Not all ambiguous words are created equal: An EEG investigation of homonymy and polysemy

Event-related potentials (ERPs) were used to investigate the time-course of meaning activation of different types of ambiguous words. Unbalanced homonymous ("pen"), balanced homonymous ("panel"), metaphorically polysemous ("lip"), and metonymically polysemous words ("rabbit") were used in a visual single-word priming delayed lexical decision task. The theoretical distinction between homonymy and polysemy was reflected in the N400 component. Homonymous words (balanced and unbalanced) showed effects of dominance/frequency with reduced N400 effects predominantly observed for dominant meanings. Polysemous words (metaphors and metonymies) showed effects of core meaning representation with both dominant and subordinate meanings showing reduced N400 effects. Furthermore, the division within polysemy, into metaphor and metonymy, was supported. Differences emerged in meaning activation patterns with the subordinate meanings of metaphor inducing differentially reduced N400 effects moving from left hemisphere electrode sites to right hemisphere electrode sites, potentially suggesting increased involvement of the right hemisphere in the processing of figurative meaning.     

Event-related potentials indicate context effect in reading ambiguous words

The aim of the study was a comparison of lexical and contextual factors in understanding ambiguous words in German. First, a sample of native speakers selected 56 words having maximally strong differences between a dominant and a subordinate meaning. After this, another sample from the same population was visually presented with sentences that activated dominant or subordinate meanings of the words and were accompanied by probes associated with dominant or subordinate meanings. This resulted in a crossed design with two factors: sentence dominant vs. sentence subordinate and probe dominant vs. probe subordinate. An analysis of event-related brain potentials revealed a large, long-lasting and highly-significant N400 wave whenever the meaning of the probe was incongruent with the meaning of the sentence and the lack of this wave whenever the two meanings were congruent. In the typical N400 space and time, the effect was independent of whether the lexical word meaning was dominant or subordinate. At other sites and times, however (e.g., at lateral frontal electrodes F7/F8, and after 700 ms), the congruence effect was significant after dominant sentences only. The data indicate that lexical factors have a rather limited influence on the activation of a particular meaning of ambiguous words. A strong context can virtually override even a very strong difference in the preference for different meanings.     

汉语同形歧义词歧义消解的两半球差异

实验探讨汉语同形歧义词(homographs)歧义消解的过程及大脑两半球的差异。被试为华中科技大学96名大学生,实验采用词汇判断任务。句子语境呈现在被试的视野中央,探测词在SOA(stimulus onset asynchronism)为100毫秒或400毫秒时呈现在左视野或右视野。结果发现,(1)当SOA为100毫秒时,在左视野(右半球)上,与语境一致的同形歧义词的主要意义得到激活,与语境不一致的次要意义也有一定程度的激活。在右视野(左半球)上,只有与语境一致的同形歧义词的主要意义得到激活。(2)当SOA为400毫秒时,在左、右视野(两半球)上,与语境一致的同形歧义词的主要意义和次要意义都得到激活。结果表明,大脑左半球对汉语歧义词的歧义消解具有一定的优势,语境敏感模型可以较好地解释本实验的结果。     

The effects of processing requirements on neurophysiological responses to spoken sentences

Ten English speaking subjects listened to sentences that varied in sentential constraint (i.e., the degree to which the context of a sentence predicts the final word of that sentence) and event-related potentials (ERPs) were recorded during the presentation of the final word of each sentence. In the Control condition subjects merely listened to the sentences. In the Orthographic processing condition subjects merely listened to the sentences. In the Orthographic processing condition subjects decided, following each sentence, whether a given letter had been present in the final word of the preceding sentence. In the Phonological processing condition the subjects judged whether a given speech sound was contained in the terminal word. In the Semantic processing condition subjects determined whether the final word was a member of a given semantic category. A previous finding in the visual modality that the N400 component was larger in amplitude for low constraint sentence terminations than for high was extended to the auditory modality. It was also found that the amplitude of a N200-like response was similarly responsive to contextual constraint. The hypothesis that N400 amplitude would vary significantly with the depth of processing of the terminal word was not supported by the data. The "N200" recorded in this language processing context showed the classic frontocentral distribution of the N200. The N400 to spoken sentences had a central/centroparietal distribution similar to the N400 in visual modality experiments. It is suggested that the N400 obtained in these sentence contexts reflects an automatic semantic processing of words that occurs even when semantic analysis is not required to complete a given task. The cooccurrence and topographical dissimilarity of the "N200" and N400 suggest that the N400 may not be a delayed or a generic N200.     

Global context effects on processing lexically ambiguous words: Evidence from eye fixations

Readers' eye movements were monitored as they read biased ambiguous target words in the context of a short paragraph. Two aspects of context were manipulated. The global context was presented in the topic sentence of the paragraph and instantiated either the dominant or the subordinate meaning of biased ambiguous target words (those with highly dominant meanings). Local contextual information either preceded or followed the target word and was always consistent with the subordinate interpretation. Consistent with prior research, we obtained a subordinate bias effect wherein readers looked longer at the ambiguous words than control words when the preceding context instantiated the subordinate meaning. More importantly, the magnitude of the subordinate bias effect was the same when global context alone, local context alone, or local and global context combined were consistent with the subordinate meaning of the ambiguous word. The results of this study indicate that global contextual information (1) has an immediate impact on lexical ambiguity resolution when no local disambiguating information is available, (2) has no additional effect when it is consistent with local information, but (3) does have a slightly delayed effect when inconsistent with local information.     

Using event-related potentials to examine hemispheric differences in semantic processing

Event-related potentials (ERPs) were used as the dependent measure in a divided visual field study examining the processing of lexically ambiguous words in the cerebral hemispheres. The goal was to determine if the N400 ERP component is sensitive measure of hemispheric differences in semantic processing. ERP waveforms were examined for lateralized target words that were related to either the dominant (MONEY) or subordinate (RIVER) meanings of ambiguous words (BANK). These waveforms were compared to trials where the prime-target pairs were unrelated. Reliable N400s, reflecting a significant difference between related and unrelated trials, were seen when targets were presented to the right visual field/left hemisphere. However, there were no N400s observed for either the dominant or subordinate conditions when targets were presented to the left visual field/right hemisphere.     

A comparison of sentence- and discourse-level semantic processing: an ERP study

Eighteen subjects listened to sentences ending with semantically congruent or incongruent words. Each congruent sentence was embedded at the end of a short story so that the final word was semantically acceptable at the sentence level but incongruent in terms of discourse context. The same stories were also presented with congruent endings. Auditory ERPs elicited by the final words in these sentences and stories were compared. Both sentence- and discourse-level semantic integration were associated with N400 and Late Positive Component (LPC) effects in addition to a new component, P550. Local and global semantic processing, although evoking the same components, were characterized by differential effects on ERP amplitudes according to the amount of text integrated and its congruence. These results indicate similar cognitive processes of context build up, underlying sentence- and discourse-semantic processing.     

Gender Stereotype Activation versus Lexical Semantic Activation: An ERP Study

It is an open question whether social stereotype activation can be distinguished from nonsocial semantic activation. To address this question, gender stereotype activation (GSA) and lexical semantic activation (LSA) were directly compared. EEGs were recorded in 20 participants as they identified the congruence between prime-target word pairs under four different conditions (stereotype congruent, stereotype incongruent, semantic congruent, and semantic incongruent). We found that congruent targets elicited faster and more accurate responses and reduced N400 amplitudes irrespective of priming category types. The N400 congruency effect (i.e., the difference between incongruity and congruity) started earlier and had greater amplitude for GSA than for LSA. Moreover, gender category priming induced a smaller N400 and a larger P600 than lexical category priming. These findings suggest that the brain is not only sensitive to both stereotype and semantic violation in the post-perceptual processing stage but can also differentiate these two information processes. Further, the findings suggest superior processing (i.e., faster and deeper processing) when the words are associated with social category and convey stereotype knowledge.     

Context modulates hemispheric asymmetries in the resolution of lexical ambiguity

Previous studies have reported a hemispheric asymmetry in processing dominant (e.g., paper) and subordinate (e.g., farmer) associations of ambiguous words (e.g., pen). The majority of these studies, however, applied randomly ordered presentation and collected right-hand responses only. Generating responses solely with the right hand and the randomly ordered presentation of association type might have affected natural hemispheric expertise. We explored the putative relationships between responding hand and experimental design manipulations in processing lexical ambiguity. Ambiguous target words were laterally presented following word pairs that could be associated to the dominant or subordinate meaning of the target word. We manipulated the responding hand and the experimental context by presenting the semantic associations in a random (Experiment 1) and a blocked ordered presentation (Experiment 2). The results of Experiment 2 supported the right hemisphere expertise hypothesis, whereas the results of Experiment 1 can be best explained by the direct access model where stimuli are processed by the hemisphere receiving them first, without relying on hemispheric expertise. We conclude that without manipulating the responding hand, there is a risk of misinterpreting direct access results as evidence for hemispheric expertise. Moreover, we suggest that a blocked ordered presentation might encourage participants to use the expert hemisphere for the blocked factor. A new theoretical framework is presented to explain the findings.     

Semantic Processing in Children and Adults: Incongruity and the N400

Semantic processing in 10-year-old children and adults was examined using event related potentials (ERPs). The N400 component, an index of semantic processing, was studied in relation to sentences that ended with congruent, moderately incongruent, or strongly incongruent words. N400 amplitude in adults corresponded to levels of semantic incongruity with the greatest amplitude occurring to strongly incongruent sentences at all midline electrodes. In contrast, children’s N400s were greater for both moderately and strongly incongruent sentences but did not differ between these levels of incongruity. This finding suggests that semantic processing may differ in adults and children.     

Understanding words in sentence contexts: the time course of ambiguity resolution

Spoken language comprehension requires rapid integration of information from multiple linguistic sources. In the present study we addressed the temporal aspects of this integration process by focusing on the time course of the selection of the appropriate meaning of lexical ambiguities ("bank") in sentence contexts. Successful selection of the contextually appropriate meaning of the ambiguous word is dependent upon the rapid binding of the contextual information in the sentence to the appropriate meaning of the ambiguity. We used the N400 to identify the time course of this binding process. The N400 was measured to target words that followed three types of context sentences. In the concordant context, the sentence biased the meaning of the sentence-final ambiguous word so that it was related to the target. In the discordant context, the sentence context biased the meaning so that it was not related to the target. In the unrelated control condition, the sentences ended in an unambiguous noun that was unrelated to the target. Half of the concordant sentences biased the dominant meaning, and the other half biased the subordinate meaning of the sentence-final ambiguous words. The ISI between onset of the target word and offset of the sentence-final word of the context sentence was 100 ms in one version of the experiment, and 1250 ms in the second version. We found that (i) the lexically dominant meaning is always partly activated, independent of context, (ii) initially both dominant and subordinate meaning are (partly) activated, which suggests that contextual and lexical factors both contribute to sentence interpretation without context completely overriding lexical information, and (iii) strong lexical influences remain present for a relatively long period of time.     

In search of perceptual influences of sentence context on word recognition

A major issue in the study of word perception concerns the nature (perceptual or nonperceptual) of sentence context effects. The authors compared effects of legal, word replacement, nonword replacement, and transposed contexts on target word performance using the Reicher-Wheeler task to suppress nonperceptual influences of contextual and lexical constraint. Experiment 1 showed superior target word performance for legal (e.g., "it began to flap/flop") over all other contexts and for transposed over word replacement and nonword replacement contexts. Experiment 2 replicated these findings with higher constraint contexts (e.g., "the cellar is dark/dank") and Experiment 3 showed that strong constraint contexts improved performance for congruent (e.g., "born to be wild") but not incongruent (e.g., mild) target words. These findings support the view that the very perception of words can be enhanced when words are presented in legal sentence contexts.     

语境情绪韵律对新异词汇学习过程的影响

模拟自然学习语境,探讨情绪韵律对具体和抽象词学习的调节作用及其产生原因。被试在高兴、愤怒、中性语境情绪韵律条件下学习抽象和具体词,记录学习过程及测试过程中的行为与脑电反应。结果发现在愤怒韵律背景下学习的抽象词加工的正确率更低、反应时更长;并且诱发了更为显著的脑电成分。表明愤怒韵律对词汇学习尤其是抽象词学习有显著的消极作用。此外,情绪韵律对词汇学习的调节作用是在学习过程中对词汇语义提取及晚期语义整合产生影响而形成的。     

Neural localization of semantic context effects in electromagnetic and hemodynamic studies

Measures of electrical brain activity (event-related potentials, ERPs) have been useful in understanding language processing for several decades. Extant data suggest that the amplitude of the N400 component of the ERP is a general index of the ease or difficulty of retrieving stored conceptual knowledge associated with a word, which is dependent on both the stored representation itself, and the retrieval cues provided by the preceding context. Recordings from patients with brain damage, intracranial recordings, and magnetoencephalographic data implicate a (probably large portion of) the left temporal lobe as the largest source of the N400 semantic context effect, with a substantial but lesser contribution from the right temporal lobe. Event-related functional magnetic resonance (fMRI) studies using semantic context manipulations are dominated by observations of greater hemodynamic activity for incongruent sentence completions or semantically unrelated words than congruent or related words, consistent with the direction of the ERP effect. The locations of the hemodynamic effects show some variability across studies, but one commonly identified region is the left superior temporal gyrus, which is compatible with the electrophysiological results. A second commonly identified region in the fMRI studies is the left inferior frontal gyrus, which does not appear to make a substantial contribution to the N400 effect.     

Age-related differences in interlingual priming: a behavioural and electrophysiological investigation

Reaction time (RT) and the N400 ERP component were measured to examine age-related differences in bilingual language processing. Although young bilinguals appear to access both languages simultaneously (i.e., non-selective access), little is known about language selection in older adults. The effect of language context on language selectivity was investigated using interlingual homographs (IH; i.e., words with identical orthography but distinct semantic features in two languages, e.g., coin meaning 'corner' in French and 'money' in English). Younger and older French/English bilinguals were presented with triplets of letter strings comprised of a language context cue, an IH, and a target word, in a lexical decision semantic priming task. RT and ERP results support non-selective language access in young adults; however, the older bilinguals used the language context cue to bias their reading of the IH. Results are discussed in terms of age-related changes in language processing and context use in bilinguals.     

Friendly drug-dealers and terrifying puppies: Affective primacy can attenuate the N400 effect in emotional discourse contexts

Words that are semantically congruous with their preceding discourse context are easier to process than words that are semantically incongruous with their context. This facilitation of semantic processing is reflected by an attenuation of the N400 event-related potential (ERP). We asked whether this was true of emotional words in emotional contexts where discourse congruity was conferred through emotional valence. ERPs were measured as 24 participants read two-sentence scenarios with critical words that varied by emotion (pleasant, unpleasant, or neutral) and congruity (congruous or incongruous). Semantic predictability, constraint, and plausibility were comparable across the neutral and emotional scenarios. As expected, the N400 was smaller to neutral words that were semantically congruous (vs. incongruous) with their neutral discourse context. No such N400 congruity effect was observed on emotional words following emotional discourse contexts. Rather, the amplitude of the N400 was small to all emotional words (pleasant and unpleasant), regardless of whether their emotional valence was congruous with the valence of their emotional discourse context. However, consistent with previous studies, the emotional words produced a larger late positivity than did the neutral words. These data suggest that comprehenders bypassed deep semantic processing of valence-incongruous emotional words within the N400 time window, moving rapidly on to evaluate the words’ motivational significance.     

Semantic memory and verbal working memory correlates of N400 to subordinate homographs

N400 is an event-related brain potential that indexes operations in semantic memory conceptual space, whether elicited by language or some other representation (e.g., drawings). Language models typically propose three stages: lexical access or orthographic- and phonological-level analysis; lexical selection or word-level meaning and associate activation; and lexical integration, sentence- and discourse-level operations. The exact stage that N400 reflects is unknown, although opinion favors lexical integration over lexical selection. Surprisingly, little research has assessed relationships between neuropsychological measures of semantic memory fund of information or verbal working memory capacity and N400. Subjects performed a homograph disambiguation comprehension task with minimal working memory load. Short sentences read: The noun was adjective/verb. The nouns were either homographs or unambiguous. The adjective/verb was disambiguating for the homograph, and congruent or incongruent for the unambiguous noun. The primary noun of interest was the subordinate homograph. Comprehension of the subordinate meaning should correlate with semantic memory stores, reflecting greater knowledge. If N400 primarily reflects lexical access operations, it should also correlate with measures of semantic knowledge. If N400 reflects lexical integration, it should correlate with measures of working memory capacity. Comprehension errors were associated with semantic memory stores, but not working memory capacity. N400 was related to working memory capacity, but not semantic knowledge, suggesting that N400 primarily reflects late-stage working memory operations. N400 to subordinate disambiguating words was larger with greater working memory capacity, and thus may index the absolute capacity of working memory rather than difficulty in contextual integration.     

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

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.     

The dynamic influence of emotional words on sentence comprehension: An ERP study

In the present study, we explored the influence of emotional words on the semantic integration of their following neutral nouns during sentence comprehension. We manipulated the emotionality of verbs and the semantic congruity of their following (neutral) object nouns in sentences. Event-related potentials were recorded to the verbs, which were either negative or neutral, and to the object nouns, which were either semantically congruent or incongruent relative to the preceding contexts. We found an N400 and a P600 effect in response to the semantic congruity of the nouns when they followed the neutral verbs. However, the P600 (but not the N400) semantic congruity effect may have been attenuated when the nouns followed the negative verbs. Meanwhile, the negative verbs elicited a larger P2 and N400 than did the neutral verbs. The results indicate that the attention captured by emotional words impaired reanalysis of the following incongruent information, demonstrating a dynamic influence of emotional words on the semantic processing of following information during sentence comprehension.     

语义整合的早期加工:来自ERPs的证据

本研究借助ERPs技术,通过操纵关键词与当前语境的语义合理性关系,考察在严格限定关键词词频变异性的情况下,语义整合过程能否反映在P2效应上。ERPs结果发现关键词呈现后,语义合理相比违背条件在右侧脑区诱发了更大的P2成分。该结果支持如果关键词低水平的变量信息(词频等)得到适当控制,ERPs技术可以检测到发生在250ms以前的语义整合过程。