Orthographic neighborhood effects as a function of word frequency: an event-related potential study

Tracking the brain signature of (mis)spelled logotypes via letter transpositions and replacements

All leading models of visual word recognition assume a hierarchical process that progressively converts the visual input into abstract letter and word representations. However, the results from recent behavioral studies suggest that the mental representations of words with a highly consistent visual format, such as logotypes, may comprise not only purely abstract information but also perceptual information. This hypothesis would explain why participants often misperceive transposed-letter misspellings with the original base words to a larger degree in logotypes (e.g., SASMUNG, but not SARVUNG, is perceived as SAMSUNG) than in common words. The present experiment examined the electrophysiological signature behind the identification of correctly spelled and misspelled logotypes (via letter transposition or replacement) in an ERP go/no-go semantic categorization experiment. Results showed that N400 amplitudes for transposed-letter misspelled logotypes (SASMUNG) and intact logotypes (SAMSUNG) did not differ significantly across various time windows (until 600 ms), whereas replacement-letter misspelled logotypes (SARVUNG) yielded consistently larger N400 amplitudes. These findings reveal that the mental representations of logotypes are particularly resistant to minor orthographic changes, which has important theoretical and applied (e.g., marketing) implications.

Event-related Potential Measures of Visual Word Processing in Monolingual and Bilingual Children and Adults: A Focus on Word Frequency Effects

How does language background influence the neural correlates of visual word recognition in children? To address this question, we used an ERP lexical decision task to examine first-language (L1) and second-language (L2) visual word processing in monolingual and bilingual school-aged children and young adults (n = 123). In particular, we focused on the effects of word frequency (an index of lexical accessibility) on RTs and the N400 ERP component. Behaviorally, we found larger L1 versus L2 word frequency effects among bilingual children, driven by faster and more accurate responses to higher-frequency words (no other language or age group differences were observed). Neurophysiologically, we found larger L1 word frequency effects in bilinguals versus monolinguals (across both age groups), reflected in more negative ERP amplitudes to lower-frequency words. However, the bilingual groups processed L1 and L2 words similarly, despite lower levels of subjective and objective L2 proficiency. Taken together, our findings suggest that divided L1 experience (but not L2 experience) influences the neural correlates of visual word recognition across childhood and adulthood.

Information entropy facilitates (not impedes) lexical processing during language comprehension

It is well known that contextual predictability facilitates word identification, but it is less clear whether the uncertainty associated with the current context (i.e., its lexical entropy) influences sentence processing. On the one hand, high entropy contexts may lead to interference due to greater number of lexical competitors. On the other hand, predicting multiple lexical competitors may facilitate processing through the preactivation of shared semantic features. In this study, we examined whether entropy measured at the trial level (i.e., for each participant, for each item) corresponds to facilitatory or inhibitory effects. Trial-level entropy captures each individual's knowledge about specific contexts and is therefore a more valid and sensitive measure of entropy (relative to the commonly employed item-level entropy). Participants (N = 112) completed two experimental sessions (with counterbalanced orders) that were separated by a 3- to 14-day interval. In one session, they produced up to 10 completions for sentence fragments (N = 647). In another session, they read the same sentences including a target word (whose entropy value was calculated based on the produced completions) while reading times were measured. We observed a facilitatory (not inhibitory) effect of trial-level entropy on lexical processing over and above item-level measures of lexical predictability (including cloze probability, surprisal, and semantic constraint). Extra analyses revealed that greater semantic overlap between the target and the produced responses facilitated target processing. Thus, the results lend support to theories of lexical prediction maintaining that prediction involves broad activation of semantic features rather than activation of full lexical forms.

Effect of contextual diversity on word recognition in different semantic contexts

Efficient word recognition is important to facilitate reading comprehension. Two important factors influence word recognition-word frequency (WF) and contextual diversity (CD)-but studies have not reached consistent conclusions on their role. Based on previous studies, the present study strictly controlled the anticipation of sentence context on target words. In the context of the semantic incongruence of Chinese sentences-that is, when the context is equivalent and low in anticipation of the target noun-CD effects were found on late processing indicators of the eye movement data of parafoveal words, and the CD feature of parafoveal words led to a significant parafoveal-on-foveal effect. However, none of these results were found in the semantically reasonable (semantic congruence) context. The results suggested that high CD words are better at adapting to unexposed or learned contexts, which was not the case for high WF words.

Dissociating different temporal stages of emotional word processing by feature-based attention

Negative emotional content is prioritized across different stages of information processing as reflected by different components of the event-related potential (ERP). In this preregistered study (N = 40), we investigated how varying the attentional focus allows us to dissociate the involvement of specific ERP components in the processing of negative and neutral words. Participants had to discriminate the orientation of lines overlaid onto the words, the word type (adjective/noun), or the emotional content (negative/neutral). Thus, attention was either not focused on words (distraction task), non-emotional aspects, or the emotional relevance of words. Regardless of the task, there were no significant differences between negative and neutral words for the P1, N1, or P2 components. In contrast, interactions between emotion and task were observed for the early posterior negativity (EPN) and late positive potential (LPP). EPN differences were absent during the distraction task but were present in the other two tasks. LPP emotion differences were found only when attention was directed to the emotional content of words. Our study adds to the evidence that early ERP components do not reliably separate negative and neutral words. However, results show that mid-latency and late stages of emotion processing are separable by different attention tasks. The EPN represents a stage of attentional enhancement of negative words given sufficient attentional resources. Differential activations during the LPP stage are associated with more elaborative processing of the emotional meaning of words.

On the syllable structure effect in European Portuguese: Evidence from ERPs

Syllable effects during visual word recognition have been observed for CV but not for CVC syllables, a puzzling effect that is not explained either by the distributional frequencies of CV and CVC syllables, syllable complexity, or syllabic neighbourhood density. Furthermore, in European Portuguese (EP), syllable effects have not been found for pseudowords, suggesting that syllable activation might not precede lexical activation. Here, we combined a colour-congruency lexical decision task with the collection of electroencephalographic (EEG) data to investigate syllable effects in EP for CV and CVC words and pseudowords, with the latter presenting a match (CVC_O+P+) or a mismatch (CVC_O+P-) between their orthographic (O) and phonological (P) syllable structure to further ascertain the locus (i.e., orthographic and/or phonological) of syllable effects. Results showed syllable congruency effects in the N100, P200, and N400 ERP components for CV and CVC words suggesting the influence of different factors underlying the syllable structure effect.

Frequency Effects on Spelling Error Recognition: An ERP Study

Spelling errors are ubiquitous in all writing systems. Most studies exploring spelling errors focused on the phonological plausibility of errors. However, unlike typical pseudohomophones, spelling errors occur in naturally produced written language. We investigated the time course of recognition of the most frequent orthographic errors in Russian (error in an unstressed vowel in the root) and the effect of word frequency on this process. During event-related potentials (ERP) recording, 26 native Russian speakers silently read high-frequency correctly spelled words, low-frequency correctly spelled words, high-frequency words with errors, and low-frequency words with errors. The amplitude of P200 was more positive for correctly spelled words than for misspelled words and did not depend on the frequency of the words. In addition, in the 350–500-ms time window, we found a more negative response for misspelled words than for correctly spelled words in parietal–temporal-occipital regions regardless of word frequency. Considering our results in the context of a dual-route model, we concluded that recognizing misspelled high-frequency and low-frequency words involves common orthographic and phonological processes associated with P200 and N400 components such as whole word orthography processing and activation of phonological representations correspondingly. However, at the 500–700 ms stage (associated with lexical-semantic access in our study), error recognition depends on the word frequency. One possible explanation for these differences could be that at the 500–700 ms stage recognition of high-frequency misspelled and correctly spelled words shifts from phonological to orthographic processes, while low-frequency misspelled words are accompanied by more prolonged phonological activation. We believe these processes may be associated with different ERP components P300 and N400, reflecting a temporal overlap between categorization processes based on orthographic properties for high-frequency words and phonological processes for low-frequency words. Therefore, our results complement existing reading models and demonstrate that the neuronal underpinnings of spelling error recognition during reading may depend on word frequency.

Multilayer networks: An untapped tool for understanding bilingual neurocognition

Cross-linguistic similarity is a term so broad and multi-faceted that it is not easily defined. The degree of overlap between languages is known to affect lexical competition during online processing and production, and its relevance for second language acquisition has also been established. Nevertheless, determining what makes two languages similar (or not) increases in complexity when multiple levels of the language hierarchy (e.g., phonology, syntax) are considered. How can we feasibly account for the patterns of convergence and divergence at each level of representation, as well as the interactions between them? The growing field of network science brings new methodologies to bear on this longstanding question. Below, we summarize current network science approaches to modeling language structure and discuss implications for understanding various linguistic processes. Critically, we stress the particular value of multilayer techniques, unique and powerful in their ability to simultaneously accommodate an array of node-to-node (or word-to-word) relationships.

Orthographic neighborhood density modulates the size of transposed-letter priming effects

We used transposed-letter (TL) priming to test the lexical tuning hypothesis, which states that words from high-density orthographic neighborhoods have more precise orthographic codes than words from low-density neighborhoods. Replicating standard TL priming effects, target words elicited faster lexical decision responses and smaller amplitude N250s and N400s when preceded by TL primes (e.g., leomn-LEMON) compared with substitution primes (e.g., leuzn-LEMON) overall. We expected that if high-density words have more precise orthographic representations (i.e., with each letter assigned to a specific position), then they should be relatively less activated by TL primes and should give rise to smaller TL priming effects. In line with our prediction, N250 (but not N400 or behavioral) TL priming was significantly smaller for high-density words compared with low-density words over posterior sites. Such an interaction was not observed for pseudoword targets. Consistent with the lexical tuning hypothesis then, this pattern suggests that the nature of the orthographic code used to access lexical representations differs depending on the number of neighboring words in the lexicon. We conclude by discussing how lexical tuning could be implemented in current models of orthographic processing.

Individual Differences in Reading Speed are Linked to Variability in the Processing of Lexical and Contextual Information: Evidence from Single-trial Event-related Brain Potentials

In the current paper, we examined the effects of lexical (e.g. word frequency, orthographic neighborhood density) and contextual (e.g. word predictability in the form of cloze probability) features on single-trial event-related brain potentials in a self-paced reading paradigm. Critically, we examined whether individual differences in reading speed modulated single-trial effects on the N400, an ERP component linked to semantic memory access. Consistent with past work, we found that word frequency effects on the N400 were attenuated with increasing predictability. However, effects of orthographic neighborhood density were robust across all levels of predictability. Importantly, individual differences in reading speed moderated the influence of both frequency and predictability (but not orthographic neighborhood density) on the N400, such that slower readers showed reduced effects compared to faster readers. These data show that different lexical factors influence word processing through dissociable mechanisms. Our findings support a dynamic semantic-memory access model of the N400, in which information at multiple levels (lexical, sentential, individual) simultaneously contributes to the unfolding neural dynamics of comprehension.

Task modulates ERP effects of orthographic neighborhood for pseudowords but not words

Words and pseudowords from high-density orthographic neighborhoods elicit larger amplitude N400s than similar items from low-density orthographic neighborhoods in the lexical decision task. This pattern could be interpreted as an increase in the amount of lexico-semantic information to be processed or as an increase in difficulty identifying a word (or rejecting a pseudoword) amongst many co-activated alternatives. In order to dissociate between these mechanisms, we compared neighborhood effects between a lexical decision task (LDT) and a letter search task (LST). Behaviorally, we found the standard neighborhood and lexicality effects in the LDT, but no significant effects in the LST. Thus, behavioral responses were sensitive to the decisions required by the respective tasks. Electrophysiologically, we found similar N400 neighborhood effects between tasks for words, but the N400 neighborhood effect for pseudowords was only present in the LDT. Moreover, the effect of neighborhood in the LDT occurred earlier for words than for pseudowords. These nuanced differences in the time course and automaticity of word and pseudoword neighborhood effects lend insight into the processes that underlie N400 effects of orthographic neighborhood and how they unfold over time. We propose that the early neighborhood effects for words across tasks were driven by highly automatized word identification processes that were sensitive to the lateral inhibition generated by orthographic neighbors. In contrast, the later neighborhood effects for pseudowords in the LDT could have been driven by task-specific processes tied to how global lexical activity is used to make a lexical decision.

An electrophysiological investigation of orthographic spatial integration in reading

During reading, word recognition speed is influenced by the amount of orthographic overlap with surrounding words. The nature of this phenomenon is not understood: some theories attribute it to low-level visual operations (i.e., parafoveal feature detectors influencing foveal letter detectors), whereas other theories assume that orthographic processing (i.e., letter position coding and word activation) occurs across multiple words in parallel. To arbitrate between these theories, we used electroencephalography to reveal the time course of orthographic spatial integration in a lexical decision task. Foveal target words were flanked on each side by parafoveal words, manipulated across three conditions: repetition flankers (e.g. rock rock rock), unrelated flankers (step rock step) and a no-flanker condition. Linear mixed-effect models were constructed to analyze EEG data on a trial-by-trial basis. Word recognition was worse in the unrelated flanker condition than in the repetition and no-flanker conditions. This behavioral pattern was accompanied by increased negativity in the N250 and N400 windows, associated with the activation of sub-lexical and lexico-semantic representations, respectively. Crucially, the absence of effects prior to 200 ms post-stimulus onset provides evidence against the involvement of low-level visual processes. We conclude that orthographic spatial integration is driven by parallel processing of multiple words, which leads to the activation of a larger set of sub-lexical nodes and more difficult processing at the lexical level when those words are orthographically unrelated.

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Words are recognized faster when they share many letters with surrounding words.

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EEG measurements suggest that this effect unfolds 200 ms after stimulus onset.

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The locus of effects contradicts the involvement of low-level visual processing.

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Instead, the phenomenon appears to be driven by parallel orthographic processing.

The role of experience for abstract concepts: Expertise modulates the electrophysiological correlates of mathematical word processing

Embodied theories assign experience a crucial role in shaping conceptual representations. Supporting evidence comes mostly from studies on concrete concepts, where e.g., motor expertise facilitated action concept processing. This study examined experience-dependent effects on abstract concept processing. We asked participants with high and low mathematical expertise to perform a lexical decision task on mathematical and nonmathematical abstract words, while acquiring event-related potentials. Analyses revealed an interaction of expertise and word type on the amplitude of a fronto-central N400 and a centro-parietal late positive component (LPC). For mathematical words, we found a trend for a lower N400 and a significantly higher LPC amplitude in experts compared to nonexperts. No differences between groups were found for nonmathematical words. The results suggest that expertise affects the processing stages of semantic integration and memory retrieval specifically for expertise-related concepts. This study supports the generalization of experience-dependent conceptual processing mechanisms to the abstract domain.

An electrophysiological megastudy of spoken word recognition

This study used electrophysiological recordings to a large sample of spoken words to track the time-course of word frequency, phonological neighbourhood density, concreteness and stimulus duration effects in two experiments. Fifty subjects were presented more than a thousand spoken words during either a go/no go lexical decision task (Experiment 1) or a go/no go semantic categorisation task (Experiment 2) while EEG was collected. Linear mixed effects modelling was used to analyze the data. Effects of word frequency were found on the N400 and also as early as 100 ms in Experiment 1 but not Experiment 2. Phonological neighbourhood density produced an early effect around 250 ms and the typical N400 effect. Concreteness elicited effects in later epochs on the N400. Stimulus duration affected all epochs and its influence reflected changes in the timing of the ERP components. Overall the results support cascaded interactive models of spoken word recognition.

The ERP signature of the contextual diversity effect in visual word recognition

Behavioral experiments have revealed that words appearing in many different contexts are responded to faster than words that appear in few contexts. Although this contextual diversity (CD) effect has been found to be stronger than the word-frequency (WF) effect, it is a matter of debate whether the facilitative effects of CD and WF reflect the same underlying mechanisms. The analysis of the electrophysiological correlates of CD may shed some light on this issue. This experiment is the first to examine the ERPs to high- and low-CD words when WF is controlled for. Results revealed that while high-CD words produced faster responses than low-CD words, their ERPs showed larger negativities (225-325 ms) than low-CD words. This result goes in the opposite direction of the ERP WF effect (high-frequency words elicit smaller N400 amplitudes than low-frequency words). The direction and scalp distribution of the CD effect resembled the ERP effects associated with "semantic richness." Thus, while apparently related, CD and WF originate from different sources during the access of lexical-semantic representations.

Cross-language Neighborhood Effects in Learners Indicative of an Integrated Lexicon

This study examined how acquisition of novel words from an unknown language (L2) is influenced by their orthographic similarity with existing native language (L1) words in beginning adult learners. Participants were tested in a two-alternative forced-choice recognition task and a typing production task as they learned to associate 80 L2 (pseudo)words with pictures depicting their meanings. There was no effect of L1 orthographic neighborhood density on accuracy in the two-alternative forced-choice task, but typing accuracy was higher for L2 words with many L1 neighbors in the earliest stages of learning. ERPs recorded during a language decision task before and after learning also showed differences as a function of L1 neighborhood density. Across sessions, L2 words with many L1 neighbors elicited slower responses and larger N400s than words with fewer L1 neighbors, suggesting that L1 neighbors continued to influence processing of the L2 words after learning (though to a lesser extent). Finally, ERPs recorded during a typing task after learning also revealed an effect of L1 neighborhood that began about 700 msec after picture onset, suggesting that the cross-language neighborhood effects cannot solely be attributed to bottom-up activation of L1 neighbors. Together, these results demonstrate that strategic associations between novel L2 words and existing L1 neighbors scaffold learning and result in interactions among cross-language neighbors, suggestive of an integrated L1-L2 lexicon.

Interactions in the neighborhood: Effects of orthographic and phonological neighbors on N400 amplitude

The present study investigated effects of phonological and orthographic neighborhood density on event-related potentials, with an aim to better specify the factors that determine N400 amplitude in single word reading paradigms. We orthogonally manipulated the number of orthographic and phonological neighbors of words using the Levenshtein Distance metric (OLD20 and PLD20, respectively). The results showed opposite effects of phonological neighborhood density (PND) as a function of orthographic neighborhood density (OND). Larger N400 amplitudes were elicited by words with high PND compared with low PND when OND was high, and smaller N400 amplitudes were observed with high PND compared with low PND words when OND was low. We interpret these findings using the notion of cross-code consistency, according to which the compatibility of orthographic and phonological representations activated by a given word influences the process of recognizing that word. Words with similar numbers of orthographic and phonological neighbors have more consistent spellings and pronunciations across the neighborhood, and generate larger N400 amplitudes.

Lexical enhancement during prime-target integration: ERP evidence from matched-case identity priming

A number of experiments have revealed that matched-case identity PRIME-TARGET pairs are responded to faster than mismatched-case identity prime-TARGET pairs for pseudowords (e.g., JUDPE-JUDPE < judpe-JUDPE), but not for words (JUDGE-JUDGE = judge-JUDGE). These findings suggest that prime-target integration processes are enhanced when the stimuli tap onto lexical representations, overriding physical differences between the stimuli (e.g., case). To track the time course of this phenomenon, we conducted an event-related potential (ERP) masked-priming lexical decision experiment that manipulated matched versus mismatched case identity in words and pseudowords. The behavioral results replicated previous research. The ERP waves revealed that matched-case identity-priming effects were found at a very early time epoch (N/P150 effects) for words and pseudowords. Importantly, around 200 ms after target onset (N250), these differences disappeared for words but not for pseudowords. These findings suggest that different-case word forms (lower- and uppercase) tap into the same abstract representation, leading to prime-target integration very early in processing. In contrast, different-case pseudoword forms are processed as two different representations. This word-pseudoword dissociation has important implications for neural accounts of visual-word recognition.

Development of neural basis for chinese orthographic neighborhood size effect

The brain activity of orthographic neighborhood size (N size) effect in Chinese character naming has been studied in adults, meanwhile behavioral studies have revealed a developmental trend of Chinese N-size effect in developing readers. However, it is unclear whether and how the neural mechanism of N-size effect changes in Chinese children along with development. Here we address this issue using functional magnetic resonance imaging. Forty-four students from the 3(rd) , 5(th) , and 7(th) grades were scanned during silent naming of Chinese characters. After scanning, all participants took part in an overt naming test outside the scanner, and results of the naming task showed that the 3(rd) graders named characters from large neighborhoods faster than those from small neighborhoods, revealing a facilitatory N-size effect; the 5(th) graders showed null N-size effect while the 7(th) graders showed an inhibitory N-size effect. Neuroimaging results revealed that only the 3(rd) graders exhibited a significant N-size effect in the left middle occipital activity, with greater activation for large N-size characters. Results of 5(th) and 7(th) graders showed significant N-size effects in the left middle frontal gyrus, in which 5(th) graders induced greater activation in large N-size condition than in small N-size condition, while 7(th) graders exhibited an opposite effect which was similar to the adult pattern reported in a previous study. The current findings suggested the transition from broadly tuned to finely tuned orthographic representation with reading development, and the inhibition from neighbors' phonology for higher graders. Hum Brain Mapp 37:632-647, 2016. © 2015 Wiley Periodicals, Inc.

Revisiting the incremental effects of context on word processing: Evidence from single-word event-related brain potentials

The amplitude of the N400-an event-related potential (ERP) component linked to meaning processing and initial access to semantic memory-is inversely related to the incremental buildup of semantic context over the course of a sentence. We revisited the nature and scope of this incremental context effect, adopting a word-level linear mixed-effects modeling approach, with the goal of probing the continuous and incremental effects of semantic and syntactic context on multiple aspects of lexical processing during sentence comprehension (i.e., effects of word frequency and orthographic neighborhood). First, we replicated the classic word-position effect at the single-word level: Open-class words showed reductions in N400 amplitude with increasing word position in semantically congruent sentences only. Importantly, we found that accruing sentence context had separable influences on the effects of frequency and neighborhood on the N400. Word frequency effects were reduced with accumulating semantic context. However, orthographic neighborhood was unaffected by accumulating context, showing robust effects on the N400 across all words, even within congruent sentences. Additionally, we found that N400 amplitudes to closed-class words were reduced with incrementally constraining syntactic context in sentences that provided only syntactic constraints. Taken together, our findings indicate that modeling word-level variability in ERPs reveals mechanisms by which different sources of information simultaneously contribute to the unfolding neural dynamics of comprehension.

Examining the N400 semantic context effect item-by-item: relationship to corpus-based measures of word co-occurrence

With increasing availability of digital text, there has been an explosion of computational methods designed to turn patterns of word co-occurrence in large text corpora into numerical scores expressing the "semantic distance" between any two words. The success of such methods is typically evaluated by how well they predict human judgments of similarity. Here, I examine how well corpus-based methods predict amplitude of the N400 component of the event-related potential (ERP), an online measure of lexical processing in brain electrical activity. ERPs elicited by the second words of 303 word pairs were analyzed at the level of individual items. Three corpus-based measures (mutual information, distributional similarity, and latent semantic analysis) were compared to a traditional measure of free association strength. In a regression analysis, corpus-based and free association measures each explained some of the variance in N400 amplitude, suggesting that these may tap distinct aspects of word relationships. Lexical factors of concreteness of word meaning, word frequency, number of semantic associates, and orthographic similarity also explained variance in N400 amplitude at the single-item level.

Frequency and regularity effects in reading are task dependent: Evidence from ERPs

Many theories of visual word processing assume obligatory semantic access and phonological recoding whenever a written word is encountered. However, the relative importance of different reading processes depends on task. The current study uses event related potentials (ERPs) to investigate whether - and, if so, when and how - effects of task modulate how visually-presented words are processed. Participants were presented written words in the context of two tasks, delayed reading aloud and proper name detection. Stimuli varied factorially on lexical frequency and on spellingto-sound regularity, while controlling for other lexical variables. Effects of both lexical frequency and regularity were modulated by task. Lexical frequency modulated N400 amplitude, but only in the reading aloud task, whereas spellingto-sound regularity interacted with frequency to modulate the LPC, again only in the reading aloud task. Taken together, these results demonstrate that task demands affect how meaning and sound are generated from written words.

Hemispheric differences in orthographic and semantic processing as revealed by event-related potentials

Differences in how the right and left hemispheres (RH, LH) apprehend visual words were examined using event-related potentials (ERPs) in a repetition paradigm with visual half-field (VF) presentation. In both hemispheres (RH/LVF, LH/RVF), initial presentation of items elicited similar and typical effects of orthographic neighborhood size, with larger N400s for orthographically regular items (words and pseudowords) than for irregular items (acronyms and meaningless illegal strings). However, hemispheric differences emerged on repetition effects. When items were repeated in the LH/RVF, orthographically regular items, relative to irregular items, elicited larger repetition effects on both the N250, a component reflecting processing at the level of visual form (orthography), and on the N400, which has been linked to semantic access. In contrast, in the RH/LVF, repetition effects were biased toward irregular items on the N250 and were similar in size across item types for the N400. The results suggest that processing in the LH is more strongly affected by wordform regularity than in the RH, either due to enhanced processing of familiar orthographic patterns or due to the fact that regular forms can be more readily mapped onto phonology.

The N400 and the fourth grade shift

While behavioral and educational data characterize a fourth grade shift in reading development, neuroscience evidence is relatively lacking. We used the N400 component of the event-related potential waveform to investigate the development of single word processing across the upper elementary years, in comparison to adult readers. We presented third graders, fourth graders, fifth graders, and college students with a well-controlled list of real words, pseudowords, letter strings, false font strings, and animal name targets. Words and pseudowords elicited similar N400s across groups. False font strings elicited N400s similar to words and letter strings in the three groups of children, but not in college students. The pattern of findings suggests relatively adult-like semantic and phonological processing by third grade, but a long developmental time course, beyond fifth grade, for orthographic processing in this context. Thus, the amplitude of the N400 elicited by various word-like stimuli does not reflect some sort of shift or discontinuity in word processing around the fourth grade. However, the results do suggest different developmental time courses for the processes that contribute to automatic single word reading and the integrative N400.

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.

ERP correlates of letter identity and letter position are modulated by lexical frequency

The encoding of letter position is a key aspect in all recently proposed models of visual-word recognition. We analyzed the impact of lexical frequency on letter position assignment by examining the temporal dynamics of lexical activation induced by pseudowords extracted from words of different frequencies. For each word (e.g., BRIDGE), we created two pseudowords: A transposed-letter (TL: BRIGDE) and a replaced-letter pseudoword (RL: BRITGE). ERPs were recorded while participants read words and pseudowords in two tasks: Semantic categorization (experiment 1) and lexical decision (experiment 2). For high-frequency stimuli, similar ERPs were obtained for words and TL-pseudowords, but the N400 component to words was reduced relative to RL-pseudowords, indicating less lexical/semantic activation. In contrast, TL- and RL-pseudowords created from low-frequency stimuli elicited similar ERPs. Behavioral responses in the lexical decision task paralleled this asymmetry. The present findings impose constraints on computational and neural models of visual-word recognition.