component was larger for unrelated than related targets (ERP semantic priming effect), there was no evidence that this difference was larger in the degraded block of either experiment. These results indicate that the behavioral and ERP measures reported here appear to be tapping into different components of the process(es) involved in semantic priming. The implication of the results for the linguistic processes underlying the N400 are discussed.     

Missed prime words within the attentional blink evoke an N400 semantic priming effect

When subjects identified a target among distractors in a rapid serial visual presentation task, the detection of a subsequent target is impaired (attentional blink). By measuring event-related potentials (ERPs) we investigated if the processing of an unidentified prime word elicits the N400 semantic priming effect. Subjects (N = 12) had to identify three target words among distractors in a rapid serial visual presentation task. We varied the association strength between a prime (second target) and a probe (third target). The detection of the prime was impaired. Missed primes did not elicit a P300, indicating that they were not explicitly recognized. Despite this difference between recognized and missed primes, the N400 effect was present in both cases. This result suggests that automatic spread of activation (ASA) can be evoked by missed primes within the attentional blink. It furthermore demonstrates that ASA is sufficient to evoke the N400 effect.     

The Relationship Between N2 and N400: Scalp Distribution, Stimulus Probability, and Task Relevance

The N2 and N400 components of the event-related brain potential were compared along several dimensions. In one task, subjects discriminated on the basis of size, and in another task, subjects discriminated on the basis of semantic category. In one set of conditions stimuli deviated infrequently along one stimulus dimension (either in size or semantic category) and in another set of conditions stimuli deviated infrequently along two stimulus dimensions (both size and semantic category). When subjects discriminated on the basis of size, infrequent deviation in the size of the stimuli was associated with a negativity that peaked around 320 ms (N2). When subjects discriminated on the basis of semantic category, infrequent deviation in the semantic category of the stimuli was associated with a negativity that peaked around 400 ms (N400). N2 and N400 were found to be generally alike in scalp distribution, hemispheric asymmetry, and sensitivity to stimulus probability. N2 was not elicited when size changes were task irrelevant and N400 was not elicited when changes in semantic category were task irrelevant.     

The N400 as a snapshot of interactive processing: Evidence from regression analyses of orthographic neighbor and lexical associate effects

Linking print with meaning tends to be divided into subprocesses, such as recognition of an input's lexical entry and subsequent access of semantics. However, recent results suggest that the set of semantic features activated by an input is broader than implied by a view wherein access serially follows recognition. EEG was collected from participants who viewed items varying in number and frequency of both orthographic neighbors and lexical associates. Regression analysis of single item ERPs replicated past findings, showing that N400 amplitudes are greater for items with more neighbors, and further revealed that N400 amplitudes increase for items with more lexical associates and with higher frequency neighbors or associates. Together, the data suggest that in the N400 time window semantic features of items broadly related to inputs are active, consistent with models in which semantic access takes place in parallel with stimulus recognition.     

The N400 and the P300 are not all that independent

This study assessed whether two ERP components that are elicited by unexpected events interact. The conditions that are known to elicit the N400 and the P300 ERP components were applied separately and in combination to terminal-words in sentences. Each sentence ended with a terminal-word that was highly expected, semantically unexpected, physically deviant, or both semantically unexpected and physically deviant. In addition, we varied the level of semantic relatedness between the unexpected terminal-words and the expected exemplars. Physically deviant words elicited a P300, whereas semantically unexpected words elicited an N400, whose amplitude was sensitive to the level of semantic relatedness. Words that were both semantically unexpected and physically deviant elicited both an N400 with enhanced amplitude, and a P300 with reduced amplitude. These results suggest an interaction between the processes manifested by the two components.     

Electrophysiological evidence of interaction between contextual expectation and semantic integration during the processing of collocations

Despite the potentially infinite creativity of language, many words are patterned in ordered strings called collocations. Final words of these clusters are highly predictable; in addition, their overall meaning can vary on the literality dimension, ranging from (figurative) idiomatic strings to literal strings. These structures thus offer a natural linguistic scenario to contrast ERP correlates of contextual expectation and semantic integration processes during comprehension. In this study, expected endings elicited a positive peak around 300 ms compared to less expected synonyms, suggesting that the earlier recognition of the string leads to the specific pre-activation of the lexical items that conclude the expression. On the other hand, meaning variations of these fixed strings (either a literal or a figurative whole meaning) affected ERPs only around 400 ms, i.e. in the frontal portion of the N400. These findings are discussed within a more general cognitive framework as outlined in Kok's (2001) dual categorization model.     

Repetition and semantic priming of nonwords: implications for theories of N400 and word recognition

ERPs were elicited by two types of orthographically legal, pronounceable nonwords. One nonword set was derived from and resembled real words, whereas the other set did not. Nonwords derived from related root words elicited N400 semantic priming effects similar to those obtained for words, indicating semantic activation of the root words. N400 repetition priming effects from nonderived nonwords were similar to those obtained for words. The elicitation of N400 by only derived nonwords would have suggested it was generated by the activation of word meanings, per se. However, both types of nonwords produced an N400, and an N400 priming effect. Because nonderived nonwords are not associated with meaning, the N400 cannot be generated by semantic activation per se. Rather, the N400 appears to be generated by orthographic/phonological analysis and is attenuated by the top-down feed of semantic information to the orthographic/phonological level.     

N400-effects to task-irrelevant environmental sounds: further evidence for obligatory conceptual processing

We assessed conceptual priming for environmental sounds in two tasks using pairs of a visually presented word (prime) and an environmental sound (probe). In the physical task, participants indicated to which ear the sound was presented. In the semantic task, participants judged whether a word labeled a sound correctly. The physical always preceded the semantic task to exclude semantic carry-over effects. In both tasks prime word color indicated whether a response was required (Go/NoGo-trials). An N400-effect for unrelated vs. related sounds was observed in all four conditions resulting from the combination of both tasks with response requirement. However, the N400-effect was reduced in the physical task and in NoGo-trials. Hence, meaning of environmental sounds may be processed obligatorily. Both automatic and controlled processes mediate the analysis of sound meaning.     

Comparing arithmetic and semantic fact retrieval: effects of problem size and sentence constraint on event-related brain potentials

Event-related potentials were recorded with 61 electrodes from 16 students who verified either the correctness of single-digit multiplication problems or the semantic congruency of sentences. Multiplication problems varied in size and sentence fragments in constraint. Both semantic and arithmetic incongruencies evoked a typical N400 with a clear parieto-central maximum. In addition, numerically larger problems (8x7), in comparison to smaller problems (3x2), evoked a negativity starting at about 360 ms whose maximum was located over the right temporal-parietal scalp. These results indicate that the arithmetic incongruency and the problem-size effect are functionally distinct. It is suggested that the arithmetic and the semantic incongruency effects are both functionally related to a context-dependent spread of activation in specialized associative networks, whereas the arithmetic problem-size effect is due to rechecking routines that go beyond basic fact retrieval.     

Event‐related potential N270 delayed and enhanced by the conjunction of relevant and irrelevant perceptual mismatch

Event‐related potential studies using delayed match‐to‐sample tasks have demonstrated the presence of two components, N270 and N400, possibly reflecting the sequential processing of multiple sources of endogenous mismatch. To date, studies have only investigated mismatch between a single cue and target. In this study, we used distractor stimuli to investigate the effect of a secondary source of mismatch distinct from the task‐relevant stimulus. Subjects performed two paradigms in which the cue and target could match or mismatch. In one paradigm, task‐irrelevant distractors were added—producing a source of task‐irrelevant perceptual mismatch. A mismatch‐triggered negativity was elicited in both paradigms, but was delayed and enhanced in magnitude in the distractors present paradigm. It is suggested that the distractors may differentially affect mismatch responses through the generation of a task‐irrelevant mismatch response.     

Semantic processing in comatose patients with intact temporal lobes as reflected by the N400 event-related potential

The present study aimed at determining whether the N400 effect (an ERP index of semantic processing) for spoken words occurs in comatose patients. The patients, treated in an intensive care unit, scored less than 8 points in the glasgow coma score at the time of the recording. Semantically related and unrelated spoken word pairs were delivered to patients through headphones at a rate of 1/3 s. Patients with an intact temporal lobe exhibited differential N400-like responses for semantically related and unrelated word pairs, which suggests that word semantics can be processed even in the comatose state. In contrast, patients with an injured temporal lobe showed no such effect.     

The N400-concreteness effect reflects the retrieval of semantic information during the preparation of meaningful actions

The present ERP study investigated when and how action semantics, i.e. the conceptual knowledge that we acquired over the course of our lives, is activated during the preparation of object-directed actions. Subjects were required to grasp one of two objects and were implicitly instructed to either perform a meaningful action (e.g. moving a cup towards the mouth) or a meaningless action with the object (e.g. moving a cup towards the eye). A larger anterior N400 was found for the preparation of meaningful compared to meaningless actions, likely reflecting the retrieval of action semantic information in case a meaningful action was required with the object. The distribution and the latency of the anterior N400-effect were strongly related to standard N400-repetition effects, thereby further corroborating the semantic nature of the effect. In sum, the present study provides new insight in the neural and temporal dynamics underlying semantics for action.     

N400/frontal negativity reveals the controlled processes of taxonomic and thematic relationships in semantic priming for artifacts

Recent studies show that taxonomic and thematic relationships are functionally and neurologically dissociated; however, there remain some discrepancies due to inconsistencies in definitions, task properties, and concept domains. This issue was further explored via the semantic priming paradigm with a long SOA of 600 ms while controlling for perceptual or functional features of artifacts involved across taxonomic and thematic relationships. Six conditions were compared: perceptual relationship (axe–helve), functional relationship (axe–wood), perceptual classification (axe–hammer), functional classification (axe–saw), unrelated condition (axe–skates), and nonword (axe–derf) conditions. Behavioral priming effects are found for all related conditions relative to unrelated conditions except for perceptual relationships, whereas semantic priming effects (smaller N400 amplitude) are found for functional relationships and perceptual classification relative to unrelated conditions but not for perceptual relationships and functional classification, indicating perceptual features are less important than functional features for artifacts. Furthermore, the frontal negativity elicited by functional relationships is smaller than all other related conditions at 400–550 ms, while it is only smaller than functional classification at 550–650 ms. These results indicate that, besides different features, taxonomic and thematic relationships are dissociated to organize object knowledge, which is primarily fuelled by feature processing, with taxonomic, or thematic, relationships further embedded with such sensory, or functional, features.     

Event-related brain potential study of expectancy and semantic matching in schizotypy

Priming studies have revealed semantic processing abnormalities in subjects that display high schizotypal traits. The objective of the present study was to further elucidate the contribution of predictive (expectancy) and integrative (semantic matching) context processing to the semantic deficit described in schizotypy. Thirty-six participants were assigned into high or low schizotypy groups according to their score on the Schizotypal Personality Questionnaire (SPQ), and event-related brain potentials were recorded while these individuals performed semantic judgments based on asymmetrically associated word pairs. Viewed in one direction (forward), the target was highly predictable from the prime, whereas in the backward direction, the prime-to-target association was weak. It was assumed that the forward condition would be dependent on expectancy generation, while the backward condition would rely on semantic matching. In the low-SPQ group, forward and backward related words evoked a reduced (less negative) N400 amplitude compared to unrelated words, resulting in a significant forward and backward N400 priming effect, respectively. By contrast, only forward related words were facilitated in the high-SPQ group, resulting in significant forward priming and a lack of backward priming. Furthermore, the N400 amplitude for forward related words was less negative within the high-SPQ group in comparison to the low-SPQ group, which indicated easier semantic access to predictable words for high-SPQ individuals. Therefore, schizotypy may be associated with an imbalance in the use of predictive and integrative context processing strategies, namely preserved, if not overallocated, expectancy generation along with altered integration of unpredictable words due to semantic matching deficit.     

N400 involvement in the processing of action sequences

Understanding others’ sequences of action is a fundamental aspect of human movement and is the key to detecting goal directed behavior and intentional actions. Human action contains semantic information whereby logical chains of events are entirely dependent on the sequence in which they are performed. The sequential nature of action ensures that an observing individual anticipates the conclusion of a viewed action. This experiment reports on the results of 15 participants who viewed videos of an actress performing actions. Half the stimuli contained an anticipated conclusion to the action whereas half did not. Results from the passive viewing of stimuli depicting eating actions indicated an increased N400 response over frontal, central and parietal regions when viewing the unanticipated conclusions of the actions as compared with the amplitude for the anticipated condition. These results show that (1) neural systems exist to rapidly discern semantic information in actions, and (2) the N400 component, which predicts semantic information in language, also anticipates information within goal directed action.