The precise time course of lexical activation: MEG measurements of the effects of frequency, probability, and density in lexical decision

Visually presented letter strings consistently yield three MEG response components: the M170, associated with letter-string processing (Tarkiainen, Helenius, Hansen, Cornelissen, & Salmelin, 1999); the M250, affected by phonotactic probability, (Pylkk?nen, Stringfellow, & Marantz, 2002); and the M350, responsive to lexical frequency (Embick, Hackl, Schaeffer, Kelepir, & Marantz, 2001). Pylkk?nen et al. found evidence that the M350 reflects lexical activation prior to competition among phonologically similar words. We investigate the effects of lexical and sublexical frequency and neighborhood density on the M250 and M350 through orthogonal manipulation of phonotactic probability, density, and frequency. The results confirm that probability but not density affects the latency of the M250 and M350; however, an interaction between probability and density on M350 latencies suggests an earlier influence of neighborhoods than previously reported.     

A corpus of consonant–vowel–consonant real words and nonwords: Comparison of phonotactic probability, neighborhood density, and consonant age of acquisition

A corpus of 5,765 consonant–vowel–consonant sequences (CVCs) was compiled, and phonotactic probability and neighborhood density were computed for both child and adult corpora. This corpus of CVCs, provided as supplementary materials, was analyzed to address the following questions: (1) Do computations based on a child corpus differ from those based on an adult corpus? (2) Do the phonotactic probability and/or the neighborhood density of real words differ from those of nonwords? (3) Do phonotactic probability and/or neighborhood density differ across CVCs that vary in consonant age of acquisition? The results showed significant differences in phonotactic probability and neighborhood density for the child versus adult corpora, replicating prior findings. The impact of this difference on future studies will depend on the level of precision needed when specifying probability and density. In addition, significant and large differences in phonotactic probability and neighborhood density were detected between real words and nonwords, which may present methodological challenges for future research. Finally, CVCs composed of earlier-acquired sounds differed significantly in probability and density from those composed of later-acquired sounds, although this effect was relatively small and is less likely to present significant methodological challenges to future studies.     

Early effects of neighborhood density and phonotactic probability of spoken words on event-related potentials

All current models of spoken word recognition propose that sound-based representations of spoken words compete with, or inhibit, one another during recognition. In addition, certain models propose that higher probability sublexical units facilitate recognition under certain circumstances. Two experiments were conducted examining ERPs to spoken words and nonwords simultaneously varying in phonotactic probability and neighborhood density. Results showed that the amplitude of the P2 potential was greater for high probability-density words and nonwords, suggesting an early inhibitory effect of neighborhood density. In order to closely examine the role of phonotactic probability, effects of initial phoneme frequency were also examined. The latency of the P2 potential was shorter for words with high initial-consonant probability, suggesting a facilitative effect of phonotactic probability. The current results are consistent with findings from previous studies using reaction time and eye-tracking paradigms and provide new insights into the time-course of lexical and sublexical activation and competition.     

Word-specific repetition effects revealed by MEG and the implications for lexical access

This magnetoencephalography (MEG) study investigated the early stages of lexical access in reading, with the goal of establishing when initial contact with lexical information takes place. We identified two candidate evoked responses that could reflect this processing stage: the occipitotemporal N170/M170 and the frontocentral P2. Using a repetition priming paradigm in which long and variable lags were used to reduce the predictability of each repetition, we found that (i) repetition of words, but not pseudowords, evoked a differential bilateral frontal response in the 150–250 ms window, (ii) a differential repetition N400m effect was observed between words and pseudowords. We argue that this frontal response, an MEG correlate of the P2 identified in ERP studies, reflects early access to long-term memory representations, which we tentatively characterize as being modality-specific.     

Neural correlates of the effects of morphological family frequency and family size: an MEG study

Schreuder and Baayen (Schreuder. R., & Baayen, R. H. (1997). How complex simplex words can be. Journal of Memory and Language 37, 118-139) report that lexical decision times to nouns are not sensitive to the cumulative frequency of the noun's morphological derivatives in its "morphological family", even though such a cumulative frequency effect is obtained in the domain of inflection. Under a decomposition view of derivational morphology, this constitutes a puzzling exception to the robust finding that lexical frequency is one of the major determinants of behavioral response latencies. If morphologically complex words are decomposed, each occurrence of a member of a noun's morphological family should add to its root-frequency. We investigated the effects of morphological family frequency on the magnetoencephalographic response component M350, which shows sensitivity to factors affecting early stages of lexical processing, including lexical frequency. We hypothesized that high morphological family frequency should have a facilitory effect on the M350, even though no such effect can be seen in response time, presumably due to competition among possible root-affix combinations. Contrary to this hypothesis, we found that high family frequency elicits an M350 inhibition, suggesting that competition among morphological family members occurs at the M350. The result is significant, since there is evidence that competition among phonologically similar words occurs after, not at, the M350. Thus, our results suggest that competition within a morphological family precedes competition within a phonological similarity neighborhood.     

高度模糊靶字下的N400语义启动效应：词汇加工理论的证据

本研究基于不可识别模糊字词仍能诱发N400的词汇加工理论的假设,让被试对模糊字进行同一字延迟判断,利用脑电技术记录不同模糊程度靶字的认知过程,来探讨N400出现的条件,以阐明N400反映的是词汇加工,还是词汇后加工。实验结果表明：与可识别、轻度模糊汉字一样,不可识别、高度模糊汉字仍然可以诱发N400;这种N400语义启动效应反映了词汇加工过程。     

An online calculator to compute phonotactic probability and neighborhood density on the basis of child corpora of spoken American English

An online calculator was developed (www.bncdnet.ku.edu/cml/info_ccc.vi) to compute phonotactic probability—the likelihood of occurrence of a sound sequence—and neighborhood density—the number of phonologically similar words—on the basis of child corpora of American English (Kolson, 1960; Moe, Hopkins, & Rush, 1982) and to compare its results to those of an adult calculator. Phonotactic probability and neighborhood density were computed for a set of 380 nouns (Fenson et al., 1993) using both the child and adult corpora. The child and adult raw values were significantly correlated. However, significant differences were detected. Specifically, child phonotactic probability was higher than adult phonotactic probability, especially for highprobability words, and child neighborhood density was lower than adult neighborhood density, especially for words with high-density neighborhoods. These differences were reduced or eliminated when relative measures (i.e., z scores) were used. Suggestions are offered regarding which values to use in future research.     

Tracking the Time Course of Word‐Frequency Effects in Auditory Word Recognition With Event‐Related Potentials

Although the word‐frequency effect is one of the most established findings in spoken‐word recognition, the precise processing locus of this effect is still a topic of debate. In this study, we used event‐related potentials (ERPs) to track the time course of the word‐frequency effect. In addition, the neighborhood density effect, which is known to reflect mechanisms involved in word identification, was also examined. The ERP data showed a clear frequency effect as early as 350 ms from word onset on the P350, followed by a later effect at word offset on the late N400. A neighborhood density effect was also found at an early stage of spoken‐word processing on the PMN, and at word offset on the late N400. Overall, our ERP differences for word frequency suggest that frequency affects the core processes of word identification starting from the initial phase of lexical activation and including target word selection. They thus rule out any interpretation of the word frequency effect that is limited to a purely decisional locus after word identification has been completed.     

Sublexical and lexical representations in speech production: effects of phonotactic probability and onset density

Phonotactic probability, neighborhood density, and onset density were manipulated in 4 picture-naming tasks. Experiment 1 showed that pictures of words with high phonotactic probability were named more quickly than pictures of words with low phonotactic probability. This effect was consistent over multiple presentations of the pictures (Experiment 2). Manipulations of phonotactic probability and neighborhood density showed only an influence of phonotactic probability (Experiment 3). In Experiment 4, pictures of words with sparse onsets were named more quickly than pictures of words with dense onsets. The results of these experiments provide additional constraints on the architecture and processes involved in models of speech production, as well as constraints on the connections between the recognition and production systems.     

Phonotactics, neighborhood activation, and lexical access for spoken words.

Probabilistic phonotactics refers to the relative frequencies of segments and sequences of segments in spoken words. Neighborhood density refers to the number of words that are phonologically similar to a given word. Despite a positive correlation between phonotactic probability and neighborhood density, nonsense words with high probability segments and sequences are responded to more quickly than nonsense words with low probability segments and sequences, whereas real words occurring in dense similarity neighborhoods are responded to more slowly than real words occurring in sparse similarity neighborhoods. This contradiction may be resolved by hypothesizing that effects of probabilistic phonotactics have a sublexical focus and that effects of similarity neighborhood density have a lexical focus. The implications of this hypothesis for models of spoken word recognition are discussed.     

FN400和N400是相同的ERP成分：来自图形材料的证据

本研究通过比较记忆编码阶段语义启动引起的N400效应和提取阶段熟悉性引起的FN400效应的地形图考察图形材料诱发的N400和FN400是否是相同的ERP成分。实验结果发现,语义启动引起的N400效应和熟悉性引起的FN400效应的地形图没有显著差异。这说明图形材料诱发的FN400和N400是相同的ERP成分,两者都反映了语义加工。本研究为FN400效应反映了语义启动而不是熟悉性的观点提供了新的实验证据。     

Masked repetition priming using magnetoencephalography

Masked priming is used in psycholinguistic studies to assess questions about lexical access and representation. We present two masked priming experiments using MEG. If the MEG signal elicited by words reflects specific aspects of lexical retrieval, then one expects to identify specific neural correlates of retrieval that are sensitive to priming. To date, the electrophysiological evidence has been equivocal. We report findings from two experiments. Both employed identity priming, where the prime and target are the same lexical item but differ in case (NEWS-news). The first experiment used only forward masking, while the prime in the second experiment was both preceded and followed by a mask (backward masking). In both studies, we find a significant behavioral effect of priming. Using MEG, we identified a component peaking approximately 225 ms post-onset of the target, whose latency was sensitive to repetition. These findings support the notion that properties of the MEG response index specific lexical processes and demonstrate that masked priming can be effectively combined with MEG to investigate the nature of lexical processing.     

Long-term knowledge effects on serial recall of nonwords are not exclusively lexical

S. Roodenrys and M. Hinton (2002) reported superior recall for nonwords with large rather than small lexical neighborhoods when constituent biphone frequency was controlled, but comparable recall of high and low biphone frequency nonwords when neighborhood size was controlled, suggesting that long-term knowledge effects on nonword recall are lexically based. We report two experiments in which the same manipulations were made, but with neighborhood size controlled at the level of neighbor type. In Experiment 1, biphone frequency significantly influenced nonword recall when neighborhood size was controlled in this way. In Experiment 2, neighborhood size significantly influenced nonword recall when biphone frequency was controlled. These findings suggest that long-term knowledge contributions to nonword recall are not exclusively lexical but are based instead on both lexical and phonotactic knowledge of a language.     

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。     

The role of temporal and spatial factors in the covert orienting of visual attention tasks

There is a biphasic pattern in response times to peripheral uninformative cues, with faster responses to targets in cued locations when the stimulus onset asynchrony (SOA) is under 300 ms and slower responses when it is over 300 ms. The effect has typically been attributed entirely to the SOA while ignoring other aspects of the cues (duration, spatial configuration). To examine these other factors, along with SOA, the present experiments included manipulations of SOA (50, 100, 200, 400, 800 ms), inter-stimulus interval (ISI; 0, 50, 100, 150, 200, 300, 350, 400, 500, 600, 700, and 750 ms), and whether or not the cue and target overlap in the same space. The results indicate that cueing effects depend on the combination of cue duration, ISI, SOA, and the spatial configuration of the cues and targets. Three factors are used to explain these time course results.     

关于知觉干扰效应的ERP研究

利用ERP技术,采用知觉干扰效应的经典实验范式,首次从神经生理水平上探究知觉干扰效应的内部机制。结果发现,递进条件和标准条件均诱发了P2,P3,N400和晚期正成分LPC。在P2,P3和LPC成分上,标准条件的波幅均显著大于递进条件;在N400成分上,递进条件比标准条件波幅更负,潜伏期更长。此外,对递进条件下靶字各模糊水平（Level 1～Level 5）的ERPs进行比较分析表明,N400成分的波幅在各模糊水平间的差异均不显著。基本支持失匹配理论及词汇自动加工理论。     

Lexical access in early stages of visual word processing: A single-trial correlational MEG study of heteronym recognition

We present an MEG study of heteronym recognition, aiming to distinguish between two theories of lexical access: the ‘early access’ theory, which entails that lexical access occurs at early (pre 200 ms) stages of processing, and the ‘late access’ theory, which interprets this early activity as orthographic word-form identification rather than genuine lexical access. A correlational analysis method was employed to examine effects of the heteronyms’ form and lexical properties on brain activity. We find support for the ‘late access’ view, in that lexical properties did not affect processing until after 300 ms, while earlier activation was primarily modulated by orthographic form.     

The neural basis of obligatory decomposition of suffixed words

Recent neurolinguistic studies present somewhat conflicting evidence concerning the role of the inferior temporal cortex (IT) in visual word recognition within the first 200 ms after presentation. On the one hand, fMRI studies of the Visual Word Form Area (VWFA) suggest that the IT might recover representations of the orthographic form of words. On the other hand, influential MEG studies of responses from the occipito-temporal regions around 150 ms post-stimulus onset indicate recognition of letters as opposed to symbols but not a sensitivity to statistical properties of letter strings associated with word form representations. Recent MEG experiments support the position that the IT does represent the visual word forms of morphemes and performs morphological decomposition modulated by the statistical relations between morphemes by 170 ms post presentation (at the M170 response). Responses to heteronyms show that the M170 does not make contact with the mental lexicon where word forms are connected to meanings. We report here an MEG study of pseudo-affixed words like brother, which masked priming studies have shown are decomposed in recognition. If the M170 response from IT does index obligatory morphological decomposition based on visual word forms but not lexical entries, we should find that the statistical relation between pseudo-stem and pseudo-suffix modulates the M170 for pseudo-affixed words, as for truly affixed words. The results of this experiment confirm this prediction. In addition, surface form frequency for these words also modulates the M170, providing some support for dual route recognition for words for which decomposition is a garden path.     

Distributional analyses in auditory lexical decision: Neighborhood density and word-frequency effects

In the present article, the effects of phonological neighborhood density and word frequency in spoken word recognition were examined using distributional analyses of response latencies in auditory lexical decision. A density × frequency interaction was observed in mean latencies; frequency effects were larger for low-density words than for high-density words. Distributional analyses further revealed that for low-density words, frequency effects were reflected in both distributional shifting and skewing, whereas for high-density words, frequency effects were purely mediated by distributional skewing. The results suggest that word frequency plays a role in early auditory word recognition only when there is relatively little competition between similar-sounding words, and that frequency effects in high-density words reflect postlexical checking.     

The earliest electrophysiological correlate of visual awareness?

To examine the neural correlates and timing of human visual awareness, we recorded event-related potentials (ERPs) in two experiments while the observers were detecting a grey dot that was presented near subjective threshold. ERPs were averaged for conscious detections of the stimulus (hits) and nondetections (misses) separately. Our results revealed that hits, as compared to misses, showed a negativity around 180-350 ms at occipital and posterior temporal sites. It was followed by a positive wave after 400-500 ms, peaking at parietal sites. These correlates were not affected by a manipulation of attention. The early negativity, called 'visual awareness negativity' (VAN), may be a general, primary electrophysiological correlate of visual awareness. The present data show that it can be observed in response to appearance of a stimulus in visual awareness and that it generalizes across different manipulations of stimulus visibility.